PLATE II. JAPANESE TOWELLING, SHOWING IMPRESSION OF FRESH DAMP LEAVES
After removing from the solution and wringing again, the goods were shaken out and exposed to the air for some minutes, during which time the color would develop—in other words, would make its final change to yellow or orange, or even to brownish-red, according to the amount of iron absorbed by the fibre.
The process, nowadays, is much the same, excepting that, for the first or iron bath, it is cheaper and easier to use a solution of the green crystalline iron salt, known as copperas, or asferrous (iron)sulphate. This can be obtained at, or through, any drug store at a very low price, as it is not necessary to buy a chemically pure product. The ordinary commercial salt is as pure as the work requires; this dissolves quite readily in warm water.
The amount of copperas to be used, to dye a particular lot of material a particular shade, can only be determined by experience and experiment. It is always easy to build up a color, i.e., to deepen its shade if it is too light, by dipping the fabric over again in the same dye-bath. Indeed there is a general rule to be observed in dyeing all colors like this iron buff or the manganese brown—as well as the sulphur and indigo colors, which will be described later—that are developed, or fixed, by exposure to the air. Whenever dark shades of these colors are desired, they should be produced by successive dippings in weak baths, rather than by one or two dippings in strong baths. This avoids rubbing, as far as possible, and lessens the injury to the cloth fibre. In general, it is best to start with a dye-bath containing some three or four tablespoonfuls of copperas to one gallon of hot water.
For the second, or fixing, bath—that is, the alkali bath—it is now customary to use a solution of soda instead of the extract made from wood ashes. Either cooking soda (bicarbonate of soda) or the stronger washing soda or soda crystals, known to the chemist as carbonate of soda, will be satisfactory, and instead of soda the corresponding potash salts may be used, though these are usually more expensive. It is possible, too, to use a bath of the so-called caustic soda, or caustic potash, known to the chemist as hydroxide of soda and hydroxide of potash. But these, as the name implies, must be handled with care because, when strong, they are likely to burn the hands and clothes. Careful analyses of dyed mummy cloths show that the ancient Egyptians were accustomed to use for their second or fixing bath, a solution of slaked lime, or lime water.
Khaki.—By mixing in the first bath of copperas or other iron salt an equal quantity of chrome alum, and then fixing and developing as above, a certain amount of greenish chromium oxide is deposited in the fibre along with the oxide of iron. This gives rise to the shade known as “khaki.” Sometimes shaded a little with manganese brown, this was the regular dye for the army uniforms, until the recent introduction of the extremely fast and very satisfactory vat dyes.
Uses.—Iron buff is chiefly used for cotton, linen, and other vegetable fabrics; on them it gives pleasant, warm shades of orange and reddish-brown. But on wool, and especially on silk, it is not so satisfactory, owing to its tendency to roughen and injure the fibre. Indeed, in the case of silk, it is likely to greatly diminish, or even to destroy, the lustre. On cotton and linen, however, it has great fastness to light and to washing. Indeed, every one who has tried to get rust stains out of a garment or a piece of table linen knows how hard a matter it is to get rid of the color.
Another important reason for using this dye is that the coloring agents are very cheap, and are easily obtained in any quantities. It has, however, some serious disadvantages, one of which is that the color, especially in dark shades, is very liable to rub. This can best be obviated by building up the shades with successive dippings; and by thoroughly washing the finished goods in a hot soap bath. The dyed goods are pretty certain to be a little stiff, and therefore hard to sew or cut, owing to the fact that the final color is composed of iron rust. When vegetable fibres are filled with a mineral matter they are naturally stiffer and harder than they were originally.
Then there is the final objection on the part of professional dyers to this color, as well as to all the other developed colors, i.e., those colors fixed by exposure to the air. It is not easy to get a smooth, even color with them, and it is very difficult to dye to shade. For handicraft work, where these two points are of minor importance as compared with the beauty of the color, this objection is not so serious, but where it is necessary to dye large amounts of yarn or cloth to a definite shade with this, or similar, dyes, it is, as a rule, far easier to use a dyestuff which does not materially change its shade after the goods leave the dye-bath.
Iron Grey.—Soon after the discovery, in different localities, of the iron buff color, it was discovered that by the action of various vegetable extracts upon the iron salts, dark grey stains could be produced which, under certain conditions, would be fairly fast to light and washing.