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DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH
THE
CLEANING AND RESTORATION
OF MUSEUM EXHIBITS
THIRD REPORT
UPON INVESTIGATIONS CONDUCTED AT
THE BRITISH MUSEUM
• * * *
tº
LONDON : PUBLISHED UNDER THE AUTHORITY
OF HIS MAJESTY'S STATIONERY OFFICE, 1926
LONDON :
FUBLISHED BY HIS MAJESTY'S STATIONERY OFFICE
To be purchased directly from H.M. STATIONERY OFFICE at the following addresses :
Adastral House, Kingsway, London, W.C.2; York Street, Manchester;
1, St. Andrew's Crescent, Cardiff; or 120, George Street, Edinburgh;
or through any Bookseller.
I926.
Price 5s. net.
:
i
PREFACE
T is now seven years since Dr. Alexander Scott, F.R.S.,
at the request of the Department of Scientific and
Industrial Research, commenced his study of the
cleaning, restoration, and preservation of museum exhibits.
The purpose of his study was to investigate, from a
Scientific point of view, such processes as were known
for the treatment of museum exhibits, and to discover
new processes based upon exact Scientific knowledge.
It was hoped that, as a result of this study, it would be
possible to place in the hands of curators, private col-
lectors and others, methods for the cleaning, restoration,
and preservation of objects of archaeological or artistic
value which could be recommended as “ safe " and
effective. Certain of Dr. Scott's results have already
been described in the First and Second Reports” upon inves-
tigations conducted at the British Museum, and since
their publication further results have been obtained. In
view of the prolonged experience of the utilisation and
efficacy of the methods recommended in the above
Reports, it appeared desirable to prepare a third Report
dealing comprehensively with the whole of the processes
examined or evolved from the outset of the work.
Dr. Scott has accordingly prepared the following account
of his work, which, read in conjunction with the two
previous Reports, will provide a survey of the knowledge
and experience gained to date at the British Museum
Laboratory.
Evidence of the value of Dr. Scott's results has
steadily accumulated. It is clear that the methods he
has devised and tested are frequently and widely used
and that, where they have been adopted, there has been
a marked improvement in the condition of the exhibits
*A comprehensive list of the Department’s publications may be
obtained on application to the address overleaf.
iii
PREFACE
treated and an arrest of their deterioration. It is
becoming more generally realised that the only “safe ‘’
methods of cleaning, restoration, and preservation are
those based on accurate scientific knowledge of the
processes themselves and of the nature of the exhibits
in question.
Attention should be drawn to the warning given in
the two previous Reports. The methods and reagents
described may be regarded as “safe " if used with
Ordinary care and discretion ; and variation of the
instructions given, or any application of the methods to
objects not specifically referred to in the text, should be
made only by skilled workers, and after careful prior
experiment upon comparatively valueless objects.
DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH,
I6, OLD QUEEN STREET, S.W.
August, IQ26.
iv.
CONTENTS
INTRODUCTION
PRINTS AND PICTURES...
STONE AND EARTHENWARE
SILVER
IRON OBJECTS
LEAD
COPPER AND BRONZE
WOOD
GLASS C & ſº
STEIN AND COLCHESTER COLLECTIONS
TEXTILES...
‘‘ FAKES ’’
NOTES
PAGE
...50,
I4
22
25
32
35
42
45
52
53
56
59
y
THE CLEANING AND RESTORATION
OF MUSEUM EXHIBITS
INTRODUCTION
ANY of the processes described in the earlier
Reports,” for the cleaning, restoration and
preservation of museum exhibits, although based
on Scientific principles, were of a somewhat tentative
nature in that time had not permitted a prolonged test
of their efficiency. It has now been possible to give these
processes prolonged trial, and their suitability has been
confirmed while further experience has suggested certain
modifications in detail which are outlined in the following
pages. -
The general scheme of operations in any restoration
work must, first of all, be to determine, as far as possible,
the various causes of deterioration, and, having done
this, to find a safe means of arresting the processes of
change and decay. By working on these lines it has
been possible to arrive at processes which, after the lapse
of five years, have shown no deleterious action of their
own, and which, so far, seem to have been efficacious in
preserving the great variety of objects which have been
subjected to treatment. That there is yet room for
many processes and methods of cleaning cannot be
denied. A constant series of new problems is provided
by the infinite range of museum exhibits, and these
problems are often modified greatly by differences in
constitution of the objects and the varying conditions
to which these have been subjected in the past.
In the following pages are set forth various types of
work with such details as may be thought of interest
and usefulness to curators of museums and to the numerous
* The Cleaning and Restoration of Museum Exhibits, Ist Report, 1921,
2nd Report, 1923. Published by H.M. Stationery Office. Price 2s.
each, net.
MUSEUM EXHIBITS : CLEANING AND RESTORATION
private collectors. It is but seldom that the problems
in their various conditions and complexities will again
present themselves just as described here, and it is hoped
that the details given may not only be of direct assistance
to collectors, but may encourage them to feel that many
valuable objects which seem irreparable on account of
the condition into which they have fallen, are still worth
endeavouring to preserve. Even if these endeavours
should only be partially successful from the point of
view of restoration, in almost every case details of
manufacture will be revealed and light thrown upon the
causes and mechanism of decay, and these facts alone
may prove worthy of being recorded, if for no other
reason than to warn others in charge of similar specimens
and faced with like problems.
A number of notes has been added at the end of the
Report in the hope that they may prove of general
utility, especially to those who have no good laboratory
facilities. Although there are many solutions, cements,
varnishes, etc., which can readily be prepared by the
amateur, it may often save much valuable time and also
secure more uniform materials and treatment if certain
preparations are purchased ready for use. Correspond-
ence on the subjects dealt with in former Reports has
indicated very clearly that many collectors have neither
the laboratory facilities nor experience to prepare many
necessary solutions and reagents, and would still find it
difficult even if instructions were given in greater detail.
On this account it was considered that reference might be
made in the “Notes '' to certain commercial products
which have been tested in this laboratory and found
efficient for the various purposes specified. Where
reference is made to proprietary articles it should be
understood that those mentioned are not necessarily the
only ones suitable or available for the purpose ; the
articles mentioned are those which happen to have been
2
INTRODUCTION
tested in the British Museum Laboratory and found
Satisfactory. It must be emphasized, however, that the
use of any commercial product the composition of which
is unknown is greatly to be deprecated. Where there is
the least shadow of doubt it is well to determine by
careful experiment the effect of a small portion in an odd
corner of the specimen before proceeding with the actual
restoration.
PRINTS AND PICTURES
N the two former Reports from the British Museum
Laboratory methods were outlined for the treat-
ment of prints and pictures which have since been
employed, in Some cases with slight modifications, over a
period of years. They have survived the test of time
Very favourably, and the experience gained in their
application to a great variety of specimens makes it
possible, at this stage, to furnish more detailed informa-
tion, both as to the methods available, and to their
Selection in particular cases.
For cleaning and restoring discoloured and “foxed ''
prints the use of bleaching powder and dilute hydrochloric
acid, when applied with the necessary caution, seems to be
safest, and the method more generally useful where the
pigments employed consist of lampblack and similar
varieties of carbon (as in printer's ink).
Hydrogen peroxide vapour was also recommended for
the clearing up of engravings, especially in cases where the
presence of water was undesirable. This was generally
applied by means of a dried stucco plate. It was found,
however, that in certain cases this environment still
contained enough moisture to wrinkle and distort the
picture and its mount. Accordingly, recourse was had
to an ethereal Solution of hydrogen peroxide, easily
prepared by shaking up the aqueous solution of hydrogen
peroxide of commerce with about an equal volume of
ordinary ether (so-called sulphuric ether). The ethereal
layer floats on the top of the aqueous one and may be
applied to the stains with a camel's hair brush, care being
taken not to allow the brush to touch the aqueous layer.
It may be noted incidentally that very pure hydrogen
peroxide solution can now be obtained commercially,
4
PRINTS AND PICTURES
declared to be “free from barium salts and from phos-
phoric acid.” A third method of applying this reagent
is in alcoholic solution, equal quantities of hydrogen
peroxide solution and absolute alcohol being simply mixed
and applied, as before, with a fine brush. The latter
method is preferable in cases where gum or gelatine is used
in the body colour of a painting. It renders the applica-
tion of the liquid more uniform and minimises the danger
of Cockling the picture or mount.
The use of the ethereal solution of hydrogen peroxide
is well exemplified in the treatment of a large number of
colour prints by William Blake, which were cleared up
brilliantly and rapidly by means of this reagent. After
treatment many of these were exhibited in the Print
Exhibition Room of the Museum, in King Edward VII’s
Galleries. The discolouration was largely due to the
ordinary cause, namely, tarnishing of the flake white
used, and in many cases this was accentuated by the
poor quality of the gelatine or glue used by Blake.
Examples of the effect of the ethereal solution are shown
in Figs. I and IA, 2 and 2A, 3 and 3A.
Alcoholic hydrogen peroxide was employed in the
case of a very interesting and valuable set of water-
colour drawings of Venice and the Venetian islands, about
fifty pictures in all, by Giacomo Guardi (A.D. I764–1835).
These varied much in the extent of the blackening of the
lead carbonate. That this was caused by the action of
the air penetrating between the leaves of the album in
which they had been mounted is shown clearly by Fig. 4,
a photograph of the upper member of a pair mounted on
one page of the album. One picture in process of restora-
tion is shown in Fig. 4A, and a restored specimen in
Fig. 4B. An illuminating example of the removal of
mould spots by this treatment is shown in Figs. 5 and 5A.
For the removal of old and coloured oil and varnish,
no reagent has been found to equal pyridine, a solvent
5
MUSEUM EXHIBITS : CLEANING AND RESTORATION
first recommended in the First Report. Although it
removes the brown colouration in nearly every case, it is
sometimes impossible to get rid entirely of all trace of
stain, where oxidation and other changes in the oil have
given rise to insoluble matter finely dispersed through
the tissue. Good examples of the successful application
of pyridine in this connection are exemplified in the
illustrations, Figs. 6 and 6A. Fig. 6 shows an Arabic
book on which oil had been spilt many years ago, and the
stain had in time become dark brown. By careful
application of the reagent with a glass brush the stain
became rapidly lighter, the coloured solvent being
removed with white blotting paper, which was replaced
with fresh as required. The page was in this manner
restored to its original whiteness so completely that no
sign of stain could be detected in it afterwards. The
negative of a photograph taken after cleaning also failed
to reveal any evidence of the stain, although this is
generally a more severe test than visual examination.
An oil-stained engraving, of no particular value except
that the stains were known to be about a hundred years
old, was made the subject of prolonged and drastic
treatment by various reagents. The initial condition of
the engraving seemed to indicate that it had been lying
in a house-painter's workshop, as stains of green, red,
deep Cream colour and pure white were all present. The
action of the pyridine in disintegrating the lumps of hard
and dried paint was most pronounced, rendering them
easily removable by a stiff brush or by the careful applica-
tion of a needle. Figs. 7 and 7A show the engraving
(dated I767), before and after treatment. No reagents
tried could weaken the stain seen at the bottom of the
picture, which remained, even after prolonged bleaching.
It was less easily wet when immersed in water than the
other parts of the paper. Amongst the reagents tried
were alcohol, carbon tetrachloride, trichlorethane, tri-
6
PRINTS AND PICTURES
chlorethylene, acetone and ethyl acetate, as well as
mixtures of some of these.
A frequent cause of disfiguration in old prints and
pictures is that caused through the agency of mould.
The stain may be due either to the actual presence of
fungoid growth, which will necessitate sterilisation of the
print, or the colour may have been elaborated sometime
in the past by an Organism which has since disappeared.
In the latter case, one or other of the bleaching methods
outlined above will generally suffice to remove the
stain.
A method of sterilisation has now been devised,
depending on the use of thymol, a reagent suggested
in the First Report as giving promise of being a suitable
medium. Thymol has been tested in various ways and
seems to be extremely efficacious ; it is easily applied
and is safe because of its want of chemical reactivity.
It may be applied in various ways, according to the nature
of the object to be treated. Pictures, engravings, letters
written in ordinary ink and similar objects are easily
fumigated by placing them in trays in a fairly air-tight
box, preferably above a large clock glass containing about
a quarter of an ounce of thymol. An ordinary electric
lamp fixed below the clock glass melts the thymol in a
very short time after turning on, as its melting point is
44° Centigrade. The air within the box soon becomes
highly impregnated with the vapour of the thymol
which in the course of four or five hours seems to destroy
the life of moulds and apparently of their spores also.
A simple experiment to test the efficiency of thymol
was made with some Japanese paper which, when kept
moist at the ordinary temperature for SOme days, always
developed crimson and bright yellow spots of mould
even when kept under glass. This seemed to indicate that
the spores of these particular moulds were in the substance
of the paper itself. A piece of this paper (A) was taken
7
MUSEUM EXHIBITS : CLEANING AND RESTORATION
and fumigated in the chamber as described above for
three hours and was then placed between two pieces of
glass, together with another unfumigated piece of the
same paper (B), in Such a manner that the specimens did
not touch each other. A third piece (C) similar to (B)
was mounted separately between glass, and all three
pieces were moistened with distilled water and set aside
(Fig. 8). In about a week (C) developed the spots as
usual. After three months (despite the moisture that was
maintained by regular wetting with distilled water), (A)
and (B) were still immune, indicating that (A) had
º º:
.” 2
E
FIG. 8.
apparently retained enough thymol to sterilise (B). On
removing the glass protecting (A) and (B) and simply
touching them with (C), both (A) and (B) developed the
coloured spots in the course of Some weeks. It appears
therefore, that any spores or mould in a dormant Con-
dition had been killed by the thymol vapour whilst between
the plates, thus demonstrating its efficacy as a sterilising
medium. At the same time, one must guard against
exposing objects, even though sterilised, to the possible
infection by mould spores, avoiding the conditions of
dampness and darkness conducive to the growth of Such
organisms.
A picture of a type different from those cited hitherto,
and of great historical interest, is that of Oliver Cromwell

8
PRINTS AND PICTURES
(by Samuel Cooper), the property of Sidney Sussex College,
Cambridge. On examination this was found to be suffering
from various forms of decay which will be apparent from
the following description. The portrait is executed in
pastel on paper mounted on an oak panel measuring
15 by 12; inches. This panel is reinforced with Oaken
fillets at top and bottom and a rabbet has been let in,
but despite these precautions to avert possible warping,
cracks have started in the wood ; these were probably
caused, in part at least, by the Screws employed. To
prevent these cracks from developing more seriously,
Oaken dovetails of X-shape have at Some later period
been let into the back, and the whole roughly smoothed
with a plane. This is clearly shown in the photograph of
the back of the panel, Fig. 9. The picture, mounted
passe partout, had a glass plate a very little larger than the
oak panel bound to it by Strips of paper. Apparently
at no distant date the glass had been removed, probably
to photograph the picture more Satisfactorily. In
fastening it together again, paste, which had not been
sterilised, had been used, for it was noticed that at
various points, mostly near the margin, mould spots were
appearing ; this was especially the case at the top. Further,
the crack which had formed had been filled up with an
oily putty which had the effect of rendering it only the
more noticeable, owing to the oil diffusing into the
paper and chalk, and both darkening and broadening
the flaw. A certain amount of discolouration of the
whites from the usual cause also required treatment.
Thus, treatment was required, (I) for moulds, (2) for
discoloured white lead, (3) for oily putty, and (4) for
rectification of the discrepancy of size in the glass and
the panel, and to keep the glass from touching the pastel
anywhere. The picture was therefore fumigated at a
comparatively low temperature (40° Centigrade) with
thymol vapour. After the fumigation it was found that
9
MUSEUM EXHIBITS : CLEANING AND RESTORATION
the remains of the mycelia and mould spots could be
removed by gently lifting them off with a very small
camel's hair brush. For the discoloured white lead, a
solution of hydrogen peroxide in ether was employed most
Successfully. The oily putty had in the course of time
shrunk in the cracks and was easily removed by means
of an Ordinary pin and the crack filled up with fine chalk
powder coloured to match the various tints. To give the
powder the necessary Cohesion a dilute solution of cellulose
acetate was used. To prevent the covering glass touching
the pastel anywhere and at the same time to prevent the
glass projecting over the panel thin fillets of wood were
fastened to the edges maintaining the glass about a
twentieth of an inch from the picture. The whole was
then fumigated with thymol Once more and bound up
first with a strip of fine linen and this covered with another
strip of thin tough paper, the flour paste employed in the
binding having I per cent. of mercuric chloride (corrosive
sublimate) added to prevent the growth of moulds or
possible attack of insects. The portrait before and after
treatment is shown in Figs. 9A and 9B.
Writings on materials other than paper and parchment
have also been treated so as to render them more legible.
One of the most interesting and at first sight impossible
problems was to render again legible what had been
written on wax, which had subsequently been partially
melted by heat. Two wax tablets, mounted together in
wood as a single page of a book, had been consulted on a
dull day in the summer of 1924, and left for a short time
near a window. On one of the rare occasions in that
summer, the sun shone out strongly for a short time
without warning, and its rays, falling on the blackened
wax melted the surface defacing the writing, See Fig. IOA.
By careful scraping with a razor blade, followed by
gently rubbing with a small pad of cotton-wool moistened
with petroleum ether, the tablets were brought back to the
IO
PRINTS AND PICTURES
condition shown in Fig. Io, when the greater part of the
inscription could again be read. Apparently the wax
surface had been blackened before being written upon,
and the effect of the stylus used in writing had so hardened
the incised lines that even on fusion of the mass they
retained their form more or less accurately.
Of quite another type were rolls of thin lead foil some
of which had incised writings on both sides, some only
On one side. They had originally been enclosed in an
Outer casing of thin sheet copper of somewhat greater
breadth than the lead sheets which latter measured
about I2 inches in length by about one and a half in
breadth. The lead strips had been tightly rolled up and
then wrapped up in the thin sheet copper, the edges of the
copper being bent over the ends of the leaden roll and one
end filled up with clay and sealed. The copper covering
was in all cases converted into a brittle mixture of copper
oxides and carbonate, and the lead so encrusted that
the writing was indecipherable except in isolated spots.
No doubt the juxtaposition of the two metals hastened
the corrosion, especially in the covering. By careful
unrolling of the lead and washing with dilute acids, usually
nitric or Sulphuric, applied by means of a pad of cotton
wool, the lead foil being extended on a glass plate, what
remained of the writings was rendered legible once more
(Figs. II and IIA).
Numbers of incised bronze and copper tablets have
been treated and the corroded surface reduced once again
to metal, making it possible for the writings to be trans-
lated, whereas, before treatment, the oxides and carbon-
ates of copper had filled and so distorted the inscriptions
as to make this quite impossible. These will be referred
to later in the section dealing with bronzes.
For the benefit of artists and others who have to
work with old drawing paper, reference may be made, in
concluding this section, to a remedy, or at least a pallia-
II
MUSEUM EXHIBITS : CLEANING AND RESTORATION
tive, for certain troubles often associated with such paper.
When old drawing paper is immersed in water it frequently
shows spots which become transparent long before the
rest of the paper has become thoroughly soaked. This
is due to the destruction of the sizing of the paper, usually
by bacterial agencies. Papers which have been taken to
Seaside places and other situations where the moisture in
the atmosphere is high are peculiarly liable to this change,
the clear spots having become a form of blotting-paper
through the destruction of the size. When water-colours
are applied to such paper these porous spots absorb an
extra large amount of water, and the pigment contained
in suspension is filtered out from the liquid, the result
being that dark patches are formed wherever such
porosity exists. To an artist who was in difficulties from
this trouble the use of a solution of cellulose acetate in
acetone was suggested, after various experiments had
been made. This was simply brushed over the surface
of the paper and allowed to dry. The best strength of
solution for this purpose seemed to be from 2 to 2% per
cent. This he reported to have been a complete remedy
for the trouble. Cellulose acetate is apt to dry with
a whitish opalescent surface when the material to which
it is applied is not perfectly dry. In this case with a
white paper this is perhaps a slight advantage. No
doubt the porosity of the paper is affected, but this
treatment seems at least to render the surface once
more uniform as far as water-colour drawings are Con-
cerned. It enabled the artist to complete numerous
somewhat unfinished drawings which had been left in
that condition for several years.
Drawing paper has been examined which bears the
characteristic circular hole made by an anobiid beetle.
Many reagents have been suggested to destroy this pest,
one of the most effective of which is carbon disulphide ;
this liquid, however, possesses the disadvantage of being
12
PRINTS AND PICTURES
extremely inflammable. Carbon tetrachloride, a some-
what less effective insecticide, is, on the other hand,
non-inflammable. It was found that a non-inflammable
mixture could be made consisting of 20 per cent. carbon
disulphide in carbon tetrachloride, which thus combines
the advantages of each and can be employed as an
insecticide either in the case of paper or furniture.
I3
STONE AND EARTHENWARE
T need hardly be pointed out that the deterioration of
Stone objects in a museum is occasioned, not by the
variety of disintegrating influences which may combine
to attack the stone of buildings, but rather through
Certain of these influences acting in a more acute
form because of the specimens having been buried in the
earth generally for many years before discovery. The
prime cause of decay is the crystallisation of salts within
the stone or immediately beneath and on its surface.
The effect of impurities in the atmosphere, especially of
our towns, where the combustion of raw coal produces
Substances such as Sulphuric acid in large quantity, is
that chemical reactions take place on our modern building
stones which change the composition of the existing
substances, converting, e.g., carbonate of lime to gypsum,
which in course of time crystallises and disintegrates
the fabric of the stone. With museum exhibits, however,
it is not so much this chemical change that we are
concerned with as the fact that most specimens that
have been excavated from the soil have their pores
already full of Salts. In many objects this is evidenced
by a white crystalline efflorescence over the surface.
When water evaporates from a porous surface the
residual solution must become more concentrated in
dissolved matter. This increases the surface tension
and therefore the force of capillary attraction, which
operates to draw more Salt solution towards the evaporat-
ing surface. Thus it is that the percentage of Salt is
high at no great depth in a porous soil, and Stone or
earthenware objects found in this environment, especially
in warm countries, always contain much salt. After the
object has been excavated the surface of evaporation
I4
STONE AND EARTHENWARE
now becomes the surface of the object, and the same law
operates to bring the crystals to this surface, though,
under museum conditions, the moisture in the atmosphere
is so Small that it may be a very long time before the
formation of a Superficial crystalline efflorescence becomes
apparent. Nevertheless, during this period crystals which
are dissolving and growing within the stone are having
a decidedly deleterious effect upon its structure. At first
sight it may seem strange that objects of hard stone
should change at all in the atmosphere of a museum,
which is maintained so that changes in temperature and
moisture are as Small as possible. While changes in
temperature alone have, in this country at least, but
slight effects on stone objects, many suffer much from
variations in moisture in conjunction with those of
temperature.
Of the salts found in stone specimens, some remain
quite dry even in a moist atmosphere, but there are others
extremely soluble, which on a damp day abstract so
much water from the atmosphere that they become
liquid drops which soak into the interstices of the stone.
On a dry day the atmosphere is ready to take up much
water vapour and these moist portions of stone dry up,
the salt crystallising in the body of the stone. Repeated
analyses of the crystals efflorescing from stone specimens
from all parts of the world show that the chief salts
which crystallise out in these efflorescences are sodium
chloride and Sulphate along with potassium nitrate.
Calcium and magnesium chlorides, nitrates and Sulphates
are also almost invariably present, but in Small quantities
only.
The usual method of removing these salts and so
arresting decay caused by their presence, is to Soak the
specimens in water with repeated changes until, after
one or two changes of distilled water this liquid is proved
to contain no chloride ; when this is the case on testing
I5
MUSEUM EXHIBITS : CLEANING AND RESTORATION
a Small portion of the liquid which has been acidified
with pure nitric acid by the addition of silver nitrate
Solution, no white precipitate is obtained. The soaking
is a very tedious process and is not too satisfactory, as
On placing a dry stone in water the crystals near the
surface are dissolved and this solution soaks further in
as the water permeates the stone, and the salts are then
Only brought out again by the slow process of liquid
diffusion. In order to obviate this objection a process
has been worked out which brings the salts to the surface
in an easily removable form without placing the exhibits
in water at all ; the efficiency of the process has been
verified quantitatively.
When a drop of water is applied to the surface of a
salt-charged stone the salts dissolve and the solution
penetrates only as far as the quantity of water and the
porosity of the stone will permit. As this drop dries it
brings the salts gradually to the surface, in the manner
already indicated, where they crystallise in due course;
but the important feature is that, in the new procedure,
instead of depending on the slow process of diffusion
the agents utilised are evaporation and capillarity which
allow of the action taking place much more quickly and
with a high degree of efficiency.
In practice, water is not applied alone as most objects
are too fragile to allow of the crystals being removed from
their surfaces. It is possible, however, to obviate this
by applying wet paper pulp (made by shaking up blotting
paper with distilled water) to the surface of the specimen ;
occasionally the wet blotting paper may conveniently be
spread in sheets forming a layer over the stone surface
which Soaks in enough water to dissolve the salts. Now
when evaporation at the surface of the pulp begins the
Solution is drawn out of the stone and crystallisation
sets in at the outside of the pulp layer instead of on the
outside of the stone or earthenware, and when quite dry
I6
STONE AND EARTHENWARE
the pulp comes off very easily bringing the salts with it.
By repeating this procedure two or three times the salts
are so much diminished in the outer layers that no further
crystallisation need be feared in an ordinary museum
atmosphere where the moisture and temperature are
kept within limits.
The crystallisation of the salts naturally takes place
most conspicuously where the porosity of the surface
is greatest and this is usually at the same time the softest
and most easily damaged part of the specimen. For the
same reason soft porous stones suffer more than hard ones.
When a stone, or even a hard air-dried clay has been
primed with stucco or given a soft and porous layer of
calcium carbonate as a ground work for painting or work-
ing into patterns, it is frequently found that this layer
is warped or raised in blisters. This is constantly being
illustrated in museum exhibits whether of stone or
earthenware, glazed or unglazed. A very good example
of how a porous limestone absorbs salts from the soil
and, although apparently perfectly clean and unchange-
able when first put into the museum case, gradually
becomes almost unrecognisable through the influence of
change of temperature and moisture upon the crystals
within the Stone, is shown in Fig. I2. This is a limestone
foot so incrusted with long filamentous crystals that until
these were removed it was impossible to tell whether
it was a right or a left foot. Figs. I2A and I2B show it
when cleaned and the crystals removed.
The Small statuette in Fig. IS was also of a porous
limestone but in this case the detailed work was not on
the limestone, but was on a coating of a slip of calcium
carbonate of varying thickness. Before treatment the
slip was being forced away from the stone in blisters of
varying size due to the formation of crystals between the
slip and the stone. The application of the wet blotting
paper dissolved the crystals, and by absorbing the solu-
I7
MUSEUM EXHIBITS : CLEANING AND RESTORATION
tion permitted the slip to be pushed back into its original
place. After thorough treatment for the removal of the
Salts, the whole was dried and painted over with celluloid
varnish SO as to retain the displaced fragments in their
places, and now the statuette may be handled with
impunity.
The large water jar of porous earthenware seen in
Fig. I4 shows the same effect of crystallisation of salts.
In this case the salts came not from the soil, but from the
water at one time stored in the vessel. The earthenware
was porous throughout and the outer layer, which was of
finer and smoother clay than the bulk of the jar, had
scaled off almost completely in the lower parts. The
use of such porous material for cooling the liquid contents,
especially in hot climates with a dry atmosphere, is well
known and extensively practised all over the world. The
water soaks through to the outer surface and is there
evaporated, abstracting much heat thereby from the jar
and its contents. The continued passage of water from
the inside to the outside naturally tends to the accumu-
lation of the saline contents on the outside, followed by
crystallisation and the gradual detachment of the outer
layers. This jar, like so many others of similar type, was
in an extremely friable condition, but by abstraction of
the salts as above described, followed by thorough drying
and subsequently by the application of weaker and then
stronger solutions of celluloid, the whole has been so
consolidated that it can be readily handled, and even
rubbed with a cloth, without any particles becoming
detached thereby. At the upper part the coarser earthen-
ware had crumbled away So much as to leave a gap of
about a twentieth of an inch between the outer crust and
the jar.
A somewhat similar case in point of cure, but where
the cause was entirely different, is that of a large Italian
drug pot (Figs. I5 and I5A), in which the bluish-white
I8
STONE AND EARTHENWARE
glaze was cracking off from the reddish ware below. This
was probably due to the fact that the temperature of the
fusion of the glaze had not been high enough to secure
complete adhesion of the glaze to the body. Hence there
was no question of any salts in the ware and the applica-
tion of celluloid solution was sufficient to prevent further
loss of the glazed layer.
An exceedingly interesting case which exhibited many
new points for investigation, and which also raised many
others which have not been completely solved, is that of a
drug pot of Lambeth ware. The earthenware body of
this specimen was almost white and the glaze bluish in
tint with deep blue lettering. The glaze had been
Chipped off almost all round the base and in various parts
there were flaws in the glazing no larger than pin-holes,
but round these black spots blisters appeared, varying in
size up to about an inch in diameter. As was expected
these proved on examination to be due to the formation
of Crystals beneath, and the only remedy in this case
seemed to be to extract the salts by soaking in water.
Distilled water was used throughout in this case and it
was changed once a week for over three months, the
washings in each case being boiled to dryness and the
residual crystalline deposits dried and preserved. In
the end it was found that the united weight of saline
matter amounted to no less than 29 grammes. The salts
were almost entirely sodium sulphate and chloride with a
notable quantity of calcium sulphate. There seemed to
be no oily or other organic matter present to any marked
extent, nor could zinc be detected, although the jar was
made for and presumably contained “zinc ointment "
when in use. Apparently, what had happened was that
the jar with its chipped base had stood in some saline
Solution, and this had permeated the mass by capillarity.
Evaporation, followed by crystallisation of the salts
occurred at each minute hole in the glaze, and this
I9
MUSEUM EXHIBITS : CLEANING AND RESTORATION
accounted for the blisters round each black spot. Figs. I6,
I6A and I6B illustrate these various points.
There are other cases in which immersion in water
and slow diffusion seem to be the only way by which the
salts can be removed. A large number of tablets of
baked clay covered with cuneiform inscriptions were
found to be crumbling owing to their salt content. The
Surface could not be touched without removing or dis-
placing the fine markings which had been pushed up from
the body of the tablet by the crystal formation below.
It was, therefore, impossible to adopt the usual practice
of wrapping them in fine muslin and then placing them
in water. The problem of removing the salts without
disturbing the finest markings was solved by giving the
tablets three coats of celluloid varnish, allowing each coat
to dry before applying the next and then immersing the
completely coated tablets in distilled water and continuing
the washing as above described. When washed free from
salts the tablets were dried and given a final coat of the
same varnish. The skin of celluloid over the surface of
the tablet allows diffusion of crystalloids to take place
readily through it. A strong white precipitate of silver
chloride was usually given within a quarter of an hour's
soaking of the tablet. Cellulose acetate solutions were
also tried, but the films were found to be so much weaker
that they did not fix the crumbled surface nearly so well
as the celluloid solution than which no better medium
seemed possible.
Another point with regard to the glaze on earthenware
was raised in connection with the vase (mei p'ing) with
imperial dragons (IA88–1505), shown in Fig. I7. The
glaze is seen to be discoloured, especially in the lower
parts, where it is thick. It was found that this brown
colour was not attacked by acids such as hydrochloric
acid, and not even by hydrofluoric acid. As the upper
part was absolutely free from discolouration it was evident
2O
STONE AND EARTHENWARE
that this was not due to any deposition of furnace dust
nor could it be because of reduction due to furnace gases.
Examination under the microscope showed the cause to
be incomplete fusion and incorporation of the material
used for the glaze. On the shoulder and wherever the
glaze was pure white it seemed to consist of brilliant
colourless spheres, and it is to this that the peculiar charm
of such glaze is due. Wherever the discolouration was
apparent, as in the thicker parts, the brilliant spheres were
mixed with others which varied in tint from dark brown
to the palest straw colour. Apparently, complete fusion
and incorporation of the materials of the glaze only took
place where it was sufficiently thin, as on the shoulder
and the edges of the lip.
2I
SILVER
ITH regard to the treatment of silver objects,
there is but little to add to the simple methods
already described in the two earlier Reports.
As is well known, silver is a very soft metal, and on this
account not well adapted to the wear and tear of daily
use. This softness is overcome to a large extent for
coinage and other purposes by alloying it with other
metals, of which copper is most usual. The amount added
varies enormously ; for example, British standard silver
contains only 7% per cent. of copper, whilst Some silver
coins of the Emperor Probus were found to contain only
4% per cent. of that metal. The method by which these
latter were coated with a thin film of silver, so as to
counterfeit a coin of high silver content has not been
Satisfactorily made out.
When alloys of silver with copper are buried in Salt-
containing soils or under other conditions which favour
corrosion, the result, as long as any unchanged alloy
remains, is that the alloy becomes coated more or less
thickly with compounds of copper interspersed with
metallic silver, either as isolated crystals or in the more
or less continuous form of a sponge. In many instances
this green coating has led to objects composed of alloys
with a high silver content being actually catalogued as
bronze. Also, many objects covered with green incrusta-
tions and likewise catalogued as bronze have been found
to be so in fact, but sometimes skilful, artistic, inlaid
silver ornament has come to light on cleaning which
was quite hidden before.
A large number of articles of silver from recent
excavations at Colchester were found to have been
converted almost entirely into silver chloride and to be,
22
SILVER
in consequence, very brittle. By treatment with caustic
soda and zinc these were slowly reduced once more to
the metal, naturally now in a Spongy condition. After
thoroughly washing out all the SOda, these were dried,
then raised to a low red heat. The fine silver sponge left
after the reduction was thus consolidated and toughened,
owing to the peculiar property which Spongy precipitated
silver has of drawing together when so heated. This
strongly heated silver has a Soft grey Colour and is
coherent enough to be burnished and rendered brilliant
once more. The objects referred to above seemed to be
part of a necklace or tiara made up of individual pieces
resembling trefoil leaves.
One important item in the Colchester collection was
apparently of the nature of a brooch with the head of
Augustus (Figs. I8 and 18A). This was at first conjec-
tured to have been made from a coin, but a more complete
examination after restoration indicated that it had been
independently fashioned as an Ornament.
Another interesting example of the reduction of the
incrustation of silver chloride was that of a pair of silver
scales (Fig. I9) in which the contact of brass pins used
in mounting the specimens gave rise to drops of green
copper-chloride Solution and the gradual growth of pure
white silver crystals radiating from the points of contact
of the pins with the silver chloride.
The use of formic acid in various strengths, both
warm and cold, for cleaning all kinds of silver alloys,
especially those with copper, has continued to give
excellent results. As was pointed out in the First
Report, the ready decomposition of silver formate into
carbonic acid and metallic silver renders the use of this
cleaning agent perfectly safe in that no corrosive action
on the silver need be feared, the surface being left in
a condition as nearly as is now possible to that which
it presented originally. The action of this acid is practi-
23
MUSEUM EXHIBITS : CLEANING AND RESTORATION
cally confined to the solution and removal of the carbo-
nates and oxides of such metals as lead and copper, the
mechanism of the reaction being conversion into formates
soluble in excess of the acid. It is frequently quite
sufficient to wash over the surface, leaving the acid on
for a short time only, and then to rub off the sulphide
and other compounds insoluble in the acid, and to finish
by washing thoroughly with pure water. A soft pad
of cotton-wool, or in many cases merely the fingers are
the best rubbers for fairly flat surfaces; a brush may be
necessary where there is embossed or engraved work.
A good illustration of the cleansing action of formic
acid is shown in Figs. 20, 20A, and 20B. No other reagent
than dilute formic acid (5 per cent.) was applied, as
described above.
The dark brown or black discolouration is usually due
to the formation of silver sulphide or of silver subchloride,
the latter being formed by the decomposition of the
normal chloride of silver by the action of light and
organic matter, and these two silver compounds are the
insoluble substances which are loosened and then removed
by gentle friction.
24
IRON OBJECTS
HE museum specimens which consist of iron or of
iron along with other metals exhibit a great
variety of problems, both in the states of decay
in which they come for treatment and in the treatment
required to arrest further change. No objects deteriorate
so rapidly as these, and the reasons for this have already
been given. Those of iron, either wrought, cast or in
the form of steel, corrode rapidly in a moist atmosphere
when salts are present in the coating of oxide with which
they are almost invariably encased. When more electro-
negative metals such as Copper, silver and gold are present,
however, this rate of decay is so much increased that it is
comparatively rare to find any metallic iron remaining
when one of these non-ferrous metals is, or has been in
metallic contact with the iron. Too often the specimen
is only a mass of iron oxide resulting from the change,
and only the general form of the mass gives any clue to
the purpose for which the iron object was originally
made. -
If, however, a comparatively thin coating of oxide
and a large proportion of coherent metal should remain,
a method of treatment which is extremely successful,
as far as appearance goes, is to boil the article with a
solution of stannous chloride kept faintly acid with hydro-
chloric acid. Small quantities of hydrochloric acid
must be added from time to time as the iron oxide
dissolves and neutralises it. The stannous chloride
prevents, to a large extent, the attack of the metallic
iron ; the free acid attacks the ferric oxide producing
ferric chloride which is reduced at once to ferrous chloride ;
the latter does not attack the metal as ferric chloride
does. The possible objection is that this treatment may,
25
MUSEUM EXHIBITS : CLEANING AND RESTORATION
and usually does, give a coating of metallic tin to the iron
rendering it a shade whiter than the pure iron. When
thoroughly cleaned, the thin layer of tin should protect
the underlying iron. To ensure this it is well, after the
treatment with Stannous chloride, to wash very thoroughly
with distilled water followed by a hot bath of dilute
caustic SOda Solution in which are pieces of granulated
tin, again to wash well with pure water, and then varnish
with thin dammar varnish or “duroprene’’ after thorough
drying. -
For the treatment of greatly corroded iron objects
having a thick incrustation of oxide containing the Salts
from the soil in which the objects have been buried,
the best scheme so far devised is to boil the objects with
a dilute solution of caustic soda (about 5 per cent.) along
with granulated zinc. The caustic soda decomposes
the chlorides and oxy-chlorides of iron, while the zinc
promotes electrolytically the passage of the chlorine from
the iron into the liquid and towards the zinc. This holds
good as long as any metallic iron remains. If all metallic
iron has disappeared and only oxides and other Com-
pounds of iron remain, the problem resolves itself into
how to make the specimens less friable and more easily
handled without falling to pieces.
The manner in which iron objects fall to pieces when
left to themselves is well shown in Figs. 21 and 22 and
how they may be restored and treated so that no further
change need be feared may be seen in Figs. 21A and 22A.
One cause of the very bad condition into which many
museum exhibits of iron have fallen is the adoption, in
the past, of a method often recommended for preserving
iron. In this method the object is first heated so as to
dry it thoroughly, and it is then immersed in a bath of
hot paraffin wax. No doubt when intelligently applied this
method has given good results, and the specimens seem
to have remained unchanged for many years. But unless
26
IRON OBJECTS
all Salts are previously removed, especially common salt,
as has been already pointed out in the First Report, p. Io,
there must always remain the danger, if not the Cer-
tainty, of deterioration taking place and becoming
apparent at some future date.
A better example to illustrate this could hardly be
found than that of a collection of Merovingian buckles
and other ornaments decorated with silver damascened
work (Figs. 23 and 23A). When viewed by looking down
upon them the silver pattern was fairly well seen, although
almost the whole surface was lifted up irregularly.
However, when viewed sideways (Fig. 23B), or in profile,
the nature of the destruction became apparent at once.
These specimens had been treated less than twenty years
ago and no doubt looked fairly well for four or five years
thereafter, but they gradually got into the lamentable
Condition in which they were brought for re-treatment.
The first thing to be done was to extract as completely
as possible all the paraffin wax with hot benzol. After
the paraffin had been removed and the objects dried,
the Salts were extracted with water along with some
Caustic Soda to decompose any chlorine compounds of
iron which had been formed. By careful washing
followed by the application of a solution of potassium
binoxalate (salts of sorrel) to dissolve some of the iron
Oxide, it became possible to push back the thin silver
work into its place and thus restore to a large extent the
Original appearance of the objects. Of course all traces
of the reagents used had to be carefully washed out in
repeated changes of distilled water until nothing more
could be extracted. The objects were then dried
thoroughly in an air-bath and, when cold, coated with
dammar varnish, partly to prevent the absorption of
moisture but mainly to fasten down the fine silver work.
Similarly, by the use of potassium binoxalate a large
portion of the Gowland collection (Figs. 24 and 24A) of
27
MUSEUM EXHIBITS : CLEANING AND RESTORATION
objects dating from about 900 A.D. were cleaned, and Some
degree of their original beauty restored to them. These
specimens consisted largely of horse trappings which were
made of iron. The iron had then been coated with copper
(probably by immersion in a solution of some copper salt),
and the copper in turn had been gilt by the application of
thin gold leaf. This gold was practically hidden by the
rust which had formed, and the whole collection looked
as if it consisted of nothing but shaped pieces of iron
oxide. All the objects had become very brittle and frail
as they were so thin, and no metallic iron remained in
any of them. By patient soaking in the binoxalate
Solution, which in aggravated cases had to be used warm,
the comparatively thin coating of iron rust over the gold
was dissolved off and the gilding revealed. The general
Scheme of the artistic work was thus brought out, and
showed that silver also had been employed to a con-
siderable extent. As was mentioned above, many of
these objects were very frail and broken and thus had to
be pieced together and strengthened by a backing of some
kind. For this purpose the material sold as “Pyruma
putty '' proved most useful and very satisfactory, especi-
ally when, after drying in the air, it was dried still further
in a steam oven at about IOO’ Centigrade. Under this
treatment it becomes very hard and has now stood two
years without deterioration. Instead of this substance,
kaolin made up into a paste with silicate of sodium or
potassium has been used with equal success when the
dark colour of the “Pyruma " has been objectionable.
The use of potassium silicate solution diminishes the risk
of “white bloom '' or efflorescence which sometimes
OCCUITS.
Owing to the great increase in volume which occurs
when iron changes into its hydrated oxide, or common
rust, the original form and structure of an iron object
may be completely obliterated, especially if the workman-
28.
IRON OBJECTS
ship be fine and the objects small. These masses, often
shapeless, may, by suitable reagents, be so dissected as
to show what they were originally. -
For example, some almost shapeless masses of rust
were among the objects resulting from Roman remains
excavated at Colchester, which consisted of articles of
iron, bronze and silver. These masses of rust were proved
to be the remains of a coat of iron chain armour, by giving
them first gentle treatment with dilute acid so as to free
them from calcareous deposits, and following this by
immersing them in caustic soda fused in a silver dish.
This yielded many portions of iron oxide in the form of
rings, and so it was possible to prove, not only what this
mass had been, but to tell the exact size of the iron rings
out of which the chain armour had been constructed.
One object of great historical interest which has been
treated with a view to arresting corrosion by rusting is
the helmet of the Black Prince (Fig. 25), which hangs
above his tomb in Canterbury Cathedral. This had become
very rusty, but, as it had never been buried in soil
and so remained free from salts, it had not deteriorated
to any alarming extent, nor had it been exposed to the
fumes of burnt Coal gas and the consequent corrosion by
sulphuric acid. It was severely pitted all over, however,
and having now been attended to it is hoped that it has
been saved from further decay. The first step of the
treatment was to remove the rust completely by means
of a soft iron wire brush (not brass); the iron was then
coated with “duroprene '' to which sufficient lamp-black
had been added to take away the unpleasant rusty-brown
tint.
The helmet was surmounted by the “cap of mainten-
ance ’’ (Fig. 26), and this, again, by the crest in the form
of a lion. The cap was in grey leather and had been
painted in red and gold. Most of this decoration had
disappeared, but during the cleaning a rose in gold could
29
MUSEUM EXHIBITS : CLEANING AND RESTORATION
be distinctly seen on a field of red. The lion was likewise
of leather (cuir bouilli), which had been moulded to the
required shape when soft and wet. The lower jaw was
missing and the tail broken in one or two places. After
the modelling the lion had been covered with a “gesso” of
whiting and glue fashioned so as to represent the mane,
&c., which was finally covered with gold leaf. When
received this was almost everywhere hidden by the dust
and grime of ages, which were retained somewhat tena-
ciously as the whole figure seemed to have been given at
one time a coating or varnish of gelatine. By washing
with water just warm enough to dissolve the gelatine,
and applying the gentle friction of a soft camel's hair
brush, the adherent dirt was removed without injury to
what remained of the gilding. The “gesso” and gilding
seemed to have been applied in diamond-shaped pieces,
very many of which had been lost. The helmet, from
its simple form, was at first thought to have been made
and used for the funeral obsequies, but examination of
the inside showed the remains of a leathern cushion,
which seemed to indicate that it had been made for
actual wear, and in all probability it was a tilting helmet
or heaume. Its weight was I2 lb.
Two other helmets were treated in much the same
way and deserve mention here as they present some
additional points of interest to collectors and curators
of museums. They, also, were much corroded by rust,
and cleaning showed that they had both been ornamented,
one with gold (Fig. 27), and the other, simpler one with
silver (Figs. 28 and 28A). Unfortunately, the rusting had
proceeded so far that no trace of any pattern beyond the
mere gilding could be made out, but on that ornamented
with silver a certain amount of the design was rendered
apparent. These helmets are in the church of White-
lackington near Ilminster and are hung over the tomb of
the Speke family there.
30
IRON OBJECTS
An interesting problem emanating from Lincoln
Cathedral was presented in determining the best treat-
ment to be applied to the I3th century iron railings and
gates in the chancel. Like the Black Prince's helmet, these
gates had never been buried and so were free from saline
impurities. They had been painted and the central
links had also been gilt. More detailed examination showed
that they had been painted twice, probably at different
dates, and the gilding probably done at a later period.
One of the coats of paint had an iron oxide basis and the
other was of a bluish grey colour and contained much lead.
The remains of the gilding were so small in amount,
and of no artistic interest, that it was considered that
they were not worth preserving. The treatment recom-
mended, after many experiments had been made with the
small panel shown in Fig. 29, was to boil with caustic
Soda Solution, wash, and dry at a high temperature, then
remove all adherent rust with a soft iron wire brush and
then paint with the same blue grey tint, and regild the
links Serving as bosses which held the component parts
together.
3I
LEAD
HE methods already described for the cleaning and
preservation of leaden objects have been in constant
use and require but little amendment as the
result of five years experience. Careful application of
dilute acids by means of a brush is usually all that is
required, and in most cases it does not matter much
whether acetic, nitric or sulphuric acid be used to dissolve
off or to decompose the lead carbonate forming the
incrustation. If acetic acid be used the subsequent
washing must be very thorough, and in every case it is
well to begin the washing with an alkali either with or
without some lead oxide (litharge) dissolved in it.
The problem often arises whether a thin coating of
carbonate ought to be removed or not. As has been
indicated in former Reports, there is a very great increase
in volume when metallic lead becomes converted into the
usual basic lead carbonate. If this corrosion has not gone
too far for removal the coating of carbonate may almost
enhance the clearness of the original detail; if the action
be stopped at this stage this procedure is safer than
cleaning off the coating, because under the latter the
metal is almost invariably pitted all over. This tends to
obscure any fine detail which was on the original
metallic surface, although the detail may be still clearly
made out on the surface of the coating of carbonate.
These facts are well exemplified in Figs. 30 and 30A,
which show how the detail survives even after prolonged
corrosion. As this coating on the leaden medal was falling
off and crumbling with the slightest touch, steps had to be
taken to arrest further change. It was decided to retain
the coating and to strengthen the incrustation so that the
medal could be handled with safety. It was therefore
32
LEAD
very carefully dried at Ioo” Centigrade in a steam-oven
and then placed under the receiver of an air-pump
arranged so that the medal could be flooded with gum
dammar dissolved in benzol, whilst still in the vacuum.
Air was then admitted and the medal removed from the
Solution, drained on blotting paper and then allowed to
dry. Treated thus the surface showed no apparent
change and no varnish-like glaze. After thorough drying
it was So much strengthened that the specimen could be
manipulated without danger, and casts were taken as a
record of its present appearance.
The following Figs. 31 and 31A show a seal of Pope
Paul III before and after thorough cleaning. They
show clearly how the increase in volume of the incrustation
rounds off the figures and causes loss in detail, and
further how restoration of much detail is possible even
though the metal be pitted considerably under the
incrustation.
The restoration of writing on strips of metal has
already been exemplified in the section on Prints and
Drawings. In further illustration of such, the IIth
century leaden mortuary cross (Figs. 32 and 32A) may be
cited. The inscriptions recorded on the modern wooden
backing were quite illegible on the cross, and accordingly
recourse had to be had to the acid treatment as a means
of recovering these. The cleaned cross shown in the
accompanying figure has finally been thoroughly washed
in caustic alkali and in distilled water, followed by
drying and coating with dammar varnish.
It may be objected that such treatment causes leaden
objects to lose much of their charm. In certain cases the
justice of this criticism cannot be disputed, although this
will depend largely on the nature of the object. In
cases where the acid treatment is necessary to bring out
detail it is desirable to clean the lead entirely, wash, dry,
33
MUSEUM EXHIBITS : CLEANING AND RESTORATION
and coat it with dammar varnish. Thereafter there can
be no harm in attempting to recover some of the original
“complexion ” by the judicious use of a perfectly neutral
medium such as pure dry kaolin, in imitation of the
carbonate commonly associated with leaden objects of
antiquity.
34
COPPER AND BRONZE
S regards their preservation and renovation, museum
objects of copper and its various alloys present a
vast and complicated field of study. Almost
invariably articles of copper contain traces of foreign
metals as impurity, notably silver, lead and arsenic,
while copper alloys are employed in an infinite variety
as regards their composition and constitution ; these
factors modify profoundly the power of the metal or
alloy to withstand corrosion. In addition to this very
variable factor of the metal basis itself, there are super-
added all kinds of circumstances which tend to promote
corrosion, such as burial in Soils containing abundance of
limestone and salts, or, as a contrast, in soils which
possess a more or less pronounced acid reaction. What-
ever may have been the condition, in times long past, of
the object or its environment, there is no doubt that the
action of moisture, which is usually present in some
degree, and that of air and carbonic acid would all play
an active part in determining its present condition. These
influences would be greatest in the case of burial in a
porous soil, or where a large surface of the object was
exposed, and in an especial degree where the metal itself
is notably porous.
It is found in practice that copper objects withstand
these agencies better than any of the copper alloys, such
as bronze and brass. In time, however, all become coated
with a layer of copper compounds, and this layer contains
the oxides of the other metals which were present in the
original alloys. This coating, when fine, continuous and
hard, has received the name of “patina.” When slowly
and uniformly formed and of a hard crystalline nature,
it may take a high polish and by its beauty add much to
35
º
tº,
& Cº. (s
MUSEUM EXHIBITS : CLEANING AND RESTORATION
tº
Jº tº
* tº º
the artistic value of an object which, originally of bronze,
was then appreciated because of the beauty of its form
and its metallic lustre. This patina is too often of a
more porous and of a softer nature than that so much
Sought after, and from its porosity tends to retain some
of the saline constituents of the soil which have led to
its formation. This retention of the salts, together with
the moisture in the atmosphere, is revealed by the appear-
ance of bright green spots, which may be either dry and
powdery, or moist and pasty, according to the nature and
quantity of the retained salts and the dryness of the
atmosphere at the time of examination. Such are the
symptoms of the so-called “bronze disease,” about which
there is nothing mysterious. The remedy is obvious,
although in many cases by no means easy to apply, and
consists in the removal of the soluble salts from the
incrustation (together with certain other undesirable
insoluble compounds). Prolonged soaking in water is
not enough, for this will only remove the soluble salts,
Such as those of Sodium, potassium, ammonium, and
calcium. Some of these have given up part of their
chlorine to form insoluble oxy-chlorides of copper and
similar compounds. The latter may be decomposed by
a large excess of water acting on them for a long time,
but it is unsafe to trust to this. It is necessary that
these compounds be decomposed by some reagent which
will not attack either the patina which is good or the
metal. The safest reagent for this purpose seems to be
a strong Solution of Sodium sesquicarbonate, which can
be used either cold, or, in aggravated cases, hot. The
specimens are left in this solution as long as chlorine is
being removed from the incrustation (test occasionally
with silver nitrate, as directed in the section on Stone
and Earthenware). This solution also acts very bene-
ficially in loosening the incrustation of earth, sand, and
clay which is a common accompaniment of objects which
36
COPPER AND BRONZE
have been dug up. The removal of these in this way
is infinitely safer than the usual mechanical method or
the equally drastic measure of treatment with dilute
acids.
The group of vases and figures shown in the illustra-
tions (Figs. 33 and 33A, 34 and 34A) demonstrate the
result of applying this simple treatment.
When objects have been coated or plated with another
metal this treatment with sodium sesquicarbonate is of
Special value. This is very well seen in the exquisite
Small gilt Cup of Korean workmanship (Figs. 35 and 35A),
which was so thickly coated with a green crust that the
whole of the artistic work was obscured and no gilding
was visible. Treatment with any reagent which would
have dissolved the incrustation would almost certainly
have removed some of the cuprous oxide underlying the
gold which was so thin that it would have floated off
and been lost.
For the reduction of the compounds of copper and
their Conversion into spongy metal in a form easily
removed, warming with a solution of caustic soda together
with metallic zinc has been much employed. This is, of
course, nothing other than a simple form of electrolytic
reduction. As the zinc can be employed in various forms,
it gives more latitude and greater adaptability to each
especial case than the direct application of the electric
Current from a battery or from the ordinary supply mains.
The latter was tried, perhaps not very thoroughly, when
this work was begun, but it was abandoned eventually
for the treatment above outlined. There is no doubt
that what may be called the “direct current method ''
can give excellent results, as shown by Professor Fink and
Mr. C. H. Eldridge,” who are experts in the use of the
* Colin G. FINK, Ph.D. and CHARLEs H. ELDRIDGE, B.S. The
Restoration of Ancient Bronzes and other Alloys. First Report, IQ25.
The Metropolitan Museum of Art, New York.
37
MUSEUM EXHIBITS : CLEANING AND RESTORATION
electric current in the restoration of bronze objects;
but for safety, and with the simple appliances at the
Command of most curators of museums and other col-
lectors, the treatment with zinc in alkaline, or it may be
in acid, Solutions will be found most generally useful.
A good example of the removal in this way of the
hard and closely adherent incrustation is shown in
Figs. 36 and 36A, which represent the bronze case for a
mummified fish, before and after treatment. The fine
detail work on the fins and scales is here admirably
revealed.
Again, the inscription and detail on the much-corroded
lamp (Figs. 37 and 37A) have been brought to light and the
process of corrosion arrested. The active progress of the
“disease ’’ is taking place at the white parts of the picture
and its effects are seen by the holes eaten in the metal in
the cleaned specimen. Not infrequently it happens that
it is necessary to clean such copper and bronze objects
when, owing to the nature of the incrustations or to other
circumstances, it is inadvisable or even dangerous to
employ any solution having an acid reaction. To meet
such cases the Rochelle salt method of cleaning was
devised (First Report, p. 12; Second Report, p. 7), which
gives excellent results and is highly spoken of also by
correspondents. It need hardly be pointed out to chemists
that its utility and safety depend on the fact that while it
may attack and dissolve cupric oxide and the compounds
derived from it, it leaves unchanged both cuprous oxide
and metallic copper.
Where there is abundance of metal and the amount
of corrosion not extensive, a solution of ammonium and
stannous chlorides kept faintly acid with hydrochloric
acid is most valuable, especially when it is desired to keep
the specimen bright and metallic looking. Figs. 38 and
38A represent a statuette of Isis which has been thus
cleaned. The interesting bronze mould for barbed arrow-
38
COPPER AND BRONZE
heads shown in Fig. 39, found at Carchemish, was given
this same treatment. Besides its own particular interest
as a specimen, the behaviour of this mould under treatment
has brought out several points of interest in its past
history and also has been the means of indicating certain
precautions to be taken in treating objects made of cast
bronze. When treated in the first instance it seemed to
present nothing unusual in its structure or behaviour.
The mould proper originally consisted of three parts in
the form of similar longitudinal sections of a cylinder
(Fig. 39A), of which only two were found along with Some
of the arrowheads cast in the mould. Each of the sections
had a handle at right angles to the cylindrical face, giving
it somewhat of the form of a hammer. After the usual
treatment and a very thorough washing, the mould and
arrowheads were exhibited in the museum. After a period
of two years in the cases one of these parts was found to
be showing signs of “ disease ’’ in a somewhat unusual
form. Examination showed this to be due to the retention
of Some of the ammonium chloride by the porous metal,
even after the prolonged washing. This porosity was
found in its turn to be due to this one piece having been
exceptionally porous, and its maker having endeavoured
to remedy this by hammering with a blunt-pointed
hammer. Where each blow fell the metal was hardened
and compressed, the space between each depression thus
produced remaining porous and capable of retaining the
solution. In the course of time these little angular
patches which had corroded most were rendered apparent
and this accounted for the honeycomb like pattern which
the “disease ’’ presented in this case (Fig. 39C). The
treatment of this mould forms an illuminating instance
of how details in the manufacture of objects made over
two thousand years ago may be brought to light by
modern research.
Another case of light being thrown on the history of
39
MUSEUM EXHIBITS: CLEANING AND RESTORATION
manufacture of an important object is presented by the
standard pint measure in the custody of the Standards
Department of the Board of Trade. This (Queen Eliza-
beth) measure, dated I602, is shown in Figs. 40, 40A and
4OB. Although heavily varnished, small white incrusta-
tions were seen all over it, and these had increased in
course of time to such an extent that this white substance
was falling from the surface of the measure. Examination
showed the incrustation to consist of the ordinary basic
carbonate of lead. The question naturally arose as to
how this could be formed on any object made of bronze.
After the varnish had been removed, the lead carbonate
was decomposed and the measure pickled in dilute sul-
phuric acid. After thorough washing and cleaning,
re-examination showed that the measure as cast was of so
porous a nature that it could not retain liquids, and its
maker had therefore endeavoured to remedy this by
dipping it in molten lead SO as to fill up the pores. The
excess of lead was then Scraped off. Figs. 40A and 40B
show well how the lead had been eaten out of the surface
by atmospheric action, and also the marks of the scraping
tool used to remove the excess of lead from the surface.
A four-pound weight of Edward IV in the form of a
thick disc which was also suffering in this way was found
to have had a similar treatment before being used as a
standard weight.
When objects, especially those of bronze, have the
incrustations on them reduced, either naturally or in
the laboratory, the reduced metal often forms a tough
layer of pure electrolytic copper. Between the object
and this layer is the unreduced oxide of tin. This thin
layer of porous oxide retains with great persistence acid
and salts and, unless these are removed, forms the
starting point of fresh corrosion. This was well exem-
plified when treating some bronze pots from West Africa
(Figs. 4I and 42). After cleaning and thorough reduction
40
COPPER AND BRONZE
of the coating of copper compounds the patches of the
redder copper were shown up on the yellower bronze
after polishing. This polishing was naturally done after
prolonged washing, but on the day after the pots had
been polished (about 24 hours) a distinct dullness was
observed round these patches of reduced copper indicating
the presence of impurities in their neighbourhood and the
recommencement of tarnishing. This is shown by the
light portions in Fig. 42, which indicate the polished
copper which is seen to be surrounded with a dull area.
These pots showed also how their makers rendered
them watertight when holes or very porous portions
occurred in the casting. Inside the pots, before cleaning,
lumps of metal were found fixed to the sides or bottom.
These proved to be lumps of copper which had been
inserted into the flaws and then hammered so as to close
the holes by rivetting. The outside was then filed or
scraped smooth. This is shown in Fig. 4I where the
copper surface is easily identified surrounded by the
bronze.
WOOD
HE preservation of wood, both dry and saturated
with water, has raised many points of interest in
deciding how best and most suitably the wood
should be treated. In the case of dry wood which has
been attacked in various ways by insects and animal life,
much work has been done elsewhere and on a much larger
scale. The questions which arise from the attack of
insects resolve themselves usually into how to strengthen
the wood, how to destroy any insect life in any phase of
its existence whether as egg, larva, chrysalis or complete
insect, and finally how to prevent any further attack
by any insect pest. The strengthening of the wood is
often attempted and also achieved by the application of
glue or gelatine so as to fill up the channels and pores in
the wood. This when dry does add very much to the
strength of the wood, but in damp atmospheres or where
there is the possibility of water reaching the wood thus
treated there is always the probability of the gelatine
becoming soft and also of its encouraging the growth
of moulds which would bring about its destruction.
One substance also recommended is paraffin wax applied
hot, or even in solution, but it does not add much in the
way of strength. It is, however, excellent as regards
resistance to dampness and even liquid water, and any
wood so treated is not likely to have any eggs deposited
on it. One substance which seems to promise well is
that solution of sodium silicate sold as “P.84.” When
this is applied at half or even a quarter of the strength
as sold the wood becomes hard and strong when dry, and
does not show any unpleasant efflorescence. The surface
42
WOOD
is such that it is most unlikely that any beetle would lay
eggs upon it and even if any larvae were hatched on it
it seems improbable that they would be able to attack
wood so treated.
When very wet wood has to be brought into the dry
atmosphere of Museums many points have to be taken
into consideration. For example, when the piles from
“lake dwellings” have to be preserved so as to undergo
no change of shape and to retain the markings left by
the tools employed by these ancient builders it is impor-
tant that as little shrinkage or deformation as possible
should occur. Experiments in progress seem so far to
indicate that the sodium silicate solution described above
gives very good results. This becomes dry and hard
when the wood is thoroughly impregnated. To enable
this to be accomplished in a waterlogged wood, is how-
ever, by no means easy with large specimens. When
small enough to go into vessels of Suitable shape which
can be evacuated by a good air pump it ought to be
possible to withdraw the air from the wood especially if
the temperature be raised somewhat. On readmission
of air to the vessel the silicate solution would be forced
well into the pores of the wood.
One problem presented for solution is that of an old
pumping cylinder and its piston which had been kept
under water for perhaps I50 years. It seems doubtful
whether it will be possible to limit the deformation so
that the shrinkages will be so slight as to allow the piston
to move in the cylinder after drying, when the direction
of the grain of the wood in these two parts is considered.
Instead of hardening and drying the specimens by
treatment with sodium silicate, glycerine seems to be the
most likely substance to give good results, especially
if the object could be warmed to about 60° Centigrade
in a bath of glycerine in a vacuum. The water would be
43
MUSEUM EXHIBITS : CLEANING AND RESTORATION
distilled out, and on the admission of air its place would
be taken by glycerine which would never dry. A variant
would be to use glycerine jelly (glycerine and gelatine)
which, after application, could have the gelatine in the
outer layers at least hardened by immersion in a solution
of formaldehyde.
44
GLASS
N many instances moisture is attracted by an object
of glass or enamel, and may be observed in the
form of little globules which, in aggravated cases,
coalesce and flow over its surface in streams. This applies
not only to specimens exposed to the outside air and
weather, but is found to take place in certain types
of glass in the museum, under conditions which seem
specially regulated to ensure indefinite preservation.
After this has gone on for some time it is observed that the
surface of the glass has lost its original brilliance, and
this can be seen more clearly by washing and thoroughly
drying the specimen. When examined with a lens, the
loss of brilliance is found to be due to a multitude of
Small pits in the glass. Enamels are likewise liable to
decay in a similar fashion, though possibly in this case
only one or two colours in a composite enamel may be
thus affected. The cause of this abnormal behaviour is
usually attributed to the use of too great a proportion of
alkali, especially potash, in the mixture of components
from which the affected glass has been made. This
excess of alkali, being that over and above the proportion
required to combine with the silica present, is held in a
very loose state of combination, if combined at all, and
attracts moisture and carbonic acid from the atmosphere,
forming a strongly alkaline liquid, which attacks the
transparent silicates of which the glass is composed,
leaving calcium and other silicates in an opaque form.
Such glass is often said to be “diseased,” and this disease
results from an unsound constitution.
45
MUSEUM EXHIBITS : CLEANING AND RESTORATION
Experiments made in order to determine the accuracy
of this generally accepted explanation afford strong
corroboration of it. Some badly “diseased '' specimens
were kept for several days in an atmosphere Saturated
with moisture and then washed. The wash liquid was
strongly alkaline and gave the usual tests for the presence
of potassium salts. The specimens were then kept in
distilled water for several weeks, the water being frequently
changed. When taken out and dried and kept in the
ordinary atmosphere they showed great improvement as
regards absorption of moisture, but when placed in a
moisture-saturated atmosphere it was found that their
tendency to attract water had not been eradicated. If
the attraction for moisture is really due to the excess of
alkali, the natural cure ought to be its removal by
treatment with an acid. For certain reasons dilute
acetic acid was first tried for this purpose, and proved to
be a great improvement on distilled water, but it was
found to be distinctly inferior to dilute sulphuric acid.
This latter acid, by neutralising the alkali, and perhaps
also because its potassium and Sodium Salts are non-
deliquescent, seemed to cure the “ disease ’’ entirely.
The strength of the acid employed need not exceed
I per cent. After being thoroughly tested in a moist
atmosphere, the specimens were once more thoroughly
dried and given a coat of thin dammar varnish, which
restores some of the original brilliance and forms an
additional protection against further change.
A problem constantly arising in museums and of
interest to collectors generally is the determination of the
age or the source of specimens of glass. This is frequently
solved by finding out whether the material is a lead glass
or is free from lead. As a glass containing lead is much
denser than one free from it, the usual method of deciding
this is to determine the specific gravity of the glass. It
is obvious, however, that this method is inapplicable
46
GLASS
when the specimen contains hollow spaces or large air-
bubbles, whether intentional or not. A method much
easier in its application and of much greater certainty is
to resort to chemical tests. If dilute hydrofluoric acid
be applied to glass for a few seconds and the liquid tested
with a Solution of hydrogen sulphide, a black precipitate
will be formed if lead is present in any appreciable
quantity. The method of applying this test is to place
a drop of dilute hydrofluoric acid on the surface of the
glass, using a Small camel's hair brush or a piece of wood
to do so, and to leave it there for I5 seconds and then to
add to that drop one of a solution of sulphuretted
hydrogen. Perhaps an easier and even more sensitive
method is to absorb the drop of hydrofluoric acid after
its action on the glass in a piece of white blotting paper
and apply to this spot a drop of sulphuretted hydrogen
Solution ; the black stain produced when any lead is
present is then easily seen. As a rule, a dilute solution of
ammonium or Sodium sulphide may be employed instead of
Sulphuretted hydrogen, since the amount of iron in any clear
glass is So Small as to give no appreciable colour in so short
a time. As soon as possible after the test has been made
the glass should be washed free from the hydrofluoric acid.
It need hardly be pointed out that glazes on porcelain,
etc., may be tested in a similar way.
If the test be carried out as described above, no mark
remains behind on lead glass and but a very faint one on
glass which is free from lead. It usually requires exami-
nation with a lens accompanied by a knowledge of the
spot selected for the test, to be able to detect any differ-
ence in the surface after the experiment has been made.
Besides naturally-occurring decay in glass, problems
sometimes present themselves which have been occasioned
by previous treatment of the glass, either in efforts to
preserve it, or to modify its colour or render it more
opaque. An example of this is to be found in the early
47
MUSEUM EXHIBITS : CLEANING AND RESTORATION
fifteenth century windows of the Lady Chapel at Wells
Cathedral. Here a grey, very closely adherent coating
was found on the inside of the windows. This is remov-
able by Scraping with a knife or similar instrument, and
it is found that the glass beneath is practically intact
and has preserved its original brilliant surface.
Analysis of the coating shows it to consist largely of
calcium sulphate (65 per cent.). Silica is also present
(I5 per cent.), and the remaining 20 per cent. consists of
water with a trace of organic matter. The only material
suggested by the analytical results is cement of some sort,
which must have been applied as a wash, either to hide or
obscure the windows.
Many solutions have been tried to loosen or soften
this coating, including the attempted conversion of the
calcium into carbonate by soaking in sodium carbonate
Solution and removing the carbonate either by friction or
by means of a dilute acid. Barium chloride solution was
also tried in the hope that the barium sulphate which
should be formed might be destitute of coherence and
be easily removable with the surrounding silica. The
best reagent so far discovered is a saturated solution of
ammonium sulphate, which, as is well known, dissolves
calcium sulphate. Ammonium thiosulphate was also
tried for the same reason, but with only moderate success.
The painting on the windows is brown oxide of iron
fritted on to the glass, or very imperfectly fused to it.
It is therefore impossible to use strong acids such as
hydrochloric acid, which readily attacks the oxide of iron
leaving only the pattern of the painting as a roughened
surface on the surrounding brilliant surface of the glass.
It might be mentioned that the body of the glass is some-
times amber coloured and sometimes bright green. In
neither variety has the inside surface been attacked by the
coating.
48
GLASS
In many of the pieces examined, the outside surface of
the glass is eroded in the usual manner, with rounded pits
which diminish enormously the transparency of the glass.
This can be mitigated by giving a coating of Canada bal-
Sam or similar varnish, but, unfortunately, such a coating
would not withstand the action of the weather for any
length of time, and would be costly to apply repeatedly.
40
THE STEIN COLLECTION
LARGE collection of very various types and of
varying dates brought from Chinese Turkestan
by Sir Aurel Stein has been cleaned and preserved
for the museum here and for the Indian Museum in Delhi.
The photographs (Figs. 43–50) serve to illustrate Some of
the specimens which may be seen in the British Museum.
A large number were of mud, containing what may be
termed a skeleton of straw or rushes. Of these, many
were elaborately gilt or painted with many colours. The
gilding and the colours were much obscured, sometimes
almost altogether hidden, by similar clay or dried mud
which filled up the hollows. Any attempt to remove this
mud directly was almost certain to bring away the gilding
and to destroy the typical moulding of the specimens.
Here, again, the use of cellulose acetate solution proved
invaluable. By giving several coats of this solution so
that it penetrated into the porous stucco behind the gilding
and into the colour layers, and then allowing it to dry
hard and thereby fix the gilding to the underlying base,
it was found possible to clean off this external deposit of
earthen matter and so to bring back the gilding and colours
almost to their original brightness by means of the solvent
(usually acetone) applied with a brush and accompanied
by gentle friction. This was especially so with a number
of small images of Buddha. The toys, besides being of
dried earth, were often of wood, either alone, or forming a
framework to support the dried earth. Examples of these
are seen in Figs. 45 and 46. In Fig. 44, which is that of
the leg of a large figure, the straw bundle is plainly visible.
Grotesque heads of painted wood and of dried earth are
shown in Figs. 47 and 48, and these also show the straw
50
THE STEIN COLLECTION
bundles. The usual museum term for the dried earth
employed in fashioning these figures is “stucco,” a term
strictly applied to plaster of Paris (or calcium sulphate)
which has set ; this term, therefore, has not been em-
ployed to describe the figures.
From burial mounds many interesting objects, not
usually found owing to climatic causes, were discovered
existing in a marvellous state of preservation. Perhaps
the most remarkable are the biscuits and cakes, some quite
elaborate in form, which are shown in Fig. 50. Even the
stains of the jam or similar preserve are still quite plainly
seen after the lapse of IIoo to 1200 years. This wonderful
preservation is due to the extremely dry and pure atmo-
sphere of Turkestan. Among the objects found were the
goggles or spectacles of metal pierced with numerous
holes, which were placed over the eyes of the dead.
These, when found, were dark green in colour and much
tarnished. On examination they were found to consist
of silver which had been alloyed with copper. They are
shown in Fig. 49.
5I
COLCHESTER COLLECTION
EFERENCE has been made in other parts of this
R. to a most interesting collection of Roman
remains recently excavated at Colchester. A few
of the bronze objects are of unusual interest and they
merit a short description here ; they have all been
subjected to treatment in the laboratory. One of great
age, as is shown by its form, is a celt, which perhaps
I,000 years later has been adapted by its Roman collector
or possessor to some much more recent purpose. This
is shown by the deep longitudinal groove cut along one
side, and by three knobs of a hard white metal let into
that side, two on one side of the groove and one on the
other. The loop of the original celt was broken. (Figs. 51
and 52.)
Another interesting object is the small bronze table
with feet. The table was originally strengthened by the
addition of two bars of bronze extending the whole
length of the table which were soldered to the under side.
In spite of this precaution the table-top was broken.
(Fig. 53.)
The figure of the griffin (Fig. 54) is only one of a
number of strikingly modelled figures of real and mythical
animals which were found.
52
TEXTILES
LOTH and tapestry of different kinds have pre-
C. various problems according to the source
of the basic material, whether animal, such as
wool and silk, or vegetable, such as linen and cotton.
These, again, may be plain, or covered with pictorial
representations which latter may depend for their effects
on painting on the material itself or it may be on the use
of threads of various colours.
Amongst the earlier problems presented was the
strengthening and restoration of Chinese paintings on
silk. Some had already been treated in China by mount-
ing them on modern silk of suitable colour, probably
with paste. This had apparently become brittle and so
lost its power of retaining the painted silk in place. A
Solution (2% per cent.) of cellulose acetate in acetone
was tried and has proved quite successful and after five
years the pictured silks seem as good as when the treat-
ment was finished. No doubt celluloid solution would be
a little tougher and therefore stronger, but it was con-
sidered undesirable on chemical grounds since there
might be in this case a tendency towards decomposition by
the action of light and air with consequent disfigurement
of the delicate fabric. It is well to have all objects which
are to be treated with cellulose acetate in as dry a con-
dition as possible so as to minimise any tendency to
produce a whitish or opalescent film. Should such appear
it is easily removed by a tuft of cotton wool charged with
acetone. Some tapestry-covered chairs were cleaned
first by a vacuum cleaner and then by careful Superficial
washing with a soft cloth soaked in a mixture of 4 parts
benzol with I part of methylated spirit which brightened
them up considerably. Where the material will stand
53
MUSEUM EXHIBITS : CLEANING AND RESTORATION
it, a brush, not too soft, gives better results than a cloth
for applying the cleaning mixture. This mixture was
employed to remove the traces of grease and oily matters
which are the usual substances by which dust and dirt
are retained by cloth in its various forms. To strengthen
the fibres and at the same time render them less ready to
pick up and retain dust, the tapestry was given a coat
of cellulose acetate solution. This undoubtedly took
away some of the brilliance produced by the benzol
mixture, a result probably due to the laying of the very
fine fibres. The final result was most satisfactory in that
it gave a very natural appearance to these I8th century
chairs instead of the unnatural brilliance left after treat-
ment with the benzol mixture, a brilliance which, it
ought to be pointed out, could not be maintained in a
London atmosphere. Cellulose acetate solution applied
to a clean white cloth in the strength recommended above
is practically invisible when dried, but communicates
a slight harshness to the treated cloth. It might be well
to point out here that preliminary experiments must
be made before applying it to many of the forms of arti-
ficial silk, as well as to any coloured or dyed fabrics.
Where slight colour (brownish) is no objection and
where strengthening of the fabric is of the first importance
the solution known as “Duroprene " has been found
most effective. This may be diluted with benzol, toluol,
or xylol So as to give a suitable strength and limpidity.
It may be diluted to one half, one third or even one fourth
of its ordinary strength.
A series of experiments made at Luxor for the best
substance with which to strengthen the very frail pall
which was over one of the inner shrines in the tomb of
Tut-ankh-Amen led to the choice of “Duroprene,” and
the diluent used was in this case xylol on account of the
high atmospheric temperature. Several other substances
were tried, but none strengthened the fabric so much and
54
TEXTILES
the slight brown colour was not a disadvantage in this
case as the pall had acquired a dark brown tint. After
treatment with the “duroprene " solution it was prac-
tically impossible to distinguish a treated from an un-
treated piece except as regards the great increase in
strength. The whole of the dissolved matter seemed to be
absorbed by the fibre and there were no remaining films
between the various threads. When solutions of cellulose
acetate and celluloid were tried they invariably left
films which connected the fibres together and so pro-
duced an opalescent effect which was objectionable and
altogether foreign to the material.
In this connection the microphotographs of linen
cloths from the tomb (Figs. 55, 56 and 57) may prove of
interest. f
“Duroprene '' solution has also been employed with
success in strengthening the cloth in some of the early
aeroplanes now in museums which, either from the dopes
employed or from other reasons, had begun to fall to
pieces.
5
55
‘‘ FAKES ’’
N a collection so vast as that of the British Museum
it would be strange if interlopers in the form of fakes
did not now and again find their way into the cases for
exhibition as genuine illustrations of art and craft. One
of the most interesting, which had been presented to the
museum by a well-known collector, purported to be a
Mexican funerary vase. In the lower part, the surface of
what was supposed to be Stone began to flake off in a very
peculiar fashion, taking place as it did in no particular
direction and not parallel to any lines due to natural
stratification. Examination of the lower portion showed
it to be covered with a layer of sand and glue which had
been skilfully applied to simulate a sandstone surface.
Further examination showed how extensive as well as
how clever the additions to the fragmentary original had
been. It had completely deceived the donor of several
other genuine antiques of similar character who was an
expert on such subjects. What had been added was
of the nature of Portland cement and the whole was given
a final coating of a uniform grey Colour of Sand and glue to
represent a fine-grained sandstone. Unfortunately for the
faker, but fortunately for the cause of truth, the alter-
nations of dry and moist days caused the coating of sand
and glue to crack and peel off and reveal the fraud. The
Figs. 58 and 58A show this specimen before and after
investigation. At the lower right-hand corner of Fig. 58
the peeling which led to the detection of the fraud is clearly
seen. Fig. 58A shows how little of the object was genuine
and how much had been added to bring it up to the
usual form presented by Such objects.
A case of quite another kind, but which resembled the
above in that it contained a substratum of genuine
56
“FAKES ’’
material which had suffered so much from bad treat-
ment that there was no chance of selling it in an un-
touched condition, was one of a valuable set of Limoges
enamels presented to the museum by a well-known col-
lector. It had been regarded by those in charge of
these enamels as an example presenting doubtful
features (Fig. 59). The reason for this was not dis-
covered until a critical examination was called for by
this example behaving as no other enamel had done.
Blisters began to appear on the surface and these on
breaking showed the well-known green colour of copper
compounds just as in the “bronze disease ’’ (Fig. 59B).
Examination under the microscope indicated what seemed
to be a somewhat reticulated coating of varnish. Appli-
cation of methylated spirit on a tiny spot of what appeared
to be a beautiful dark blue part of the enamel produced
a pure white spot at once. Examination of the blisters
showed that they also had a pure white layer overlying
the copper. The investigation finally showed that what
remained of the original enamel had been added to by
applying a thin layer of plaster of Paris which was painted
upon by brilliant varnishes charged with suitable pig-
ments, and the whole then varnished over to give a
brilliant and uniform surface. This was done with such
consummate skill as to deceive even an experienced
collector. The blisters which aroused suspicion as to
genuineness were due to the salts in the plaster of Paris
attacking the metallic copper and producing a notable
increase in volume at these points of attack.
The subject of the picture is “The Entombment,” and
it is quite sufficient to look at the face of the Virgin and
the right foot of the dead Christ to understand why
Suspicion as to its genuineness and value were aroused.
After cleaning, its genuineness was no longer in doubt
(Fig. 59A), but the effects of its rough treatment in the
past were clearly revealed.
57
MUSEUM EXHIBITS : CLEANING AND RESTORATION
A specimen of yet another type, namely, a bronze
vessel (Fig. 60) which was showing signs of active corro-
sion, was placed in Sodium sesquicarbonate solution as
recommended above. It had not been long in this
solution when it came apart into two pieces (Fig. 60A).
These were easily seen to be pieces of two entirely different
objects which, though they were of no use or interest
separately, when cemented together and the joint cleverly
hidden by putty-like material and painted a suitable
green all over, gave an object unique in its design, although
not differing sufficiently from similar specimens to
arouse active suspicion. The figures explain themselves.
The above examples suffice to show that in cases of doubt
as to the authenticity of objects presumably antique,
expert scientific examination may afford valuable and
sometimes conclusive evidence.
58
NOTES
LTHOUGH most of the solutions and other prepara-
tions recommended in the foregoing pages may
readily be prepared by curators who have simple
laboratory conveniences at command, it may prove
useful to give the names of some of the preparations on
the market which have been used with success in the
work at the British Museum Laboratory. A few hints
as to the use of apparatus of a simple nature are also
added.
For treatment of engravings and printed matter
generally which involves bleaching, the most useful
vessels are the papier-mâché dishes used in photographic
work. They are lighter than the earthenware ones or
those of enamelled steel, are not liable to fracture, and
cannot give rust spots as do the latter when the enamel
chips off.
Brushes can be obtained in infinite variety, whether
as to size or softness or hardness. It may save trouble
to point out that for use in caustic alkali solutions, brushes
with bristles of vegetable origin must invariably be used,
and for the rubbing of coins and similar Small objects
what are known as “Egyptian tooth-brushes" are very
convenient. They are made of a fibrous wood frayed
out at one end for about IO or I5 millimetres. The usual
diameter is about that of an ordinary lead-pencil, but
larger sizes are also made which are quite short and fit
into a ring-shaped handle.
For some purposes, glass-haired brushes such as are
made and sold for ink-erasers and for the retouching of
photographic negatives are of great utility.
Cotton-wool pads are in constant demand for gentle
washing and for the application of solvents and similar
59
MUSEUM EXHIBITS : CLEANING AND RESTORATION
purposes. These may in many cases be held simply in
the hand, but this is inconvenient and undesirable when
the Solutions attack the skin. The best way to make a
simple brush of this material is to take a tuft of the
cotton-wool and tie a piece of string round it, leaving
two long ends; thread these ends through a piece of
glass tube (which ought to have the sharp edges taken
off by heating in a flame), and pull the string so that the
cotton-wool forms a tight plug and pad at the end of
the tube. If a rounded-end pad of closer texture be
wanted, this is easily obtained by pushing a tuft of the
wool through a glass tube until it projects sufficiently
beyond the glass. Of course, metal tubes can be used in
place of glass. Copper tubes, for example, would be
employed when hydrofluoric acid was being used.
Zinc metal is used in several forms, as zinc dust,
zinc powder, and granulated zinc. The first is an
extremely finely divided form and must be bought. It
ought to be fresh, as some samples are so active that they
oxidise spontaneously and so become useless even in a
closed bottle, the grey-black powder becoming almost
white. The powder form is prepared by melting zinc in
a ladle and pouring it into a mortar, preferably of iron,
and stirring it vigorously whilst solidification is taking
place. The zinc is then easily broken up into a coarse
powder which, for convenience, may be sifted into
different degrees of fineness. In this condition it is
probably in its most useful form for the treatment of
bronze and other objects in conjunction with caustic
Soda solution. The ordinary granulated zinc is made by
pouring molten zinc from a height into a pail of cold
water, then draining and drying it thoroughly before
storing it. In this form also it is very useful for metallic
reductions when used either with caustic soda solution
or dilute acids.
“Pyruma putty " has been mentioned when treating
60
NOTES
of heavily-rusted iron objects. After being heated and
dried it sets very hard. It must be applied in thin layers
as thick patches do not seem to harden readily throughout.
Similar results are obtainable by the use of kaolin (China
clay) made into a paste with sodium silicate solution.
This can be tinted to any desired colour by the addition
of a suitable pigment.
The question of cements for the great variety of
purposes required in a museum is far too large for treat-
ment in detail here. A very useful one may be made by
dissolving celluloid in a mixture of equal volumes of
acetone and amyl acetate. This may be made of any
consistency desired and may be strengthened and im-
proved for Some purposes by the addition of substances
like gum dammar in a suitable solvent such as benzol.
For most purposes, however, collectors will prefer to
employ a cement of similar nature called “Necol,” which
is put up in collapsible tubes and is very easy to apply.
Applying it as stated in the directions given on each tube,
or applying to the surfaces to be joined a coating of
celluloid varnish and allowing this to dry thoroughly, far
stronger and better joins are made than those ordinarily
made with shellac. “Necol ’’ when dry is unattacked by
water and is therefore much to be preferred to any form
of transparent cement based on gelatine.
Solutions of cellulose acetate and of celluloid are of
very great value and are amongst the most useful
varnishes and cements. The strengths for cellulose
acetate which are most frequently employed are I, 2%,
and 5 parts in IOO parts of acetone. For most purposes
good commercial acetone is quite good enough ; for delicate
work, however, redistilled acetone should be used. The
solvent for celluloid which is most used is, as has been
stated, a mixture of equal volumes of acetone and amyl
acetate, the addition of the latter being necessary in this
case. As regards strengths, those similar to the ones
6I
MUSEUM EXHIBITS : CLEANING AND RESTORATION
suggested for the acetate will be found most generally
useful. Old photographic films do admirably for the
celluloid, but before use the gelatine coating must be
removed from both sides of the film. If this is not done
a troublesome deposit of thin gelatine films will settle out
from the solution.
Celluloid films give a tougher and more transparent
film than cellulose acetate, which latter is apt to become
opalescent if the objects to which it is applied are at all
damp. The acetate is much less combustible than the
celluloid film, but for most purposes this is not of import-
ance. As the celluloid is made from cellulose nitrates,
celluloid solutions should not be used with coloured
objects as there is always the possibility of the nitrates
being decomposed by light, especially in conjunction
with damp.
Plaster of Paris is largely used for making backings
and supports for many objects where the presence of water
is not an objection. Only the purest brands of plaster
should be used and none should be employed which give
more than a quarter of a gramme of soluble matter per
Ioo cubic centimetres when 3 grammes are added to a
IOO cubic centimetres of water. Several quick-setting
brands are sold which contain alum and other soluble
Substances. These may give rise to serious trouble Owing
to their crystallising out and breaking up the surface of
specimens to which such samples may be applied. It
often happens that a backing or a filling is required which
must contain no water. Such a substance is readily made
with celluloid solution and various substances in the form
of coarse or fine powders. Such fillings are especially
useful when they have to be applied to objects impreg-
nated with cellulose acetate or celluloid. For example,
Some large Chinese pictures on dried mud or clay which
were in pieces had to be mounted and retained in their
places in wooden frames So as to prevent vibration.
62
NOTES
These were treated at the back with celluloid solution to
prevent the crumbling of the clay and then embedded in
a paste or putty made of sand and Io per cent. celluloid
Solution. This sets into a hard mass with just sufficient
elasticity, when dry. A rod made of this mixture a foot
in length and having a half-inch square transverse section
gives just a Sensible amount when attempts are made to
bend it. Other substances which for the above purpose
were not so efficient were kieselguhr and kaolin. Saw-
dust is a very useful substance to use in conjunction with
celluloid, especially when the mixture has to be applied to
wood. A mixture of sawdust in various colours with
cellulose acetate or with celluloid is on the market as a
commercial product. The former is sold as “Non-
Inflammable Plastic Wood,” and the latter simply as
“Plastic Wood.” An excess ought to be used as the
pasty mixture shrinks appreciably on drying, but it sets
So hard that it can be cut, planed and worked generally
like wood when quite dry. It may be noted that the
celluloid-sand mixture recommended above can be pre-
pared in such concentrations that no appreciable shrinkage
takes place, the product resembling a piece of sandstone.
“Duroprene,” already mentioned in connection with
textiles, seems to be a solution of a chlorinated rubber and
is an excellent varnish for the protection of metals from
rust or corrosion even after prolonged immersion in water
and dilute acids. It dries to a tough and non-tacky film
which takes paint and varnishes well.
For a filling for metal, especially wrought or cast
iron, a preparation sold as “Mendeesi '' is very useful.
When properly applied it sets very hard and can be filed,
ground and polished. It contains no ammonium chloride,
and does not rust to any appreciable extent. It consists
largely of finely divided iron mixed with calcium sulphate
and Some phosphate.
“Plasticine '' for modelling is useful in many ways,
63
MUSEUM EXHIBITS : CLEANING AND RESTORATION
such as for holding together broken objects in their correct
position after applying a cement until such time as the
latter is hard enough to take the strain. It is useful
also for making moulds and taking impressions and these
moulds are very suitable for making plaster casts as the
plaster does not adhere to the greasy surface of the
plasticine. For large models in a warm climate it is not
to be recommended. This was shown by the gradual
deformation of the large models of the battle-fields in
Northern France in one of the Australian museums.
Experiments made here showed that this could be pre-
vented by applying a coat of celluloid varnish (5 per cent.)
which formed a tough skin able to resist change of shape.
Plasticine is sometimes applied in museums to keep
Small objects in their places on glass shelves especially
where these are subjected to vibration. It should not
be used where the objects are of ivory or of any substance
of a porous nature as the plasticine is apt to give up some
of the “vaseline '’ or greasy constituents to the objects
and cause brownish stains.
In the treatment and repair of objects made of leather
it is often necessary to fill up cracks and gaps. For this
purpose gutta-percha may be used when softened by
heat. To ensure its secure adhesion to the surface of the
leather the latter should be coated with a solution of
gutta-percha in chloroform. Another substitute for
leather suitable as a filling is what is known as “Chatter-
ton's Compound.” This is made into a very stiff semi-
liquid paste with carbon disulphide and applied to the
cracks in this form. The gutta-percha may be used in its
ordinary brown form which looks very like leather, but
sometimes it may be useful to have it a pure white and
this is sold in Small rods for dental purposes.
No collection of notes would be complete without some
reference to the difficult problem of patination. The
problem is difficult because of the different composition
64
MOTES
of the metal and alloys and of the treatment to which
they have been subjected. If we have to deal with a metal
Such as Copper much will depend on its purity, that is, its
freedom from other metals. The pure electrolytic copper
deposited from Copper Sulphate ought, one might suppose,
to be ideal. It is just because of this purity, however,
that difficulties arise.
AS has already been pointed out the exquisite patina
found on many bronzes owes its beauty and its solidity
to the presence of oxide of tin coloured by compounds
of Copper. Pure copper therefore cannot be expected
to give rise to such a coating.
Again, many bronze objects are not homogeneous,
and consist in One part of an alloy richer or poorer in tin
than that in another even when cast at one time. It
is not uncommon to see side by side a white alloy along
with a yellow alloy, the separation resembling that of a
mixture of oil and water into layers after having been
thoroughly mixed. Again some parts may have been
converted either wholly or partially into a mixture of
Copper and tin oxides.
Where there is much metal remaining, and it is only
in Such cases that it is worth trying to produce by
chemical means a patina resembling that which results
from the slow action of natural agents, the usual method
is to subject the metallic object to the action primarily of
acid fumes So as to form an adherent layer of copper
compounds, the colour of which may be modified later
by the action of Salts or alkalis.
When a simple blackening or a grey tint is sufficient,
a very dilute solution of sodium sulphide is the simplest
and best reagent. Enough solution should be used so as
to cover completely the object to be coloured. For
Success it is essential that the metal be bright and quite
free from grease of any kind. The action is simply to
form a film of sulphide over the metal. Other substances
65
MUSEUM EXHIBITS : CLEANING AND RESTORATION
used to produce films are solution of the chlorides of
arsenic, antimony and platinum which deposit these
elements on the copper, bronze or brass. A similar result
may be attained by the use of a dilute acidified solution
of tellurium potassium chloride which gives a very per-
manent and pleasing grey black colour.
What is difficult to obtain upon any restored bronze
is the green patina, and especially to have it cover the
whole surface in a uniform and satisfactory manner.
The usual procedure is to apply to the surface an acid,
either in the liquid or in a gaseous form—in the former
case either by immersion or by means of a brush or a
tuft of cotton-wool, in the latter by suspending it in a
closed jar along with a dish containing the acid Solution,
which must be of such a strength and nature as to give
off fumes at the ordinary atmospheric temperature.
In spite of a very large number of experiments, it is
impossible to recommend any one Solution as certain to
give good results. One which has in many cases been
very successful is a solution containing ammonium
chloride (sal ammoniac) and perchloric acid. For pure
copper and alloys which contain but little tin the addition
of stannic ammonium chloride is useful, as it provides a
body of stannic oxide which assists in the foundation of a
natural patina. Acetic and lactic acids in conjunction with
ammonium-chloride solution often give excellent results.
After the action of the acid mixture, followed by prolonged
washing, the colour may be changed considerably by
immersion in caustic soda or in Sodium carbonate or bi-
carbonate solutions, the caustic Solutions tending to give
a blue rather than a green tint to the copper compounds.
For gaseous treatment acetic acid has been recommended,
followed by fumigation with ammonia (Fink and Eldridge,
see p. 40). One of the most successful experiments was
made with a bronze hand cleaned by momentary immer-
sion in nitric acid, followed by dilute sodium sulphide,
66
NOTES
and then washing and drying, and finally suspending it
over diluted hydrochloric acid to which some potassium
chlorate crystals had been added. The chlorine and
Oxides of chlorine produced a very hard patina of a dark
green colour which has remained unchanged in the
laboratory for five years.
Another very good mixture which gives a green coating
which adheres well is a solution of potassium binoxalate
and ammonium chloride in the proportion of 4 parts
of the former to I5 parts of the latter in about 280 parts
of water.
There is no doubt, however, that after the cleaning
and thorough washing of the bronzes, the safest and
most expeditious method, and that most under control,
is to apply a suitable colouring or paint consisting of
Copper carbonate suspended in shellac varnish. Any
shade from the bright green of malachite to the deep
blue of azurite, is thus available. In this way much
more artistic effects are readily produced. It may be
objected that this is merely “faking,” but it is not really
more so than by producing on the surface a layer of
Copper compounds of a green colour, even if it be done
by purely chemical means. It is safer in that no corrosive
chlorine compound is left in the metal, however porous,
and the shellac varnish is an admirable protective coating,
however damp the atmosphere may be.
With regard to the preparation of stannous chloride
Solution for the cleaning of objects of bronze and metallic
iron, granulated tin may be dissolved in hydrochloric acid
(concentrated commercial acid) diluted with an equal
volume of water, or solid stannous chloride may be
dissolved in water to which a tenth part of its volume of
concentrated hydrochloric acid has been added. This
should be kept in a good stoppered bottle along with Some
granulated tin. For use, a strong solution of ammonium
chloride should be added when and as required. Some
67
MUSEUM EXHIBITS : CLEANING AND RESTORATION
workers have reported that they have been troubled by
the stannous chloride solutions gelatinising, but when
prepared in either of the ways given above this has
never been found to occur.
In making up solutions, it is always advisable to
Conduct operations in a fume cupboard or under some
form of specially constructed draught hood; when such
is not available, it is preferable to work in the open air or
in a very well ventilated room. Special precautions must
always be taken to ensure that acids and strong alkalis
do not come in contact with the skin or clothes; if such
an accident should occur, immediate steps must be taken
to neutralise the corrosive agent, ammonia being liberally
applied in the case of acid burns and vinegar in the case
of attack by caustic alkali. After the affected parts have
been rendered neutral, they must be washed very
thoroughly in running water.
*68
INDEX
Alloys,
copper, 35, 65
silver, 22
A nobiid beetle, destruction of, 12, 13
Bleaching agents, 4, seq.
Bleaching powder, 4
“ Bronze disease,” 36, 38
Bronze with hidden silver inlay, 22
F3rushes,
Egyptian tooth, 59
glass-haired, 6, 59
wire, 29, 31
Burns, 68
Calcium carbonate slip, 17
Caustic soda as paint remover, 31
Celluloid solutions, 61, 62
Celluloid varnish, use as a protective
coat during soaking, 20
Cellulose acetate,
solutions, 50, 61
use in rendering water-colour
paper uniform, 12
Cements, 61-63
“Chatterton’s compound,” 64
Chlorides, test for, 15, 16
Cotton-wool pads, 59,60
Cupric oxide, solvent for, 38
Dammar varnish, 26, 27, 34, 46
“Diseased glass,” 45, 46
“Duroprene,” 26, 29, 54-55, 63
Filamentous crystals in limestone,
17
Flake white, tarnishing of, 5, seq.
Formic acid, use in cleaning silver,
23, 24
“Foxed ” prints, 4
Glaze,
discolouration of, 20, 21
incomplete adhesion of, 19
result of pin-holes in, 19
Gum Dammar, use with celluloid, 61
Hydrogen peroxide,
in alcoholic solution, 5
in ethereal solution, 4
Vapour, 4
Insecticide, non-inflammable, 13
Iron oxide, methods of dissolving,
25, 27
Juxtaposition of different metals
conducive to corrosion, 11, 23,
25
Kaolin-waterglass paste, 28, 61
Lead objects,
artificial patina, 34
cleaning, 32
question of removing carbonates,
32
“Mendeesi,” 63
Moulds, see Sterilisation
Mould spots, removal of, 5, 7
“Necol,” 61
Oil and varnish, solvent for, 5, 6
Oil paint, softening, 6
Paper pulp, preparation and use of,
16
Papier-mâché dishes, 59
Paraffin wax, 26, 27
Patina,
artificial on bronze, 67
black, 65, 66
green and blue, 66
Patination, 64, seq.
Photographic films, use for old, 62
Plaster of Paris, 62
“Plastic wood,” 63
“Plasticine,” 63, 64
Potassium binoxalate, 27, 28, 67
Proprietary articles, 2
“Pyruma putty,” 28, 60
Reduction by caustic soda and
zinc, 23, 26, 37
Rochelle salt, 38
Salts,
in body of pottery, 19
in plaster of Paris, 57, 62
in stones which have been buried,
15
Salts of Sorrel, 27
Silver coins appearing like bronze,
Silver, percentage in coins, 22
Sodium sesquicarbonate, 36
Specific gravity test for glass, 46, 47
Spongy silver, strengthening, 23
Stannic ammonium chloride, 66
69
INDEX
Stannous chloride,
acidified, 25
preparation of solution, 67
Sterilisation,
of paper, 7
of paste, 10
Stone decay, mechanism of, 14
Test,
for chlorides, 15, 16
for lead in glass or glaze, 46, 47
Textiles, cleaning and strengthening,
53, 54
Unsterilised,
glue, danger of, 5
paste, 9
Wood moist, drying without warp-
ing, 43
Zinc, how to granulate, 60
Printed under the authority of HIS MAJESTY'S STATIONERY OFFICE
By Harrison and Sons, Ltd., 44–47, St. Martin's Lane, W.C.2.
(B 34–3278)0 2639—1161/121 1500 10/26 H & S, Ltd. Gp. 34.

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case -oº º ºs- oxºcºs,
- ACRED TO Tºrº-





ºvºſ '91-I
"Sº '91）


FIG. 39A.


FIG. 39B.


FIG. 39C.

FIG. 40B.
---
---

*Icº
"Z+ '01. I
"Iſſº“ĐI H

FIG. 43.
FIG. 44.
- -
---
--
-


*
cº
FIG. 45.
FIG. 46.
-
---
(…)
-ºcº


---
º

FIG. 49.







'99. “DIGI
|（， ） _
ſae


'+g "ĐI H




ºvºg "ÐI LI'89 º 1：1
：： | ， ، ، ، ، ، ، ،
ſaev ， ， ， ，
， , ， ， ， ， ， ， ， ， ，


*V09 （ĐIH
'09 （51 H

UNIVERSITY OF MICHIGAN
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