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.