In the manufacture of patent leather there, are two distinct operationsthe first being the preparation of the leather for the reception of the varnish, and the second, coating the leather with brilliant and transparent varnishes. The first thing is the preparation of the linseed or drying oil, which is done as follows :Five gallons of linseed oil are boiled with four pounds and a few ounces of white lead, and an equal amount of litharge, (each in a state of fine division), until it becomes of the consistence of a syrup. This mixture is then united with an ochre or chalk, according to the quality of the skins that are to be treated, and it is evenly spread on both sides of the leather, and well rubbed in. Three very thin coats are applied, allowing each to dry before the other is put on, and the surface is ground down with pumice stone. This process of laying on the drying oil and rubbing down is continued until a sufficient quantity has been laid on to prevent the varnish from penetrating the leather. To the presence of so much lead in patent leather we think we may ascribe the prevalence of tender feet, corns and bunions, among those who are in the habit of wearing boots and shoes of this material, as it has a very drying and drawing action ; and persons who so indulge, look shiny about the feet at the expense of their health. They had better exert themselves a little, by using paste blacking, and thus be able to walk in comfort and with ease. The leather being thus prepared, a mixture of the linseed oil and lead with fine ivory black is made, and a little turpentine added, to make it flow easily ; tliis ia laid on by means of a soft brush, and five or six coats are applied. This gives the surface of the leather a rich black, shining, pliable surface, over which, when dry, the varnish may be applied. The varnish is composed of one pound of either asphalte, Prussian blue, or fine ivory black, ten pounds of thick copal varnish, twenty pounds of the linseed oil prepared as before described, (by boiling with litharge and lead), and twenty pounds of spirits of turpentine. The various tints are given by the various coloring materials added ; thus, asphalte gives a reddish color, Prussian blue a greenish blue metallic tint, and the ivory black, which is the most common, a beautiful and brilliant black. The chief uses for this leather are the manufacture of boots and shoes, and the aprons and fittings of wagons and carriages.
This article was originally published with the title "Patent Leather" in Scientific American 13, 11, 88 (November 1857)