The Engineer's and Mechanics Encyclopædia,
comprehending practical illustrations of the machinery and processes employed in every description of manufacture of the British Empire.
With nearly Two Thousand Engravings.
By Luke Hebert, civil engineer, edifor of the History and Progress of the Steam Engines, Register of Arts and Journal of Patent Inventions, etc.
In two volumes.
VOL. II.
London: Thomas Kelly, 17, Paternoster Row.
MDCCCXXXVI (1836).
Russia Leather is prepared in Russia by a scries of processes not essentially differing from our own. The tanning material is, however, seldom oak bark, the bark of the black willow being preferred; and where this cannot be obtained, birch bark is the next in request. Their dyed leather is usually red or black. For the red, the hide is first soaked in alum water, and then dyed with Brazilwood. The black is given, as usual, with an iron liquor. The leather is then smeared with birch tar, which gives the peculiar smell so much prized (and which, when used for book-binding, has the valuable property of protecting the book from worms), and is finished by various other manipulations. The streaked or barred surface is given to the leather by a very heavy steel cylinder, wound round with wire, which makes the indentations.
Saffian or Dyed Maroquin Leather, of excellent quality, is extensively prepared at Astracan and other parts of Asiatic Russia, Only bucks' and goats' skins are used for this purpose, and the favourite colours are red and yellow. The general method of preparing the pelt is the same as in this country for the dyed Morocco leather; that is, by lime, dog's dung, and bran. Honey is also used after the branning. The honey is dissolved in warm water; and some of this liquor is poured out on each skin, spread out on wooden trays till it has imbibed the whole of the honey; after which it is suffered to ferment about three days, then salted in a strong brine and hung up to dry. The skin is then ready to receive the dye, which, for red, is made with cochineal, and the Salsola ericoides, an alkaline plant, growing plentifully in the Tartarian salt deserts; and the colour is finished with alum. When dyed the skins are tanned with sumach. To the very finest reds a quantity of sorrel is used with the cochineal bath; and the subsequent tanning is given with galls instead of sumach, which renders the colour as durable as the leather itself. The roughness always observed on the surface of the skins, is given by a heavy kind of iron rake with blunt points. The yellow saffians are dyed with the berries of a species of rhamnus (the Avignon berry answers the same purpose), or with the flowers of the wild chamomile.
Real Morocco Leather, as prepared from goat skins at Fez and Tetuan, is thus described by M. Bruffonet in the Bulletin des Sciences. The skins are first cleansed, the hair taken off, limed, and reduced with bran, nearly in the same way already described for the English Morocco leather. After coming from the bran they are thrown into a second bath, made of white figs mixed with water, which is thereby rendered slimy and fermentable. In this bath the skins remain four or five days, when they are thoroughly salted with rock salt alone (and not with salt and alum), after which they are fit to receive the dye, which, for the red, is cochineal and alum; and for the yellow, pomegranate bark and alum. The skins are then tanned, dressed, supplied with a little oil, and dried.
Shagreen. — This singular and valuable leather is a manufacture almost peculiar to Astracan, where it is prepared by the Tartars and Armenians. For making shagreen, only horses' or asses' hides are taken, and it is only a small part from the crupper, along the back, that can be used for this purpose. This is cut off immediately above the tail, in a semicircular form, about 34 inches upon the crupper, and 28 along the back. These pieces are first soaked in water, till the hair is loose, and can be scraped off; and the skin, again soaked, is scraped or shaved so thin, as not to exceed a wetted hog's bladder in thickness, and till all the extraneous matter is got off, and only a clean membranous pelt remains. The piece is then stretched tight on a frame, and kept occasionally wetted, that no part may shrink unequally. The frames are then laid upon a floor, with the flesh sides of the skins undermost, and the grain sides are strewed over with the smooth, black, hard seeds of the alabuta, or goose-foot, (Chinopodium album,) and a felt is then laid upon them, and the seeds trodden in deeply into the soft moist skin; the use of this is, to give the peculiar mottled or roughed surface, for which shagreen is distinguished. The frames, with the seeds still sticking to the skins, are then dried slowly in the shade, till the seeds will shake off without any violence, and the skin is left a hard, horny substance, with the grain side deeply indented. It is then laid on a solid block, covered with wool, and strongly rasped with two or three iron instruments (the particular forms of which it is unnecessary to describe), till the whole of the grain side is shaved, so that, the impression of the seed is very slight and uniform. The skins are then softened, first with water and then with a warm alkaline lye, and are heaped warm and wet upon each other, by which means the parts indented by the impression regain much of (their elasticity; and having lost none of their substance by paring, rise up fully to the level of the shaved places, and thus form the prominent grains, or the granular texture Seculiar to shagreen: the skin is then salted and dyed. The beautiful green dye is given by soaking the inner or flesh side of the skin with a saturated solution of sal ammoniac, strewing it over with copper filings, rolling it up with the flesh side inwards, and pressing each skin with a considerable weight, for about 24 hours, in which time the sal-ammoniac dissolves enough of the copper to penetrate the skin with an agreeable sea-green colour: this is repeated a second time, to give the colour more body. Blue shagreen is dyed with indigo, dissolved in an impure soda, by means of lime and honey. Black shagreen is dyed with galls and vitriol. The skins are finished with oil or suet.
Ei kommentteja :
Lähetä kommentti