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.