Scientific American 35, 20.5.1848
The true morocco leather is goat-skin tanned and then dyed on the side of the grain. Sheep skins are treated in the same way. The skins are steeped first in a fermenting mixture of bran water for a few days, they are then worked upon the horse, steeped in fresh water for 12 hours, and rinsed in the same. They are next drained, steeped in weak lime-pits for a proper time, till the hairs can be readily detached. They are now subjected to the action of a blunt knife upon the horse-beam, in order to strip off their hair, after which they are cleansed in running water. Any excrescences must be carefully removed with the fleshing knife, and their edges neatly pared. The next process is rubbing them strongly with a piece of hard schist set in a wooden frame, in order to expel by pressure any lime which may still adhere, and to soften the grain. They are now worked upon the horse-beam with the blunt knife and subjected to a species of fulling, by being agitated by pegs in a revolving cask along with water. Many manufactures prefer a weak alkaline ley, or putrified urine, in the lime bath.
The skins are immersed for a night and a day, in a bran bath, in a certain state of fermentation, then worked on the horse, and salted, to preserve them till they are to be dyed.
Preparatory to being dyed, each skin is sewed together edgewise, with the frain on the outside, and it is then mordanted either with a solution of tin, or with alum water. The color is given by cochineal, of which from ten to twelve ounces are required for a dozen skins. The cochineal being boiled in water along with a little tartar or alumn for a few minutes, forms a red liquor, which is filtered through a linen clith, and put into a clean cask. The skins are immersed in this bath, and agitated in it for about half an hour, they are taken out and beaten, and then subjected to a second immersion in the cochineal bath. After being thus dyed, are rinsed and tanned with Sicillian sumach, at the rate of two pounds for a skin of moderate size. This process is performed in a large tub made of white wood, in the liquor of which the skins are floated like so many bladders, and moved about by manual labor during four hours. They are then taken out, drained, and again subjected to the tannin liquor; the whole process requiring a space of twenty-four hours. The skins are now unstiched, rinsed, fulled with beetles, drained, rubbed hard with a copper blade, and lastly hung up to dry.
Some manufactures brighten the color by applying to the surface of the skins, in a samp state, a solution of carmine in ammonia with a sponge; others apply a decoction of saffron to enliven the tint. At paris the morocco leather is tanned by agitation with a decoction of Sumach in large casks made to revolve upon a horizontal axis, like a barrel curn. White galls are substituted for sumach; a pound being used for a skin. The skins must be finally cleaned with the utmost care.
The black dye is given by applying with the brush a solution of red acetate of iron to the fgrain side. Blue is comminicated by the common cold indigo vat: violets of a light blue followed by cochineal red; green, by Saxon blue followed by a yellow dye, usually made with the copped roots of the barberry. This plant serves also for yellow. To dry olive, the skins are first passed through a solution of green vitriol, and then through the decoction of barberry root, containing a little Saxon blue. Puce color is communicated by logwood with a little alum; which may be modified with the addition of a little Brazil wood. In all these cases, whenever the skins are dyed, they should be raised, wrung or rather drained, stretched upon a table, then besmeared on the grain side with a film of linseed oil applied by means of a sponge, in order to promote their glossiness when curried, and to prevent them becoming horny by too rapid drying.
The last process in preparing morocco leather is the currying, which brings out the lustre, and restores the original suppleness. This operation is practiced in different manners according to the purpose the skins are to serve. For pocket-books, portfolios, and case making in general, they must be thinned as much as possible upon the flesh side, moistened slightly, then stretched upon the table, to smooth them; dried again, moistened, and lastly passed two or three times through the cylinder press in different directions, to produce the crossing of the grain. The skins intended for the shoemaker, the saddler, the book-binder, &c., require more pliancy, and must be differently curried. After being thinned, they are glazed with a polisher while still moist, and a grain is tormed upon the flesh side with the roughened lead plate or grainer of the curriers, called in French pomelle: they are glazed anew to remove the roughness produced by the pommel, and finally grained on the flesh side with a surface of cork applied under a pomelle of white wood.