CHAPTER IV
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.
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.