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.
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.