The tanning of goat-skins (from which our morocco is made), sheep for imitation morocco, and small calf-skins for book-binding is done by sewing up the skins, and filling the bag with a decoction of sumac in a warm state. They are kept iu an active state for twenty-four hours or so, which sufficiently saturates them.
A process has been patented by Mr. Prellcr, of Bermondsey, within the last few years, by which the heaviest skins are convened into leather in a very short space of time; but the process is tawing rather than tanning, and is used for machinery belts princi pally.
'airing consists in dressing the skins with antiseptic materials, so as to preserve them from decay; but by this operation no chemical change is effected in the gelatine of the skins; hence, tawed leather can be used in the manufacture of glue. In tawing, the first process is careful washing, next dressing them with lime, then removing the hair or wool, and lastly, steeping them in some one or more of the various mixtures which are used for converting skins into leather by this method. The method of tawing lamb skins will give a fair idea of the process, which is, however, much varied, according to the kind of skin and the experience of the worker. Lamb-skins of home-production are generally limed on the flesh-side with cream of lime, which enables the wool to be easily pulled off. Dried lamb-skins are generally submitted to the heating process, to get the wool removed. The pelts, after being washed, are rubbed on the convex piece of wood called the beam; and when stipple, the flesh-side of each skin is thickly besmeared with a cream of lime; and when two are so treated, they are laid with the limed surfaces in contact; and a pile of them being made, they are left for a few days, when they are 'examined by pulling the hair. If it separates easily, then the lime is washed out, and the hair with the unhairing knife, as in the case of hides, unless it is required to be kept on, as in the case of skins for door-mats, etc. After thorough cleansing, the pelts are steeped for two or three weeks in a pit filled with water and lime, being taken out from time to time, and drained on sloping benches. When removed finally from the lime-pit, the skins are worked with the knife, to render them still more supple, and they are then put into the branning mixture. This consists of bran and water, in the -proportion of two pounds of bran to a gallon of water. From this mixture, in about two days, they are transferred to another bath, consisting of water, alum, and salt. After the proper amount of working in this mixture, they undergo what is called the pasting, if intended to form white leather. The paste is a mixture .of wheaten-bran and Sometimes flour and the yolks of eggs. They are usually worked in a rotating cylinder with this paste and water, and are found in time to have absorbed the paste, leaving little more than the water. If the skins are not intended to be white, other materials
are often used, and much pigeons' and dogs' dung is employed, some large leather dressers expending as much as L'100 per annum upon each of these materials. Lastly, the skins are dried and examined, and, if necessary, the pasting is repeated; if not, they are dipped into pure water and worked or• staked by pulling them backwards and forwards on what is called a stretching or softening iron, and smoothed with a hot smoothing-iron.
Another kind.of dressing is by treating the skin with oil. By hard rubbing with cod oil, or by the action of " stocks" after the skin has been properly cleaned with the lime, the oil works into the skin, displaces all the water, and becomes united with the mat& rial, rendering its texture peculiarly soft and spongy Wash-leathe• or chamois-leather is so prepared, and for this purpose the flesh-halves of split sheep-skins are chiefly used: Besides tanning and terming, many kinds of leather require the currier's art to bring them to the state of completion required for various purposes. The currier receives the newly tanned skins, and finds them harsh to the feel, and rough on the flesh-side. He removes all the roughness by carefully shaving with a peculiar knife. After soaking in clean water, he then scrapes the skin with considerable pressure upon a scraping-tool or slicker, and thus removes any irregularities. The moisture is then removed as much as possible, and oil, usually cod oil and tallow, are rubbed over the leather, which is laid aside to dry completely, and as the moisture leaves it, the oil penetrates. When quite dried and saturated with the oil, the skin is rubbed on a board with rounded ridges, by which a peculiar grained appearance is given, and the leather is rendered very pliable. In currying, almost every variety of leather requires some variation in the processes employed, hut the currier's object is in all cases to give a suppleness and fine finish to the skins.
Morocco leather, formerly an article of import from the Barbary coast, is now pre pared in large quantities in this country from goat-skins; sheep-skins are also used for imitation. It is always dyed on the outer or grain side with some color, and the leather dresser in finishing gives a peculiar ribbed or a roughly granulated surface to it, by means of engraved boxwood balls which he works over the surface.
Russia leather is nuich valued for its aromatic odor, which it derives from the pecu liar oil of the birch-bark used in tanning it. The fact that this odor repels moths and other insects renders tint leather particularly valuable for binding books; a few books in a librhry, bound in Russia leather, being effective safeguards against insect enemies.. It is also said to destroy or prevent the vegetable evil called mildew, to which books are so very liable.