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and the whole cloth afterwards dyed with madder and bleached, the pattern will appear in red and brown.
The mordants are applied to the cloth either by a pencil, or by means of blocks on which the pattern is cut.
Care must be taken that the printing from the block does not spread, or that the impresa signs from the several blocks do not interfere with ape another when more than one is applied. For this purpose it is necessary, that the substance used as mordants should have a degree of consistence that may prevent them from spreading, Flour paste, or starch, is mixed with the mordant when it is applied by blocks, and gum arabic when it is but on by a pencil. This thickening requires exact, ness : if too little is used, the pattern will spread; and, if too much, the cotton will not receive a sufficient quantity of the mordant, and will take the dye imperfectly
In order that the impression given by the blocks with the mordant may be seen easily before it is dyed, the mordant is tinged with some colouring matter that will not remain fixed. Decoction of Brazil-wood is used for this
purpose. Before printing, the cotton cloth is well bleached and calendered, and laid smooth on a table : the blocks are applied by hand, and struck with a mallet. The cotton is then dried well in a room with a stove, which not only fixes the mordant more securely, but drives off part of the acetous acid from its base, by which the mordant will combine in a greater proportion, and more intimately with the cloth.
To discharge the paste and gum used with the mordant, the cloth is next to be washed with warm
water and cow-dung; this, also, discharges such parts of the mordant as are not properly fixed, enough being still left to fix the dye. The cloth is then rinsed in clear water. It is then dyed in the usual manner.
The principal dye-stuffs used by calico-printers are indigo, madder, quercitron bark, and weld.
After dyeing, the cloth is well washed, exposed on the grass, and bleached; by which all the parts not touched by the mordant are restored to their original whiteness.
In this manner various colours may be given by one dyeing, merely by varying the mordant. Thus, if one pattern be printed with alum alone, a second with a mixture of alum and iron liquor, a third with iron liquor alone, and a fourth with iron liquor and galls, and the piece be afterwards dyed with quercitron or weld, and the ground bleached in the usual manner; the first pattern will be pure yellow, the second will be olive, the third of a dark drab colour, and the fourth nearly black, while the ground will be white.
As indigo does not require any mordant, it is applied at once, either by a pencil or by a block and paste. But, as has been mentioned under dyeing, indigo will not combine with the cloth except in its disoxygenated or green state; and, if applied thus by the pencil, it would return to the blue state before it had time to fix upon the stuff. The indigo is, therefore, prepared by boiling with potash, made caustic by quicklime, to , which is added orpiment for the disoxygenation of the indigo. This solution is thickened with gum. It must be excluded from the air, otherwise it would attract oxygen and return to the blue or insoluble state. Dr. Bancroft proposed substituting brown sugar
for orpiments, as it is equally efficacious in disoxygenating the indigo, and will also serve instead
Some calicoes are printed only with one colour ; others have two; others three, or more, even to the number of eight, ten, or twelve. The smaller the number of colours, the fewer are the processes. To give an example where six colours are used.
1. A nankeen yellow, of various shades down to a deep yellowish brown or drab, is given by acetite of iron put on with gum or paste, and afterwards plunged into the potash ley.
2. Yellow, by a mordant of acetite of alumine, the dyeing by quercitron bark and bleaching.
3. Red, by the last process, only madder is substituted for the bark.
4. Light blue is given by making a block for all those parts that are to be white, and printing by it on the cloth a composition of which wax is the principal ingredient, or pipe-clay and paste. The cloth is then dyed in a cold indigo vat, and the wax removed by hot water.
5. Lilac flea-brown, and blackish brown, are given by acetite of iron, and dyeing afterwards with madder.
6. Dove-colour and drab, by acetite of iron and quercitron bark.
The same mordant will frequently do for several colours. Thus, suppose one part of the cloth should be printed with acetite of alumine, another with acetite of iron, and a third with a mixture of these two mordants, and the whole afterwards dyed with quercitron bark; then the following colours would appear, viz..yellow, drab, olive; and various depths of shade will be given by varying the proportions of iron in the mordant.
If some parts of the yellow be covered over with the indigo liquor, applied with a pencil, it will be converted into green. By the indigo, also, any parts that are required to be blue may be pencilled.
If, instead of quercitron bark, the cloth printed with the three mordants just mentioned be dyed with madder, then the colours exhibited will be red, brown or black, and purple.
Other processes are still more complicated when a great number of colours are required. New mordants are applied to parts of the pattern already printed, and the cloth again dyed, by which those parts only receive a new colour.
Sometimes the dye stuff and the mordant are mixed together in the first instance, and printed on the cloth, which is a great saving of time and expense; but the colours thus produced on the cloth are not permanent: washing, or even exposure to the air frequently destroys them.
Tanning is the art of converting the raw skins of animals into leather.
The skin is composed chiefly of two parts, a thin white elastic layer on the outside, which is called the epidermis, or cuticle ; and a much thicker layer, composed of a great many fibres, closely interwoven, and disposed in different directions: this is called the cutis, or true skin.
The epidermis is that part of the skin which is raised in blisters. It is easily separated from the cutis by maceration in hot water. It possesses a very great degree of elasticity. It is totally insoluble in water and alcohol. Pure fixed alcalis dissolve it completely, as does lime likewise though slowly.
When a portion of cutis is macerated for some hours in water, with agitation and pressure, the blood, and all the extraneous inatter with which it was loaded, are separated from it, but its texture remains unaltered. On evaporating the water employed, a small quantity of gelatine may be obtained. No subsequent maceration in cold water has any farther effect; the weight of the cutis is not diminished, and its texture is not altered; but if it be boiled in a sufficient quantity of water, it may be completely dissolved, and the whole of it, by evaporating the water, obtained in the state of gelatine.
It was mentioned, when treating of chemistry, that gelatine with tannin, or the tanning principle of vegetables, formed a combination, which is insoluble in water. Upon this depends the art of making leather; the gelatinous part of the skin combining with the tannin of the bark usually employed. The
process which has long been used in this country is as follows; the leather tanned in England consists chiefly of three sorts, known by the name of butts or backs, hides, and skins. Butts are generally made from the stoutest and heaviest ox hides, and are managed as follows: after the horns are taken off, the hides are laid smooth in heaps for one or two days in the summer, and for five or six in the winter ; they are then hung on polęs, in a close room called a smoke-house, in which is kept a smouldering fire of wet tan ; this occasions a small degree of putrefaction, by which means the hair is easily got off, by spreading the hide on a şort of wooden horse or beam, and scraping it with a crooked knife. The hair being taken off, the bide is thrown into a pit or pool of water, to