BOUGHT WITH THE INCOME FROM THE SAGE ENDOWMENT 'FUND THE GIFT OP 1S9X .A'iU.U^ T/yi SifiXi liSnfiSfif. „?"'' enamels, o.in,an? ^924 031 236 668 Cornell University Library The original of tliis book is in tlie Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924031236668 CLAY GLAZES AND ENAMELS, WITH A SUPPLEMENT ON CRAZING, ITS CAUSE AND PREVENTION. BY HENRY R. GRIFFEN, C. E. THE WHOLE FORMING A TREATISE ON Glazing and Enameling Brick, Terra Gotta and Pottery. Including Exact Recipes and Formulas for all the Principal Colors now in use and Full Instructions for their Prepara- tion and Application. INDIANAPOLIS, IND.: T. A. RANDALL & CO., PUBLISHERS, F»RICE 0S.OO. COPYRIGHTED, 1896, BY. T. A. BAMDALL & CO. PREFACE. The subject of the manufacture of glazed brick and sajiitary ware has been ti-eated more by English writers from an En- glish standpoint than it has by American writers. The clays of our country are so little known to-day, in respect to their adaptability to this pm-pose, and tlie majority of them are so different from the English clays in use, that English experi- ence and receipts are hardly applicable to om- purposes. We have no clay or class of clays that are known to be specially adapted to the manufactm*e of these goods, and, in conse- quence, we cannot have cut and dried rules for their produc- tion. The treatment given each day must depend upon its various characteiistics, and must vary therewith. As our ex- perience becomes greater we may develop aj clay or class of clays that are specially adapted to the business, and may be able to agi-ee upon a best method of handling them. Until that time, each individual must do the best he can, and use such methods and schemes as he finds best adapted to the clays with which he has to deal. There is a gi-owing demand for enameled goods, and a de- sire on the part of many to meet this demand, but lack of experience, and especially of guidance, through books on the CLAY GLAZES AND ENAMELS. subject, written fi'oin a home standpoint, have discouraged tliem from undertaking it. For sucli people this little work is written. It makes no pretense of being either new or com- plete, but simply gives the views of the wi'iter, formed from considerable experience with American clays. It represents what he has found best in treating them, and is not written for the initiated. In many ways these views are very differ- ent from those of the English writers on the subject, but the clays fi-om which they are formed are also difCei-ent. There will also be found many points in common between us. My sincere hope is that, cnide and incomplete as the work may be, it will be of assistance in some particular. McHenry, 111. HENRY R. GRIFFEN, C. E. CHAPTER I. Historical and Introductary. Enameled brick have been unearthed in China which ai-e supposed to be four thousand years old. I have seen speci- mens of these brick, and the glazed sui-face^is as perfect to- day as it was when made. They are really glazed porcelain brick, and the term enameled, as applied to them, is a mis- nomer. The body of the brick is thoroughly vitrified, and of a fair color. Prom the superior color of the face, these brick were evidently coated with a slip of better quality than the body, and the;n glazed. No evidence of a slip can be detected, however, as the gradation from glaze to body is so gradual that it is impossible to tell where one begins and the other ends. Were they burned in one fire or In two? History does not tell us, and the brick themselv^ are silent on the subject. From their nature, they were evidently not burned open, or, if so, were not set more than two. or three high. The probabilities are that they were burned in saggers, as the vitrification is so complete that they probably would stand very little beyond their own weight. How many of the enameled brick of to- day, of which we are so proud, will live through four thou- sand yeai's? Have these brick existed through four thousand CLAY GLAZES AND ENAMELS. years? We cannot say positively, but whether they have or uot, they are capable of it, and, furthermore, they will last forever. They are practically indestructible, and when we of to-day make as good, glazed brick we will have just reason to be proud of them. The Assyrians and other nations have produced enameled brick, usually made of a rather soft, lightly baied body, and coated with an extremely soft enamel. How they have man- aged to hold together so long is a mystery. The English have been making enameled brick and glazed sanitary ware for years; just how long I do not know. Their product has been of better quality than anything made in this country up to a very few years ago. Enameled brick have been made in Philadelphia for the past fifteen to twenty years, and in Zanesville, O., for a num- ber of years. The process emi^loyed is the double fire, regu- lar enameling process. In most of these factories the body was and is of a red day. I believe the first plant for the manufacture O'f glazed brick by the single-fire process was established at Oaks, Pa. This plant was built in 1888. It was soon followed by the Sayre & Fischer Company, of Sayreville, N. J., and they, in turn, by the Tiffany Pressed Brick Company. There has been in existence for some years, at Somerset, Mass., a plant that, when known to the writer, used the double-fire process on a fire-clay body. The American Enameled Brick Company has lately commenced operations. Process and methods ore un- knoAvu to me. Besides tliese concerns, tliere av& several places where a few enameled brick are made. The glazed sanitary business has not, I believe, reached very large proportions as yet, though there are several concerns making this class of CLAY GLAZES AND ENAMELS. 9 gooUs. Glazed terra cotta is also being made to a limited ex- tent. Tlie demand for tliese goods is certainly on the increase, and will be for years to come. The consumption of enameled brick alone in Great Britain has been very large, and it will be so in this counti-y when the supply is assured at reason- able prices. The importation of enameled brick has been at- tended with considerable annoyance, and the manufactm-e of a good article at home meets with much encouragement. Statistics on impoi-tation are impossible to obtain, as goods of this chaa'acter are not specially classified, or have not been until lately. The importation of enameled brick must amount to three or four milliou per year, and the importation of glazed sanitary ware is large. . From the Statistics of the Glayworking Industi-les of the United States for 1894 we obtain the infonnation that in 1893 about four and one-half million enameled brick were made, and that these were sold at an average price of $90 per 1,000. I see no mention, in tliat work, of glazed sanitary wai-e, so take it for granted no one was making It in 1893. Oiu- clays have not been thoroughly investigated with a view to their suitableness for this class of work, but I have no hesitation in saying there are tliousands of them, of which 70 or 80 ]>er cent, could be used in the composition of bodies suited to it, and there are hundreds of localities where the whole of the components of a suitable body can be found within a veiy small space. Often two clays, either one of whicii alone would be eminently iinsuitable, in nearly every \\ay, when properly combined make a fine body, and there are many clays which are nearly right, and a slight admix- tm'e of another clay, of proper qualities, renders perfect. 10 CLAY GLAZES AND ENAMELS. It may require a glazing expei-t to determine when these conditions exist, but the following pages may enable the reader to determine^it in a number of cases. Tliere is a wide field as to methods and schemes that may be employed, and much time and money is often wasted try- ing to use a method that is ill adapted to the clay. Just how far it pays to try to glaze a clay that is not adapted to the simpler and cheaper methods is for each individual to deter- mine for himself. But it is easily determined that it never pays to turn out a finished product of inferior quality. So let the method be one that, with the clay in use, will produce a fine article, or change the clay, even at considerable expense, to suit the method. In regard to kilns I have said little, for there is such diverse opinion on this subject, and people's ideas are generally so firmly fixed that the less said the better. I may be criticised for giving so few receipts, but I consider them so almost utterly useless, except as suggestions, that I do not consider them worth the room they taJie up. The re- ceipts that are given are practical receipts, and upon the proper clay and at the proper heat will give fine results. The quality of some of the enameled brick now being made in this counti-y seems to be excellent. The Statistics of the Clayworking Industries of the United States in 1894 makes the following statement in regard to some tests of enameled brick made in this country: "The specimens were cubes averaging about 1.88 inches on each edge, with the enamel on one face, and were tested on the Emory Hydraulic Testing Machine, at Columbia College, New York. The pressure was applied parallel to the iace having the enamel on it. The specimens were crushed at an average pressure of 4,250 pounds per .squai-e inch, and in no case did the enamel crack or scale be- fore the specimen failed." CLAY GLAZES AND ENAMELS. 11 Below is given analyses of English clays used for the man- ufacture of enameled brick and glazed sanitary wai-e. For these analyses I am indebted to "The Manufacture of Glared Bricks and Glazed Sanitary Ware," published by H. Greville Montgomery: —No. 1 Strong.— Silica (Si02) 70.55 Alumina (AlzQs) 20.27 Oxide Iron (Fe^O^) 1.45 Lime (CaO) , 75 Magnesia (MgO) .24 Water 6.52 Organic Matter 22 100.00 —No. 2 Strong.— Silica 76.03 Alumina 16.55 Oxide Iron 1.18 Lime 67 Magnesia trace Water 5.25 Organic Matter » 32 100.00 —No. 3 Strong.— Silica 60.32 Alimiina 26.45 Oxide Iron 1.94 Lime 63 Magnesia .■ 55 Alkalis 08 Water 11.02 100.99 12 CLAY GLAZES AND ENAMELS. — No. 1 Tender. — SiUca 64.92 Alumina 25.53 Fen-ic Oxide 2.14 Lime 33 Alkalis 50 Water and Organic Matter 6.71 100.13 —No. 2 Tender.— Silica 51.11 Alumina 34.60 Ferric Oxide 3.75 Lime 56 Allialis 03 Water and Organic Matter 9.95 100.00 —No. 3 Tendei-.- Silica 61.10 Alumina 28.75 Ferric Oxide 1.43 Lime 27 Allialis Water and Organic Matter 8.55 100.10 From wliat is said in regard to them, I judge that the sti'ong clays ai'e considered much better than the tender clays. These analyses are of value for comparison only. The following may be of considerable interest to many: The Statistics of the Clayworking Industries of the United States in 1894 contains 139 analyses of tii'e clays, 25 analyses of kaolins, 37 analyses of pottery clays, 167 analyses of brick clays, ."it analyses of paving brick clays, 8 analyses of terra cotta clays, 8 analyses of pipe clays and 9 analyses of residual CLAY GLAZES AND ENAMELS. 13 clays. Among the fire clays I find eight clays whose chem- ical analyses would be about the same as the English analysis; among the kaolins one, and one other that could be made up by mixing two clays that occur in the same locality; among the pottery clays none; among the bi'ick clays one; among the paving brick clays none; among the terra cotta clays none; among the pipe clays one, and among the residual clays one; or, out of 444 analyses, there are thirteen clays whose chem- ical analyses would suit the manufactm-e of enameled brick according to English methods and irules. Out of these thir- teen clays there may be none whose physical properties would be coiTect. This cannot be predicted from a chemical analysis alone. These clays are divided among the States as follows: Arkansas, 2; New Jersey, 3; North Carolina, 1; North Dakota, 1; Pennsylvania, 2; Texas, 1; Washington, 1; Indiana, 1, and Wisconsin, 1. This leaves out Ohio. I happen to know there are several clays in Ohio eminently fitted for high heat, open burning, and possessing the proper physical properties. There are quite a number of analyses that show a little too much of the alkalis, or too much iron, or too much lime and magnesia, to be worked according to English methods, but if the physical properties are correct, they will yield to American methods whenever the attempt is made to make them yield. CHAPTER II. Selection of Clay and Mlxtares. In the manufacture of enameled or glazed clay material everything depends upon the correct selection of the clay or clays that will be suitable to the process or method employed. The principal methods of manufacture at our disposal ai'e two in num,ber, single fire and double fire, but these are capable of subdivision, the single fire process into high heat and low heat, also into open burning, or biuming where the material must hold its own weight and the weight above it, and bm'ning in saggers, or where the material is supported by other and spe- cial material designed for that purpose. The double fire pro- cess can also be subdivided in the same way. This makes, in all, eight subdivisions— single fire high heat, open; single fire high heat, in saggea-s; single fire low heat, open; single fire low heat, in saggers, making four, and the same subdivisions of the double fire process making the other four. The selec- tion of clay will be in some respects diflrerent for each of these subdivisions, or it probably would be more eon-ect to say the use of one or the other of these eight plans would b© indicated by tlie nature of the clay that is to be used. All English writers say that only refractory or high heat clays must be CLAY GLAZES AND ENAMELS. 15 used for glazed work. Witli this opinion the writer decidedly disagrees. So long as the heat is high enough to enable one to make an acid-proof and weather-proof glaze, ajnd the body under the glaze is burned to the proper condition, just as good material can be made as at a higher heat. This can be ac- complished considerably below the English high heat stand- ard. The high heart; used in England is, as nearly as can be ascertained, about the heat at which Albany slip day begins to flow, or run thin on the sharp edges of trial pieces, and to lose its beautiful brownish black color and take on a partially transparent appearance and grayish hue. Good glazed maite'- rial can be made from this heat down to the point where Al- bany slip day begins to fuse and becomes a brown semi-glaze. If the clay is suited to it, the single Are, high heat, open burning method is undoubtedly the most satisfactory, but such days seem to be difficult to obtain in the United States. The values of the otheir methods will probably appear as we ad- vance with the subject. The question in this country is; not so much What clay can I obtain to make glazed goods? as Can I glaze the clay I have? The design in this chapter shall be to treat the subject in stich a way as to enable the reader to determine the proper answer to either of these qviestions. —High Heat, Smgle Eire, Open Burning Method for Brick Where the Material Carries Its Own, Weight and the Weight of That Above It— This method of manufacture requires for its perfect suc- cess a day or mixtui-e of days, or day and grit, that shall possess certain qualities. The clay must not only stand the high heat to which it is- exposed, but it must stand this heat and, at the same time, stand a weight Of about fifteen to 16 CLAY GLAZES AND ENAMELS. twenty pounds to the square inch. This weight to be carried by the lower bricks would not be so great could they be set directly on each other, but as they have to be separated by rolls of clay, the weight acts upon a small surface. The clay should not only possess this qviality, but should have a fairly large margin of safety. In order that crazing or shivering should not result, the proportion of silica to alumina should be about three and one-half to one. In order that the clay should stand the weight, it should not approach closely to the point of vitrifaction, but should derive its bond lai'gely from the pure clay or silicate of alumina it contains; it should, therefore, contain little iron and fluxes. A fairly representative analysis of a clay suitable for this method of manufacture would be about as follows, and the more nearly the day, or a mixture of clays, can be made to conform thereto, the more certain is success, other qualities being right; Alumina, 20 per cent.; silica, 70 per cent.; watei-, G to 7 per cent.; fluxes and iron, 3 to 4 per cent. Such a clay will, as said before, derive its sti'ength of bond from the silicate of alumina largely, the fluxes not being suf- ficient to take up anything like all of the free silica, unless the heat be beyond anything obtained in kilns. The pure clay (silicate of alumina) will begin to harden directly the combined water is driven off, and will hai-den slowly and evenly up to well beyond the heat contemplated, consequently such a clay is slightly afEected by slight differences in heat, and the bricks are likely to come from kiln nearly uniform in hardness and size under the variations that may occur in the fire. A state- ment of facts may strengthen this position. Analyses of five different makes of English brick showed that the original clay could not have v^ied 2 per cent, from the above figures in CLAY GLAZES AND ENAMELS. 17 the silica present in tlie most extreme ease, and not more than 1 per cent, in the alumina present, and the average was almost identical with the flgm'es above. A mixture the writer was using was analyzed at the same time, and agreed almost ex- actly with the figTU'es above. This mixture had been made without any previous Icnowledge of the chemical constituents of the English bricks, but had simply been the natural result of continued effort to secure a perfect enameled brick. The physical characteristics of the proper clay are more difficult to describe and still more difficult to obtain in a single clay. The clay should possess plasticity or tougliness enough to enable the brides to stand the large amount of handling they receive without showing it to too great an extent. It should be as little subject to laminating in pug mill or brick machine as possible. It is better that it be a strong, hard diying clay that does not abrade or chip easily. A shrinkage of not over', one inch to the foot is better than a greater shrinkage, as it is easier to adapt a good white coating to a light shrinliing brick. If a high slu-inking clay is brought down to loroiier limits by the addition of grit or grog it is apt to lead to a wavy- faced brick, imless the giit is ground extremely fine. Very fine grinding is expensive. Clay must be homogeneous through- out, or capable of being made so by thorough pugging, else unequal shrinkage will produce wavy face. It is of the utmost importance that the clay, or a mixture of clay and grit, should possess at some point of stiffness, dry- ness, temper, temperature, or whatever it may be called, three combined qualities: It must not drag in pressing, so as to come from the repress with top corners depressed, making a crooked, untrue brick; it must not crack in pressing, and it 18 OL.AY GLAZES AND ENAMELS. must dry perfectly straight from that point until it is abso- lutely dry, without checking and without too much precaution being necessary. If the bricks are to be dipped while soft, this point must be while blanks are soft, otherwise it may be when blanks are stiff. Many clays possess one of these qualities, or, by selecting the proper point of stifEnees, will possess two of them, but the three combined at any one point are difficult to obtain. The softer the blank the less apt to crack in pressing, but the more apt to come out of press with down comers, and the less apt to dry straight. This point will be fully dwelt on under repressing. A clay of a sticky nature — that is, one that does not easily polish— wiU be easier to make a slip or enamel adhere to than one of a fatty or easily polished nature. Such a clay is apt to contain or possess more of the requisite physical character- istics. It will possess plasticity, even when much grit is added; it will usually be a hard dryer and less subject to lamination; It may be a bad warper and checker in drying, may drag more in press, but these difficulties are all overcome by the addition of grit. Therefore, as a rule, a light shrinking, sticky clay, of the proper chemical composition, mixed with grit, will be found to more nearly comply with all the requirements than a fatty or greasy polishing clay. —Same Method as Above at Lower Heat. — All the physical characteristics must be the same, but the chemical composition may or must be somewhat difEerent. Slightly more alumina and fluxes are allowable, or more silica, with much more flux. There is a wider range in chemical composition allowable at a low than at a high heat. At the extreme of the low heat range it is dangra-ous to place the CLAY GLAZES AND ENAMELS. 19 bricks without extraneous support. The low heat clays are not apt to stand any excess of fire and support much weight at the same time. — High and Low Heat in Saggers or Other Support, Single Fire.— Here we must have all the qualities of the open fire pro- cess up to the time that bricks are ready for the kiln. The burning qualities may be the same or may be very different. A much wider range of clays may be used when bricks ai'e supported than when they are not. The clay may even be a vitrifying clay and yet bum safely. The great point to watch under this process is that the composition of the clay shall be such that the finished bricks will neither craze nor shiver. This requu-es a clay whose alumina-silica ratio shall be about 1 to 3%, a little more silica being allowable with much flux than with little flux. The amount of lime may vary much, depending upon whether a low or high heat is used, and whether the finished brick is to be porous or vitrilied. This is also true of the alkaline fluxes. —The Double Fire Processes.— Any clay that makes a smooth, straight, true brick; that will not craze or shiver its glaze, and that does! not possess any of the few bad qiialities that will be mentioned later, may be used for these processes. If the business is strictly a glazed business, the clay must possess such physical charac- teristics as will produce a large percentage of perfect bridis under the conditions existent. If the business is glazed brick and common building brick, so that pei-fect bricks can be se- lected for glazing, tliis does not mattei' so much. The matter 20 GDAY GLAZES AND ENAMELS. of laminatiou enters very slightly, if at all, into these pro- cesses. —Fatal Defects in Clay.— Iron spots developing at heat used. Lime in lumps will produce flaws and breaks in face. Volatile matter in clay that stains enamel is fatal to the single fii'e process. Coal in clay is harmful, but not fatal. —Goods Other than Brick.— In goods that are made by hand and not repressed many of the physical qualities are of less importance, and some are of greater importance. The tendency to laminate is usually ob- viated by pugging the clay in a very soft condition, and the handworktng further eliminates it. The properties that cause cracking and down comers in repressing have not to be con- sidered, but the straight drying, and burning, and checking qualities are of greater importance ia large, heavy pieces and in thin pieces. The selection, or rather picking and assorting, of clay for large pieces should be done with great care, as a little bad material will spoil a large piece of great value as easily as a brick of small value. For sinks, baths and goods that undergo close examination, and that must, therefore, be perfect, more careful selection is necessary than for goods that are not submitted to close in- spection. —Semi-Dry Process. — / So far as is known, this process has never been successful except with two fires. It requires a property in clay that it does not seem to possess, or, if it does, it is a very rare qual- ity—that is, the capability of being wet after having been CLAY GLAZES AND ENAMELS. 21 strongly pressed in' the semi-dry condition, without cracliing in. drying. If macliinery can be gotten up that will handle the clay in a quite wet condition, what might be called semi- plastic, this process might be made the most successful one. This process eliminates all waviness of face, and leads to the production of bricks with a beautiful surface. The experience with this process is so slight that it is impossible to say much about clay selection, except that it may contain more alumina without crazing, and must contain less silica to avoid shiver- ing, than for the plastic processes. _ CHAPTER III. Preparation of Clay. The clay for the plastic process should be thoroughly ground and pugged. The methods of doing this may be any of the methods in use that do not leave the clay in a flaky or lam- inated condition, but the preferable method is that of the diy and wet pan. The dry pan should have slotted screen plates, with slots of not over one-sixteenth inch in width, and if gi-it is used it should be gi'ound with the clay. If more than one kind of clay is used they should be ground together. After leaving the dry pan, the clay and grit should be elevated to a screen, either of the revolving or shaking pattern, or the sci-een may be a fixed, inclined screen. The mesh should be No. 10 and scTeen made of No. 20 wire. This gives about a one-six- toentli-inch opening between the wires. The preferable screen will be found to be a six or eight-sided revolving screen, with clappers or beatei's so aiTanged that each angle of the screen raises them and allows them to fall on the flat side. This will keep the meshes of the screen clear, and it will do good serv- ice. A regular wu'e screen is much cheaper and will give bet- ter service than a perforated steel sci-een. The tailings from scTeen should be earned directly back to the dry pan, so as to insure a constant uniform mixtm-e. CLAY GLAZES AND ENAMELS. 23 The dust from grinding the clay will be a great annoyance and injury to the men and m^hlnery unless some precautions are adopted to prevent its getting into the parts of the build- ing where these are located. A very good plan is to inclose the dry pan, except whea-e the clay is fed into it, and then locate, in the face of this inclosure, a large exhaust fan or disc fan. This will cause a strong draft inward at the feeding point, and will carry all dust into pan. Leaders may be brought from other dusty points, and the one fan made to exhaust the dust from them also. The dust that is expelled by the fan may be carried in a large tube to a convenient place and discharged into a room with muslin sides; or this room may have a very large and low wooden stack leading outdoors. In the first plan the muslin will clog with day dust, and will not allow the air to pass through, causing some extra labor and annoy- ance. In the second plan some of the very finest of the dust will escape and be lost, but if the stack is large enough so there is very little draft in it there will be very little lost, and still less if shelves are placed in it occasionally so as to form eddies. The dust which is collected in this way is oitsa found useful for special purposes. The wet pan is too well known to require description. The only caution I have to give is to obtain a mill with rather nar- row-faced wheels. It is the best pugging device for clay out of which glazed material is to be made because it does not tend to laminate the clay, and is, at the same time, a thorough mixer. With u little experience the charges can be all brought to a uniform consistency. The next best device is a good pug mill, not one of the broad-bladed, sharp-angle, quick pug mills, but what might be called an old-fashioned mill, with, not too wide blades, say four inches, and set at a very slight angle. The 24 CLAY GLAZES AND ENAMELS. capacity of such a mill may seem small, compared with its size, and the ix)ssible exti'a powei" it may take, but it will be found to pay in the long run, or at least that has been the writer's experience; but of whatever pattei-n it may be, it must be a mill that does not laminate the clay that is being used, but must deliver a compact, solid stream, free from air and laminations. In the wet pau a definite and fixed amount of clay and water can be mixed together every time, and a constant, uni- form condition of pugged material be maintained. This is a very important element of success, and is the only true founda- tion upon which to erect any hope of uniformity in size of fin- ished product. With the pug mill tlje same degree of certainty may be reached by using a soak pit. This method, however, necessi- tates an exti-a handling of the clay and takes considerable room if the daily output is at all large. I have seen sm-pris- ingly unifoi-m results from the use of a single pug mill, where a constant sti'eam of dry, ground clay and a constant stream of water were admitted. This plan takes the entire attention of one man, and he must be a good one, biit as the clay is en- tirely handled by machinery, it makes a very cheap method of pugging. A second pug mill fed by the fii-st would give tlie man in chai-ge of the pugging opportunity to correct any errors made in the §rst mill and would improve the clay. The stiffness of the pugged clay vrill, of course, depend en- tirely upon the subsequent method of manufacture. CHAPTER IV. Methods of Making the Blank. There is probably little doubt that the best enameled brick can be made fi-om a well-made hand-made blank, but there is just as little doubt that hand-made blanks are often poorly made. The hand-made blank is made from soft clay, so that there is more moisture to be gotten rid of to get the bricks ready for the press than with some of the stiff clay processes. In getting rid of so much moisture it is difficult to do it uni- formly and regularly, one day with another, so that while it is, as I have said, undoubtedly capable of making the best fin- ished product, it is the most wearing process on the manage- ment. A description of methods employed in this country for hand- made brick wiU probably be of interest. The clay Is pugged stifCer than for common, so-called mud building brick; in fact, its stiffness is as great as possible for it to be, and yet be ca- l>able of being driven into a mold. The method of delivering to the brickmaker is a matter of the manager's ingenuity, and the best method to-day becomes old-fashioned to-morrow, in these times of rapid improvements. The molds are better made of brass, and should be one-half inch deeper than the desired depth of brick. On the making table should be firmly fastened 26 CI/AY GLAZES AND ENAMELS. a wooden, block that fits the mold loosely, but neatly; on top of this block should. be fastened a wooden or metal piece, the size of the indent desired in the bottom of the brick. Two holes of about 5-16 of an inch in diameter should be drilled through the wooden block parallel with its top face and with their centers 21-32 of an inch below it. These holes should be one to two inches from end of block; 5-16-inch iron rods should then be di'iven through these two holes, allowing the ends to project about a half incli each side of the block. The tops of these rods will then make four supports for the brick mold, and the mold will telescope on the block one-half inch. The distance from block to top of mold will be the desired thickness of brick. In molding the brick the clot is formed partially by beating and pai-tially by rolling, and as the clay is so stiff it must be driven into the mold with great force in oi-der that it may completely fill the corners. The mold and blodt should first be lightly oiled with kerosene of 110 degi'ees fire test. After the mold is filled, the siutjIus clay should be cut off to the level of the top of mold with a wire, tightly stretched on a steel bow. The piece cut off the top should be placed on the table with the cut edge down, and the additional clay for the next brick placed on top of it. This will insure a more solid brick. The ofCbearing boys should be furnished with boards covered with canvas that neatly fit the mold. This board should be placed over the brick, and then, while the fingers hold the mold by the ci-oss rod, the thumbs should press upon the board and press the brick out of the mold on to the drying fioor. This will be found to be quicker and better than to shake the brick loose from the mold, and will insm* a true, straight brick and clean molds. The use of oil oo mold should be as OLAY GLAZES AND ENAMELS. 27 sllglit as possible. After block and molds have been gotten into good working condition oiling will not have to be done oftener than every four or five bi-ick. The floor upon which briqlt are placed to dry should be true and straight, and not too hot. The drying floor may be heated by furnaces or by steam, either live or exhaust. Great care must be taken to remove all the brick from drying floor in exactly the same con- dition, as far as moisture is concerned. The dried blanks should either be piled and covered or piled in air-tight bins and allowed to stand a day or two before being pressed. This will even up the moisture to some extent. The iKtints to be watched are that the molder forms a solid lump of clay out of which to make his briclt, and that he drives them uniformly, and without allowing the clot to cut on edge of mold when driving. Also, the drjaiig should receive great attention. A man and two boys will easily make 2,500 brick per day. The soft-mud machine process has never been practically ti'ied by the writer, but the details would be the same as the hand process, except in the mere making of the blanks. The objection to all of the stiff-mud processes is the diffi- culty of getting a blank free from ah- and laminations. Ex- perience with a few clays cannot enable one to lay down rales for all clays, but the tendencies of certain types of machine can undoubtedly be pointed out with some degree of accuracy, especially when that experience has been combined with close study of the working of machines on clay generally. The plunger machines all tend to make a blank filled with air holes just below the surface. In the repress; the cavities containing air become reduced in size and the air compressed. Where the bricks are afterward dipped in the slip or enamel the sm-face becomes softened, and the air in these cavities ex- 28 CLAY GLAZES AND ENAMELS. pands and forms numerous blisters upon the enameled face. The auger machines tend to laminate the clay. If these laminations come within about one-half inch of the surface to be enameled, the dipping into the liquid slip or enamel will develop blisters, often of enormous size. The remedies are to adopt a moisture, or stiffness, in mating the blanks, at which the tendency to lamination Is reduced to a minimum, and mucb good may be done by placing a number of knives in the die to cut the surface of the bar of clay to a depth of a little over half an inch. This seems to break up the laminations to a very great degree, but if the clay is one that does not easily knit together again it may lead to cracks across tbe face of brick. Clays differ veiy much in their tendency to laminate, and some may be worked in a much stiffer condition than oth- ers. There is also undoubtedly considerable difference in the tendency of different machinesi to laminate the clay. On eic- count of the headers and quoins to be made, it is more con- venient to make side-cut than end-cut brick, and the writer's experience has been that the laminations are less injurious in side-cut than in end-cut brick. Large die resistance seems to reduce tbe laminations or throw them so far below the sm'- face as to be less injurious. Each person will have to study the working of the clay he proposes to use, and from that study, determine the style of machine best adapted to it. The treatment of stiff -mud, machine-made brick is the same as the hand-made brick, except that they do not require so much drying, and, as the brick can be delivered upon boards from the cutting table, a different system of drying can be used^ A very satisfactory plan has been found to be to have steam-heated racks just in front or back of brick machine, upon which the boards, with a convenient number of brick upon CLAY GLAZES AND ENAMELS. 29 them, may be placed to dry. This plaa requires considerable attention, as the end briclvs dry first, and a man must con- stantly watch them and get them off the drying pipes when in proper condition. The writer has examined the working of roller die ma- chines with considerable interest, and, from what he has seen, concludes that there is much less tendency to lamination in this type of machine, even when the clay is stiff enough to go directly to the repress. The bricks from several machines of this type have been examined and not a trace of lamination discovered. There was at that time some diflBculty with the wearing qualities of the roller die, which may since have been overcome. It is easily, seen that a machine that will make a brick that can be repressed at once will effect a wonderful saving, both in time and money, and will also affect some- what the uncertainties of the business. The whole attention may be concentrated upon the proper making of the blanks, instead of being divided among several operations. For the single-fire process, where the dipping is done after the pressed' brick is thoroughly dry, and for the double-fire process, laminations and air in brick are not quite so objec- tionable, but the repressing, even without immediate dipping, will develop some blisters if the laminations or air are present. CHAFTBR V. Repressing. This is a necessary operation in tlie manufactm-e of enam- eled brick. At the same time it leads to much trouble and difficulty. An unpressed piece of clay is easy to enamel and have it smooth and perfect, for, even if laminated or filled witli air cavities, there has been no distortion of laminations or compression of the air, and when the surface is moistened by the sUp or enapel there is a very slight or no tendency to blis- ter, but repressing seems to magnify every defect of structure in the brick. The laminations are distorted and the contact between laminated faces seems to be ruptured. The laminated condition is certainly much more apparent to the eye, as can easily be seen by breaking a few unpressed brick and a few pressed brick. In a pressed brick the air in the larger air cav- ities is much compressed and leads to large blisters after dip- ping, and, besides this, there seems to be a number of minute air cavities, or it may possibly be simply an expansion of some of the particles of clay itself that leads to a rough, irregulai- face. These latter irregularities are very small, but still they are great enough to show quite a difference in the appearance of a pressed and impressed brick after dipping. Pin holes are much more prevalent in the pressed than in unpressed brick. OLAY GLAZES AND ENAMELS. 31 The blanks may be repressed either by hand or machinery. The best hand represses are probably the Perfection Press, 'mad& by C. W. Raymond & Co., Dayton, O., and the Tltley Screw Press. Either of these presses would be much improved by some device for an automatic adjustment of indent that would make every brick of equal thickness. The adjustment of thickness cannot be done with escape holes or vents, as this causes a flow in the day while under pressure. This flow leads to a stratified arrangement of the day, which will show after- wards in the enameled face. The effect of this flow will be somewhat reduced by siibsequent repressing in a tight box, but will not be entirely removed. The best power press for this class of work on the market, up to 1894, was the Perfect Press, made by Pullan & Mann, Leeds, England. This press is arranged with a driving pulley that allows the press to stop automatically at each complete revolution, or at the finish of each brick, allowing the finished brick to be removed and the new blank to be placed in posi- tion without danger of the hands of the operatives being caught. A very small motion of a lever serves to immediately start the press. This press is arranged with an automatic movable indent, which is pressed bade by the clay in the brick to a greater or less extent, depending upon the amount of clay in the brick. After the indent is pressed back it is locked in position by a double wedge, and a slight additional pressure is given, with the indent fixed. On the up or delivery stroke the wedges are loosened and the indent is forced out by a heavy spring and is in position for the next brick. There is one criticism that can be made of this press, and that is that the indent-forming plate is out, or prepared to make a large Indent. This large indent-forming plate strikes the brick and 32 CLAY GLAZES AND ENAMELS. unduly distorts it and tends to crack it. It would be better if a press could be made In which the main plimger were brought down to within a tilfle of the proper thickness, and the indent- forming plunger then forced into the brick up to a certain pressure and locked, then a slight additional pressure given with Indent and main plungers locked together. \ The ultimate capacity of the Perfect Press is about 6,000 bricks per day, but about 5,000 is a good day's work. It requires one man and two boys for Its proper operation. ' The precautions to be taken are the same whether the press is a hand or power press, but, if a sizing press, there is no ne- cessity of weighing or otherwise bringing the blanks to uniform size. The blanks should be struck on the faces that are to be enameled with a paddle, and afterwards smoothed up with a knife. The condition in which the bricks should be pressed is somewhat different for each and every clay. The blanks should be, as a rule, as stiff as they may be not to crack in pressing, and yet to press up well in the comers. The pressure should be sufficient to make sharp corners, but should not be excessive, else longitudinal ci'acks will result. As little oil should be used as possible, and this should be as largely com- posed of low test kerosene as possible. Where low test kero- sene alone will do the work it is advisable to use it. but in some cases a heavier oil will have to be mixed with It. Care should be taken to keep pliingers well fitted, so that there will be as little finning as possible. When finning does occur the offbearing boy should place the brick on a table, and, with his offbearing paddle, turn the fin down on the flat side of brick. This will be foiind better than attempting to remove the fin, as the turned-down fin will afterward be removed with the cleaning brush, leaving a clean, sharp edge, whereas a re- CLAY GLAZES AND ENAMELS. 33 moval of the fin while the brick is soft is apt to leave a ragged edge. The two main troubles to b© avoided at the press are cracks in brick and down comers. These are due to almost directly opposite causes, and in some clays it is very difficult to avoid one without running into the other. The softer the blank the less the tendency to crack, but the greater the tendency to drag at the comers. A brick body with plenty of grit in it Is less apt to drag at comers than a pure clay body. The method of handling and transporting the brick from the press to the enameling room and on through the other depart- ments will vary with the amount of daily output. With a large daily output a car system would undoubtedly be advisable, but with a small output a simpler method can be used to ad- vantage. A method with which the writer was thoroughly fa- miliar proved to be a good one. This plan required level and smooth floors throughout all departments, from press to kiln. It consisted of boards placed on skids that would raise them about fom- inches from floor. These boards were placed along- side of press and filled with sixty brick. When full, a two- wheeled cart or truck, with large wheels, about three feet in diameter, with bent axle, and pick-ups suspended from said axle, was run over the load. By pulling down on the handles of truck the load was lifted from floor and wheeled to any part of the building and set down. This is a cheap plan, as the investment is chiefly in boards. Three or four trucks will suf- fice for the handling of quite an output— one at presses, one or two for the dippers and one for the kiln gang. CHAPTEE VI. Slipping, Glazing and Enameling. Tlie object in tbis chapter will be to teach the reader how to slip and glaze or to enamel clay. This cannot be done by- giving a lot of receipts and stating they ai'e the best or worst in the comitry. The only course open to him would be to search the country for a day that would fit the receipts. Were he lucky he might find it the first time, and were he unlucky he might not run across it at the one-thousandth experiment. What must be done is to take the clay as we have it or as we can easily get it, and so mix it as to make it fulfill the condi- tions described in the selection of clay, as nearly as possible, and then adapt a slip and glaze, or a slip and enamel, or an enamel to it. In the manufacture or mixing of slips, glazes and enamels we are not limited by distance or the amount of transportation, as they form such a small proportion of the total weight of the output, so we can take our supply of ma- terials from the whole country, or even import them, without running up expense materially. A description of the different materials and their functions will probably be first in order. —Ball Clay.— This is usually a very tough, plastic clay, and a heavy CLAY GLAZES AND ENAMELS. 35 slirinker in drying and bm-ning. There are many different qualities, and tlaey all vary as to the amount of shrinljage, color and hardness to whidi they burn, but, as. a rule, they are cream-colored or slightly gi'ayish when burned, burn hard and close, and shrink about one and one-half tO' two Inches to the foot. If the body complies with the condition that it should shrink one inch to the foot, it is easily seen that a pure ball clay slip would be apt to crack on it. The color of such a slip would be poor, but it should stick like wax to the body. There are some ball clays that do not stick well. The use of such a clay should be avoided. No. 4 English ball, from George Knowles & Son, Ti-enton, N. J., is a good ball clay. — China Clay. — This, as foimd in the trade, is a washed clay, usually a so- called koalin that has been mixed into thin slip and floated in such a way as to get rid of all sand, mica and coarse impuri- ties. As only fine qualities of clay are worthy of the expen.sc of washing, china clays are usually of good white color, bul vary very much as to plasticity, some of them being very plas- tic and some of them being extremely short or lean. They burn to all degi'ees of hardness, from so soft as to easily scratch with a knife to vitreous. The shorter or leaner the china clay, usually the whiter it will burn. These clays are prepared principally for potters' use, and the plastic qualities are esteemed highly by the potters, so as the clay decreases in plasticity it must make up for it by increased whiteness in order to retain its value in their eyes. Nothing very definite can be said about china clays on ac- count of this wide variation in them. What would be true of one would be decidedly untrue of another. The china clays 36 CLAY GLAZES AND ENAMELS. most used hj the -writer have been the National China Clay, obtained from the National ICaolin Company, Brandywine Summit, Pa., and English China Clay, No. 7, obtained from George Knowles & Son, Trenton, N. J. These two clays are opposites, the first being a plastic, high shrinking, vitrifying, cream-colored or cream-white clay, the second being a short, medium slirlnking, soft burning, but extremely brilliant white clay. Were the typical brick body dipped in a slip of National Clay the slip would crack, probably, but would stick well and would glaze a creamy white. Were it dipped into a slip of the No. 7 China, the slip would shell off in drying, or, even did it stick, it would be too soft to be of amy use. —Flint— In this coimtry ground quartz or quartz sajad; in England usually the so-called flints, obtained in the chalk cliffs. Flint, when pure, should bum to a brilliant white color. It expands in burning, and can only be melted or vitrified by the heat of the oxy-hydrogen blow pipe. Its use in slips is for its whitening properties and to decrease shrinkage. In glazes this material furnishes the silica to form the compoimd silicates forming the glaze. Flint should be finely ground so as to pass through a No. 150 brass wire sieve. Cornish stone and Cornwall stone are two English materi- als never used by the writer, and the properties of which ai-e unknown to him. Whenever a receipt containing Cornish stone is to be tried he substitutes four pai-ts felspar, one part clay, one part flint. —Feldspar, or Felspar.— This is orthoclase or potash spar, a double silicate of alum- CLAY GLAZES AND ENAMELS. 37 ina and potash. Albite or soda spar is little met with. The feldspar of commerce varies somewhat in chemical composition, consequently in fluxing properties, but as a rule it melts at a bright yellow heat, sometimes into an almost transparent glass, at others into a white semi-enamel. It is esteemed most the more fusible it is, and the better the color of the fused samples. It should be perfectly free from dark specks. An analysis of the Brandy wine Summit felspar shows: Silica, 65.21; alumina, 18.13; potash, 16.66. —Whiting, or Paris White.— This is principally carbonate of lime, with some little mag- nesia and other impurities. It should bum white. At high heats it combines with silica or with silica and alumina, and acts as a flux. At very low heats this combination does not take place unless aided by some low heat flux, as potash, soda, lead, etc., and even then, if much lime is present, the combina- tion of all the lime is difficult to effect. The province of whit- ing, as well as other forms of lime, in a glaze is to toughen the glaze. It is an additional base, and makes a more complex silicate. The complex silicates are usually more durable than the simple silicates. Lime also prevents the coloring effect of iron to some extent. —Plaster of Paris.— Anhydrous sulphate of lime, becoming a hydrated sulphate when mixed with water. Supposed to prevent cracking of slips when put on to dry clays, and is a whitening material when pure, probably througli the lime action upon the iron of the clay. 38 CLAY GLAZES AND ENAMELS. —Gypsum.— Natural hyaratcd sulphate of lime. This is plaster of paris before it has been bm'ued and made into plaster. — Barytes.— There are two materials which are used uudev this name, oue the sulphate, the other the carbonate of barium. They are both fluxes at a high heat, and tend to make a glaze still more complex. —Fluor Spar.— Fluoride of lime. A lime flux, acting at a somewhat lower heat thau the carbonate or sulphate of lime. —Cryolite.— A double fluoride of aluminium and soda. A very good, ex- tremely soft flux, insoluble in water, not to be used in large quantities. —Oxide of Zinc— This is a flux, and, at the same time, a whitening and lirightening material in the glaze. —Soft, Insoluble Fluxes.— Carbonate of lead, or white lead; oxide of lead, or red lead; litharge, borate of lead, aluminates of potash and soda, borate of lime. —Soft, Soluble Fluxes.— Salts of soda and potash. Tills is a large number of materials with which to work, and almost any conditions can be made to exist by their proper combination. CLAY GLAZES AND ENAJIELS. 39 Now, what is enameling? As usually employed, it is to coat a material of one kind and color with a material of another kind and color that shall have a smooth, glossy face. In order that enameling may be successiul the coating must adhere per- fectly to the material to be coated. The uatm'al adhesion in slips is the adhesion of clay to clay. This may be enhanced by tlie addition of fluxes. In enamels we must rely upon the fluxes almost entirely. In order that the adhesion may be perfect, the body and coating must con- tract in such relative proportions as not to break the bond be- tween them, for tJiis bond, once broken, when the natural ad- hesion of clay to clay is relied on, cannot be restored, and where the adhesion produced by fluxes is relied on it cannot be restored to its fvillest extent. The slip or enamel should shrink more than the body, not to an extent to produce cracks, but still, to some slight extent, its shrinkage should be greater than the body. If it shrinks less than the body it will surely shell off, and so there should be a margin of safety, for even should the bond between tlie body and coating not be broken to such an extent as to cause immediate shelling, it may cause an unreliable article. It is very peculiar that, in drying, the slip will not stand the least compressive sti-ain without shelling, but no amount of tensile strain seems to tend to produce this effect. In work that is slipped we may have adhesion to the fullest extent the slip is capable of, biit if it is a soft bm-ning slip at the heat used, its capabilities in this direction will be small. Such a slip may not chip or shell off. but the glaze over it once broken through it can easily be scraped off. We there- fore must have a slip that not only adheres well, but that will burn hard at the heat used, i 40 OL.AY GLAZES AND ENAMELS. The shrinkage can be controlled by the amount of ball clay or other high shrinking clay used in the slip, and the hard- ness of the bui'ned slip by tlie amount of flux it contains. In high heat work or work where the heat is beyond the melting point of feldspar this is undoubtedly the best flux to use, but in heats below this some other flux must be used. I will not go into the relative merits of the different fluxes at this point, but will take it up later. As a starting point we will assume a mixture as follows: A good, tough ball clay 40 No. 7 English China Clay 30 Flint 20 Feldspar 10 Our imaginary brick is dipped into this slip immediately after it comes from the press and put away to dry. The slip will probably either crack, shell or be all right. In the first event we have too much shrinkage, and should replace some of the ball clay with either china clay or flint; in the second event we should reverse the operation, and in the third event we should jput the brick into the kiln and bum it. When the brick is taJien from kiln there are nine different conditions that may exist. It may be cracked, peeled, or all right in these respects, but too hai"d— that is, vitrified— and body may show through. It may be ci'acked, peeled or solid, but too soft. It may be cracked, peeled, or solid and of the prop«: hardness. If cracked and too hard, addition of flint will probably rem- edy both troubles. If addition of flint stops the cracking, but still the slip burns too hard, replace a little of the feldspar with flint. If peeled and too hard, it shows that shrinkage has not been great enough, so replace some of the feldspar with ball clay. CLAY GLAZES AND ENAMELS. 41 If this stops the peeling, but the slip still bums too hard, re- place a further quantity of feldspar with flint. If the first re- placing of feldspar with ball clay brings to proper degree of hardness, but does not stop the peeling, replace some of the flint with ball clay. If solid, but too hard, replace a portion of the feldspar with a mixture of ball clay and flint, in the proportion of two of ball clay to one of flint, or in the same proportions as they exist in the original mixture. If cracked, but too soft, add feldspar. If this does not make the slip hard enough, resort to cryolite, trying different per- centages from one to ten. It is seldom advisable to go be- yond 10 per cent of cryolite. If cracking still continues re- place some of the ball clay with flint. If peeled, but too soft, replace some of the flint with ball clay. Continue this until peeling stops. If slip remains too soft, add cryolite. If solid, but soft, ti-y adding feldspar. If feldspar will not harden slip, add cryolite. If proper hardness, but cracked, replace some of the ball clay with mixture of flint and spar, two of flint to one of spar, or as they are propoiUoned in the original mixtui'e. If proper hardness, but peeled, add ball clay, or add ball clay and remove a little of the spar. If proper hardness and solid, the proportions of the different ingredients are correct. Any additions or changes that are here suggested will lead either to a continuance of the same condition in a less marked degree or else to one of the other conditions, so that these nine conditions and their probable remedies will lead out of all diflS- culty. The only failure that will be met with will be when the 42 CLAY GLAZES AND ENAMELS. heat is so low that 10 per cent, of cryolite will not make tlie slip burn hai'd enough. In that case make a flux by burning together in kiln a mixture of equal parts of borax and feld- spar. Grind this very fine and use it instead of feldspar, but when this has to be resorted to the heat is probably too low to admit of a reliable glaze being used. We ai'e now supposed to have a slip tliat adheres well and is of the proper hardness, but nothing has been said about its color. The color of the original slip given would probably be a ci'oam white. Staining with blue stain would give it a whiter appearance, but, at the same time, possibly a slightly gi-eenish tint. If better color is desired, it might be obtained by using more gi'it in body, reducing the shrinkage. This would admit of less ball clay in slip, or bricks might be slipped after they are thoroughly dry. In this case, much less ball clay, possibly none, would be used, and unless the heat is higli an artificial flux might have to be resorted to. Much can be done to im- prove the color by using a good white enamel or semi-enamel over the slip. With heavy shrinking, low heat clays, a good white slip is difficult to obtain, and somi-euamels must be used. Slipping dry clay I have found the most difficult to do. A slip with much plastic material in it cannot be used, as it will crack unless the bricks are dipped in very thin slip, allowed to dry and dipped again, repeating this operation several times, or until the coat is thick enough. Tliis multiple dipping is ex- pensive, and is apt to give some trouble by blistering. A short slip on a dry brick is almost cei-tain to pin-hole badly, so prob- ably the best way to work, where the heat is low and the brick body is such that a considerable amount of ball clay must be used in slip, is to slip the body while soft witb such ball clay slip. Then glaze with an enamel or semi-enamel, or allow the CLAY GLAZES AND ENAMELS. 43 biick to dry and dip it again In thin white slip, then glaze. The white slip for the dipping after the brick is dry will have to be varied to suit the heat. I have always found ball clay and flint to work better than a china clay. The ball clay should not amount to more than 10 per cent, of the whole, the bal- ance to be made up of flint and spar, with iwssibly 4 per cent, to 5 per cent, oxide of zinc. If spar will not make the slip bm'n hard enough at the heat used, substitute the artificial mix of spaa- and borax mentioned above. Should this slip not hide the off-colored slip under it, from 5 per cent. to. 10 per cent, oxide of tin will help it very much. Lime will not help much to Whiten low heat slips, but Svill help to whiten high heat slips. The pure white brick are the only ones that this trouble will have to be taken with. The ott'-colored white will stain for color.s just about as well as a pure white. / The glaze should be very different in the percentage of clay it contains for wet dipping than for dry dipping. The compo- sition of the glaze can be given a little more accurately for dry work than for wet. In dry dipping it should contain about 5 to 7 per cent, of a moderately tough china clay. For wet dip- l)iug it should contain from 10 to 20 per cent, of a tough ball clay that burns a good color. From 11 to 13 per cent, will , probably hit the majority of cases. Soluble fluxes should, as a rule, be avoided in the glaze, especially for wet dipping, as they soak into the body, and, in most cases, cause the face that has been dipped to shrink so much more than the balance of the brick that it cracks. Where the glazing is done on the dry brick soluble fluxes do not seem to have this objection to such an extent. Where the clay will stand it without cracking, solu- ble fluxes are excellent, as they help bind body and slip to- , gether. 44 CLAY GLAZES AND ENAMELS. The make-up of a glaze is dependent entirely upon the heat, or, in other words, is dependent upon where you wish it to melt. The clay, for reasons given above, may vaiy from 5 per cent to 20 per cent, of the whole. I prefer the glazes with more clay in them when it is possible to use them. From 4 to 8 per cent, of lime should be used, though the lime may run much higher. If little clay is. used considerable feldspar should be used, so as to get in sufficient alumina. These three things will make a glaze, and a good one, but it will take a high heat to melt it. A study of the receipts which follow, together with reference to the description of materials and the object of each, will enable the reader to figure out the law of glazes. CHAPTER VII. Receipts. White Slip for Brick- English Ball Clay, No. 4 40 English China Clay, No. 7 16 Ground FUnt 37 Feldspar 7 100 1.61 ounces of liquid blue stain @ 22% ounces to pint. This slip should weigh from 23 to 24 ounces to the pint. Buff Slip for Brick- Albany Slip Clay 5 Buff Clay 23 Calcined Buff Clay 11 Flint 30 , English Ball Clay, No. 4 27 Eelspar 4 100 Blue Stain- Flint 59.90 Oxide of Zinc 8.16 Nitrate of Soda 4.73 Oxide of Cobalt 27.21 100.00 This blue stain should be well mixed and pulverized, placed 40 CLAY GLAZES AND ENAMELS. in a clay vessel lined with flint, and fired at a very high heat, then broken up and ground extremely fine. It should be so fine as to pass throtigh a No. 16 millers' silk bolting cloth easily when in the slip state. It should always be used of such a thickness that one pint of the liquid stain will weigh 22% ounces. When charging the gi-inding pan put four oxmces of calcined plaster to every six pounds of stain. This will pre- vent settling. The calcined plaster is any old mold that has been calcined at a bright red heat. Different shades of blue can be made by adding blue stain to white slip above. For pearl or very light blue add one-quarter ounce of liquid stain to every pound of dry white slip. For medium blue add one-half ounce of liquid stain to every pound of dry white slip. For dark blue add one ounce of liquid stain to everj' pound of dry white slip. Shades between these, or darker or lighter, can be made by varying the amount of stain. Grays can be made by mix- ing hvS and blue and adding a small percentage of oxide of chromium. Sage Green.— White slip, vnth 12 per cent, oxide of chi'o- mium added. Blue Green.— White slip, with 12 per cent, oxide of chro- mium and 2 per cent of liquid blue stain added. White Glaze, No. 1, for Dipping Wet- English Ball Clay, No. 4 11.G9 Felsjoar 41.5.5 Flint 31.1G Pai-is White 6.50 Fluor Spar 2.G0 Cryolite 2.60 Sulphate of Barium 1.30 Oxide of Zinc 2.60 100.00 CLAY GIjAZES and ENAMELS. 47 This glaze should weigh from 27 to 27% ounces to the pint. White Glaze, No. 2, for Dry Dip- National China Clay 4.50 English China Clay, No. 7 7.19 Felspar 41.55 Flint 31.16 Paris White 6.50 Fluor Spar 2.60 Cryolite 2.60 Sulphate of Barium 1.30 Oxide of Zinc 2.60 100.00 White Glaze, No. 3, for Dry Dip- English Ball Clay, No. 4 4.32 English China Clay, No. 7 6.36 Paris White 7.50 Pelspai- 41.32 Flint 30.00 Fluor Spar 1.27 Sulphate of Barium 1.27 Cryolite 2.54 Oxide of Zinc 2.72 White Lead , 2.70 100.00 White Glaze, No. 4, for Wet Dip- English Ball Clay, No. 4 14.18 Felspar 33.46 Flint 18.90 Paris White 20.47 White Lead 11.03 Oxide of Zinc 1.18 Borax 78 100.00 48 CLAY GLAZES AND ENAMELS. Chocolate Brown Glaze for Wet Dip- Albany Slip Clay 50.38 English Ball Clay, No. 4 4.65 Felspai- 20.15 Flint 9.69 Paris White 2.71 White Lead 3.1092 Oxide of Zinc 7752 Boracic Acid 3876 Cryolite 7752 Eluor Spar 3876 Sulphate of Barium 8876 Oxide of Manganese 1.5504 Chromate of Iron (Native) 1.5504 Chromate of Lead (Yellow) 3.1092 Red Oxide of Iron 3876 100.0000 In preparing this glaze weigh out the stains (oxide of manganese, chromate of iron, chromate of lead and red oxide of iron) first and gi-ind extremely fine, then add the other materials. In all glazes it is well, unless the cryolite, fluor spar and sulphate of barium are fine, to put these in the pan first and gi-ind them thoroughly before putting in the other materials. These slips and glazes will be found to work well, where suited to the contraction of the brick, at the heat at which Albany sUp clay fuses into a smooth, almost black glaze, with possibly a slight tendency to show thin on the sharp edges of trials. I prefer the glazes without lead, simply because the lead glazes are so heavy that they are hard to dip without running heavy on the low edge of brick. From^ experiments made since using these glazes I believe additional oxide of zinc would improve them. The small amount of soluble flux CLAY GLAZES AND ENAMELS. 49 in white glaze No. 4 and in the chocolate bi'own glaze did not seem to do any harm. In case the color is not satisfactory, from 3 to 10 per cent, of oxide of tin added to glaze will probably improve. The lesson in Chapter VI must be borne in mind, and if the slip cracks or shells it must be altered in accordance therewith. The glazes may be softened with lead or a little cryolite, or, preferably, with the artificial mix, made by melting together equal parts of feldspar and borax and substituting this mix for part of the feldspar. In alter- ing glazes never forget, if they work well in all respects but fusibility, to keep the clay the same percentage of the new mixture that it was of the old; that is, if you add a material, add clay also; if you take out a raaterial, take out clay also. The following receipts will work on bodies that shrink less than the bodies that suit the mixes given above: White Slip, No. 2, for Wet Dip- English Ball Clay, No. 4 12 Flint 25 English China Clay, No. 7 44 Felspar 8 Plaster of Paris 11 100 White Slip, No. 3, for Dry Dip- English Ball Clay, No. 4 10 Flint 56 Felspar 28 Plaster of Paris 6 100 The glazes given above will work over these slips, Nos. 1 and 4 over Slip No. 2, and Nos. 2 and 3 over Slip No. 3. For 50 OLAY GLAZES AND ENAMELS. work over colored slips it is better to soften the glaze a little. If glaze has partially opaque spots in it when used over colors it requires more flux, and, at the same time, probably less lime. For soft glazes we must resort to lead as a flux. Many of the English writers will state that this is wrong, but our crock- ery glazes are nearly all lead glazes. We can freeze ice cream in vessels coated with a lead glaze, then boil water and acids in them, and they stand it perfectly through years and years of use. Brick have been in walls for twenty years at least, coated with a lead glaze even softer, and very much softer, than anything I advocate, and they are perfect to-day. These brick have been exposed to the weather during that time. Many glazes that contain no lead are much less reliable than a good lead glaze. The greatest objection to a lead glaze is the danger to the operatives of lead poisoning unless great care is taken. The boys that brush off the glaze from edges after brick are dry should wear sponges' over mouth and nose, or some device that will prevent their inhaling the dust. I have worked in lead for nineteen years and have never been poisoned thereby, and have not known of a case of lead poi- soning from this source that was not directly traceable to gi'oss carelessness. The following is a lead glaze of about the extreme degree of softness. This will be found reliable where the heat suits it: Glaze No. 5— Enghsh Ball Clay, No. 4 11 Felspar 30 Flint 15 Pai'is White 8 Oxide of Zinc 4 White Lead 32 100 CLAY GLAZES AND ENAMELS. 51 This glaze will fuse at about the heat where Albany slip clay becomes a brown semi-glaze. It cannot be put on all clays by the single fli-e process. The clay must be one that burns hai'd at a low heat, so that the clay will be burned clay and have some strength before the glaze begins to melt. In alter- ing this glaze retain the full percentage of clay, as this seems to be what makes it applicable to the single fire process. Without the clay in it the glaze will draw up in drops. By mixing this glaze with glazes Nos. ,1 and 4 different degrees of fusibility can be obtained. I must repeat my advice above, however— get along without lead, if possible; try to get the fusibility with the artificial mix so often mentioned. We now come to the subject of stains. I will give a num- ber of receipts for stains, but cannot voueli that the colors given will always be obtained, so much is dependent upon the materials employed, the skill in compounding and the heat to which they are fired, but stiU more is dependent upon the glaze over them, if they are used as stains for slips, or the glaze with which they are mixed, if used as glaze stains. For instance, crimson, if mixed with a clay slip, will yield almost no color at all; if mixed with a slip containing little clay, a large quantity of paris white and some glaze, will, wtien coat- ed with the proper glaze, yield a fine crimson color. If the glaze contains much borax the resulting color will be purple or lilac. If the glaze contains little or no lime the result will be a reddish brown. So if mixed with glaze. In a lead glaze, short in lime, the result will be reddish brown; in a glaze with much lime the result will be crimson; in a glaze with, much borax the result will be purple or lilac. By proper compound- ing, then, crimson stain can be made to yield almost any color 52 CLAY GLAZES AND ENAMELS. ft'om brown, through red brown, to crimson; through the crim- son into pm-ple, and then to lilac, and pink can also be ob- tained from it. Lime will ruin orange. I want to say right here that with chromium, iron and cobalt, properly used, nearly any color can be made; that is, with one or all of these used as stains, and used in the proper way. Certain tones are not attainable, but the crude color is. From cobalt we get our blues, in any shade, by proper combinations. Prom chromium alone we get greens of all shades, reds, crimsons, pinks, lilacs, browns. From iron alone, reds, oranges, yellows, browns. Cobalt and chromium, properly used, give us the different shades of blue-greens and purples; chromium and iron, the rich shades of brown; cobalt and iron, grays and blacks; chromium, iron and cobalt, rich blacks and sombre greens. For some tones we resort to the other metals. Copper for greens, uranium for amber, yellow and some browns; iridium for the finest blacks, platinum for grays that will come uni- form in color, gold for rose and certain purples, manganese for certain browns, antimony in low heat work for certain light yellows, titanium for certain pinks, nickel for peculiar greenish-gray effects, but particularly as a modifier of the other metals. Cei-tain peculiar and fine effects are obtained by the use of chromates, using them as direct stains. Chromate of iron (native) gives different shades of brown; chromate of iron (precipitated) gives a much redder brown; chromate of cobalt gives from Ught greens to dark blues vnth a greenish effect; chromate of copper gives some very peculiar greens, some Qt them very fine; chromate of manganese, from light greenish brown or browni* green to a very deep, rich green brown or bronze green; chromate of nickel gives some very pretty greenish grays. The chromates of potassium, magne- CLAY GLAZES AND ENAMELS. 53 sium, barium, zinc, lead and lime can be made to yield either greens, reds, pinks or purples, depending upon titie treatment given them, remembering that lime, in combination with tin, brings out the red effects, and that borax or boracic acid alters this into purplish tints. Without lime or tin the tendency is to greens. I will only give some of the high heat stains. There is no use of going into the soft overglaze colors, as very few of them will stand beyond a cherry red heat. Chrome greens, cobalt blues, iron yellows, browns from chrome and iron, nickel greenish grays, uranium yellows, platinum grays and iridium blacks, and their combinations, will usually stand well up to very high heats. The tone of the color varies as the heat changes, but they can be relied on to give quite certain ef- fects. Gold and antimony colors stand little heat. Copper stands to about the point where Albany slip clay begins to fuse. It then loses the beautiful green tint and begins to get brown. Manganese stands to a good heat, but changes color quickly; so does iron, when used in large quantities, especially when used in or under a strong lime glaze. —Pinks.— No. 1. Fire Hard- Oxide of Tin 60 Paris White 32 Bichromate Potash. » 8 100 By hard fli'e is meant to the heat where Albany slip clay becomes a rich brownish black glaze, even to the point of running and turning gray. 54 CLAY GLAZES AND ENAMELS. Medium Fire.— Till Albany slip clay becomes a smooth brown or black-brown glaze. Medium Easy.— Till Albany slip clay becomes a brown semi- glaze, or between a semi-glaze and a glaze. Easy Fire.— Till Albany slip clay, 90 parts, red lead, 10 parts, becomes a semi-glaze. No. 2. Fire Hai'd- Oxide of Tin 47 Paris White 23.5 Flint 23.5 Bichromate Potash 6 100.0 No. 3. Substitute chromate of lead for bichromate potash in No. 1. No. 4. Substitute chromate of lead for bichromate potash in No. 2. No. 5. Substitute chromate of barium for bichromate potash in No. 1. No. 6. Substitute chromate of barium for bichromate potash in No. 2. Others can be made by substituting chromic acid or green oxide of chromium for the bichromate potash in Nos. 1 and 2. Slightly different results will be obtained from each. I prefer the insoluble chromate of lead or chromate of barium. No. 7. Hard Fire- Oxide of Tin 64 Pai-is White 32 Chromate of Lead 4 100 CLAY GLAZES AND ENAMELS. 55 Lilac. Medium Easy to Medium Fire- Oxide of Tin 4.17 Borax 41.67 Flint 29.16 Feldspar 8.33 No. 7 Pink 16.67 100.00 This will stain a lead glaze lilac by using about one of lilac to two of glaze, or, by mixing with clay, will make a lilac slip. Can be made stronger by using more of Pink No. 7 or by using more of the chromate of lead in making Pink No. 7. Common oxide of manganese is contaminated with iron and does not yield a good brown. Pure oxide of manganese is ex- pensive. Permanganate of potash yields quite a pure man- ganese, but must first be fritted. Below is a good way of frit- ting for a good red-brown stain. The stain will be gray, but it will make a red brown glaze: Brown Frit. Medium Fire- Feldspar 66.67 Permanganate of Potash 33.33 100.00 From 3 to 20 per cent, in glaze will produce from violet to red brown. Crimson. Medium Easy Fire- Pink No. 6, after burning and grinding fine 42.83 Paris White 9.53 Flint 9.53 White Lead 9.53 Oxide of Tin 14.29 Boi-ax 14.29 100.00 56 CLAY GLAZES AND ENAMELS. 33 1-3 per cent, crimson, 33 1-3 per cent, lead glaze, 16 2-3 per cent, parts white and 16 2-3 per cent. No. 4 ball clay will make a crimson slip. 10 per cent, crimson, 3 per cent, oxide tin, 15 per cent, white lead, 6 2-3 per cent, paris white and 65 1-3 per cent, lead glaze will make a crimson glaze. Matt Blue. Fire Very Hard— Aluminate of Potash 33.80 Hydrate of Alumina 11.27 Oxide of Zinc 22.54 Flint 16.90 Nitrate of Potash 0.86 Oxide of Cobalt 5.63 100.00 Grinding and firing again will improve. This is a much simpler method than the ones usually given for Matt Blue, and produces fine results. Matt Blue, No. 2. Very Hard Fire- Hydrate of Alumina 73.40 Oxide of Zinc 18.35 China Clay 2.75 Oxide of Cobalt 5.50 100.00 Mazarine Blue. Medium Easy Fire- Paris White 16 Red Lead 10 Flint .10 Nitrate of Soda 4 Oxide of Cobalt 60 100 This is a very strong blue. CLAY GLAZES AND ENAMELS. 57 Blue, No. 1. Fire Hard- China Clay 40 Oxide Zinc 20 FUnt 10 Nitrate of Soda 10 Oxide of Cobalt 20 100 There are so many ways of making black, each suited to the particular situation, and, possibly, not to any other situa- tion, that it is useless to give receipts. Chromate of iron (na- tive), from 80 to 98 per cent, with oxide of cobalt, from 20 down to 2 per cent., will make black under proper conditions. Albany slip clay and cobalt, iron and cobalt, manganese and cobalt will make black. These blacks will have a brownish, bluish or greenish tinge. If the business' will stand a cost of $50 to $150 per pound for black, it can be made from iridium, but usually it is better to be content with a slight tint in the black. A deep blue glaze over red slip clay will make a jet black when the depth of color of the red and blue are prop- erly adjusted. Use a mazarine blue stain for making the blue glaze. If the brightness of the blue is killed by adding a little iron, copper or manganese to the blue glaze the result is usu- ally better. Grays are the same as blacks. Copper, man- ganese and cobalt will make blue grays, green grays or brown grays, depending upon the proportions. Chromium, iron ajid cobalt will give a very pretty series of grays in light tints. BufC clay and cobalt or bufC clay, manganese and cobalt will yield good grays. Chromate of iron (native) and cobalt will yield good grays from light to very dai-k, but for really fine high heat neutral grays we have to tm-n to platinum. The high heat greens ai-e usually made from chromium in 58 CLAY GLAZES AND ENAMELS. some of its many forms, the lower heat green glazes from cop- per. The black or red oxide of copper cau be used direct in glaze without previous burning. Green, No. 1. Hard Fire — Flint 40.70 Paris White 4.42 Borax 10.62 Oxide of Zinc 8.85 Plaster of Paris 10.63 Bichromate of potash 22.12 Oxide of Cobalt 2.66 100.00 Green, No. 2. Grind Only- Green, No. 1 94 Oxide of Cobalt 6 * 100 Green, No. 3. Hard Fire- Flint 31.67 Paris White 20.28 Bed Lead 8.87 Plaster of Paris I'.ei Fluor Spar 10.02 Bichromate of Potash 21.55 100.00 Green, No. 4. Hard Fire- Oxide of Zinc 14.81 Flint 37.04 Borax 18.52 Oxide of Chrome 22.22 Oxide of Cobalt 7.41 100.00 CLAY GLAZES AND ENAMELS. 59 Green, No. 5. Hard Fire— Fluor Spar 20 Whiting 15 Flint 25 Oxide of Chromium 40 100 Green, No. 6. Hard Fire- Flint 29.00 Paris White 28.12 Oxide of Nickel 28.58 Oxide of Chromium 14.30 100.00 Green, No. 7. Hard Fire— Paris White 6.78 Oxide of Zinc 40.68 China Clay 40.68 Oxide of Chromium 1.69 Oxide of Cobalt 10.17 100.00 Green, No. 8. Hard Fire- Red Lead 22.22 Flint 22.22 Paris White 27.78 Tin Asii 11.11 Oxide of Chromium, 16.67 100.00 The shade of green can be altered by addition of cobalt— that is, made more blue— and can be deadened by adding a little manganese. The browns are nearly all derived from combinations of iron and chromium or from manganese. The chromium may 60 CLAY GLAZES AND ENAMELS. be used as chromate of potash or oxide of chromium, and the iron either as Iron scales or oxide of ii'on. These, when com- bined with oxide of zinc, produce the lighter or claret browns, and, when combined with fluxes, produce darljer browns. The browns can be mixed with the chrome pinlis to advantage for red browns. Cobalt will mix with the chrome reds and pinks, produdng pm'ples. In experimenting with colors, after having perfected the white, it is vmdoubtedly better to buy the stains in the form of underglaze colors rather than to bother with making them. After certain tints are secm'ed, then it may be well to learn how to make the stains for their production, but even then, if the business is one requiring constant new colors, and there is no certainty that there will be a constant demand for any one of them, it pays better to buy stains than to make them. Of course, if there is a constant demand for certain colors, then it pays to make the stains. A pound of crimson stain will cost about one dollar and a half, and it can be made at a cost for materials of about I314 cents, but by the time a few pounds are mixed, then burned and ground, and the second mix made and burned and ground, there is veiy little advan- tage In maJiing It. If made by the hundi-eds of pounds it would pay handsomely. The lai-ge number of color mills nec- essary where stains are made, or else the constant and care- ful cleansing of a few, is quite a source of expense. On paper it looks very jirofitable to make the stains, but in reality it is not, unless, as I have said, there is a constant demand in fairly large quantities. CHAPTER VIII. Preparation of Slips, Glazes, Etc The preparation of slips, glazes and enamels is a simple op- eration, but is one' requiring great accuracy and a mind per- fectly free from other cares. It is very easy to make mistakes, and they are generally quite disastrous. With the number of materials that must be handled and the diverse and often odd weights that must be used, it is sometimes quite perplexing to one vcho is not in the habit of doing it. Of course, constant use of certain formulae makes the operation of veeighing out mixes largely mechanical, but often this is the source of great- est danger, as the mind is apt to v^ander to other matters, and a mistake is the result, so the old advice to keep your mind on your business comes in with full force. The an'angement of mixing and grinding rooms will vary so for different kinds of work and for the quantity of work to be done by this department that any attempt to even indicate it in a work of this character would be hopeless. There should be sufficient bins in the mixing room to hold all materials of which large quantities are used, and these bins should never be changed, so that the mixer can find any material, even in the dark, If necessary. I have found the 62 CLAY GLAZES AND ENAMELS. most convenient arrangement to weigh in to be a shallow box, holding about two hmidred pounds of felspar, with a piece of wood firmly fastened level with the top of each side, and pro- jecting eight to ten inches beyond the ends. These pieces of wood will form two handles at each end, so that the box can be can'ied in the same manner as a stretcher. The scales used should all b© ai-ranged for the same kind of weights. I have frequently seen a large and medium sized pair of scales ar- ranged for avoirdupois and a set of grain scales arranged for ti'oy, or apothecaries' weights, and the operator had to spend much time In reducing one system to the other. Of course, this only applies to exi>erimental work, as grain scales are not used in regular work. Pint measures and small vessels for experimental work are best to be of granite ironware of good quality. For dipping vessels I have failed to find anything better than a good wooden washtub. Glazes should all be ground. Slips may be prepared either in a blunger or a grinding pan. The latter is preferable, even for slips. It is not so rapid or economical to work as the blunger, but does better work. , The storage tanks or vats will depend upon the size of the business. If it is small, small, deep tubs holding, say, one hundred gallons, and that are low enough to be easily stirred by hand, ai'e all that is necessary, but even in a small business large vats, containing a stirring device, kept constantly running, will be found advisable for white slip ajid white glaze; in a large business a number of such vats will be required. The stirring device should run very close to the bottom of vat, so as not to allow much ac- cumulation under it. The charge of slip or glaze being weighed out, it should be fed slowly into the blunger or grinding pan, which has CLAY GLAZES AND ENAMELS. 63 previously had a little less than the requisite amount of water put into it. Charge the clay first, then the lighter non-plastic materials, then the heavy non-plastic materials. In case plas- ter of paris is used, it should either be charged first or mixed with water by hand and added. If the capacity of preparing apparatus is limited much time may he gained in iweparation of slips by putting the clay to soak in a tub or barrel over night. The sieving may be done by hand, but even in small •plants a mechanical device will pay.( ft is better to use two sieves, passing the material through a No. CO or No. 80 brass wire sieve first, and then through a No. 100 brass wu'e sieve for slips, and thi-ough a No. 100 brass wire sieve and then a No. 150 for glazes. | This saves the finer sieves, which are weaker and more expensive. The very best sieving arrange- ment known to me is a frame suspended from a shaft above and oscillated through about a two-inch or three^inch space very rapidly, I should judge about six hundred times per min- ute. The sieve is placed on a slight slant, and is entirely open on the low side. This sieve is entnely mechanical, the sieved material falling through it into a box below, from which it may be conveyed to its final destination. The giit and dirt gradually works to the low edge and drops off into a trough or box placed for its reception. There may be two of these sieve frames, and the material can pass directly from one to the other, or a single frame can be arranged so that the sieve can be easily and quickly changed, and the charge, as it is sieved the first time, can be elevated into a proper tank, and when the first sieving is finished it can be passed through the second sieve. After passing through the second sieve it can be elevated by pumps into the final receptacle. All slips and glazes should be resieved just before using. A No. 100 64 CLAY GI/AZES AND ENAMELS. sieve is fine enough for this purpose, as the object is simply to break up any stringiness or lumplnessv and is usually best done by the dipper or his boy. If you use English ball clay, No. 4, and a vat system, aUow your slips and glazes to be- come at least a month old before using. If you use the hand system and carry no stock, and for orders for siKJcial colors, use the slip or glaze immediately. In a few days a fermen- tation takes place in liquids containing this clay, and it fills with gas bubbles. After a month or so this fermentation ceases, and the slip or glaze becomes smoother and tougher than at first Where possible, carrying slip over the winter is a good thing. Allow it to freeze and thaw as much as possi- ble, re-blunge and sieve, and a very smooth, fine slip will re- sult. Where colored slips are made by staining white slip and colored glazes by staining white glazes, it is advisable to reduce such receipts to slop receipts, either adding sO' much dry stain to so many buckets, gaUons or pints of slip or glaze, with the slip or glaze of a fixed weight per pint, or adding a certain quantity of slop stain, at a fixed weight, to a certain quantity of slip or glaze, at a fixed weight. This enables one to use old slips and glazes even for colore, without the neces- sity of carrying a stock of these colors. As this is written more for those who are experimenting in this business than for those who understand it, a brief de- scription of the easiest way to prepare slips and glazes by hand vdll be in order. In receipts where English ball clay. No. 4, is used, much labor is necessary to reduce it to the proper degree of fineness, as it is a very gummy, tough clay, and contains considerable vegetable matter. Gi-ind or break the clay fine. Always put water into the mixing vessel first and add the clay to the water; never poiu* the water on the clay. CLAY GLAZES AND ENAMELS. 65 For slips you aeed a No. 40, a No. 60 or 80 and a No. 100 sieve; for glazes, a No. 60, a No. 100 and a No. 130 or 150 sieve, all of bi-ass. Never use a silk lavcn except for stains. After the materials are all thoroughly soaked and mixed with the hand and worked as fine as possible, for slips, rub the mixture through a No. 40 s.ieve, using a block of hard wood to rub with. Rub until every particle of clay Is through. Then nib through the No. 60 or No. 80, then through tlie No. 100. After it has been rubbed through the No. 100 sieve, shake It tlirough the same sieve, and it is finished. For glazes, treat in the same way, subs.tituting the 60 sieve for the 40, the 100 for the 60 or 80, and tbe 130 or 150 for the 100. The slip or glaze should be thicker than is needed, when you commence, as the rinsing of vessels, etc., will tliin it considerably. The thickness of a slip can be much affected by acids and alkalis, acids usually thickening and alkalis thinning. This may be the reason that aging makes such a difference in the thick- ness of some slips. Chemical combinations may take place that alter its acidity or alkalinity. In sieving, always have the mixture to be sieved as thick as possible. The material becomes much cleaner without using such fine sieves. There is now being made a No. 200 brass wire sieve cloth which makes a very good substitute for the No. 16 silk lawn. If soluble fluxes ai'e used in either glaze or slip, these glazes or slips must be mixed of regular thickness, as water cannot be taken off without removing some of the flux dissolved in it. The thickness to which slips and glazes should be mixetl depends upon the condition of the clay to which they are to be applied, and can only be learned by experience. The weight per pint will vaiy, depending upon the character of the materials used. The more tough clay the lighter the mix- 66 OLAY GLAZES AND ENAMELS. ture will weigh for a given thickness, and the more heavy material (such as barytes, lead, etc.) the heavier it must weigh. All stains and frits should be groimd exceedingly fine, cer- tainly fine enough to pass easily through a No. 150 sieve, and it is better to have them pass through a No. 200 wire sieve or a No. 15 or No. 16 silk lawn. There are a number of machines for the grinding of these materials. There is a modification of the Alsing mill, a porce- lain-lined nimble, carrying flint pebbles. These machines grind wet or dry, but are expensive. They are rapid grinders, and their dry grinding is of great value. They are easily cleaned to change from one color to another, and where the stains are carried in stock dry the use of this machine obviates the necessity of drying the material afta* it is ground. In the wet mills there are a number of difCeremt styles, some high-priced, quick-grinding machines, others low in price, but slow grinders. ■As a rule, a number of the slow, cheap machines will be found' better than a few of the high-priced, rapid grindara. There will be less changing of colors in each mill. The thorough cleaning of a wet mill is a great nuisance. The mills driven from overhead are preferable to the undergeared mills. I have had experience with both, and my opinion is very decided in this particular. With a plant of overgeared mills we rarely, if ever, had any trouble, and with a plant of undergeared mills, made by the same mak«-, we were nearly always in trouble. The pumping machinery for slips and glaaes can be of the simplest character. Common cucumber pumps, arranged to drive by power, will be found to answer every purpose for ele- vating slips and glazes. They are very cheap and will give good service. One of them will handle slip enough for at least CDAY GLAZES AND ENAMELS. 67 sixty million brick before it is worn out. In a small brick plant the pump would probably rot out before this quantity of slip would be used. The little calculation was made from a cu- cumber pump in a pottery that handled five to six tons of clay in slip form every day. and would wear from two to three years. It is probably needless to say that all slip and glaze vats should be covered, and that every precaution should be taken to keep all prepared material scrupulously clean. CHAPTBU IX. Dipping and Cleaning. There are different ways of dipping. Eacli way has its ad- vocates, and there are undoubtedly good points about each. For most days it is advisable to put a thin coat of slip on with a brush before the dipping is done. This preparatory coat shovdd be well brushed in, and especially about the edges and ends. A flat camel' s-hair brush, about the width or slightr ly wider than the brick, is the best for this pm'pose. If oil on the brick is at all bothersome, a very little strong ammonia water mixed vrith the slip used for brushing will be fotmd a very good thing. With some clays that are inclined to pin- hole a preparatM"y dip will be found advantageous. This pre- paratory dip may be made largely of the same material as the brick, but, of covirse, made very fine. I prefer, however, to use white slip, even for the preparatory dip. In case the preparatory dip is a fairly good white, the finishing slip coat need not be so thick. For wet dipping, when no prepai-atory dip has been used, the slip should be as thick as it can be made and at the same time work smoothly ; if ridges form from the corners diagonally across the face the slip is too thick. CLAY GLAZES AND ENAMELS. 69 There is the single-hand method and tlie metliod whicli uses both hands. For the first method the brick is taken by the back and, with a sweeping motion through the slip, is dipped. The brick should be held with the face to be dipped a little out of level. ( The edge that is in advance should be a little higher than the back edge. The edges of the brick should be vertical to the direction of the sweep; that is, if the stretcher face is being dipped, the direction of the sweep should be par- allel to the heads.J For bricks dipped on two contiguous sides there are two methods. One is to dip one edge, remove the brick entirely from the dipping tub and tm-n, and then dip the other edge. I prefer to start on the head and dip that with a cm-ve away from the body; that is, the brick is placed in the slip with the header end below the surface and the stretcher face vertical to the sm-face of the slip; then, with a turn of the wrist, the brick is turned, remaining in the slip all the time, until the stretcher side becomes parallel to the surface of the slip and below its surface; then, with a sweep- ing motion to the left and parallel to the heads, the whole brick is removed from the slip. This second method avoids the streak near the corner that is apt to be formed by the first method. Where two hands are used, the brick is held by each end, dipped and then turned directly away from the body. The two-hand method has the advantage of not marring the bi-ick so much as when only one hand is used, but it is not so quick. A dipper and two boys will slip and glaze from 1,600 to 2,000 brick per day. After the slip is on there are two com'ses open, either to glaze the brick while wet or to allow them to dry thoroughly before glazing. In the first case the brick are allowed to stand 70 CLAY GLAZES AND ENAMELS. until the moisture from the slip lias nearly all soaied into the brick and the slip has a very slight shine, something like a piece of thoroughly vitrified clay. This shine only shows in a proper light by reflection. The glaze dipping is done in the same manner as the slip dipping. If the brick are allowed to dry before the glazing is done they should be thoroughly dry, and, better, dry and hot. The face to be dipped should first be dipped into water and then into the glaze. This method sometimes gives ti'ouble by producing numberless small blis- ters. The reason tov this does not seem well understood, but in my opinion it is due to the water from the glaze peneti'at- ing clear through the slip and causing an expansion in it. Anyway, the dryer and hotter the brick the less apt is it to occm% and the tougher the slip used the less apt is it to occm'. After the brick are finislied the drying should be veiy slow at first, or until the slip and glaze are both well set, and the drying that is done should be with very little heat. I notice that one writer on this subject condemns steam heat at this stage of the operation. I prefer it to any other kind of heat, simply because it is easily conti'olled, can be turned on or off at short notice, requires little attention, and does veiT satis- factory work. The arrangement of dipping room may be one of many, but, whatever it may be, it should be one of such a nature that the brjck can remain upon the dipping shelves until dry unless a car system is in use. A system that requires the biick to be removed fi-om the dipping shelves and placed else- whei'e to dry adds an extra handling which tends to further mar the brick and adds to the expense of manufacture. There- fore, the dipping rooms should be combination dipping and drying rooms. This can easily be managed by having parallel CLAY GLAZES AND ENAMELS. 71 rows of shelving, far enough apart to allow the clipper tO' work between them. Each set of shelves can be arranged with steam pipe, and the whole room can be arranged with the necessary arrangements to secure ventilation, so as to carry off the moisture. If I remember correctly, there are about ten ounces of water to be driven out of each brick, and a pi-o- ductlon of 10,000 bridt per day requires the daily evaporation of 100,000 ounces, or over 6,000 pounds, or over three tons of water. These rooms should be arranged so as to hold a day's work as nearly as possible, so that when once filled they can be closed up and not interfered with until the brick are diy. After the brick are slipped and glazed and thoroughly di-y, the surplus slip and glaze which the dipping operation has placed on the sides and ends must be removed. This is best done with a wire brush made of the old card wire from a woolen or cotton mill. This is a -stiff steel-wire brush, made on leather, and can be purchased at almost any woolen or cotton mill for a mere song.' Tho belt is usually five to six inches wide. This should be cut into pieces about fom- inches long and tacked on to an inch pine board a little larger than the piece, say about 4%x6 inches. The length and weight of the wire out of which this card vrire is made vsiries consider- ably. I cannot give the proper number, as I never knew it by number. The correct size is one of the medium numbers. If the wire is too coarse or too long it will chip the edges, and, if too fine, will not give good service. With a proper brush of this character the surplus slip and glaze can easily be removed and a slight crook in the brick can be straightened. If the briish is not properly handled the corners will be rounded, edges chipped, and the brick gener- 72 CLAY GLAZES AND ENAMELS. ally be rendered anything but sightly. The brick should be placed on Its edge, the one opposite to the enameled edge, the brush placed firmly on the flat side and parallel there- with, and then drawn with a sliding, and at the same time downwai'd, motion across the brick. The motion should always be slightly away from the enameled edge and towiu-d the body of brick, else the wires may chip off some of the slip or glaze. If there is much tendency for either slip or glaze to peel the cleaning operation will probably make it show itself. When dipping the brick, particles of clay are bound to drop from them into the dipping tub, and after a number of brick are dipped the slip or glaze becomes quite dli'ty. This necessi- tates constant cleaning by resieving. A very good plan is to have a sieve made of about 100 wire for slip and 120 for glaze, this sieve to be made so that it will fit into the dipping tub and be about fom- or five inches below the surface of the slii) or glaze. By removing and cleaning this sieve occasionally all the dirt will be kept out of the tub. A small hand sieve should be furnished each dipper with which to remove particles of dirt that ai'e seen on the surface of slip or glaze. In setting brick on dipping shelves be careful that they are not set too fai' back, foi-, if they are, when they shrink in dry- ing it will be found that the lower corners of many brick will be cracked loose. After the brick are cleaned they should be directly set on the cars or other device for transporting them to the kiln. If the two-wheeled ti'uck previously described be used, racks should be made that will fit one on top of the other, and with heavy sides a little higher tlian the width of a biick.^ Five of these I'acks in height can be handled by a pi-operly constructed CLAY GLAZES AND ENAMELS. 73 truck, and, with thirty brick to each rack, will make a load of ono hundred and fifty brick; or the racks may be uiadt; nar- rower, if so desired, so that the load will be reduced to one hvmdred brick. A wooden floor in kiln shed is not advisable, and if a brick floor is used there will be some sihakins and jarring of the load in passing over it. This will cause much chipping of the brick unless some precaution is taken. A very good device to obviate this difficultj' is to have sti-ips of straw- board, about one-eighth inch thick, and a little naiTower than the brick, placed between each row of brick as tlie.v are placed in the racks. This will make it Impossible for the brick to knock against each otliei-, even if the load gets a severe jar. I forgot to mention the number of dipping and drying rooms needed. It will take throe days, or should take three days, to dry the brick. This, together with the day taken to dip them and the day to clean them and get the room ready for the next lot, will malie in all five days, so that five such rooms will be required, and it is better to have six, so as to take just one week in making the round. Bach room will take a space of 1 feet by 36 feet for each 1,000 brick daily capacity; that is, for .j,000 brick six rooms, 20 by 36, will be needed, and for 10,000 brick per day six rooms, 40 by 36 or 20 by 72, or some other proportion that will give this space. This seems like considerable space for a small capacity, but once built and paid for it will be found much more sa.tisfactory than any attempt at concentration. Where the whole of the dipping is done on the dry or burned brick the ordinary methods of drying may be used and the business much concentrated, but there are difflculties with dry dipping that probably more than counterbalance this advantage, and the cost of an extra setting and burning cer- tainly is against dipping bui-ned brick. CHAPTER X. Setting and Btu-ning. So fai' in oiu- opefations we have expended labor only. The material spoiled can all be sent back and reworked, but we are now to undertake an operation which, if unsuccessful, will entirely ruin it, except the small proportion that might be used as grit. It will certainly pay us, then, to see that no brick already impei'fect shall enter the kiln. To this end it is well to punish severely any cleaner who passes through an im- perfect brick. The brick are right under the cleaner's eyes, and no defect can escape his attention if he keeps his eyes open. After seeing that we have perfect brick to enter the kiln it would be the height of foolishness to set them in any- thing but a perfect kiln; but here opinions differ. Which is the perfect kiln? For enameled brick economy of fuel cuts less of a figm-e than in some other branches. Let us suppose our brick have cost us eighteen dollars per thousand, set in the kiln, and we set 20,000 in the kiln. This kiln full of brick has cost, then, $360.. We will assume we should get 90 per cent, of firsts brick, and that the kiln consumes forty tons of coal at $3 per ton; that the cost of bvtrning and emptying kiln is $40. We would have 18,000 No. 1 brick at a total cost of $520, or $28.88 per thousand. We will take another kiln that CDAY GLAZES AND ENAMELS. 75 will consume only twenty tons of coal, but, we will say, due to its poor burning, we get 15 per cent, additional bad brick, or 75 per cent, in all of No. 1 brick. We would have 15,000 No. 1 brick at a total cost of $460, or $30.66 per thousand. We will ta,ke another kiln and assume it burns five tons of coal, but spoils an additional 15 per cent, in the bui-ning. We would then have 12,000 No. 1 brick, at a total cost of $415, or $34.58 per thousand. I have taken exti'emes in the difference of amount of fuel consumed and have been very mild in the dif- ference in percentage of pen'fect brick ijroduced, and yet we see the less economical kiln produces a larger output and at less cost per thousand. Now. I do not mean to argue that the best kilns are the least economical; on the pontrai'y. I believe the best kilns are the most economical — that is, the most eco- nomical of their style. I merely wish to warn those who con- template building kilns for the jjurpose of bmiiing enameled brick not to look so much to the economy of fuel as to the eiflciency of the kiln. Put up a kilu that will bm-n evenly throughout and trust to luck on the coal bill. Having a per- fect kiln, don't overcrowd it at a risk, foi' even if you succeed in getting 25,000 brick in it instead of 20,000. and thereby have an additional 7 pei- cent, spoiled, it does not pay. supposing the kiln to bm-n with the same fuel. Again, let the setting be perfect for the material employed. If your brick will stand the weight perfectly set eight feet high, set them that way, but don't risk them ten feet high. If they will not stand well over fom- feet high, make some an-angement for supporting them. If they will not stand open burning, bum in seggai's. Tlie difference in cost between saggers and open bm'ulng is not so tremendous as some writei-s try to make out. It is probably from $3 to $3.30 per thousand. 76 CLAY GLAZES AND ENAMELS. The uixiraft kiln will probably stand more faulty constme- tiou than the down-di'aift kiln and give fair results, but the down-draft kiln, when properly constracted, will give excel- lent results. The best kiln, in my opinion, for this class of work, is the down-draft, with under-draft to center. It is un- der perfect control, and there is no long hold necessary to bring up the bottom; in fact, the bottom can be firca uotter than the top if desired. It is an extremely economical kiln. This is undoubtedly due to its even-burning qualities. No fuel is wasted waiting for cool spots to heat up. As usually built, with annular flue for the waste heat, it is an expensive kiln to build, but this might be obviated without samflcing its good qualities. It is better not to build the kilns too large; beyond eighteen feet in diameter I believe to be a mistake. The English are probably ahead of us on Idln building for this class of work. It is natural that they should be, not only on this point, but on othera also, as they have had yeai-s of ex- perience. I understand they use rectangular kilns in many in- stances, and I have had di^cribed to me kilns Avorking in suc- cession; that is, the waste heat from one kiln drying off and watersmoking the next. In this country, so far as I have seen, round kilns are used, of various styles, plain up-draft and plain down-draft, and .down-draft with iinder-di-aft. For open fire the kiln usually should not exceed eight feet in height to spring of crown, though there may be clays that will stand higher setting. For setting in saggers the kiln may be as high as fourteen feet to spring of crown. There ai-e two methods of setting open. One is to set in concentric circles, all brick on end, with enameled faces about one inch apart. After setting three high on enu, cover and tie the two rows with a tile; then set three high to top, occasion- CLAY GLAZES AND ENAMELS. 77 ally tying two rows or circles together. There should be oc- casional openings left through the rings, so that the ditEerent flue spaces will not be isolated. Between the double rOws a two to two and one-half inch space should be left. Where it is desired to set quoins, the brick stretchers are set five to six inches apart, each course covered and the quoins put be- tween the stretchers. The other method is to set two to three feet high in parallel straight courses, and then to set two or three feet more, the line of the second set being at right angles to the first. Some brick are set on end and some on edge, the headers being used as ties. In this method very few, if any, tile ai-e used. This second method gives a more uniform draft, but it is more difficult to keep the brick sti'aight. The setting in saggers is Impossible to describe, but it is easy to obtain setters who thoroughly understand it. The advantage of saggers is great, as there is unimpeded draft in all direc- tions, and a kiln so set will bum more uniformly. Each bi-ick has to bear its own weight only, so that clays may be used that would be unfit for open burning. Also, many clays will bm-n easily in saggers without cracking that are almost im- possible to burn in an open-fire kiln. A convenient size for saggers is 9%xl0 inches by 9% inches deep. Such a sagger will hold six English size brick, set across the 9%-inch way, and will have a space of one inch between the faces, or the same sagger will hold eight American size brick, set the other way, and leave a one-inch space between the faces. The burning of enameled brick may be done with either hard or soft coal or fuel oil. There seems to be no special ad- vantage in any one of these fuels except the local one of ex- pense. The firing S'hould be slow and steady. Especial pains should be taken not to allow the heat to go down at any point 78 CLAY GLAZES AND ENAMELS. from the begiuniug to finish. About five days is necessary to burn a liiln set open, but the burning oan be done in three or four days when the brick are placed in saggers. The same care is necessary from the time the wateremoke commences to leave the brick until -it is all out, as with other brick, and between these points the firing must not be pushed. With lime glazes the cooling can be done slowly from the time kiln is finished until cold, but with glazes containing lead the kiln should be cooled as rapidly as possible for three or four hours, or until it has perceptibly cooled, and then it should be closed up and cooled slowly. ' Muffle kilns are sometimes used, but they possess no ad- vantages and many disadvantages. They are expensive to burn and keep in repair, and are difficult to bum evenly. ' The finished brick are usually assorted into three grades. The No. I's are the perfect brick; the No. 2's are those with slight defects, but good enough to present a fair appearance; the No. 3's are those which are unfit for use as enameled brick, and include the cracked and chipped brick and those which are underfired or overfiired. The packing is usually done in barrels, and sawdust makes the best material in which to pack. Where they can be handled open at the building it is cheaper to pack directly in the car, using straw or sawdust as a pack- ing material. The brick really carry better than in barrels. Some manufacturers are using boxes made of corrugated or indented strawboard, and eaxjh brick is placed in a separate box. This makes a very nice way of packing the brick, espe- cially if they are piled in stock in these boxes, as they are not apt to receive any injury, but if a large stock is carried con- siderable extra capital is locked up in these boxes. A comparison between the economy of English kilns and CLAY GLAZES AND ENAMELS. 79 kilns on this side of the water is probably in order at this time. I quote the following from an English writer: "The quantity of coal required to complete the burning of a kiln of 18,000 bricks is found to be from twenty-four to twenty-six tons, the coal employed being of first-rate quality and of high calorific value." This is a little better than I have been able to do, burning in saggers in an up-draft kiln, but in down-draft kiln, with under-draft, brick placed in saggers, about thirty pounds of sagger to forty-two pounds of brick, I have burned 7,500 English size brick with seven tons of bituminous coal, and I understand in larger kilns 15,000 are being burned with from ten to twelve tons of bituminous coal. The heat used was certainly not lower than the English, as three brick, from three of the best English makers, were placed in the kilns on this side and the glaze was overfired. CHAPTER XI. Majolica Glazes and White Enamels. Majolica wai'e is ware that is decorated with colored glazes. These colored glazes, may be transparent or opaque, though they are usually transparent. Prom this has come the custom of calling colored glazes majolica glazes, especially if they are low heat glazes, as majolica is generally made at a low heat on account of the greater variety and beauty of colors attain- able at a low than at a high heat. There was a. time when I thought it impossible to make these glazes so that they would not craze, but have since found that they will stand, on a proper body, as well as any other glaze. Beautiful results can be obtained by the use of these glazes, but they are not to be depended upon where uniformity of tint is necessary. There is usually more or less flow of the glaze, which causes slight variations in the depth of color, and also slight variations are bound to occur in the thickness with which it is put on, no matter how much care may be exercised. The receipts that follow are suited to some clays by the single-fire process, and slight changes will adapt them to many others. They are suited to all clays by the double-fire process, provided they have white slip under them, and further pro- CLAY GLAZES AND ENAMELS. 81 vided they do not craze or shiver. The heat necessary is where Albany sUp clay commences to show signs of fusing. "A," or Transparent Glaze— National China Clay 4.10 Felspar 30.74 Oxide of Zinc 3.69 Paris White 8.19 Flint 16.38 White Lead 36.90 100.00 This glaze should be finely ground and used raw, or witli- out fritting. If found too hard, it may be softened with white lead, but, if found soft, the heat is too high and the colors will not be good. A little tin, say about 5 per cent., may be added for white. Lilac Glaze- Lilac Frit, in chapter on receipts ... 33 "A" Glaze 66 Oaldned Molds 1 100 The frit and calcined molds should be ground together un- til exceedingly fine, then the "A" glaze should be added. This glaze will be i)artlally opaque. Brown Glaze — Brown Frit, in chapter on receipts . . 16.0 "A" Glaze 80.6 Red Lead 3.0 Calcined Molds 4 100.0 The brown frit, calcined molds and red lead should first be groimd together very fine, and then the "A" glaze added. 82 OLAY GLAZES AND ENAMELS. Yellow Glaze- Red OxMe of Iron 1.75 "A" Glaze 98.25 100.00 The oxide of iron should be ground very fine and then the "A" glaze added. The yellow oxide of ui-anium used in quan- tities varying from % per cent, to 2 per cent, instead of iron will give some fine yellow tints. Green Glaze — Black Oxide of Copper 4 "A" Glaze 96 100 Grind the oxide of copper very fine, then add the "A" glaze. This glaze requires careful firing, as a little overfire will give it a brownish tint For lighter tints use less oxide of copper. Pink Brown- Lilac Frit 22.12 Brown Frit 4.92 Red Lead 82 Calcined Molds 41 "A" Glaze 71.73 100.00 Grind the two frits and the red lead and molds together, then add the "A" glaze. Gray— 1 lb Oxide Copper. 2 pints at Stain. 3 buckets of "A" Glaze. 1 bucket of Brown Glaze. The copper should be ground fine, then the stain and brown CLAY GLAZES AND ENAMELS. 83 and "A" glaze should be added. Stain should weigh 22% ounces to pint, and white and brown each 29 ounces to pint. This receipt can be reduced to soilds by substituting foiu'teen pounds of dry glaze for each bucketful of liquid glaze and seventeen ounces dry stain for the two pints liquid. Blue Gray— % lb Oxide of Copper. 2 pints of Stain. 2 buckets of "A" Glaze. 1/^ bucket of Brown Glaze. Moderately Dark Blue— 3 pints Stain. 2 buckets "A" Glaze. If the glaze has been ground, it is only necessary to meas- ure and mix. These tints can all be varied. The iron yellow cannot be made much darker than above receipt and remain yellow, but can be lightened to any extent. The lilac and brown will mix in any proportions. The grays can be made of many shades by varying the proportions of the different stains. Other shades of green may be made by using oxide of chrome. It is better to frit the oxide of chrome with some lead and flint, or use the green stains in chapter on receipts. The blue can be made in any tint from very pale blue to mazarine. Different shades of brown can be made by using ohromate of iron (native), chromate of iron (precipitated), com- mon oxide of manganese, or mixtures of chromium and iron. The majolica glazes require careful firing, as differences in tempei-atm-e alter the tint. To obtain the very best results rapid firing and cooling ai-e requisite, but very fair results can be obtained even with five or six days' firing and y&cy 84 OIAY GLAZES AND ENAMELS. slow cooling. These colors can be purchased, but, while beau- tiful in tint, I have always found the piu-chased colors very diflicult to fire. As a rule they will not stand anything like the amount of hardship that the above receipts will stand. Enamels for heats above the fusing point of Albany slip clay ai'e, so far as I know, made by using a certain proportion of oxide of tin or tin ash. The receipt for lilac frit, with oxide of tin substituted for the No. 7 pink frit, will make a fair base for white enamel. Below is a complicated white enamel receipt that gives beautiful results on burned clay. It is a strong white, and will conceal red brick clay completely without any white slip under it. It takes stains perfectly, and a large number of beautiful tints can be made from it. Regular White. Medium to Hard Fire — Felspar 100 Borax 72 Oxide of Tin 48 Flint or Flint Sand 8 228 No. 8 Flux. Quite low heat, simply sufficient to thoroughly fuse- Red LeaA 6 Borax 4 Flint 2 12 White Enamel- Regular White 8 No. 8 Flux 1 9 CLAY GLAZES AND ENAMELS. 85 Common Frit. Medium Easy Fire — Felspar 140 Flint 140 Paris White 70 Boracic Add 80 Carbonate of Soda 70 China Clay 60 Borax 50 610 Hard White. Medium to Hai-d Fire — Oxide of Tin 16 Common Fiit 12 Felspar 8 Dry Borax 8 White Lead 4 Dry Carbonate of Soda 1 49 ' The white enamel given above will not stand much heat. If found too soft, substitute the hard white for a portion of or all the regular white in the receipt. This enamel will have to be set so that the glazed face is level, or else it will run. I do not recommend it for general work, but it will give beau- tiful results where its use is admissible. CHAPTER XII. Bathtubs, Sinks, Etc. The demand for these goods is quite large, and the prices paid for them malie them extremely profitable, unless the profits are too much cut down by losses in the course of man- ufacture. The same general laws apply to this branch of glazed work as to enameled brick, but the methods employed are quite different. The ware is molded in plaster molds. This requires men skilled in this work.. The clay required may be different, in some of its qualities, from clay for en- ameled brick, as it is not subjected to heavy pressure in a re- press, and as the method of manufacture tends to eliminate all tendency to laminations, the non-laminating quality of the clay is not of so much importance. The most important point of all la the clean burning qualities of clay. The slightest tendency to iron specks, lime flaws or coal flaws is extremely objectionable. A single flaw is just as capable of spoiling a bathtub worth many dollars as it is of spoiling a brick worth fewer pennies. ; The clay must dry without either warping or checking, and must also burn without either of these defects. Tlie cracking of heavy pieces is occasioned by different con- ditions. Sometimes it is from the clay being too rapid a dryer and drying at edges and comers, while the center remains wet. CLAY GLAZES AND ENAMELS. 87 If this is the case, drying in air-tight rooms may overcome the difficulty. With other clays cracking occurs only in the part of the piece upon which it rests, and is due to the clay not being strong enoiigh to overcome the resistiince of fric- tion produced by its own contraction. In this case, drying upon heavy blocks of clay that will shrink with the piece may overcome the difficulty. This throws the strain upon the block instead of on the piece. Bathtubs are sometimes dried in a sort of hammock or sling made of four-inch webbing, or they may be dried by tilting them at an angle of 45 degrees, bring- ing the weight upon two sides, and consequently distributed over a larger surface. It is difficult in nearly all clays to dry a bathtub and keep it absolutely straight, and much care must be taken. ,The sides of the large-size tubs are about six feet by two to two and one-half feet, and about one and one-half to two inches thick, and only held at bottoms and ends. ' The top edge will easily warp, and, once warped, it is hard to do anything with it. Heavy clay strips, made of the same clay as the tub and notched to fit over the top edge, will form a tie that will prevent either edge from warping independently. These ties will need constant attention; in fact, the whole busi- ness is one requiring the constant personal supervision of an expert. I have been connected with one case in which the cracking of large pieces was finally traced entirely to the water with which the clay was mixed. This water was drawn from a pond, and it was finally noticed that when the water became muddy cracks were sure to follow. By taking the water direct from a spring the cracking was entirely overcome. I merely cite this to show to what apparently insignificant and remote causes grave troubles may sometimes be traced. CLAY GLAZES AND ENAMELS. Our English writers tell us to pick the day carefully by hand so as to get rid o* bad clay. This Is unsafe, as by the slightest carelessness— in fact, even when great care is exer- cised—some bad clay will get through and spoil work. My advice is to use a piu-e clay. It can be obtained. Then, if you desire, you can hand-pick that, keeping the very best for bathtubs and the other for the smaller pieces; but do not use a clay which places you at the risk of carelessness or lack of judgment on the part of a workman, especially when it may completely ruin goods. The preparation of grit for these goods will vary with the character of clay used. Coarse grit, say up to one-eighth-inch mesh, and plenty of it, tends to reduce cracking and warping, while fine grit tends to make much smoother surfaces, but, as usually prepared, does not prevent cracking. In grinding fine gi-it much of it is reduced to powder and mixes with and shortens the clay. If double sieving is resorted to, by which all the powder and extremely fine gi-it is eliminated and noth- ing but clean grit, free from dust, is used, it will, of course, in- crease the expense somewhat, but a very fine faced goods can be made without much tendency to crack. The elimina- tion of dust is probably easiest done by washing grit. With some clays it will be a question of steering between two evils —rough, coarse-looking goods on one side and cracks on the other. The judgment of the manager then comes in. Some clays require weathering; others work best without it. This point will have to be determined by experiment. As a rule, a mixture of clays is better than a single clay. If you have a clay that works well, and can be relied upon to run uniform in quality, nothing can be better; but most clays vary, and by mixing two or more kinds a variation in one of them, only CLAY GLAZES AND ENAMELS. aCfects the mlxtui-e to the extent to which that clay is used. All of the clays are not likely to vary in the same direction at the same time, consequently the mixtm-e, as a whole, is apt to remain more uniform than when a single clay is used. The mixing and pugging of clay must be very carefully at- tended to. There is probably no doubt that the wet pan is the best pugging device for this class of work. If hard clays are used (I do not mean flint clays), it is often better not to pug too long, and when a limit is once fixed it should be ad- hered to so as to obtain uniformity. If a plastic or natui'al clay is used, the more thoroughly it is pugged the better, as a rule. There may be a few exceptions, but they are rare. The molding, I have already sadd, is done in plaster molds, and must be done by an expert. The forming of large pieces, like bathtubs, so as to have perfectly even thickness and true, smooth finish, is a matter of considerable skill. If the molding is poorly done no amount of care can make a perfect piece of it. The enameling is done with slip and glaze, the same as with brick. The small pieces, that are easily handled, can be lined with slip by pouring it in and allowing it to run evenly, and then pouring it out again, but the usual method is to put the slip on with a flat brush when the ware is partially dry. Some prefer to put the slip on after the goods are thoroughly dry. In this event, a short slip, with some liquid glue added to it, is the proper thing to use. The slip is put on in several coats with a brash. Each coat must be allowed to dry thor- oughly before the next is applied. Only a small amount of slip must have the glue added to it at one time, for it will start to ferment and spoil very quickly. I The glaze is invariably put on after the ware is thoroughly 90 OI/AY GLAZES AND ENAMELS. dry. It is usually put on with a brush, but some manufac- tui'ers prefer to pour it on. This requires considerable experi- ence and skill in order to obtain smooth results. The preparation of slip and glaze is accomplished in the same manner as for glazed brick. The following receipts will be found to give good results when the clay is suited to them. The rules regulating the ad- justment of slips and glazes to body are the same as for brick. Slip, No. 1— No. 4 English Ball Clay u Flint 48 Felspar 10 English China Clay, No. 7 30 Plaster of Paris i 100 The No. 4 English Ball Clay can be obtained from George Knowles & Son, Trenton, N. J. Slip, No. 2— English Ball Clay, No. 4 4 English China Clay, No. 7 40 Flint 44 Felspar 12 100 Glaze, No. 1 — Felspar 62 Flint 11 Paris White 12 Frit, % and i/^ Felspar and Borax. . 11 China Clay 4 100 CLAY GLAZES AND ENAMELS. 91 Glaze, No. 2. Frit- Borax 26.88 Paris White 17.78 Fliat ' 17.78 China Clay 17.78 Felspar 19.78 100.00 Glaze- Take of above Frit 15 Paris White 11 Felspar 48 Flint 21 China Clay 5 100 The burning is done in muffled kilns usually. No special cautions need be given in regard to the setting of the smaller ware. Bathtubs should be set on end in sand, or, if the end cracks -when set in this way, set them on bats of clay in sand. If the tubs have been dried on a clay bat, the same bat will do to set them on; if not, bats should be made specially for this purpose. The heat should be raised gradually and steadily, great care being taken, in the earlier stages, not to push the kiln. The finish must be made with great care, as overfire may warp, and underfire vrill not fuse the glaze. There are so many points about this business requiring special knowledge and skill that it should be entered upon very slowly and care- fully, and, possibly, should not be undertaken except under the conti'ol of an expert. —Qualities and Tests.— The perfect enameled brick should possess a smooth, fine face, .without any waviness. The face may be either bright 92 CLAY GLAZES AND ENAMELS. and smooth, with high lusti'e, or, as some prefer, only a me- dium lustre and egg-shell surface. Tue beauty of the latter finish is that slight waves or uneveuness of surface are not quite so noticeable as when the lustre is high and the polish perfect. It should be absolutely certain to neither craze nor peel; it should possess considei-able strength, and the different brick should be of absolutely uniform size. When we con- sider the different conditions under which these brick are used and the very severe treatment they sometimes get, it is not surprising that even good brick will occasionally fail by peel- ing. I have seen glazed brick piled outside buildings, with- out cover, fully exposed to the elements and thoroughly satu- rated with water before being laid in the wall; then laid in the winter months and exposed to zero weather before they had had the least opportunity to dry out. The brick stood this severe treatment, but, had they failed, the contractor should have blamed no one but himself. Such treatment of glazed brick is almost criminal, certainly outrageous. Think of the enormous strain it must be to build in a saturated brick, whose only exposed surface is impervious to water, and then freeze the water that is in the pores of the brick. We have all seen bricks that have been wet and then frozen, and we know how the expansion caused by the freezing causes a coat of ice, sometimes neai'ly one-eighth of an inch thick, to form on the surface. But how is the ice or water to exude from a built-in brick where even the front is not open for its passage? I do not think any maker of glazed brick should be expected to guarantee his brick against such treatment, and I think he would be perfectly excusable in refusing to do so. One might as well be expected to guarantee a boiler not to burst under a pressure way beyond what it is calculated to stand. CLAY GLAZES AND ENAMELS. 93 There Is only one way of being able to make such a guaran- tee, and that is, in both cases, to make the article so that it will not hold any water; make the boiler solid and the brick thoroughly vitreous. Then the idiots will not be able to burst either of them. I probably write strongly on this subject, but no sti'onger than I feel. I have been too much worried by the treatment given to brick of my own make to write very calmly on the subject The woret part of the matter is that every fault is blamed on the brick, and no one is willing to admit that the brick may have received unfair treatment. This unfair treatment is more apt to be given to American than to Imported brick, because the latter are invariably shipped packed either in barrels or boxes, and are kept in the original packages until needed, while American brick are frequently shipped loose. I have seen glazed brick built in high, heavy walls, and tied to the main wall every ten courses, the joints in the glazed brick being as fine as they could be made and the joints in the common brick very coarse and heavy. This must bring an undue strain upon the enameled Ijrick. ' Testing of glazed brick is a matter about which very little seems to be known in this country. Craaing- tests are easily made by subjecting the brick to alternate heat and cold, but peeling is certainly somewhat mysterious. I have seen brick fail when saturated with water and fi-ozen that have stood perfectly in the wall, and I have seen brick stand this test perfectly that were notoriously bad for peeling when laid in the wall. Peeling from pressui'e is a test easily made. A good brick should not lose its enamel until at the point of failure of the brick. I do not think it quite fair to expect them to stand fully up to this point, in case it is high, but they should stand 94 CLAY GLAZES AND ENAMELS. well beyond any pressure they can be subjected to in the building. If some means can be found to place a glazed brick under pressm-e that has been previously moistened to a rea- sonable extent, but not saturated, then, while still under pressm-e, to freeze it, I believe it would be found to be a fair peeling test. The brick should also be confined, or placed under conditions as near those that will exist when it is laid as possible. If the brick have been made by the slip and glaze method or slip and enamel or semiTenamel methods, the slip should be well burned and should adhere perfectly to the brick body. Many brick whose slip does, not seem to adhere perfectly stand well in walls, but they do not inspire the same confi- dence on the part of architects as hard-burned, close-adhering slips do. Color is entirely a matter of taste, but the enamel brickmaker should be able to make a perfect white, though possibly the cream white, ivory or bufC may sell in prefer- ence. Colors are not often demanded in large quantities, but ability to make them is necessary, so as to be able to supply what demand there may be for them. My experience has been that the greatest demand in the color line is for brown and gray, with blue, possibly, next in order. I do not include buff as among the colors, as the demand for it seems to be nearly as gi-eat as for white, and this color must be kept constantly in stock. —A Discussion of the Last Five Years' Writing on the Sub- ject— During the past five years there has been much written in the Clay- Worker, and somewhat in other papers, on this sub- ject. There has also been one English work published that OLAY GLAZES AND ENAMELS. 95 is devoted entirely to it. It is very interesting to review all this matter and note the diverse ideas of diffei-ent writers and the inconsistencies of some of them. I want to call attention to some of the marked contrasts and inconsistencies, and show therefrom that there must be many roads to siuaiess in this business, imless the writings referred to are untruths. One writer condemns emphatically the use of lead, potash, nitre and all low-heat fluxes in brick glazes, and also con- demns and ridicules the use of a frit, then, in giving the materials that should be used in glaze, mentions flint glass. Flint glass is composed of flint, lead, potash and nitre in vary- ing proportions. An average receipt would be as follows: Sand 100 Read Lead 66 Potash 33 Nitre 10 Gullet (old scraps) 60 to 100 So we see, in advising the use of flint glass, this writer advises the use of lead, potash and nitre, and yet, in another place, condemns the use of the same. In advising the use of flint glass he also advises the use of what is nothing but a frit, and, unfortunately, a frit the exact composition of which is unknown to the user, and which he would have no guaran- tee of being able to duplicate. Is it not much better to make the flint glass for one's self in the shape of a frit? The pro- portions can then be varied to exactly suit the requirements. Again, glazing dry only is recommended by some and glaz- ing wet only is recommended by other writers. Molding hand- molded brick in water is advised by some and in oil by oth- ers. I think there is very little doubt that if the clay can be molded easily by the slop method it is much better than to 96 CLAY GLAZES AND ENAMELS. iise oil. The less oil that is used on a brick to be enameled the better. One of the most amusing statements I met with was to the effect that a white enamel was more midform in color than a white made by the slip and glaze method. We all know that a white enamel is only translucent, while a white slip is absolutely opaque. A white enamel is apt to flow to some extent, while a white slip is immovable. A white enamel be- comes more thoroughly fused as the heat raises. A proper white slip is very slightly, if at all, affected by changes of heat; that is, so far as color and opacity are concerned. Yet, notwithstanding all these facts, the above statement was made, which amoimts to saying that a translucent material is a better hider than an opaque one, a flowing material more apt to stay of even thickness than an immovable one, and a material easily affected by difference in heat is less apt to be affected than one less easily affected. In every case the reasoning seems to me to be just hindside foremost. I do not wish to be understood as condemning the enamel process- hardly!— as I frequently use it myself; but it Is foolish to claim as its good qualities just those in which it is most deficient. Its good quality, in my opinion, is its perfect adhesion in low- heat work; that is, it is possible to obtain a good white on bufC clay, by using an enamel, without the use of a slip, and as the enamel is a fused glass it adheres perfectly to the brick body. Slips are sometimes difficult to attach thoroughly to low-heat bodies. One writer actually insinuates that another miist be telling an untruth, or that he has not expressed his meaning, when he states that enameling proper can be done on green clay, and further ventures the assertion that it cannot be done; also ventures the assertion that an enamel cannot be made without previous fritting. A third writer says that enameling CLAY GLAZES AND ENAMELS. 97 proper can be done on the green brick, but does not advise any one to try glazing on tlie green. Now, what are the facts? First, an enamel proper can be made either wholly of frit, partially of flit and partially of raw material, or wholly of raw material. A glaze can be made in the same way, and either enamel or glaze, when made either partially of frit and paitially of raw material, or wholly of raw material, can be successfully and easily applied to green clay. Either enamels or glazes can be made to burn at any degree of heat, I believe, although I will not be certain of the enamel at the extreme high heat of the porcelain kiln, as I have never tried it at that heat, but I have used it with success tO' veiy nearly porce- lain heat. Again, a writer condemns the use of oxide of zinc when working on green clay, while others advise its use and claim that it improves glazes. All I can say is that I have never no- ticed any bad effects from oxide of zinc used in reasonable quantities, but, on the contrai-y, have found it to be a good whitening and brightening material in a glaze. I really be- lieve most of the zinc is volatilized before the firing is com- pleted, but in its volatilization It seems to carry off deleterious matter; possibly the oxygen given off from it during the burn- ing has a beneficial effect. Oxide of zinc used in large and injudicious quantities tends to cause a slip or glaze to crack. Another statement met with is that there is less liability to craze when glaze is put on thin than when it is put on thick, and then a thickness of three-thirty-seconds to one-eighth of an inch is mentioned as the proper thickness. The first part of this statement is undoubtedly true of some bodies, but the exact opposite statement is just as true of other bodies. On vitrified or hard bodies, as a rule, the thinner the glaze the better, while on soft, porous bodies often the thicker the glajze or enamel the better. As to a thickness of three- thirty-seconds to one-eighth inch, I should consider such a 98 CLAY GLAZES AND ENAMELS. thickness altogether too great and unnecessary. From one- thirty-second to one-sixteenth inch thick I have always found ample. One-eighth inch of enamel on an English size brick would be about one-thirty-fifth part of the whole. The enamel would certainly, have a higher specific gravity than the brick, so its weight would be not less than one-fourth of a pound, or two hundred and fifty pounds to the thousand brick. Take the low figure of 4 cents per pound mentioned by this writer and we have a cost of $10 per 1,000 brick for the item of en- amel alone. Many enamels cost nearer 10 cents per pound; in that case the cost would be $25 per 1,000 brick for this one item. Bricks can be slipped and glazed for $2 per 1,000 easily— that is, for cost of material— and I have done it for 90 cents per 1,000. The writer also stated in an article in the Clay- Worker that "my experience has led me to believe that only high-heat clays are adapted to the single-fire method." I wrote quite strongly on the subject, but now wish to state that fm-ther experience leads me to retract the whole statement, and to state, instead, that my experience leads me to believe that there is a large range of heat through which clays can be adapted to the single-fire method. The conclusion to be drawn from all these differences of opinion is that there are many different lAethods and ways of making enameled brick, and that none of us knows anywhere near all of them. —Comparison of Methods.— The method employed of necessity depends upon several conditions — the natm-e of the clay obtainable, the character of the business and the conditions under which the goods must be produced. The one who has nothing but high-heat clay is forced to work at a high heat in order to produce solid goods, and the same is true throughout the scale. The manufacturer CDAY GLAZES AND ENAMELS. 99 of glazed goods only should adopt the cheapest and best meth- ods. The one who makes glazed goods simply as a side issue should adopt the method that is best suited to the conditions existing at his works. The reasons for this are obvious. Com- petition is close, and, while possibly to-day there may be suf- ficient profit in the business to stand expensive methods, the time is not far distant when only those who are fitted to man- ufacture fine goods at a low cost will be in existence. There Is no doubt that the single-fire process is cheaper than the double-fire process, and I believe there is very little doubt that as good material, and probably better, can be turned out by the single-tire process. The single-fire process i-equires more skill on the part of the practical man, and, as has been shown, requires a clay or clays suited to it. When these conditions are fulfilled I do not see how it is possible for the double-fire process to beat it in any way. I have heard the ai'gument advanced that by the double-fire process the straight, perfect brick only need be enameled and the others sold without enameling, thereby avoiding the loss of the crooked brick or imperfect brick. The only answer to this argument is that by the single-fire process, with proper clay, properly handled, there should and will be extremely few crooked brick, and probably no more imperfect brick than will come out of the gloss kiln by the double-fire process. If this is the case, the difl:erence in favor of single fire will be in the cost of the first burning by the double-fire process. I cannot see a single valid argument in favor of the quality of material produced by the double-fire method, and there are many against it, especially where the first bui-n is at a higher heat than the second. There is also no doubt that in single-fire methods open placing is cheaper than placing in saggers. In regard to slip and glaze on one side and enamel on the other there is much argument. Some claim finer effects for one and some for the 100 CLAY GLAZES AND ENAMELS. other. One dipping is claimed for enaxael as against two or three dippings for slip and glaze, and tihe smaller cost of ma- terial is claimed as an advantage for the slip and glaze pro- cess. We will consider the pros and cons. Slip will cost not over 50 cents per 1,000 brick and glaze from 50 cents to $2 per 1,000. Enamel will cost from $5 to $20 per 1,000, unless a lime enamel, and these are usually very uncertain. Dipping costs not over 75 cents per 1,000 for each dip, so that twice dipping only costs 75 cents more than a single dip, and three times dipping only $1.50 more than a single dip. The cost is evidently in favor of slip and glaze. I have always found glaze more reliable and certain than enamel. I cannot see any reason why there should be any advantage in enamel over glaze, except as cited, when heat used is too low to enable a slip to be well fastened, but do see why there should be an advantage in glaze over enamel. The glaze is relied upon simply for gloss and finish, and is not expected or supposed to help conceal the body. Slight variations in heat may vary the gloss slightly, but, with a proper slip under the glaze, does not change the color. Variations in thickness do not apprecia- bly affect color. Enamel gives the gloss and at the same time has to hide the body. Enamel is not absolutely opaque, but is simply, translucent, conseciuently variations in thickness or heat affect the color materially. As to glaze running and en- amel not, it is all nonsense. Either can be made so that it will run or not, depending upon the way it is compounded. It is a little more difficult to keep an enamel from running, because it is necessary to put it on thicker than glaze. The greatest objection to enamel is the thickness with which it must be used. It will not flow out to a square edge, neither will a glaze, but the enamel, being used to a greater thick- ness, makes a rounded comer that is nbticeable, and when brick are laid in the wall It is quite objectionable. The great- est objection to the slip and glaze process at a low heat is CLAY GLAZES AND ENAMELS. 101 the great difficulty of attaching the slip to the brick. This Is not true at a high heat. At a high heat the clay Itself in the slip burns solid and strong and becomes firmly fixed to the clay of the brick, but at a low heat this fixing must be done by using fluxes, and It becomes a problem of great nicety to avoid peeling on one side and translucency of slip on the other. Low-heat processes are evidently slightly cheaper than high- heat processes, but not so much so as one would think. After a kiln is once heated up to a low-heat finish it takes compar- atively a small per cent, more fuel to rvm it up to a high heat. In other words, the bulk of the fuel is used in getting the kiln redhot. Low-heat clays usually feel variations in the fire more than high-heat clays, so do low-heat glazes and en- amels, consequently low-heat processes are slightly more risky than high-heat processes. Take it all through, then, considering cost of production and risk, the high-heat, single-fire, open-burning process, under good management, I have always felt, possesses an advantage of from $5 to $10 per 1,000 over any other process, all other things being equal. This is undoubtedly, then, the process for the maker of enameled goods only. But this does not im- ply that all other processes should be abandoned or that their users will be forced to abandon them. I do think that all other processes will be forced out of factories devoted only to glazed goods. But a great deal of glazed material can and will be made as a side issue, and where the process can be adapted to the machinery, processes and heat employed in the manufacture of the bulk of the business such glazed side issue can hardly fail to be profitable. Ofttimes the main busi- ness of the manufacturer gives him advantages on the glazed business through information obtained and facilities for pro- duction of the particular class of goods. Enameled brick can sometimes be made as a side issue at a very good profit, as they can be set in the kiln where the regular goods will not 102 OLAT GLAZES AND ENAMEDS. go, and consequently may be considered as occupying no room and taking an inappreciable amount of fuel. The adaptation of the process to the heat and conditions existing is often diffi- cult, but rarely impossible. CEAZING— ITS CAUSE AND PREVENTION. The use of glazed clay products in buildings is of very an- cient origin. Specimens of this character of work are in ex- istence to-day which are supposed to be between three and four thousand yeai-s old, and the surface is as perfect as the day it was made. These ancient clayworkers evidently un- derstood their business thoroughly. There may have been bad work, also; if so, It has not lived to tell the tale, and so it will be — good material will outlast generations, while the poor stuff will hardly outlast its maker. In building, the most es- sential property of the material used should be durability; after that we can look for beauty of form, of finish and of color, and artistic blendings of these into a pleasing and use- ful whole, but without durability we ai'e building simply for to-day, and, besides this, what is more displeasing than signs of premature decay. Glazed clay has been used in buildings in the United States for a few years. During that time its use has decidedly in- creased, but still it may be said to have barely commenced. The demand for such material is evidently not a fad, but has been almost forced upon the architects by the many merits of the perfect article, beauty and cleanliness being among these, but the latter is undoubtedly one of the principal merits. The 104 CLAY GLAZES AND ENAMELS. perfect glazed siirface will be washed clean by every heavy rain, and will not absorb any of the moisture. The introduction of glazed clay products has been consider- ably constrained by the fact that all goods of this class are not perfect, and consequently there has been a lack of confi- dence on the part of architects as to their standing qualities, when used for external work in our severe climate. This lack of confidence is being gradually removed, due to the improve- ment made by our manufacturers, and, with its removal, we find a demand springing up, and growing at a tremendous pace, for the higher class and more artistic material in terra cotta, both for inside and outside work, but this demand can only be sustained by the production of perfect goods. The two gi-eatest causes that Interfere with the production of perfect material of this class are peeling or shelling and crazing. The first of these is a fatal defect, but, fortunately, one that is not very prevalent, while the second is, unfortu- nately, almost universally prevalent to a greater or less ex- tent. The question as to what extent crazing militates against the usefulness of the material is a very pertinent one, but still more pertinent is the question. How can it be avoided? In light colored surfaces crazing is certainly unsightly, and the crazed places collect dirt; consequently the material does not possess the merit of cleanliness to its fullest extent. In dark colored surfaces an extremely careful examination may be necessary to detect the crazing, and consequently the ap- pearance of the siu^ace is not affected, but the element of un- cleanliness still remains. Under the head of how to avoid crazing, I think the fact vvill be brought out that it does not Increase peeling, but, on the contrary, it will be shown that glazed surfaces which craze are less apt to peel than those CLAY GLAZES AND ENAMELS. 105 which do not craze. I do not mean to imply that the absence of crazing would indicate peeling; not at all. The perfect ma- terial will neither maze nor peel, and the imperfect material, unless horribly bad, is not apt to develop both difficulties. If horribly bad, both difficulties will possibly show themselves so qtiickly that the material will never be laid in the wall. Whether crazing leads to disintegration and decay or not, it certainly does lead to the appearance of it, and, so far as this goes, must be considered as a grave defect. The fact that makers of glazed goods try so hard to avoid crazing proves conclusively, without further argument on my part, that it is considered a grave defect. The subject of crazing seems to be suiTounded by more of mystei-y and seems more difficult to overcome than any other one trouble met with by the manufacturer of glazed material. I have never yet talked with any one having a knowledge of the subject who had any idea of the existence or possibility of the existence of any law governing it, but all seem to think it Is a matter largely of chance, and only to be overcome by constant experimemting, and experimenting guided by no fixed idea or principle, but simply conducted haphazard. If results be favorable, well and good; if not, try, try again, either imtil favorable results are obtained or until the problem has to be abandoned, due to the exhaustion either of the experimenter's patience or pocketbook. Glazers ai-e usually very seci-etive, and it may have been, in the conversations I have held with them on this subject, my impressions were derived more fi'om a determination on their part not to advance their ideas than from a lack of them. There undoubtedly is a law governing crazing, as there Is governing all phenomena. The great difficulty is to ascertain 106 CLAY GLiAZES AND ENAMELS. this law. All laws have been established through theories. At first the theory advanced may have been only partially cor- rect, or later developments may have entirely exploded it, but without a theory advanced, to be either exploded or sustained, a law can hardly be discovered. I have held a theory or principle in regard to crazing for the past eight years, and have always worked in accordance therewith. During that time I have never been baffled by the crazing difficulty, and I believe this success is due to the mer- its of the theory. My researches may not have extended far enough to discover the flaw in it, if there be one, and even should there be one, the theory has been vei-y far ahead of no theory, as is evidenced by my experience. It is this theory I pvu-pose to advance, with the hope that it may be of some as- sistance to the craft. I am unable to lay down any iron-clad rules, on account of the extreme variations in clays used for bodies, but will give the deductions from nineteen years' ex- perience, and hope to be able to put it before my readers in such a way as to be practical. It is much to be regretted that the secretive spirit, mentioned previously, exists. Had I had access to articles on this subject my nineteen years of worli would probably have been productive of more valuable re- sults. As it was, I had to start with almost no light and make It for myself as I went along. For eleven years I was work- ing entirely in the dark, without principle or guide, and it was an extremely slow and discouraging way of working. During the last eight years my advance has been much more rapid, and results obtained have been certainties. I do not mean to give the impression, from what I have said, that glazers generally do not know how to mix bodies and glazes that are adapted to each other, and in which the CLAY GLAZES AND ENAMELS. 107 glaze will not craze, but their knowledge is usually limited by their actual experience. With the bodies and glazes with which they are familiar they know that if crazing occurs a little of this or a little of that added to the body will stop it, or some different mixture of glaze will overcome the difflculty. I do not refer to this knowledge from experience with particu- lar mixes, but to that broader knowledge which is able to take clays as they are found, possibly entirely different from any- thing ever prasented to it before, and, after a few preliminary experiments, adapt a glaze to it that will not craze or adapt the clay to a glaze. This adapitation I am not foolish enough to claim as being so complete as to be perfect under improper conditions of firing; in fact, as I will point out later, the proper heat is a most important factor. Clay, in the unburned condition, varies very much, indeed. There are not only the chemical variations, which are very many, but also the physical differences. These chemical vari- ations and physical differences are largely independent of each other. Toughness is usually considered a sign of a large per- centage of alumina in the clay and shortness a sign of a large percentage ot silica, but this is not necessarily true, as the physical condition of the material In the clay affects its plas- ticity wonderfully, and clays are met with containing large amounts of silica that are very plastic and clays containing large amounts of alumina that possess very little plasticity. Bm'ning eliminates many of the physical differences, and only the chemical variations remain. The nearer we approach the fusing point of the clay the more completely are the differ- ences in the original physical characteristics eradicated, until, at the point of complete fusion, they are wholly era/iicated. As an illustration of my meaning I will imagine two materials, 108 CliAY GLAZES AND ENAMELS. one a pure ground felspar, containing, say, 25 per cent, alum- ina, 55 per cent, silica and 20 per cent, potash, the other an artificial mixtui-e of clay, silica and potash. This artificial mixture can be made so that when burned it will contain ex- actly the same chemical elements as the felspar, and in ex- actly the same proportions. The, first of these two materials will be nearly white in color, and will not possess any plas- ticity; the second may be white, yellow or gray, and will pos- sess considerable plasticity. For the benefit of the hypercrit- ical, who may claim that a pure enough clay does not exist for this Imitation of the chemical elements of felspar to be pos- sible, I will say that they may imagine impurities added to the spar so as to obviate this difficulty that will answer for purposes of Illustration just as well. If these two materials are made into cakes or brick while wet and placed In a kiln, and specimens drawn out at diiferent heats, it will be found that, up to the point where the combined water is driven out of the clay, there will be about as great a difference in the physical characteristic of strength or bond as there was in the raw material. After this point is passed the felspar samples will harden more rapidly than the other samples, and at the point of Vitrifaction the two materials will be almost Identical, physically and chemically, while at the point of thorough fu- sion they will be exactly identical, every iota of physical dif- ference having been eliminated. The difference in fineness of material probably shows through a greater range of heat than any other physical char- acteristic, and is only finally eliminated by complete fusion. Difference in fineness also affects chemical combination to a considerable extent, and at points below that of complete fu- sion leads to different chemical results, even though the chem- CLAY GLAZES AND ENAMELS. 109 ical elements may exist in exactly the same proportions. For instance, coarse silica combined with a certain percentage of flux, subjected, to a certain heat, may result in a glass, holding in suspension much uncombined silica, whereas fine silica, combined with the same percentage of the same flux, subject- ed to the same heat, may result in a vitreous, semi-vitreous or even porous mass. The first will be a silicate mixed with sil- ica, the second will probably be either a different silicate or a silicate mixed with a smaller quantity of silica. The flux will take up more of the fine silica than it will of the coarse. In the clays used for glazing eixtreme difference in coarseness of material is not apt to be encountered, and the thorough grinding and working which is given to tlie clay tends fm"ther to reduce this difference. The problem of crazing has to do only with burned clays, consequently it can have nothing to do with the original phys- ical characteristics that have been eliminated by the burning. In vitrified clay products it is then almost entirely a chemical problem; in semi- vitrified bodies it may be a trifie less of an absolute chemical problem, and in porous bodies original phys- ical characteristics may affect the problem to a marked de- gree. I am free to confess that on this latter point I do not feel thoroughly posted, but my opinion is that within the lim- its of the probable variation to be met with in clays used for glazing the effect of physical structm-e is slight. The chemical elements found in clay ai-e necessarily alumin- ium and silicon, with more or less iron, and there are fre- quently any or all of the following elements: Sodium, potas- sium, calcium, magnesium, sulphm' and carbon, also, of course, hydrogen and oxygen; besides these, there may be others, such as barium, fluorine, chromium, manganese, gold, titanium, etc., 110 CLAY GLAZES AND ENAMELS. etc., but these latter are usually in such small quantities as to have very little effect upon the burned product from the point of view of this article. The sulphur, carbon and hydrogen and oxygen in the form of vcater are mostly or entu-ely elim- inated by the burning. The binding material in all conditions, either raw or burned, is the silicate of alumina, or pure clay, which contains silica, 4G.3 per cent.; alumina, 39.8 per cent., and water, 13.9 per cent, when unburned, and, when thor- oughly burned, contains silica, 53.82 per cent., and alumina, 46.18 per cent. All silica in excess of 46.3 per cent, in the original clay is a weakening element, except as acted upon by the fluxes which the clay may contain. Sodium and potas- sium are the fluxes at all heats, having an affinity for silica and readily forming silicates therewith. These alkaline sili- cates are binding elements. Iron enters into the fluxing de- partment at different heats, depending upon the form in which the iron is present, but it is safe to say that it does not enter so early as the sodium and potassium. Magnesia is a flux at a higher heat. Lime is peculiar, and evidently possesses a double property. I have not investigated it in all its combina- tions, especially when combined with large quantities of iron, but so far as I have gone the indications are clear and positive that in reasonably pure clays lime is actually a resistant, and consequently a weakening element, below a yellow or bright yellow heat, oi-, say, below the fusing point of Albany slip clay, and becomes a strong flux beyond this heat. Lime also differs from sodium and potassium in the fact that it has a limit of fluxing power. A proportion of one of lime to about five of silica is the most fusible mixture of these two sub- stances. Further additions of lime add to the refractoriness of the mixture, whereas the greater the amount of soda or potash the more fusible the mixture. CLAY GLAZES AND ENAMELS. Ill Th0 number of bases affect the fusibility of a clay. For instance, mixtures of lime and silica, potash and silica, soda and silica and alumina and silica can be made that will fuse at the same temperature; a combinaition of any two of these mixtures will fuse at a lower temperature; a combination of any three at a still lower temperature, and so on. If the fusi- bility is affected and lowered by the number of bases, the burning qualities at heats below fusion or vitrifaction must be affected, because any given heat must be nearer the vitrify- ing point of the compound than of the simple body, conse- quently the compound body must be closer or less porous. From the short consideration given above to the chemical elements found in clays and their efCeot on bm-ning qualities, we find thajt we can divide the component parts of burned clay into two divisions, one divi^on containing the weakening ele- ments, the other the binding elements, the binding elements being the silicates of alumina, iron, soda, potash and magnesia, and the weakening element the free silica, with lime, some- times in one division, sometimes in the other, depending upon the heat at which the burning was finished. I do not mean to claim that a clay composed of piu:e sili- cate of alumina is necessarily stronger than one containing an excess of silica, but do claim that at the same heat and under the same conditions of firing, the first will be stronger than the second. In other words, silica, added to a pure clay, will weaken it; silica, added to an impure day, may weaken or may strengthen. All depends upon the proportion of silica and, fiuxes in the original clay. If the clay already contains enough silica to satisfy and saturate the fluxes, additional sil- ica will weaken; if not, it may strengthen, but further addi- tions of silica beyond the point of the satisfaction of fiuxes will weaken. 112 CLAY GLAZES AND ENAMELS. In lUush-ation of the action of lime in pure clays, I would like to cite one experiment out of many. This particular ex- periment I consider very conclusive. I had been experiment- ing for some time on hai'd porcelain bodies without success, and thought I would go r'ight back to first principles and in- vestigate the action of the different fluxes. I made one mix- ture of clay, flint and felspar and another mixture of the same clay, flint and felspar, adding quite a percentage of lime in the form of paris white. Each mix was made into a number of small thin cups and placed in a small experimental kiln and burned. When I opened the kiln I found the felspai- pieces quite well vitrified and ti-anslucent, the transmitted light quite yellow. The pieces with the lime in were porous, very slightly shrunken, and so soft as to be easily scratched with a knife point I decided to try the same pieces again at a little higher heat. I did so, drawing my trial pieces at regular intervals. I approached the proper heat, and all my pieces could be seen in the kiln when I drew ti'ial piece. In about an hour I opened the kiln again to draw a trial, when I was very much sur- prised to notice that some of my little cups had disappeared. I thought it about time to discontinue further firing on that kiln. I did so, and fully expected to find next day, when I emptied kiln, that my felspar pieces had melted, but I was very much mistaken. The felspar pieces were all there, and in about the same condition as when first fired — a little more thoroughly vitrified, slightly more translucent and the trans- mitted light a little whiter. The lime pieces were little pud- dles of glass on the kiln bottom. I think this proves quite conclusively that, lime changes suddenly from a resistant to a flux. In regard to action of silica, will cite another experiment. OLAY GLAZES AND ENAMELS. 113 also due to the bai'd porcelain experiments. I used for sag- gers in some of my experiments a regular body clay we were using. This clay was a mixtm-e of a white burning ball clay, china clay, flint and felspar. These saggers, which, by lue way, were little things, not larger than a teacup, did not stand my heat very well, and would get oroolied, and sometimes blis- ter, so I thought I would fix them by adding flint or silica. I took some sli]> of the mixture above, that saggers had been made of, and added, without weighing, sufficient silica to make this sUp stiff enough for a potter to work as clay. I had some saggers made and used them to hold my little experimental cups. They were failures as saggers, but they gave me the key to my whole trouble with the porcelain. When subjected to porcelain heat these saggers vitrified throughout, glazed themselves beautifully, and were a beautiful clear white in color. Prom the fact of their glazing and warping, not a slight warp, but the sides doubled over until they almost touched the bottom, I conclude that had the heat been continued long enough they would have melted. The clay, without silica added, never showed any signs of melting. Both these facts — that is, in regard to lime and silica — are too well known in glaze making to need comment. All glaze makers know that lime added to a low heat glaze makes it more refractory, and lime added to a high heat glaze makes it less refractory. Sil- ica added to glaze sometimes makes it more and sometimes less refractory. Some years ago I came across the statement, vouched for by an eminent scientist, whose name I have forgotten, that all solid silicates produced by fire expand an equal amount be- tween zero and their melting point, and therefore, given the rate of expansion, the temperature at which fusion will take 114 CLAY GLAZES AND ENAMELS. place can be calculated. It is this law which I consider is the law governing crazing and upon which my theories are founded. Whether this law is absolutely correct or not through all possible combinations makes little difEerence for the purposes of this article, so long as it be approximately correct. If the law be true, a silicate which melts at 1,500 degrees will ex- pand on being heated and contract on being cooled just twice as much per degree as a silicate which melts at 3,000 degrees. Bodies and glazes are compound silicates, or are, at least, largely composed of compound silicates, and the conditions under which glazed goods are made are such that the glaze must possess a lower fusing point than the body upon which it is used. Under this law, then, there is always a difEerence between the two in the amount of expansion or contraction produced by changes of temperature. This difference is great- er or less as the point of fusion of the body differs more or less from the point of fusion of the glaze. When this differ- ence is great enough and the body possesses sufficient strength to rupture the glaze the result is ci'azing. When the body is so weak that the strain ruptures the body, the result is shiv- ering. We have, then, these two opposite manifestations of strain having existed between body and glaze, the only differ- ence between the two being as to whether the body or the glaze fails under the strain. The law above refers only to perfectly free or unimpeded expansion and contraction. In glazed work the expansion or contraction of glaze is restrained or impeded by the body and the expansion or contraction of body is impeded by the glaze. The measure of this restraint is the amount of strain pro- duced. One limiting element of the possible amount of sti'ain CLAY GLAZES AND ENAMELS. 115 is the strength of the weaker, and another limiting element is the elasticity of the more elastic. For instance, were a bar of iron coajted with an absolutely non-elastic coating weaker than the iron, and then the whole subjected to a change of temperature that would enlarge the iron 1 per cent, the coating would be ruptured immediately, while a volume of air might be inclosed in the same coating and subjected to a change of temperature that would double its volume. If unimpeded, without producing a strain near great enough to ruptm-e the coating. Again, the iron might be coated with a very weak coating possessing some degree of elasticity, and an expansion of 1 per cent, would not pro- duce a material strain upon the coating, while the air might rupture the coating long before its volume had doubled. These are extreme cases, but thoroughly illustrate my meaning. So much for theory. Now, If the theory is correct, It should perfectly suggest the proper relation between bodies and glazes, and its suggestions should harmonize perfectly with practice. If the theory does this perfectly, it can be relied upon and can be carried out to its utmost limits, and by means of such theory advances in practice can be made in a short time that would require a long time without it. Right here I will restate the law. All silicates produced by fire expand an equal amount between zero and their melt- ing points. For "silicates produced by fire" I will substitute "bodies and glazes," when it would read as follows: "All bodies and glazes expand an equal amount between zero and their melting points." Now, what is the obvious suggestion of this theory in or- der that strain between body and glaze may be reduced to a minimum? Evidently that their melting points should be iden- 116 CLAY GLAZES AND ENAMELS. tical. This Is obviously impracticable, and the practical sug- gestion would then be to bring their melting points as nearly- together as the conditions will admit. This would suggest that when the glaze is melted the body should at least be vitrified, and the more thoroughly vitrified the better. A thoroughly vitrified body is a strong body and has large strain producing capacity. We would therefore expect to see a vitrified body craze its glaze at once or else not at all. If it crazes its glaze at once, it must be from one of two causes— either the melting points of body and glaze are too widely separated or the glaze possesses too little elasticity to stand the slight difference in amount of expansion and contraction. I think these state- mens are all directly deducible from the law and correctly stated. Now, how do they agree with practice? Our most per- fect types of glazed vitrified bodies are found in the porcelains of the Chinese, Japanese, French, Germans and others. These porcelains do not craze in use, and can be relied on through time and almost through eternity. Chemists' porcelain stands sudden alterations of temperature, even from almost zero to a white heat, and even stands heat applied to one portion, while the balance remains comparatively cool. Household porcelain also stands large changes in temperatm-e perfectly; in fact, when failure occurs, it is not from crazing, but from cracking of the whole mass. I have never seen a piece of genuine hard porcelain craze in use. Yet this type of goods does craze, but the crazing, when it occurs, occurs in the kiln. The manufacturers of hard porcelain understand the simple laws which govern crazing in their goods thoroughly, and they state that when goods are found ci'azed in kiln it is either be- cause glaze is not thoroughly fused and possesses very little, if any, elasticity, or because the body is not thoroughly vitri- CLAY GLAZES AND ENAMELS. 117 fied. The first is an accidental occurrence due to bad burn- ing, the second a constant occurrence so long as improper body- is used. The remedy for the second cause of crazing is to add flux to body and continue burning at the same heat or take some flux out of the glaze and use a higher heat. We then see that prac- tice in the best type of vitrified glazed bodies agrees perfectly with the law. I am sorry I am unable to give the experience of the stoneware makers in this country, but have not the slightest doubt but that it also agrees perfectly with the law. For many reasons it is impossible that we should all be makers of glazed vitrified bodies. Now, what suggestions does the law ofCer to makers of glazed porous bodies. We can easily see that in such bodies there must be a large difference between the melting points of body and glaze. From the law we would then deduce that there is a great difference in the tendency of the two to expand and contract under changes of temperature, consequently a great tendency for body and glaze to mutually strain each other, consequently a great tendency, unless overcome by other conditions, to craze. The tendency to craze is there, and it is unfortunately too often en evidence. We have seen, in glazed vitrified bodies, that when the ten- dency to craze existed, crazing occurred at once, and that when crazing did not occur at once it never shows, and we therefore assume that the tendency does not exist or is very slight. In glazed porous bodies crazing may occur at any time — in the kiln, in a day or a week, in months, or not for years. When it does occur it proves that the tendency was there during the whole period, and has either been increased through changes in condition, or glaze has failed, due to crystallization or loss of elasticity. Crazing in porous bodies is so general that I 118 CLAY GLAZES AND ENAMELS. think we have a right to assume that the tendency is univer- sal. If so, the law is upheld by practical experience. The law offers no direct remedy, but simply tells us that in glazed porous bodies there must be a constant struggle be- tween the body and the glaze, and leaves it for us to deter- mine the best means of securing to the glaze the winning of the struggle. These means are either to make the glaze so elastic that it does not feel the straining of the body or to make the body so weak that it is incapable of producing suf- ficient strain to rupture the glaze. I am perfectly willing to confess that I do not feel much at home on the first of these two plans. I do not know what makes a glaze elastic and what does not, except to a vei-y slight extent. These facts can only be ascertained by long continued researches — either by testing different glazes on a fixed body and noting which glazes stand the longest under certain fixed severe tests, or by actually testing glazes, in the form of bars of glass, in a testing machine. Either method would be extremely slow and probably unreliable, the first es- pecially so, from the possible double variations in the firing of body and glaze, and the second from variations in the firing of glaze and impossibility of preparing perfectly uniform test pieces. A certain quantity of lime in a glaze, I believe, in- creases the toughness and elasticity of the glaze very much. Care must be taken with low heat glazes not to use too much, as the lime, being a resistant at a low heat, will cause the glaze to come from kiln imperfectly fused. I made some ex- haustive experiments in this line, some years ago, with a glaze containing 8 per cent, of lime. This glaze crazed on a semi- vitreous body. I tried additions of lime in the form of paris white, 5 per cent, at a time. The first addition of lime ma- CLAY GLAZES AND ENAMELS. 119 terlally affected the crazing for the better. The second and third additions stopped it altogetlier. At the fourth addition crazing reappeared, although the glaze did not show any signs of imperfect fusion until I reached the sixth addition, or 30 per cent, in all. I repeated this experiment a number of times, with the same results. I have been told since that my results were not due to increased elasticity of glaze, but were ob- tained because the lime prevented the glaze from expanding and contracting so much. This later view I will admit to a certain extent, for it is just in agreement with my whole argu- ment. I was evidently raising the fusing point of glaze by the addition of lime, consequently was making its expansion and contraction per degree less, but I think there must have been an effect beyond this which I can only attribute to increased elasticity. As directly bearing upon this point, I will cite the great claims made as to the toughness and dm'ability of what are known as lime glass lamp chimneys. When quite low heat glazes have to be used, I feel positive that a good lead glaze possesses greater strength and elasticity than a glaze depend- ing upon alkaline fluxes. Underfiring produces a weak, non- elastic glaze, and is a frequent cause of crazing. This I think reasonable, as an underfired glaze is not thoroughly fused; the full and complete chemical combinations have not taken place, and there undoubtedly is more or less material merely held in suspension in an unfused state, and adding nothing to the strength or elasticity of the glaze; in fact, by separating the molecules of glass, detracting from these qualities. This brings me to the subject of enamels. The opacity of enamels is caused by unfused material held in suspension, and, as stated above, this tends to a lower ultimate strength and elas- 120 CLAY GLAZES AND ENAMELS. tic limit. My whole experience with enamels has been In ac- cord with this belief. I find it more difficult to produce en- amels that will not craze than to produce glazes that will not craze. As there has been much discussion as to what consti- tutes an enamel, I will state when I use the term I meau an opaque glass, opaque due to holding in suspension unfused lime, barium, tin, wolfram, arsenic or any ocher material that does not combine and flux with the glass containing it. The natural glaze, known as Albany slip clay, I know from experi- ence, is an extremely tough, elastic glaze, standing almost any amount of hardship, even to being taken from the kiln at full heat and rapidly cooled. I understand there are several other natural glazes possessing the same qualities. I have often tried to imitate or copy the qualities of Albany slip clay in an arti- ficial white mixture, but without perfect success. The analy- sis of Albany slip clay, as given by Professor Orton, is as fol- lows: Silica, combined 17.02 Silica, free 38.58 Total Silica 55.60 Alumina 14.80 Water, combined 5.18 Phosphoric Acid .15 Oxide of Iron 5.85 Oxide of Manganese .14 Lime 5.70 Magnesia 2.48 Potash 3.23 Soda 1.07 Moisture and Carbonic Acid 4.94 Total 99.14 Albany slip clay is a moderately high heat glaze, possess- CLAY GLAZES AND ENAMELS. 121 ing the property of standing almost any amount of heat with- out blistering. An examination of the analysis shows us noth- ing especially peculiar, but if we try synthesis we may find something that will look different. The same chemical mix- ture can be produced by the following: National China Clay 27.05 Brandy wine Summit Felspar 19.39 Ground Flint 32.41 Phosphate of Lime 33 Carbonate of Lime 9.85 Oxide of Iron 5.85 Oxide of Manganese 14 Soda 1.07 Magnesia 2.48 Moisture 61 Total 99.18 We now notice one great peculiarity, or, at least, it is so to me; that is, the large amount of clay— and national china clay is a tough, plastic clay, that stands a high heat. Such a glaze would, in my opinion, be an impossibility without the iron, for it is so aluminous that it would surely blister before it would melt. The question is. Does the Albany slip clay derive its extreme elastic qualities from the iron or from the alumina? I think from the alumina, for artificial glazes stained with iron do not show any marked superiority, in elastic qualities over-the unstained glaze. We notice that all the natural glazes possess this aluminous or clayey property in a marked degree. This is also one of the marked peculiarities of hard porcelain glazes, yet they will not stand one-tenth part of the hardship that Albany slip clay will; in fact, the adjustment of body to them has to be made with great exactness, whereas Albany slip clay will stand on nearly any clay that does not shiver. 122 OLAY GLAZES AND ENAMELS. So it may be that the natural glazes derive their strength and elasticity from the eombinatlon of iron and alumina. Thorough annealing of the glaze by slow cooling of kiln certainly must produce a tougher and more elastic glaze than where kiln is cooled rapidly. Some glazes require rapid cool- ing from the time the kiln is finished until the glaze has hard- ened or set, but I know of no reason to prevent slow cooling from that time until the kiln is emptied. Taking glazed ware from kiln while hot is certainly a very prolific source of craz- ing. Some of the coloring chemicals seem to weaken or lessen the elasticity of a glaze in a very marked degree. Among them I will particularly mention copper and uranium. Others seem to strengthen the glaze, as cobalt and chi-Omium. Iron I have previously mentioned as a possible strengthening ele- ment in certain combinations. A thick coating of glaze is less elastic than a thin coating. Sometimes we see a glaze crazed where the glaze is thick, and not where it is thin. This is a sign of close, strong body under the glaze. The body pos- sesses sufiicient strength to break glaze, and does so in the thick spots, but in the thin spots the elasticity of glaze keeps it from rupture. We sometimes see Just the opposite of this; that is, crazing takes place in the thin spots, but not in the thick. This is almost a certain sign that the body under glaze is silicious and unable to break a thick coating of glaze, but perfectly able to break a thin coating; it is also a pretty sure sign that the shivering point is close at hand. I regret that I am unable to give more explicit directions for producing a tough, elastic glaze, but I have already explained the difficul- ties attending experiments and investigations from which sure deductions regarding elasticity can be made. The work of a CLAY GLAZES AND ENAMELS. 123 glazei- is not of such a character as to lead to accurate Inves- tigations in this direction. My conclusions are that much more can be done to stop crazing tlirough the body than through the glaze, for all my experience has been that if on a given body a certain good glaze crazes badly, when burned at a cer- tain heat, it is extremely difficult to make a glaze that will not craze on that body, if burned at the same heat, and, if one does succeed, the same course of procedure is not likely to succeed on a different body. Yet we have the natural slip glazes as a proof that combinations are possible that will be successful on the majority of bodies. All that I am able to say, in sum- ming up, is to get plenty of alumina, say 10 to 12 per cent., in the glaze, either by using felspar or clay; also use sufficient paris white or gypsum or plaster of paris to be equivalent in calcium to from 4 to 8 per cent, of lime. Make the silica — that is, total silica, derived from the clay, the felspar and the ground silica that may be added— about 40 per cent, in low heat glazes, up to as high as 73 per cent, in extreme high heat glazes. Combine these three elements with the proper fluxes to effect thorough fusion at the heat used and the result will be a good glaze. If it crazes on the body used, it is easier and more certain to alter the body than to ti-y to make a more elastic glaze. We now come to the second method for the prevention of crazing in porous bodies, viz.: by making the body so weak that it cannot produce sufficient strain upon the glaze to break it. I have used the words weak and strong throughout this article because I knew of no others to substitute for them, and yet I am afraid they will be misleading without explanation. By a weak body is not meant an open, coarse body. Fine, dense and strong looking bodies often possess this quality, in 124 CLAY GLAZES AND ENAMELS. the sense in which I use it, in a very marlsed degree, while many open, coarse bodies are very strong. This element of weakness is impossible to determine by appearance, but is soon determined by the action of a glaze upon a body possess- ing it, or its opposite is determined by the body's action upon a glaze. I do not even believe that what I would call a weak body under the action of a glaze would be weak if tested in a testing machine; judging from appearance, hardness and ring, in many cases, it would not. In order that my readers and self may have the same un- derstanding of these two words, weak and strong, as used in this article, I will cite a few experiments and their results as illustrations. If we take national china clay and make it into small tile, one-fourth inch thick, subject them to a potter's ordinary bis- cuit heat, and glaze them on one side with an ordinary lead glaze, they will nearly all come from the gloss kiln crazed. If we take a clay known in the trade as Key's wad clay, and treat it in exactly the same way, the tile will all come from the kiln in hundreds of pieces. I would call the national clay a strong clay and the Key's clay a weak clay, because the na- tional clay burst or ruptured the glaze and the Key's clay was broken by the same glaze. If we repeat the experiment, sim- ply varying it by glazing the tile all over, the national clay tile will still craze, but the Key's clay tile, if they have no sharp edges, may come from the kiln in perfect condition, and will probably remain so. In this latter case, the glaze being on both sides of the tile, the forces exerted balance each other, and the body is under a compressive strain, instead of a bending or twisting strain. If the tile have sharp edges we will find those edges in the Key's clay tile nipped ofC, as though it had CLAY GLAZES AND ENAMELS. 125 been done with a pair of pincers. Both of these clays are very- plastic, tough clays, the Key's clay being the tougher of the two. They are both fine grained clays and they both burn very hard at the heat mentioned. I think that Key's clay would be pronounced the stronger by almost anybody, if tested in the usual manner— by ring, hardness, etc. The only difference in appearance between the two sets of tile, with rounded edges and glazed all over, will be in color and in. the fact that one crazes and the other does not. This is not chance, but is due to some inherent dlflierence in the clays. I have already shown the difference between the two when glazed on one side only, and, from that difference, claim the Key's clay as being the weaker clay, and I claim that it is this same peculiar weak element that makes the Key's clay a non-crazing olay when glazed all over. The clay has not the particular kind of strength necessary to break its coating. Crude Brandywine Summit clay will act exactly as national clay does in regard to crazing, and English china clay No. 7 will act exactly as the Key's clay does in regard to shivering. The Brandywine Siunmit clay is a coarse, open clay, that does not burn at all hard at potter's biscuit heat; in fact, can almost be cut with a knife, and a piece from one-fourth to one-half inch thick can easily be broken with the hands. English china No. 7 is a short, very fine grained clay, that burns soft. Near Mlllville, N. J., is found a clay that Is very peculiar. This clay becomes semi-vitreous at the heat mentioned, and is an extremely heavy, close, hard and strong appearing clay, when burned, yet it shivers. I could cite a number of instances of crazing in hard burning clays and crazing in soft burning clays, of shivering in hard burning clays and shivering in soft burn- ing clays, crazing and shivering in both plastic and non-plastic clays, in coarse grained and fine grained clays. 126 CLAY GLAZES AND ENAMELS. We see, then, that both crazing and shivering are independ- ent of plasticity, grain and hardness to which clay burns; in fact, they are both independent of physical characteristics, not only of the original physical characteristics, but even of those characteristics left after burning, except this peculiar weak- ness or strength, which is not apparent to any tests but those of the glaze itself. Can we find a point in common between the crazing clays? and can we find an opposite point in common between the shivering clays? If we can, I think it will be perfectly safe to assume we have found what leads to crazing and what leads to shivering. This common point will be found in the ratio of silica to alumina. All the crazing clays will be found to be high in alumina and low in silica, and all the shivering clays high in silica and low in alumina, and there is a comparatively small margin of safety. I do not mean to claim that there is a sharp line, which, if overstepped in either direction, will in- evitably lead to either crazing or shivering. The amount of flux in the clay and the heat at which the clay is burned have some effect upon this point. For high heat clays, with small percentage of flux, a ratio of three and one-half of silica to one of alumina, or 70 per cent, silica, 20 per cent, alumina, is about the proper proportions, and a clay running as high as 74 per cent, silica is almost certain to shiver, and one running as high as 25 per cent, alumina is aJmost certain to craze. Finely ground flint added to a crazing clay in sufiicient quantity will, I think, invariably produce a shivering mixture. A crazing clay and shivering clay can be mixed together in such proportions as to either craze, shiver, or stand perfectly. In adding ground flint we produce often a mixtiu-e that is weak to ordinary tests, while a strong burning silicious clay CLAY GLAZES AND ENAMELS. 127 added does not produce such a mixture. Therefore, I have al- ways found It better to- work with mixtures of silicious and aluminous clays rather than with an aluminous clay and silica. So far the law of expansion and contraction has not entered into my discussion on the second method of avoiding crazing in porous bodies, but we must not lose sight of the law. If my experiments made with lime bodies are to be relied upon, lime bodies will be porous bodies at low heats, and yet will possess a comparatively low melting point. Such bodies will, then, possess two good qualities: From their porousness and weakness they will not have the strength or capacity for pro- ducing much strain upon the glaze, and from their low melting point will not have a very great tendency to produce strain. Slight capacity and slight tendency together ought to make a non-crazing body. This is confirmed by practice. Clays con- taining much lime are less liable to craze than clays that do not contain lime. The lime must be in a finely divided state and uniformly distributed, or it will lead to other diflSculties as obnoxious as crazing. The direct addition of lime in the form of well-ground paris white will serve the pm-pose, but would be too expensive except where the cost of body is a slight percentage of total cost or where profits are great. A short description of my methods in handling a new clay will probably do more to illustrate the application of the prin- ciples I have endeavored to set forth than anything else I might write. After having determined the adaptability of the clay to the purpose in hand by examining and testing its plas- ticity, shrinkage, liability to check in drying, texture, and, if a material requiring repressing, the action of the clay in the repress should be thoroughly looked into— after, as I have said, testing all these points, the next point I ascertain Is the heat 128 CLAY GLAZES AND ENAMELS. at whicli the clay burns. I probably woiild put the clay in a regular kiln, burning to whatever heat I happened to be using, and from its appearance determine whether the olay was apt to be a porous clay or to be one easily vitrified. I would then make some special tests on this point. If the clay should be one that is easily vitrified I would treat it as a vitrified body under the mles I have laid down for such bodies; that is, use as high a heat glaze as I could and burn until the glaze was thoroughly fused and body thoroughly vitrified. Ninety-nine times out of the hundred this would lead to perfect goods so far as crazing is concerned. If the body should be a porous body, I would glaze it with a good glaze that works well at the heat I was using, and, after getting a number of trial pieces from kiln, would subject them to severe tests of alter- nate heating and cooling. If grazing resulted, I should add silica sand, or fine silica, or, preferably, a silicious clay that burns hard. I should try several different mixtm'es, probably adding sufficient silica or sihcious clay in my extreme mixture to produce shivering. I should then test these trial pieces as before. We will say I made mixtures containing 4 per cent., 8 per cent., 12 per cent., 16 per cent., 20 per cent, and I found that the 4 per cent, mixture crazed and the 20 per cent, mix- ture shivered, the 8 per cent., 12 per cent, and 16 per cent, mixtures standing well, I should use the middle, or 12 per cent., mixtm-e; but, were I adding silica, it is more likely that both the 4 per cent, and 8 per cent, mixtures would craze and the 16 per cent, and 20 per cent, mixtures shiver, leaving me only the 12 per cent, mixture good. I should then repeat my trials with a 9 per cent., 10 per cent., 11 per cent., 12 per cent., 13 per cent, 14 per cent and 15 per cent, mixture, and from the result of these tests determine where my safest mixture lay. CLAY GLAZES AND ENAMELS. 129 Were I a thorough analytical chemist, I should analyze the clay and then mix from this analysis. I have never yet been fooled vrhen I had a complete analysis to work from. Were my original clay a shivering clay I should follovy the same plan, simply using a strong burning aluminous clay to mix vcith it instead of a silicious clay. Some may wonder whether, in trying to avoid crazing by the method here outlined, there Is not danger of producing a body so weak as to be useless as a building material. With proper care I think not. If silica, finely ground or in the form of fine sand, is used, there is great danger of this result, but if a hard burning silicious day is used there is not. Occasion- ally a clay is met with like the Brandywine Summit clay, pre- viously mentioned, that is aluminous, and yet so refractory as not to bum reasonably hard at a practicable heat. With such a clay one would think that the mixture of a shivering clay would result in a very poor building material, but, if the proper clay for admixture is selected, this is not so. For instance, the clay from Millville, N. X, mixed with Brandywine Summit clay, makes a strong, dense brick, that neither shivers nor crazes. The two clays are as near opposites as we often see. The Brandywine Summit olay contains about 25 per cent, alumina, 65 per cent, silica, 7 per cent, water and only 3 per cent, of iron and fluxes. The Millville clay contains alumina, 11 per cent.; silica, 74 per cent.; water, 2 per cent., and 13 per cent, of iron and fluxes. If we mix these two clays, three parts of the fii-st to two parts of the second, we obtain a mix that will contain 19 2-5 per cent, alumina, 68 3-5 per cent, sil- ica, 5 per cent, water, 7 per cent, of iron and fluxes. If 20 per cent, of fine ground flint should be added to the Brandywine Summit clay it would stop the crazing, but it would make a 130 CLAY GLAZES AND ENAMELS. brick too soft for use. The chemical composition of such a mixtiire would be: Alumina, 20.83; silica, 70.83; water, 5.83; iron and fluxes, 2.5. It is rather rare to find a single clay which contains all the properties desired by the glazer, and most of those who undertake the glazing business will have to make up their minds to mix clays, and, in many cases, to trans- port a certain percentage of their mixtures some distance. I have forgotten to call attention to the peeling in slip and glaze work. The more sllicious the body the more difficult to obtain perfect adhesion of slip, so that special attention will have to be paid to this point. Perfect adhesion can be obtained, but not with the ease with which it can be done upon an aluminous clay. All that I have said is from a single fire standpoint, except in one illustration, where I mentioned a previous biscuit bum. This was done merely to prevent any one from thinking the shivered or broken samples might have broken during the burning instead of afterwards. In the single fli-e process, body and glaze get exactly the same fire, and when one is imder- flred the other is undei"fired, and when one gets a hard Are, so it is with the other. The double fire process complicates the crazing problem to a very great degree. Tbe same laws apply, but their applica- tion is much less apparent. There is a double set of variations in the bvuTiing, producing an endless variety of combinations, of which I might mention the four principal combinations: First, hard bm-ned biscuit or hard biu-ned body, with hard burned glaze ; second, soft burned body, with soft burned glaze ; third, hard bm-ned body, with soft burned glaze; fourth, soft burned body, with hard burned glaze. The biscuit, or first burning, is at a much higher heat than the gloss, or second CLAY GLAZES AND ENAMELS. 131 burning, except in hard porcelain, wbicli I do not Include as a double fire process, for, while it goes through two burnings, the gloss, or final bm-ning, is so much above the biscuit that it may be considered the only real burning the goods receive, and they are really in the same condition as single fired goods. In the regular double fire process, then, we have these four prin- cipal conditions, with a fifth which might be mentioned, viz.: medium biscuit and gloss. With a body just about at the ex- treme limit for shivering, that is, quite silicious, and at the same time containing considerable felspar and 4 or 5 per cent, of lime, I have seen shivered goods, crazed goods and perfect goods, all produced trom the same kiln. The heat used in bis- cuit was such as to vitrify the body in the exti-emely hot places and the body was quite soft in the extremely easy places; in fact, I have seen plates come from the kiln vitrified on one side and soft on the other, and it was not from bad firing, either, but from the extreme delicacy of the body due to the lime combination. The same kilns and same burner produced enormous quantities of what would be called uniformly burned goods when a less delicate body was used. In this lime body the high heat biscuit was almost certain to craze, whether bm-ned hard or easy in gloss. The medium biscuit would stand if well fired in gloss, and would craze if it got an easy gloss fire. The easy biscuit was indifferent under an easy gloss fire, sometimes standing, sometimes crazing, and sometimes even shivering. The easy biscuit, with hard gloss fire, was sure to shiver. A whole article on the subject of crazing might be written and the facts drawn fi-om this one experience. I cite this extreme case, and claim that in the double fire process this same condition of affairs is always apt to exist to a certain ex- tent. I believe that the tendency to such a condition can best 132 CDAY GLAZES AND ENAMELS. be reduced to a minimum by using a body containing little flux, either spar or lime, and burning the biscuit at an ex- tremely high heat. Such a body will harden slowly under the firing and will feel changes in temperature slightly, conse- quently the variations in the heat of biscuit burning will pro- duce very slight variations in the condition of body. This body should be coated with a glaze that stands considerable excess of heat without blistering, and then the heat in gloss should be carried to such a point as to insure thorough fusion of glaze, even in the easiest part of kiln. Once having obtained such a combination that will not craze, I think the manufacturer could feel relieved of the fear that crazing might suddenly develop. I have carefully examined English goods made by the double fire process that have an excellent reputation for not crazing, and I find Invariably that they are a soft but totigh body, coat- ed with a completely fused glaze. Such a body could only be made, with safety, upon the lines laid down above. ,^" Analyses of five of the best makes of English enameled I brick bodies show an average composition as follows: Alum- ina, 21 per cent.; silica, 74 per cent; iron and fluxes, 5 per cent. This Ti^ould coiTespond to an analysis In the unburned clay about as follows: Alumina, 19.62 per cent.; silica, 69.16 per cent.; water, 6.54 per cent.; Iron and fluxes, 4.67 per cent. The extreme variation in the five analyses was not over 2 i>er cent, in sihca and not over 1 per cent, in alumina. Three of the samples were from England proper, one from Scotland and one from "Wales. This shows either that these makers under- stand the law of chemical composition, or that practical ex- perience has made them unknowingly observe the law. To-day chemical science does not play a very important part in the business of the clayworker, because the chemical expert CLAY GLAZES AND ENAMELS. 133 and practical clayworker have not been combined in one per- son, but tlie day is coming wlien they will be combined, and data -ttill be obtained, based upon chemistry, that will enable the chemist-clayworker to predict to a nicety from chemical analysis and an examination of the unbrn-ned clay the action of such clay under the various heats and conditions to which it may be exposed. When that day comes om* business will be a science rather than a matter of guesswork. HENRY R. GRIFFEN. TABLE OF CONTENTS. CHAPTER I. Page. HISTORICAL AND INTRODUCTORY 7 to 13 Ancient Cblnese Brick 7 Assyrian Enameled Brick— English Enameled Brick 8 American Enameled Brick 8 Value of Enameled Brick 9 Suitable Clays 9 Methods and Schemes for Production 10 Quality of Some American Enameled Brick 10 Analyses of English Clays ' 11-12 Occurrence and Distribution of Suitable Clays in the United States 13 CHAPTER II. SELECTION OF CLAY AND MIXTURES 14 to 21 Classification of Jlethods of Mauufactm'e 14 High Heat. Single Fire Open Burning Method l."i Lower Heat, Single Fu'e Open Bm-uing Method 18 High and Low Heat in Saggers or Other Support, Single Fire 19 The Double Fire Processes 19 Fatal Defects in Clays 20 136 CLAY GLAZES AND ENAMELS. Goods Other than Brick 20 Semi-Dry Process 20 CHAPTER III. PBEPARATION OF CLAY 22 to24 Grinding and Pugging 22 CHAPTER IV. METHODS OF MAKING THE BLANK 25 to 29 Hand Making ' 25 Drying Hand-Made Brick 27 Soft-Mud Machine Process 27 Stiff-Mud Machine Processes 27 Drying Stiff-Mud Machine Brick 28 CHAPTER V. REPRESSING 30 to 33 Lamination, Blisters and Pinholes 30 Kinds of Presses 31 Precautions ■.. 82 Methods of Handling Product 33 CHAPTER VI. SLIPPING, GLAZING AND ENAMELING 34 to 44 Ball Clay 34 China Clay 35 Flint and Feldspar 36 Whiting, or Paris White, and Plaster of Paris 37 Gypsum, Barytes, Fluor Spar, Cryolite 38 Oxide of Zinc, Soft Insoluble Fluxes, Soft Soluble Fluxes. 38 Slipping and Slips 39 Glazes 43 CLAY GLAZES AND ENAMELS. 137 CHAPTER VII. RECEIPTS 45to60 White Slip for Brick— Buffi Slip for Brick— Blue Stain 45 Sage Green Slip— Blue Green Slip— White Glaze, No. 1. . .46 White Glaze, No. 2— White Glaze, No. 3— White Glaze, No. 4 47 Chocolate Brown Glaze 48 White Slip, No. 2— White Slip, No. 3 49 Glaze, No. 5 50 Stains 51 Pinks 53 Pinks 54 Lilac— Brown Frit— Crimson 55 Matt Blue— Matt Blue, No. 2— Mazarine Blue 56 Blue, No. 1 57 Green, No. 1— Green, No. 2— Green, No. 3— Green, No. 4. . .58 Green, No. 5— Green, No. 6— Green, No. 7— Green, No. 8. . .59 CHAPTER VIII. PREPARATION OF SLIPS, GLAZES, ETC 61 to 67 Arrangement of Room 61 Weighing Box— Dipping Vessels— Measuring Vessels 62 Storage Tanks or Vats 62 Charging Pans— Sieving 63 Hand Preparation 64 Thickness of Slips and Glazes , 65 Stains and Frits— Grinding Machines— Pumping Machin- . ery 66 CHAPTER IX. DIPPING AND CLEANING 68 to 73 Thickness of Slip 68 138 CLiAY GLAZES AND ENAMELS. Methods of Dipping 69 Arrangement of Dipping Room 70 Gleaning Brushes 71 Dirt in Dipping— Care in Handling 72 Amount of Room Needed for 1,000 Brick 73 CHAPTER X. SETTING AND BURNING 74 to 79 Economy of Kilns 74 Up and Down-Draft Kilns— Height of Kiln 76 Methods of Setting Open 76 Size of Saggers— Burning 77 Assorting Brick "^8 CHAPTER XI. MAJOLICA GLAZES AND WHITE ENAMELS 80 to 85 Majolica Ware 80 "A," or Transparent, Glaze— Lilac Glaze— Brown Glaze. . .81 Yellow Glaze— Green Glaze— Pink Brown Glaze— Gray Glaze i 82 Blue Gray Glaze— Moderately Dark Blue Glaze 83 White Enamel 84 CHAPTER Xn. BATHTUBS, SINKS, ETC 86 to 102 Qualities of Clay .' 86 Slip, No. 1— Slip, No. 2— Glaze, No. 1 90 Gl^ze, No. 2 91 Qualities and Tests of Enameled Brick 91 A Discussion of the Last Five Years' Writing on the Sub- ject ^ Comparison of Methods 98 CRAZING— ITS CAUSE AND PREVENTION 103 to 138 Books for... Brickmakers. "CLAY QLAZES AND ENAHELS," Henry R. Qriffen, C. E. $ 5.00 "BRICKMAKER'S HANUAL," Morrison and Reep, 3.00 "BRICKmAKINQ AND BURNINQ," J. W. Crary, Sr., a. 50 "TABLE OF ANALYSES OF CLAYS," Alfred Crossley, i.oo "VITRIFIED PAVINQ BRICK," H. A. Wheeler, E. M., 1.00 "PRACTICAL FARM DRAINAGE," J. J. W. Billingsley, i.oo Mailed, postage free, on receipt of price. Address T. J\. RANDALL & CO., Indianapolis, Ind. Subscription Price, $2.00. Sample Copy Free.