Although coloured calf-skins may be bought almost as cheaply as "smooth" calf (uncoloured ones), yet there are many places where coloured calf cannot be procured. Skins may be purchased already sprinkled or marbled at most leather shops. This plan of sprinkling and marbling the whole skin is good enough for cheap or half-bound work, but for extra work it is far better to sprinkle, marble, or otherwise colour the leather when on the book. Hand-colouring is coming again into use, and by degrees getting known throughout the trade.
When an acid is used on leather, it is essential to wash as much as possible of it out with water immediately after it has done its work, or in a few months the surface of the leather will be found to be eaten away and destroyed. It is a fault of some binders, that if they use a chemical on leather or paper, they are not satisfied to have weak acid, allow it to do its work slowly, and, when the proper moment has arrived, stop its further action. They frequently use the acids as strong as possible, and neglect to wash out the residue. The consequence is, the leather or paper rots. To avoid this, the recipes given below are selected for their harmless character.
Iron sulphate (copperas) is the chief ingredient in colouring calf black. Used by itself, it gives a greyish tint, but if a coat of salts of tartar or other alkali be previously used it strikes immediately a rich purple black. It can be purchased at 1d. per lb.
(6) Boil 1 qt. vinegar with a quantity of old iron nails or steel filings for a few minutes; keep in a stone jar, and use the clear liquid. This can from time to time be boiled again with fresh vinegar; an old iron pot must be kept for boiling the black.
(a) Dissolve 1/4 lb. salts of tartar (oxalic acid) in 2 pints boiling water, and bottle for use. This is mostly used for colouring; it has a very mellow tone, and is always used before the black when a strong or deep colour is required. It is poisonous, and must not be used too strong on the calf, or it will corrode it.
(6) For a plain brown dye, the green shells of walnuts may be used, broken up, mixed with water, and allowed to ferment. The liquid is strained and bottled for use. A pinch of salt thrown in will help to keep it. This does not in any way corrode the leather, and produces the best uniform tint.
(6) Into a bottle put some turmeric powder, and mix well with methylated spirit; the mixture must be shaken occasionally for a few days until the whole of the colour is extracted. This is a very warm yellow, and produces a very good shade when used after salts of tartar.
For all the following a preparation or ground of paste-water must be put on the calf, that the liquids may not sink through too much. The calf must be paste-washed all over equally, and allowed 'to get thoroughly dry. It will then be ready for the various methods. Perhaps to wash it overnight and let it stand till next morning will be the best and surest plan. It matters very little whether the calf is on the book or in the skin.