DYES, PATINES[10] AND GILDING
[10] _Patine_ represents a veneer, or wash of colour, applied on the
surface, or in the hollows of leather, to intensify its tone, or to give
artificial effects, such as those of verdigris, rust, or antiquity.
Partly owing to its nature, and partly owing to the tanning process,
leather is susceptible to the action of the dyes used to colour it in
degrees varying according to their composition and penetration. We will
not attempt to enumerate all the dyes that may be employed or to describe
their composition. Excellent results can be obtained with ready made
preparations, and some brief remarks on the subject are all that is
necessary for the purpose of this work.
Practical experience alone is a reliable guide in the selection of dyes,
as, whatever their base may be, they all vary greatly in use. It may be
remarked that there are many aniline dyes which are more durable than
vegetable ones, although there are others which merit their reputation for
instability. The colour of dyed leather cannot be expected to remain
unaffected by constant exposure to direct sunlight, but it should not
alter with ordinary use.[11]
[11] See the remarks on Leather for Bookbinding in the Note at the end of
this volume.
It is obvious that, in proportion as the colours sink into the leather,
they will lose in brilliancy, but on the other hand, this very absorption,
which allows colours to be superposed and appear translucent, gives a
depth rarely obtainable in materials of less capillarity.
[Illustration: 13. TOP OF CASKET COVERED WITH BROWN CALF, CUT AND SLIGHTLY
EMBOSSED. BY FLORENCE HORNBLOWER. MODERN ENGLISH.]
The following notes are intended merely as a general indication of the
manner of treating the various substances used in colouring leather.
The substance sold by druggists under the name of potassium is very
violent in its action and would burn the leather as well as the brushes
used to apply it. It should only be employed, and that very sparingly, for
such purposes as black lettering. Pearl-ash should be used in preference,
but also with great caution, or it will not only destroy the surface, but
rot the substance of the leather.
Potash is soluble in water to saturation point, that is to say, a given
quantity of water will not dissolve more than a given quantity of potash.
It is very difficult to measure the exact strength to use; that which is
barely sufficient to penetrate and colour a surface artificially made
smooth by rolling, will sink in where the leather has been cut or punched
and immediately darken it considerably. It is a good plan therefore to
experiment on a spare piece of the leather. Potash lye is more easily used
in the right proportion, and may be employed for staining very light
coloured leather.
Soda has the same effect as potash, except that it is a little less
strong; both substances have always been much employed in dyeing skins.
Permanganate of potash is supposed to dye a mouse-grey colour, but it is
most uncertain in its action, as it depends entirely on the porosity of
the leather. Xanthin and catechol browns are pleasing in appearance, but
their effect is less rich than that obtained with potash. They become
improved by hard rubbing with encaustic.
Sulphate of iron has a strong and persistent odour and is also somewhat
injurious. It is useful, however, and produces a colour varying from a
light shade to an intense violet black. When used over potash, a dead
black is obtained.
REDS
Alizarin, the colouring principle of madder, which can also be obtained
from coal-tar, is employed in many colour combinations and gives a fine
durable red. Hydrochloric acid changes it to violet. Carthamine and
cochineal also produce good reds; the latter is turned orange by the
action of hydrochloric acid.
Hydrochloric acid turns ammoniacal cochineal pink, but merely discolours
the red made from archil. Direct extracts of red wood are unaffected by
it.
The colouring matter of logwood, extracted by treating the powder obtained
from an aqueous decoction of the wood with spirit, is sold as hematoxylin.
Metallic salts convert it to a violet black, salts of tin change it to
pink, alkalis to blue, and acids to yellow. Durable pinks are obtained
directly from carthamine, the colouring matter of _Carthamus Tinctorius_.
YELLOWS
The base of most fine yellows is picric acid. The chromates of zinc and
baryta give very permanent yellows, which are particularly useful in
mixing greens.
The vegetable yellows are less durable. They include turmeric, which is
especially fugitive, and quercitron; the former is turned red, and the
latter brown, by the action of hydrochloric acid.
Orange tints are easily obtained by using red over yellow, first allowing
the yellow to dry completely; or they can be bought ready prepared with
alizarin. Mandarine and nasturtium tints can also be bought ready
prepared, or may be made by a mixture of vegetable colour, such as saffron
and arnotto.
[Illustration: 14. EMBOSSED AND PUNCHED BROWN CALF BINDING. _RUBÁIYÁT OF
OMAR KHAYYÁM._ DESIGNED BY MARY G. HOUSTON. MODERN ENGLISH.]
BLUES
Good and durable blues are obtained from indigo and alizarin.
GREENS
Greens of every composition are fugitive, especially those sold ready
mixed. Better results are obtained by applying yellow and blue one over
the other than by the direct application of the colour, but when the range
of tints thus afforded is too restricted, recourse must be had to some of
the numerous dyes varying in tint from greenish yellow to deep olive.
Successive applications of sulphate of iron and picric yellow will produce
the latter colour, and a vegetable green, which, however, is not very
durable, is made from buckthorn berries.
* * * * *
All the dyes which have been just enumerated, which form, however, but a
very small proportion of those in existence, are employed in dyeing
textiles. These materials have first to be treated with mordants such as
tannin, chrome or sumach, in order that they may take the dye, whereas
leather is already prepared to receive it by the tanning process.
Ordinary water-colours based on glycerine or albumen can be used in the
decoration of leather, but are recommended only for colouring small parts
of a design, partly because liquid colour is more easily applied over
large surfaces, and partly because, being less transparent, they do not
lend themselves to the process of rubbing which plays so important a part
in _patine_. Oil or spirit colours, on the other hand, possess a
transparency which allows of their being used over a ground coloured with
a different medium. When the leather on which they are painted is undyed
it should first receive a coat of paste.
Colours sold under the name of _patines grasses_ will produce a groundwork
of great brilliancy, if well rubbed before they are quite dry.
The use of _gouache_ should be limited to the hollow parts of incised or
punched leather.
Gold and bronzes are also used with good effect.
DIFFERENT METHODS OF COLOURING LEATHER
Colours obtained from potash and sulphate of iron——dark green, dull red,
etc.——are much used for groundwork. Potash produces a warm brownish-red,
and tints, varying in colour from a pale to a dark slate grey, are
obtained with sulphate of iron. As already stated, a coating of picric
yellow over the latter will give a dull green.
In colouring large surfaces, it is best to use soft sponges, or small pads
of cotton-wool covered with soft linen. The pads can be held by the edges
of the linen and the sponges may be mounted on handles, but the best
protection for the hands against staining is a pair of very soft rubber
gloves like those used by surgeons.
The leather is first damped all over and the colour then applied in a
succession of even washes. Care must be taken not to unduly darken any
part of the leather by using too much colour, bearing in mind that
different parts of the skin will vary greatly in porosity. In colouring
groundwork with various superposed tints, the actual results are often
entirely different from those one has had reason to expect. So far as is
possible, in order to prevent this from happening, it is advisable not to
mix the colours of different makers on the same piece of work without
knowing their composition, or first experimenting with them on a spare
piece of the leather.
A second colour should never be added until the underneath one is dry, or
a muddy effect will result. If the colour becomes too dark, or if the
second stain predominates unduly instead of merging into the underneath
one, the whole work, fixed firmly on a board, should be dipped in water
and scrubbed with a very soft brush and some soft soap. It should then be
allowed to dry in the sun. This method of making the colour lighter can
only be used when the ornament is not in relief; it has been found
particularly successful in treating potash and sulphate dyes.
Ox-hide, light or fawn-coloured calf, pigskin and white morocco are
leathers suitable for colouring. They are, however, very absorbent, and
will require an application of paste before staining. This will also be
found indispensable in colouring the white split sheepskins used in
mosaic.
In staining leather for mosaic, several successive applications of colour
will be required, especially in the case of greens which sink in quickly.
In addition to plain dyeing, there are various methods of producing shaded
groundwork, marbling, sprinkling, etc.
SHADED GROUNDWORK
For shaded groundwork diluted colour is applied with a sponge or pad
worked over the leather with a circular movement, and the uniform tint
thus obtained is darkened as required by further applications with
stronger colour. In shading a ground from one colour to another, as for
example from dark olive to malachite green, orange red and pale yellow,
the edge of each colour, as it is put on, is covered with a piece of thick
paper, which must be firmly held in place, in order to prevent the colours
mixing where they come together.
MARBLING
A sponge with large holes is dipped in potash, sulphate of iron, or some
other deep coloured dye, and lightly applied over the surface of the
leather so that parts of it corresponding to the holes in the sponge are
left untouched; or the first application of colour may be made evenly over
the leather and the marbling worked, as described, in a second
application. Many varieties of pattern can be obtained by moving the
sponge in different ways. Leather may be bought ready marbled by a
gelatine process.
TREE MARBLING
The leather is first lightly pasted over, and drops of water, more or less
large, are scattered upon it by jerking the handle of a small couch-grass
whisk full of water against the left wrist held a few inches from the
surface of the leather. A very little colour is then taken in the brush
and jerked in the same manner over the drops of water, with which it will
partially mix and give the effect of roots branching out in all
directions. Variety can be obtained by applying the water with a sponge
instead of the brush, and the colour in large drops over the whole or
certain parts only of the field, or by using dyes of different colours
which give curious effects in combining. After applying the dye, the
surplus moisture is absorbed with blotting-paper.
The leather may be bleached to a light tint by means of an oil-paint brush
dipped in decolorant[12]; the bristles of the brush are pushed back with
the finger and when released jerk the acid in fine drops over the surface.
The leather must be freshly and thoroughly damped so that the outline of
the bleaching shades off into the ground.
[12] See page 71.
SPRINKLING
Sprinkling is done with a rather close iron grating and a long narrow
brush like a plate-brush. The dye is prepared on a flat plate and the
brush dipped in it, the superfluous liquid being removed against the edge
of the plate. The brush is rubbed backwards and forwards on the grating
held horizontally a few inches above the leather over which it scatters a
fine shower of the dye. Should the colour froth on the grating, the brush
must at once be rubbed upon oiled paper. Sprinkling may also be done with
a vaporiser for fixing drawings, but it is difficult to get a sufficiently
fine shower so that the drops do not merge into each other.
[Illustration: 15. MIRROR CASE OF PUNCHED BLACK LEATHER, _CUIR BOUILLI_;
EXECUTED BY MISS CASELLA. MODERN ENGLISH.]
The above process is a useful one when parts of the leather are to be
“reserved,” i.e., to remain untouched by the dye. For this purpose a piece
of strong paper is cut to the shape of the part to be reserved and pasted
lightly to the leather during the process of sprinkling, after which it is
damped and removed. Another method is to paint the reserved parts with one
of the two preparations given by Mons. Belleville in _Le Cuir dans la
Décoration Moderne_, afterwards removing it with benzine or petroleum
spirit:——“Eighty parts of colophony, 4 of yellow wax, 6 of spermaceti, 4
of tallow, 60 of spirit of turpentine and 10 of alcohol.”
Or, “One hundred parts of virgin wax, and the same of castor oil, with 25
of borax and 25 of copal varnish.”
* * * * *
Instead of reserving the parts of the leather, the dye may be removed
subsequently by means of reagents called decolorants. Sulphuric,
hydrochloric, oxalic, nitric, or muriatic acid diluted with water in the
proportion of one in five, can be used for this purpose, but their effect
should first be tried on a spare piece of the leather, as it will vary
according to the nature of the dye on which they are used. It should be
noticed that, in mixing the acid, the right quantity of water must be
measured out and the acid carefully added drop by drop. If water is poured
into acid it causes an explosion.
The outline is traced rather deeply on the leather, so that it is still
visible after the groundwork has been dyed. When the dye has sunk in, the
decolorant can be easily applied with a paint-brush. On modelled leather
dyed bronze green, a rag or piece of cotton-wool dipped in decolorant and
quickly passed over the relief, will lighten the colour and produce the
effect of bronze with the exposed parts rubbed lighter by use. Should the
effect of the acid be too strong, the colour may be again deepened by
washing the leather over with a yellowish gold stain, which will only take
effect on the relief, since it will merge into the darker colour of the
rest of the work. The same process may be employed on white calf with a
light olive dye to obtain the effect of old ivory. Even when much diluted,
however, the action of these acids must in the end be injurious to the
leather. They should be used with great care and never undiluted. Where
possible, washing the leather over afterwards with water will, to some
extent, diminish their harmful effect.
Stencilling is another process by which portions of the leather forming
the ornament are reserved from the dye used in colouring the ground. The
design is cut out of a very thin sheet of copper or tin. A large
short-haired brush[13] is used to take the dye from a plate, or pad, and
is then rubbed very lightly over the stencil firmly fixed on the leather.
Only the parts unprotected by the stencil will take the colour. The brush
must not be too full or the dye would have a tendency to run under the
stencil. The most suitable dyes are glycerine inks and marking inks
containing nitrate of silver. A variety of colours may be mixed with
glycerine for this purpose. The ink thus obtained is transferred to a
cloth pad, such as is used by printers, from which the brush will only
take the required quantity.
[13] _Pompon._
When the leather is dry a lighter tint, transparent enough to allow the
stencilled design to be visible through it, may be washed over the whole.
Excellent effects of considerable richness can thus be produced. The depth
of colour is further increased by the process of rubbing, which is
necessary to the proper _patine_ of leather. If done with wax, encaustic
or varnish, it is an effective protection for the surface of the leather
against deterioration from outside causes. With certain soft leathers, if
the colour has not sunk in deeply, rubbing with the finger alone will give
it great brilliancy; with other leathers the rubbing will produce an
effect in proportion to the degree of porosity of the skin. It should
always be done before the colour is dry, but not until it has penetrated
sufficiently into the leather not to return to the surface with the
pressure. The middle finger is used. A certain amount of polish can be
given to the leather by rubbing it only with the finger (moistened with a
little oil to allow it to slide easily), or, for a large surface, with the
side of the hand instead of the finger. When a medium is used, it is
applied with a circular movement by means of flannel or rag; a flannel
brush consisting of a series of little flannel rolls, which can be bought
at a surgical instrument-maker’s, is very useful for a large surface
requiring much rubbing. Pure wax, which must be softened in the hand to
make it spread evenly, encaustic and spirit varnish are all efficacious in
preserving the colour and increasing its transparency.
Another method giving excellent results consists in applying opaque
colour, _gouache_ or bronzes in the hollows of a design and removing the
surplus of the colour by rubbing. In this way an incised design can be
boldly outlined in light on a dark ground, and may afterwards be bleached
within the outlines if desired. After cutting the design on the leather,
the whole surface is washed over with potash or any other dark stain, a
coat of paste is then applied and immediately wiped off, so that some of
it only remains in the hollows. When the paste is dry, some rather liquid
_gouache_ is washed over and run into the lines, any remaining on the
surface being removed by vigorous rubbing with a damp rag. The same
process may be applied to the hollows of punched leather. In using bronzes
or gold in powder, some spirit varnish or specially prepared varnish is
necessary to make them adhere. After applying the varnish, the surface is
wiped over to remove all except that which is deposited in the
interstices, and when this is sufficiently dry to hold the powder, the
latter is put on with a very soft, short-haired brush and adheres to the
varnish. The surface is then rubbed in the manner already described. All
powder colours do not mix equally well with varnish; green and blue
bronzes often change colour when brought in contact with it. Gold and
silver powder give good results, used either dry or mixed with gum on
shells. Chinese vermilion may also be employed with varnish, but other
colours are more suitable for this purpose when prepared in the form of
_gouache_.
GILDING
Special manipulation is required for gold leaf applied to the decoration
of leather. For gilding over a whole surface, as for instance an aureole
round the head of a saint, the following is the best method. Several
layers of starch paste are painted with a brush over the part of the
leather to be gilded, and followed when dry by a little gelatine paste. A
coating of some special preparation is then applied and allowed to dry to
the right condition to retain the gold leaf, which varies according to the
nature of the preparation; the degree of moisture can be tested with the
finger. Gold leaf is sold in small books and is exceedingly thin. A
flexible knife, like a palette knife, is used to manipulate it, and a
single leaf is laid on a cushion of deerskin stuffed with wadding, and cut
to the required size. It is then placed over the preparation on the
leather and lightly pressed down with a very soft, round, short-haired
brush.
[Illustration: 16. BLACK MOROCCO BINDING WITH APPLIED PANELS OF TOOLED,
CUT, PAINTED AND GILT CALF. _LE ROMAN DE TRISTAN ET ISEUT._ DESIGNED BY
ROBERT ENGELS. MODERN FRENCH.]
For gilding with hot tools a specially prepared powder made of resin or
gum is used. This powder melts with the heat of the tool and causes the
gold leaf to adhere to the leather only where it comes in contact with the
parts of the tool cut in relief. The process is as follows: Some powder is
lightly spread over the part of the leather to be gilded and a piece of
gold leaf laid over it, the tool is heated sufficiently to melt the powder
without burning the leather and is carefully applied on the right spot,
the surplus gold being afterwards removed with the short brush. The tools
used by bookbinders are slightly convex, so that firm and even pressure of
the whole tool can be exerted by first inclining the handle towards the
gilder, and then raising it while still maintaining the pressure and
inclining it at the opposite angle.
Gold can also be applied with a brush in the form of powder suspended in
liquid gum or spirit varnish. If it does not spread evenly, owing to there
being too much liquid in proportion to the powder, dry powder may be added
where necessary with a short brush when the liquid is almost dry.
Shell gold is applied with a slightly damped brush and, when dry, may be
burnished with an agate or punch; the design of the punch will stand out
in bright gold on a ground of dull gold. The pressure of the wrist is
sufficient to work the punch and a hammer should not be used.
* * * * *
There is an interesting field for the artist’s enterprise in the discovery
of new processes for the decoration of leather by means of colours and
bronzes. It is not possible within the limits of a single chapter to give
a complete list of the many methods that may be employed.[14]
[14] As a conclusion to this chapter, the French edition quotes from the
_Bulletin de la Société de l’Encouragement pour l’Industrie Nationale_
some extracts from the _Report of the Committee on Leather for
Bookbinding_, published by the Society of Arts in London (1901), which
will be found in the Note at the end of this volume.