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Field Museum of Natural History

Museum Technique Series

No. 2

NEW USES OF CELLULOID AND SIMILAR
MATERIAL IN TAXIDERMY

BY

Leon L. Walters
Taxidermist, Division of Reptiles

Wilfred H. Osgood
Curator, Department of Zoology

EDITOR

Chicago, U. S. A.

June. TQ25

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Field Museum of Natural History

Museum Technique Series

No. 1

NEW USES OF CELLULOID AND SIMILAR
MATERIAL IN TAXIDERMY

BY

Leon L. Walters
Taxidermist, Division of Reptiles

Wilfred H. Osgood
Curator, Department of Zoology

EDITOR

Chicago, U. S. A.

June, 1925

Tit, Z-

NEW USES OF CELLULOID AND SIMILAR
MATERIAL IN TAXIDERMY

BY LEON L. WALTERS

The present paper deals especially with the correlation of form
and color in making replicas of natural objects. When this was
first put into practice, in preparing small reptiles, celluloid was used as
a medium in conjunction with pigment. The process has become rather
generally known as "the celluloid process," although, strictly speaking,
celluloid is only one of various materials that have been employed. In
explaining this process, it is hoped not only to give practical suggestions
for actual work, but to bring about a clearer understanding of the re-
lation of form and color as they exist in the natural object.

Taxidermy has realism as its ideal and so every factor that con-
tributes to what we see in a living creature should be isolated and
studied. This brings up the question of just what constitutes all we
see or regard as "life" or the appearance of life in the living model.
Among animals many subtle phenomena exist. How much or how little
any of them may actually contribute to our impression is speculative.
If there be anything not expressed through form or color, it cannot
be translated into glass, marble, celluloid, metals or other materials
available to the taxidermist or sculptor. Motion, which is almost insep-
arable from the majority of subjects, has the greatest influence in
forming our impressions ; but we cannot have motion. Allowing for
a suspense of motion, however, it is not established that the entire ap-
pearance of life does not lie within the limits of the various intricacies
of form and color. It may be conceded that attempts to secure the ap-
pearance of life fall short of absolute realism, but before forming a
theory to explain the failure, it should be made entirely certain that
technical shortcomings are not responsible for what may be lacking.
We accept many parts of a replica as being perfect. The replica, itself,
may be but a part, such as an artifical human eye. Each feature will
be compared with the real eye. If we can appreciate or suspect a differ-
O ence, can we not finally resolve and attribute this difiference to some

K?

1

4 Field Museum of Natural History — Technique, No. 2,

specific fault in color, translucence, form, proportion or marking? The
difference may finally be found to be due only to the lack of contraction
and expansion in the pupil.

Form refers to the general bulk of the figure, its anatomical struc-
ture, posture or attitude, and also deals with the most minute details
of the surface. In color, besides the correct tint, we are concerned
with duplicating the particular degree of translucence that is found in
the various visible parts of the specimen. Pigments, as prepared for
normal Use, are very opaque materials. Although mixed with oils or
varnishes, their opacity is not appreciably reduced. Natural objects on
the other hand are relatively translucent and in them the coloring agents
are scattered through a layer of considerable thickness, the colored parts
having the appearance of being lightly pigmented. If a thin shaving is
cut from the surface of a natural object, the shaving will appear much
less colored than the normal area surrounding it. Quite a thick layer
may be necessary to secure the full color effect. It is found that by
taking artificial pigments, correct as to tint, and mixing them with the
proper quantity of translucent material, a result can be obtained that,
so far as the eye is concerned, will equal the object to be duplicated.

We will assume that the various considerations regarding form
have been dealt with and that a mold of the object has been made. If
we make a cast from this mold, its form will be exactly that of the ob-
ject from which the mold was made. While the form is correct, the cast
has only the monochrome color of the material used in its making. It
is then necessary to color the cast, but any coating of pigment, however
slight, rises above what may be called the true surface and the form
is no longer correct. This change of form may not be great or may
not be perceptible when translucence is sacrificed and the most opaque
pigments are used for the coloring. However, it has been found that
in the average instance, a thick coating of coloring material is required
for the correct color qualities. This thick coating very decidedly alters
the fine surface details of the cast. While a model of translucent or
partly colored materials, such as celluloid or wax, could be cast in
the normal way, there would yet remain the matter of applying the
colors that are at variance with the general color selected. In this we
have the problem jlist presented. To color the finished cast through
the use of dyes would not necessarily alter the surface form. How-
ever, it will be shown that different colored bodies of varying degrees
of pigmentation exist in definite locations beneath the surface. The
surface layer may be translucent and practically uncolored, the main
coloration existing directly beneath this surface layer. Very often the

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Celluloid in Taxidermy — Walters. 5

different layers are of strongly contrasting colors and the color effect
of the whole is due to this particular arrangement. Dyes would neces-
sarily color these surface layers as well as the deeper portions.

The obvious solution of the color problem is to apply colors to
the mold and not to the finished cast. Each color is applied or painted
in its proper location on the interior surface of the mold. In the final
result the surface details remain unimpaired, all the colors appearing
within the true surface. But slight reflection is needed to see that this
condition prevails in the natural object. This briefly presents the
fundamental principle of the process. After the application of the
materials necessary to secure the full color appearance, layers of other
materials, such as cloth and wire-cloth are added for further strength
and support. The replica, entirely complete as to coloration, is then
removed from the mold.

Problems of Form.

Field and laboratory studies of living animals. — If the exhibit is
to have its greatest value, it is essential that studies be made of the
animal in its natural home. The selection of an interesting phase of
its life from a biological or from an artistic standpoint is made from
such studies. The animals' habits may be well known and the general
character of the exhibit may be determined upon beforehand, but even
then, it is necessary to supply by direct observation and attention the
innumerable details that are necessary to a truthful and convincing
reproduction. Such studies have the same relation and importance to
the museum preparator that personal sittings and studies have to the
portrait painter or sculptor. With reptiles and amphibians field studies
can be supplemented very favorably by further studies of caged speci-
mens in the laboratory, but allowance must be made for the abnormal
conditions. The value of such studies is mainly in the anatomical
structure and details for Use in coloring. In a general way, frogs and
toads can be expected to act in a fairly normal way in surroundings
that can be made nearly natural for them. The behavior of lizards
may be expected to be farthest from normal.

In the course of studies made by Mr. Karl P. Schmidt and myself,
in Central America, we observed that a captive crocodile did not walk
but progressed by short rushes. However, Under natural undisturbed
conditions, crocodiles would swim to the edge of the water, stand
high upon their legs and walk out on the bank. This dinosaur-like
position assumed in walking was surprising and interesting and was
chosen for one of the specimens for a group. These crocodiles would

6 Field Museum of Natural History — Technique, No. 2.

lie on the bank for hours at a time, holding the mouth open. This
peculiar habit is interesting, displays the interior of the mouth and
shows the peculiar structure of the throat valve. The crocodiles would
also lie motionless in the water with only the nostrils and eyes ex-
posed. This shows an interesting adaptation to an aquatic existence.
These were the primary reasons for selecting the positions chosen for
the reproductions. In the case of these crocodiles, plaster was trans-
ported and molds of the reptiles were made on the bank of the lake
where they were collected. Skins were preserved for pattern, and color
notes were taken for later use in making the reproduction. Large
specimens such as these present difficulties connected with the large
amount of plaster required and the extra care necessary in packing the
molds for shipment. The alternative is to remove the skin and pre-
serve it together with the skeleton and data for its rebuilding in the
laboratory. The plaster mold is then made from a reconstructed form.

The Use of live specimens presents a number of advantages in this
work where color is so important, and, fortunately, live specimens are
very readily available among reptiles and amphibians. Ordinarily
they are captured alive when collected. They can be kept captive in
a sack or box and can be shipped without provision for feeding. Am-
phibians can be shipped in cans containing dampened moss, the lids
punctured from the inside with holes for ventilation. All are easily
kept in the laboratory, a feeding of once or twice a week, ordinarily,
being sufficient to keep them in good condition. Occasional specimens
do not do well and soon become emaciated. The plaster molding must
be done before this occurs, for if no other specimen is available, it
will be necessary before molding to remove the skin and adjust it
on a carefully prepared clay model, a contingency to be avoided if
possible. In most instances, a mold of a reptile or amphibian can be
satisfactorily made directly from a freshly killed specimen.

Selection of specimens. — It is desirable that the specimen be in
normal physical condition and present the average size of the species.
It should be neither a record specimen as to size nor be much under
the average. Care should be taken to retain the relative sizes of the
species represented. An undersized specimen may be used as possibly
being the best available at the time. Also, an oversized specimen
of another, although smaller, species may be used. It seems a small
matter at the time but, later, these specimens will be exhibited side
by side in the same case, and, with reptiles as with fish, relative size
is one of the points strongly impressed on the observer. The more

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careful and detailed the technical work in the reproduction and the
accessories, the more confidence the observer will have in other
features of the work. The same applies to coloration. Often it may
be necessary to consider exhibition of more than one specimen in order
to cover the color variations, especially if distinct color phases exist.
A study of the species in regard to relationship or taxonomy is neces-
sary to determine and fully represent the characters of greatest im-
portance. The number of exhibits that can be prepared is limited.
Therefore, considerable care should be exercised in study of the species
and in selecting the specimen that is to be perpetuated.

Composition and pose. — After studies have been made of the
subject in the field, some interesting trait or habit desirable to represent
will nearly always be discovered. This is the direct result of study
of the animal in its natural habitat and involves judgment in selecting
what is best to represent, due regard being given to technical problems
of reproducing and final installation in the museum. The personal
equation barely enters in the positioning of the specimen. This was
the case in regard to the crocodiles referred to, although here, personal
ideas are allowed some play in selecting and arranging the ground
work and in arranging the specimens upon it.

In deaHng with snakes, however, we have an additional problem.
Few snakes have distinctive habits that would lead to an immediate
choice of position. A cobra might logically be posed in its charac-
teristic attitude with the forward part of the body reared off the ground
and the hood spread. The rattlesnake has a characteristic position
when it takes the defensive, the body being tightly coiled and the neck
and head taking the form of the letter S. It would be very well to
illustrate two or three of the dozen or so species that exist, in this
position. Many snakes that live on the ground have no peculiar or
distinctive habits that would lead to a choice of a position. It is with
such as these that the personal element enters and the specimen is
arranged according to the ideas of the individual in regard to compo-
sition or design. The snake lends itself readily to an almost unlimited
variety of positions that are anatomically correct. Diverse angles and
curves, when carried out in the arrangement of a snake, are usually
accepted as giving the most pleasing design, and if the casual opinion
of a number of persons is asked, nearly all will agree that certain
arrangements are decidedly more pleasing than others. The same in-
fluences that are common in regard to design in art apply here. Used
judiciously and closely limited, design, while in itself having no relation
to the problem of making a truthful natural history reproduction, may

8 Field Museum of Natural History — Technique, No. 2.

become an asset, but when persisted in without close restraint through-
out an entire series, the effect is monotonous and displeasing. An
injudicious display of this tendency is unfortunately in evidence in
nearly all work on snakes. In any event, the specimen should never
have the appearance of being designed, and it is better not to use
theories and ideas in regard to design that, in this work, would produce
a recognizable similarity and duplication when a number of specimens
finally occupy a single case.

Preparation of the specimen for molding. — The preparation of the
specimen for molding and the working of the molding material are
of great importance. If the model cannot be brought to a state en-
tirely satisfactory as to form, the reproduction will necessarily preserve
the same objectionable features. If detailed surface form is lacking
or is lost through poor molding, then this process will be of little
utility. Before molding, the specimen should be fully restored to life-
like condition in so far as form is concerned. As in all taxidermy, a
thorough study and familiarity with anatomy in relation to modelling is
necessary. Even when a mold is to be taken immediately after the
death of a reptile, it is necessary to study during life the positions of
all the parts that would be influenced by death, so that before molding
they can be restored to their life-like positions. Failure to detect the
small changes that take place after death and to restore them is one
of the reasons why casts have been, in general, unfavorably considered.
Restoration of the eyes, for example, to their life-like position is nearly
always slighted. Among amphibians and reptiles, with the exception
of snakes, the eyes are retracted on the death of the specimen. The
eyeball mtist be brought to its natural position before molding. It
may be necessary to cut certain of the eyelid muscles, or to entirely
remove the natural eyeball and replace with an artificial eye. Proper
support of the abdomen, throat and other parts must be provided. If
this cannot be accomplished with the freshly killed specimen, the remedy
is to make the necessary studies, remove and preserve the skin and,
later, in the laboratory, adjust this skin on a reconstructed clay figure.
When this is contemplated, the skeleton should be saved to accompany
the skin and the anatomical studies and casts that are made in the
field. The fine details of skin texture need no particular attention in
fresh specimens except with frogs and toads in which the warts often
flatten down soon after death.

All possible preparation and study should be made before the
specimen is killed so that after killing, the work of positioning, re-
storing and molding can take place without delay. If the specimen is

Celluloid in Taxidermy — Walters. 9

to lie on a branch or any part of a log, the selection of this branch
or log should be made beforehand. Details of the position can be
arranged after killing, but the general position should be determined
in advance.

Methods of killing. — In killing the specimen, the requirements are
that it be accomplished as readily as possible and that after death the
muscles shall be relaxed. Drowning is very satisfactory in most cases.
During the winter it is not always possible to do this unless the speci-
men is placed in warm water, as at that season, when placed in cold
water, reptiles and amphibians readily pass into a state of suspended
animation and are not harmed. A saturate solution, about i to 100
of chloretone (a chloroform deriviative) and water is useful, especially
for amphibians. Specimens placed in this liquid are quickly killed
and the muscles are left relaxed. Often shortly after death, warts
and protuberances in the skin of frogs and toads lose their plumpness
and full size, and the specimen is no longer useful for molding. The
molding of the specimen must take place before this occurs.

Use of skins and preserved specimens. — Remarks, so far, have dealt
mainly with the Use of live specimens under favorable conditions.
There are many cases where live specimens cannot be obtained. The
only available material may be in the form of an old mounted specimen,
a dried skin, an alcoholic, a fresh salted skin or a skin in pickle. When
a skin has been allowed to dry, the surface form is greatly altered, due
to the wrinkling, shriveling and flattening that takes place. With the
mounted specimen or dried skin, the skin must be placed in a bath,
usually of salt water or fresh water with an antiseptic added in order
to soften and plump it to a condition comparable to that of a fresh
skin. When this is accomplished, as in the majority of cases it can
be, a clay figure is constructed and the skin is adjusted and modelled
on this figure. In addition to softening the skin sufiiciently to permit
its proper adjustment, the finer details of the skin surface, of tuber-
osities, of scales and wrinkles must be plumped to their original full
form as in Hfe. In the alcoholic specimen, the details of the skin sur-
face are usually well preserved. The hardening, due to action of
alcohol and other preservatives, such as formaldehyde, must be suffi-
ciently overcome to allow for the manipulation and adjustment of the
skin. This cannot always be done, but long soaking in salt water will
greatly improve the condition. If the skin is a freshly salted one, or
is in salt brine pickle, it is only necessary to wash in fresh water
sufficiently to remove the excess salt. With dried skins, old mounted

lo Field Museum of Natural History — Technique, No. 2.

specimens, or any skins in doubtful condition it is generally possible
to remove a part for preliminary experimentation. While such skins
can be brought to a condition in regard to the surface details of form
that would be a great improvement over their previously shrunken and
shriveled state, it is not always possible to bring them to the condition
desired. The importance of these details cannot be minimized. Any
treatment of the skin that has an astringent action, or even the slightest
drying, results in changes of form that are universally characteristic.
The eye generally recognizes even the smallest changes that take place,
although the mind may not be able to readily analyze and point out
these changes.

With extremely rare species, it would be possible to restore a
specimen, approximately, even by resorting to modeling the skin sur-
face, but cases warranting such expenditure of time, coupled with the
inevitable inaccuracies, will be very few or none. Usually such speci-
mens lack reliable color notes or other data for proper anatomical
construction of the figure and correct posing in a natural surrounding.
A scientific institution has no need or desire to wander too far from
the paths of actuality in its exhibits any more than in any other branch
of its work. A fabrication in form and color can be no less a mis-
representation than if it were in written words. The worker should
know the requirements of his work to the extent that he can determine
what he can do and what he cannot do with the material available.
He should recognize the difficulties with each particular piece of work
and determine, beforehand, whether or not he is in a position to over-
come these difficulties in a reasonable manner. Lacking usable data
regarding the life or habits of the species, he supplies it if he can.
He looks up color descriptions and checks up color notes with markings
that may remain on alcoholics to determine whether or not he can use
them with assurance of a reasonable degree of accuracy. A skeleton
and photographs may supply information as to anatomical construction,
while the skin itself or a small sample of it can be experimented with
in order to discover whether or not it can be plumped to a condition
in which the surface detail will approximately equal that of life. Even
with everything else satisfactory, there may be some outstanding prob-
lem in connection with the color which the experience and experi-
mentation of the worker at the time may not be sufficient to solve.
It is wise then to drop that particular job and turn to something else
that can be done properly. At a later time a way may be discovered
to overcome the previous technical difficulty or supply the missing
information. Then it is time to do the work. At the best, there are

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Celluloid in Taxidermy — Walters. ii

many technical complications and difficulties in the work of making a
reproduction of this kind, and in spite of the greatest care, a large
percentage of errors will creep in.

While this process may appear to be primarily a process of coloring,
it must be remembered that the great object of the difficult and tedious
application of the colors to the interior of the mold is preservation
of the details of correct form. Anything unsatisfactory in the form
will be perpetuated in the reproduction. The particular defect will
stand out above all merits, and the specimen will be remembered by
its faults rather than its virtues. Features that are correct are passed
by without particular thought except to note that they are as was
intended.

Molding. — The molding is a vital step between the original model
and its final reproduction. No matter how satisfactory the model may
be, defective molding will ruin the result. In any case, the final form
will be no better than that obtained in the mold. The making of
plaster molds and the proper handling of plaster is a matter of ex-
perience and close study. It may be years before a careful workman
will be reasonably satisfied with his plaster work. Satisfaction may
often mean a relinquishment of ideals but this is not necessarily so.
It would be futile and misleading to attempt to lay down rules to guide
work in which only observation, experience and long, careful study
lead to results. The present process requires the mold to be made in
such manner that every part of it is accessible in order to do the
coloring that follows. Snakes, turtles, and many subjects will be posed
for lying positions and so quite an area of the under surface of their
bodies is hidden. As this is not seen, it need not be reproduced and
will then present an opening through which much of the coloring can
be done. The head and neck or other parts must be made in sections,
using various piece mold processes. Often it is possible to mold the
part entire with strips of tin or lead inserted in the body of the mold
where it is desired to have the line of separation. The strips should
not quite touch the specimen. After the plaster has completely set,
separation is brought about by breaking, the strips of tin controlling
the line of fracture. The best result is obtained when the line of
fracture disappears on joining the two halves thus produced. An
objection is in an occasional broken fragment which must be saved
and replaced. All molding must be done without disarranging parts
of the specimen by the pressure of supports or dividing strips.

The plaster should be very hard when set, otherwise a film may
detach and remain on the surface of the specimen and points may be

12 Field Museum of Natural History — Technique, No. 2.

broken or rubbed off when the specimen is removed from the mold.
Generally speaking, the hardness of gypsum plaster is in proportion
to its density, and so it is desirable to use the minimum amount of
water consistent with the requirements of handling. Also, a thin
section of plaster will be harder on its inner surface than a thicker
section of the same plaster. If the surface of the specimen is smooth
and polished, the surface of the mold should appear glassy and pol-
ished. The mold surface should be free from bubbles. One of the
common causes of surface bubbles is the adhesion and inclusion of
air, mainly in cavities between scales and in sharp depressions. These
can be removed by applying the first plaster to the surface and into
the cavities with a soft brush before the bulk of it is applied. All
but the smallest molds should be reenforced with a plaster and fiber
coating as a precaution against breakage in handling.

Many amphibians have slimy surface secretions, albuminous in
character, that prevent the proper setting of plaster. There are several
ways to render these albuminous substances inactive on the plaster.
Treatment with a coagulating medium previous to molding is apt to
cause a hardening of the skin and bring about other changes detrimental
to form and the easy positioning of the specimen. Probably the best
procedure is to pose the specimen as quickly as possible in a lifelike
position and without treatment of any kind, to depend on a coagulating
medium that can be included in the plaster mixture. Alum seems to
serve this purpose fairly well. Besides acting as a coagulant of the
albumen, it combines with the plaster, causing an accelerated and more
complete recrystallization.

The colors, bound in cellulose nitrate or acetate, can be painted di-
rectly upon the plaster surface of the mold, although it is occasionally
advantageous to employ a method of separation, the principle of which
was employed by Carl E. Akeley in making up his mammal manikins
and which is in general use today in manikin work. This consists in
sizing and surfacing the mold with the thinnest possible film of a
material that is imaffected by the cellulose acetate or nitrate solvents
used in making the model and is, itself, soluble in solvents that will
have no effect on the model. In ordinary practice, in connection with
cellulose acetate or nitrate models, when the model is completed and
ready for the removal of the mold, the mold is placed in water. The
water softens the plaster and it is readily broken away and any frag-
ments of plaster still adhering to the reproduction are removed with
a stiff brush. If a sizing of gelatine, casein, gum arable or other water
soluble material has been used, this sizing is dissolved on the final

Celluloid in Taxidermy — Walters. 13

soaking of the mold in water, thus cleanly releasing the model from
the mold.

Coloring Problems.

General problems. — In making replicas of natural objects, such as
are now being considered, coloration requires altogether different pro-
cedure from that for which pigments are designed and normally used.
Ordinary painting is coloring a surface with a coating of pigment
mixed with a drying oil or varnish, either for protection or for the
purpose of decoration. Other things being equal, the pigments most
desired for use in painting are those that when finely divided have
the greatest covering power. It is among these commercial pigments
that we find our coloring agents, but their use in the usual manner is
impossible.

Throughout nature, we have relatively few objects that present
the same appearance to the eye. Form is often the primary means of
identification. However, with form eliminated and with two equally
smooth and polished surfaces, we may in one case, have marble, and
in the other, granite. The relatively greater general translucence of
the marble is evident and is recognized by the eye, and this does not
at all mean that the object must be held between the eye and the source
of the light. The eye is trained in making analysis and identifications
of this kind. The surface has its form, variable, characteristically
modified or very exact, and this we recognize. Aside from that, we
see below the immediate surface and through the different bodies
which may be of every degree of translucence or opacity. The object
may be as opaque as the commercial pigments, themselves, which are
selected in part for their opacity, but this is very rarely the case in
plant and animal Hfe. From this point of extreme opacity, there will
be a gradual reduction in pigmentation until a point nearly as clear
and as translucent as glass is found. As an example, in a snake we
have a nearly colorless transparent scale on the abdomen. In a layer
below this is the pigmentation which approaches the general tone of
ivory. In making a reproduction of this, it is necessary to reproduce
all the parts in their various degrees of translucence as well as in
correct tint. Also, they must be located in their proper order, first
the nearly transparent surface scale and then below this the successive
colored and partly translucent areas. Artificial ivory was never suc-
cessfully reproduced until these conditions were exactl}^ met. Although
ivory and its natural pigmentation are chemically unrelated to the
mediums of the reproduction, celluloid and zinc white, it is impossible

14 Field Museum of Natural History — Technique, No. 2.

by sight alone to distinguish between the real and the artficial. This
is due to correctness of details in regard to translucence and arrange-
ment. The vertebrate eye furnishes an exaggerated example of such
arrangements, as do also the fins and scales of fish. We are not
deceived by these outstanding examples as we are with the more subtle
and less pronounced problems represented in the great majority of
subjects. A human hand furnishes an interesting study in this con-
nection. The veins are overlaid by a rather thick dermal coat of dif-
ferent coloration. The nails present an interesting problem of a
translucent surface with the coloration in the underlying parts.

Another type of coloration, wholly dependent on structural forms,
is found very generally in fishes and, occasionally, in amphibians and
reptiles. This produces the iridescent so-called metallic colors which
exist in combination with pigment colors. Often their source is deep-
seated but in other cases they originate on or are reflected from the
surface of the scales or skin. These conditions are not successfully
reproduced. Artificial pearls are now made from the silvery substance
found on the scales of small fish. An industry developed in the
Mediterranean regions supplies this material. This substance can be
dyed or colored to approximate some of the conditions in the real
pearl. The eflfects seen in mother of pearl are due to minute convolu-
tions in the shell layers. The combined effect of the numerous trans-
lucent shell layers is barely perceptible when a cast is made of the
surface layer only. . With but few exceptions, the coloration due to
structural forms has the general appearance of the opal. Opals are
not now artificially reproduced, so at the present time, we are limited
to the use of commercial pigments, dyes, fish scale pearl and the vari-
ously colored bronzes as coloring agents in attempts to secure the
effect of this type of coloration.

Use of pigments in a translucent medium. — Excepting the examples
of structural coloration above mentioned, it has been found that the
conditions of coloration can be reproduced by utilizing ordinary com-
mercial pigments added in carefully guaged amounts to a translucent
material. In practice, the transparent material is reduced to a
liquid state and then incorporated with the appropriate coloring mate-
rials. The solvents on evaporation leave colored translucent masses
that can be made to resemble any particular part of the model. In
order to give these colored masses or colored layers their proper location
within the body and still preserve the surface detail as obtained by
molding, the colors are applied to the interior surface of the mold of

FIELD MUSEUM OF NATURAL HISTORY.

TECHNIQUE. NO 2, PL. V.

Fig. 1. REPRODUCTION OF Green Tree Frog.

Fig. 2. MUHLENBERG'S TURTLE.
Reproduced soft parts combineil with original shell.

ni. 2 4 1925

Celluloid in Taxidermy — Walters. 15

the object, first the surface colors and following these the underlying
colors or markings in succession. Each section can be given its proper
relative position with respect to the surface and its individual degree
of translucence.

The thought will occur that this is not so much a process of coloring
as of making a model. This is exactly the case. The ideal sought is
that of making an exact duplicate of the specimen as it appears in life.
Whatever process is necessary to approach this ideal must be adopted.
The colored materials are to be washed on, put on with a knife, needle,
brush or by any method that serves the purpose and does not leave
evidence of man's handiwork. Brush marks and similar effects cannot
by any process of reasoning be justified here. Reason is too often
clouded by custom and accepted methods of an established art tend to
be used regardless of real applicability.

Working Mediums.

Qualities required in translucent materials. — The material used as
a translucent basis for the colors should be in the original state as
nearly transparent and free from color as possible. A material having
an initial translucence that is almost perfect is necessary in obtaining
the brightest tints. The working out of complicated patterns and the
coloring of the material, itself, call for its reduction to a liquid state.
It must permit thickening and thinning, and applying with much the
same facility that paints and varnishes are applied. There should be,
after application, a reasonable and controllable rapidity in drying and
solidifying. The materials, themselves, must be able to withstand with-
out change the conditions to which the finished product will be sub-
jected. These include the effects of dampness, heat, cold, dust, cleaning
and handling, and the accidents to which a museum specimen is subject
in the course of time.

Many materials which are useful in some instances cannot be used
in others. All have their disadvantages. Any material, to be successful,
will require much study and experimentation, and to say that a par-
ticular one is not usable may only mean that the difficulties have not
been sufficiently studied. Casein and gelatine have qualities that make
them applicable in this work. The varnish gums and drying oils, and
especially linseed oil, are valuable and useful. Cellulose acetate and
the cellulose nitrate products, pyroxylin and celluloid have been most
generally used. The term "pyroxylin" applies to the cellulose nitrates
that are soluble in amyl acetate and other commercial solvents. They
have a nitrogen content varying from 10.5 per cent to 12.2 per cent

i6 Field Museum of Natural History — Technique, No. 2.

and are used in lacquering and waterproofing solutions, in the manu-
facture of artificial silk and leather, and in many other processes in
which the handling is through the use of solvents. Cellulose nitrate,
alone, is not moldable, but when it is mixed with camphor the resulting
product, with the aid of heat and pressure, can be molded. The term
"Celluloid" was the first trade name applied to this product and is
still the most widely known. It is generally established as applying
to all the moldable cellulose nitrates, and is Used here in this sense.
Other well known trade names of moldable cellulose nitrate products
are "Pyralin," "Zylonite," "Xylonite," "Fiberloid," "Viscoloid," and
"Cellonite."* In the manufacture of pyroxylin, primary considerations
are uniformity of solubility and viscosity. Celluloid is soluble in the
usual pyroxylin solvents, but as it is designed for molding and not for
use as a lacquer, there is much variation in the degree of solubility and
viscosity. When used as a lacquer, the ingredient, camphor, while
normally of no value, has no detrimental effect.

Cellulose nitrates. — The cellulose nitrates, in their original state,
are transparent. They can be dissolved in a rather large range of
solvents for many and varied classes of work. The solvents employed
are not dangerous to health if common precautions are taken for re-
moval of the fumes with hoods and fans. The solutions are of very
high viscosity, said to be seven times that of an alcohol- shellac solution,
and this presents much difficulty and inconvenience when it is desired
to deposit heavy layers. It is not possible to reduce this viscosity
greatly although there are means by which it can be lessened. The
flexibility and degree of hardness of pyroxylin are satisfactory. Speci-
mens made of this material will withstand accidental blows and drop-
ping on the floor without being damaged. It is water-proof and the
specimen can be washed at any time with soap and water and, if
necessary, scrubbed with a stiff brush. The coloring, being beneath
the surface, is unaffected by any kind of abuse that will not actually
destroy pyroxylin. It is unaffected by ordinary changes of tempera-
ture. If heated to 336° F, it decomposes, but as a general rule does
not inflame. If a sample is brought into contact with a flame, it will
ignite and the flame will travel through the mass, but it can generally
be extinguished by a sharp breath of air. It is interesting to note that

*For information on the general subject, without reference to the particular
problems of the taxidermist, two important works by C. E. Worden are avail-
able. These are:

Nitrocellulose Industry. 2 Vols. New York, 191 1.

Technology of Cellulose Esters. D. Van Nostrand Co., New York, 1916,

FIELD MUSEUM OF NATURAL HISTORY.

TECHNIQUE. NO. 2. PL. VI.

Face of Black Howling Monkey.
Reproduced soft parts combined with original hair. (.Muzzle slightly foreshortened)

J'Ji. 2 4 1925

Celluloid in Taxidermy — Walters. 17

holes can be bored through a mass or sheet of celluloid with a red hot
iron without the ignition of the mass. Opticians often wave celluloid
spectacle frames back and forth above a flame in order to heat suffi-
ciently for bending.

Cellulose nitrate and its products, in the original state and without
additions, are subject to deterioration. This is said to be due to faulty
methods of manufacture and to the fact that the nitric acid, while
originally combining with the cellulose, tends in time to free itself from
combination. In the free state, it affects the cellulose, making it more
brittle and giving the mass a characteristic brownish tinge. This action
is hastened by exposure to heat and light. Such deterioration does not
always take place, at least not at the same rate, for some samples do
not show perceptible change after several years of exposure. The
brittleness is not of serious consequence as it is only evident on flexing,
and in this work the surface coatings are joined to a solid structure,
but the change of color is very important as all the brighter colors
would be affected. Any neutralizer of the acid as it develops, will
retard or entirely offset this detrimental action. The range of neutral-
izers that can be incorporated in a water white celluloid, and still not
affect its clearness, is limited. With pigmented celluloid, however, a
large range of effective neutralizers is available, most pigments as well
as white lead and zinc white rendering the product stable. I have
organ keys containing zinc white as the pigment which show no ap-
parent deterioration after forty years. In view of the uncertainty as
to the stability of different samples of cellulose nitrate, it is desirable
to use celluloid, pyralin or similar material that has withstood the
effects of time and exposure incident to service for at least several
years, and has still retained its original clear color and flexibility. To
this, when reduced to a lacquer, neutralizers should be added as a
further precaution, and in coloring, so far as possible, acid neutralizing
pigments should be incorporated. Although this practice may not be
entirely sound, it seems to justify the use of celluloid instead of py-
roxylin, the cellulose nitrate which is designed for and is best adapted
for lacquer work.

Cellulose acetate. — When cellulose is treated with a mixture of
acetic anhydride and acetic acid, products are obtained having the ap-
pearance and general properties of the cellulose nitrates but possessing
also some distinct advantages. These are known as the cellulose acet-
ates. Cellulose acetate is not moldable but becomes so with the addition
of camphor. "Cellit" is a trade name given to a cellulose acetate con-

i8 Field Museum of Natural History — Technique, No. 2.

taining camphor and stands in the same relation to cellulose acetate
that celluloid does to the cellulose nitrates.

Cellulose acetate has the hardness, the flexibility, and the initial
transparence of the cellulose nitrates. In motion picture films, in
which it has the greatest field of use, it is much less inflaminable than
the nitrate. Although inflammability is frequently m.entioned in con-
nection with museum preparations, it is really of little consequence.
The finished specimens will never be subjected to such conditions as
prevail in the use of films, and a case of spontaneous ignition in an
isolated body of cellulose nitrate, if it does occur, must be very rare.
We are surrounded by innumerable cellulose nitrate products and it is
probable that no one reading this has ever personally experienced a
case of spontaneous combustion in such a body. Cellulose acetate, when
subjected to tests, shows a stability much beyond that of the nitrate.
It also has an advantage over the nitrate in the fact that any possible
release of the acetic acid used in its manufacture can do no harm, as
acetic acid does not, in small quantities, have a harmful eflFect on cel-
lulose. Solutions of cellulose acetate have an equally high viscosity
when compared with the nitrate. Many solvents are common to the
two, while each has a series of solvents in which the other is insoluble.

Future Problems.

Technical study. — An extended technical study is necessary for the
successful handling of cellulose acetate and cellulose nitrate and their
products. The actions and properties of the solvents and non-solvents
utilized must be tested by many experiments. Progress is not possible
without study and familiarity with the materials sufficient to enable the
compounding of formulae to fit the many variable needs as they arise.
These problems must be experienced to be understood. For reference,
a record of all formulae and experiments, whether successful or not,
should be kept on filing cards. There are many interesting problems
of technique which, at the present time, are not completely solved.
Rapid progress is being made and it is hoped to reach definite conclu-
sions, soon, in regard to the most important matters. Full discussion
of these would be premature and is beyond the scope of this paper.

Scope and possibilities. — Although especially adapted and first ap-
plied to reptiles and amphibians, the foregoing discussion of principles
and methods applies to practically every branch of work with which
a museum preparator has to contend. Plants with complicated colora-
tion often present details of surface form that it is desirable to pre-

Celluloid in Taxidermy — Walters. 19

serve exactly. The feet and bills and exposed skin surfaces on the
heads and bodies of birds are important subjects. Young birds are
outstanding examples. Many of them are entirely naked, and the tis-
sues are often so translucent that the viscera and other abdominal
organs and many of the bones are distinguishable. Thinly haired
mammals or mammals with exposed skin surfaces are subjects in which
the skin coloration and fine details of form are of vital importance in
connection with a life-like appearance. Most of the young of mammals
are hairless. Many others are so thinly haired that the glow of the
skin surface, especially with the lighter fleshy tints, decidedly affects
the general color appearance. To extend these methods to mammal
work, the variation from the regular procedure requires a method
which provides for the correct transference of the hair. This first
calls for the construction of an armature and a clay figure in the ordi-
nary way. The skin in a freshened, soft and plump condition is ad-
justed on this form. The molding material, typically plaster, is applied in
such manner as to entirely surround the individual hairs and take an
exact impression of the skin surface between. When the mold is
completed and re-enforced, it is separated along lines previously estab-
lished, and the interior clay structure removed, the skin remaining
attached to the mold by the embedded hair. Through dehairing treat-
ments, such as are in use in tanning operations, the tissues surrounding
the hair roots are acted upon and the skin detached and removed from
the mold. The mold then presents an accurate negative of the skin
surface with the root of each hair protruding and exposed. The colors
are prepared and applied in the usual manner, the liquid cellulose
acetate or nitrate surrounding each hair root. On the evaporation of
the solvent, the hair is left enclosed and embedded in the solidified
material. As a means of support, this artificial skin is continued into
alternate layers of cloth and wire cloth, the resulting structure being
similar to that used in ordinary mammal work. The removal of the
mold leaves the specimen complete with the natural hair set in an
artificial skin which has correct color and translucence. In this mam-
mal work, molds have been made of plaster compositions, of waxes
and of other materials and, therefore, different methods of removing
them have been employed.

Future Taxidermy. — The idea is widely accepted that taxidermy is
necessarily an art of low standing. It is full of great technical diffi-
culties and these are sufficient to account for the grade of work pro-
duced from which opinion is formed. As these difficulties are over-

20 Field Museum of Natural History — Technique, No. 2.

come, a gradual recognition of its possibilities and an increasing interest
in it may take place.

Sculpture is devoted to expression through form. Stone and metals,
into which its work is finally translated, preclude the possibility of
complete realism. Such realism is dependent not only on color and
general form but on the most minute detail of the surface structure.
This can only be obtained by direct molding of actual surfaces ; it
cannot be modelled in clay or cut in marble and is, therefore, outside
the possibilities of sculpture.

Realism, therefore, is the province of taxidermy. It has a distinct
field of its own, well worthy of the best effort. In this field, the pos-
sibihties by no means have been exhausted and it is to be hoped that
the future may see much further progress.

EXPLANATION OF PLATE VIL

Fig. I. Waste mold of a crocodile, made in four pieces, two of which are joined.

Fig. 2. The mold after partial application of pigmented celluloid. The coloring
is continued and followed by reenforcing materials to give strength
to the model. The preserved skin shown in the foreground is used
as a guide for color pattern but the tints are based on detailed field
notes.

Fig. 3. The completed model of the walking crocodile, shown in Plate IH,
emerging from its plaster case. The plaster, softened by water, is
chipped away with hammer and chisel.

FIELD MUSEUM OF NATURAL HISTORY.

TECHNIQUE, NO. 2. PL. VII.

i1;l imm w^ m

/ 1925

U^'IYCP"ITY OF il

UNIVERSITY OF ILLINOIS-URBANA

3 0112 074281350