Blue.—The only two substances used for dying blue are woad and indigo. Indigo has a very strong affinity for wool, silk, cotton, and linen, all of which may therefore be dyed with it without the assistance of any mordant. But indigo is soluble only in sulphuric acid ; it is therefore necessary either to employ the sulphate of indigo, or to render it soluble in water, by depriving it of its oxygen. The first process is frequently employed for dying wool or silk ; but for linen or cotton, the latter is generally resorted to. When the sulphate is em ployed, one part of indigo is to be dissolved in four parts of concentrated sul phuric acid, and one part of dry carbonate of potash added to the solution, which is then to be diluted with eight times its weight of water. The cloth must be boiled for an hour in a solution of five parts of alum and three of tartar, after which it must be removed to a bath containing a greater or smaller proportion of the sulphate of indigo, according to the shade which the cloth is to receive ; and in this bath it must be boiled until it acquire the desired colour. The alum and tartar are not intended to act as mordants, but to facilitate the decom position of the sulphate of indigo. The alkali added to the sulphate answers the same purpose. But the most common method of employing indigo is to deprive it of the oxygen to which it owes its blue colour, and thus reduce it to the state of green pollen, and then to dissolve it in water by means of alkalies or alkaline earths, which act very readily upon it in that state. It is deprived of oxygen either by admixture with other substances possessing a greater affinity for oxygen, as the green oxide of iron, or various metallic sulphurets ; or it may be mixed in water with certain vegetable substances which readily undergo fermentation : the ferments most commonly employed are woad and bran. During this fermentation, the indigo is deprived of its oxygen, and is then dissolved by means of quicklime or alkali added to the solution. The first of these methods is usually followed in dying cotton or linen ; the second, in dying wool and silk.
Of Yellow.—This colour is most commonly obtained from weld, fustic, or quercitron bark. The cloth requires to be prepared before dying, by com bining it with some mordant ; that most commonly employed for this purpose is alumina.
Of Red.—The materials employed for this colour are lac or kermes, cochi neal, archil, madder, ,carthamus, and Brazil wood ; and the ordinary mordants are alumina, and the oxides of tin ; various shades are produced by intermix ture of the dying materials above named, or by first dying the stuff with one or more of them, and subsequently passing it through a yellow bath.
Of Black.—The substances employed to give a black colour are red oxide of iron and tannin. These two substances ',have a strong affinity to each other, and, when combined, assume a deep black colour, not liable to be decomposed by light. Logwood is usually employed as an auxiliary, because it commu nicates lustre, and adds considerably to the fulness of the black. Cloth, before it receives a black colour, is usually dyed blue, which renders the colour much fuller than it would otherwise be ; for inferior cloth, a brown colour is some times given by means of walnut peel.
Of Brown, or Fawn Colour.—Various plentiful and cheap substances are employed to give a brown or fawn coloured ground, as birch, sumach, alder bark, but more especially decoction of walnut peels, or walnut bark or root. The shades produced by the bark or rind of the walnut tree are particularly fine, the colours solid, and it renders the wool, when dyed in it, flexible and soft. From the above colours variously combined are derived the endless gradations of tint imparted to the various fabrics of silk, wool, cotton, and linen. Of these compound colours we shall notice a few of the principal.
Of Green.—This is a mixture of blue and yellow, the shade varying accord ing to the prevalence of either ingredient. The cloth is generally first dyed blue, and then immersed in a yellow bath ; but when sulphate of indigo is employed, it is usual to mix the ingredients together, and dye the cloth at once.
Of Violet, Purple, and Lilac.—These are all mixtures of blue and red, and depend upon the different shade produced by the proportion of one colour to the other. Wool, cotton, and linen, are first dyed blue ; the two last are then galled, and soaked in a decoction of logwood, or of green sulphate of iron ; they are then dyed scarlet in the usual manner : by means, however, of cochineal, mixed with sulphate of indigo, the process may be performed at once. Silk is first dyed crimson with cochineal, and then dipped in the indigo vat.
Of Orange.—This is a mixture of yellow and red. A remarkable differ ence exists in the affinity of various substances for colouring matter, animal substances generally taking the dye much more readily than those of vegetable composition—thus wool and silk are more easily dyed than cotton and linen ; the latter article, indeed, has so slight an affinity for the dye that it is extremely difficult to impart to it a bright and permanent colour. The procesies and manipulations in dying are few and simple, and require principally a good eye to judge accurately of the gradations of the tints, and care and attention in pre paring the ingredients, and in maintaining the baths at a proper temperature.
Mr. J. Hall, of Ordsall, near Manchester, has recently obtained a patent for an apparatus, shown in the engraving on the following page, the object of which is to cause the goods to be exposed to the action of the liquor in the dye vat in a more equal manner than is done in the ordinary method. In the dye vat a are placed six small rollers, 1 to 6, one at each corner, and two near the middle, on the same line with 1 and 4. At about half the depth of the vat are placed two large rollers b and c, about one foot asunder ; one end of each of the axes of these rollers comes through a stuffing-box, and on the axis of b is placed a cog-wheel, which is connected with the axis by a pin passing through it that can be withdrawn at pleasure ; on the axis of c is a similar wheel gearing into b, and may be thrown out of gear when required by the lever d. On the top of the vat is the roller e, whose axis turns in bearings fixed in each side of the vats ; and upon this roller another roller/ rests, which can only move in a vertical direction, its axis being square, and confined by guides g. At one end of the vat is a roller h, supported in two upright forks, and having a small wheel on its axis ; another wheel k on a short axis is placed between the last mentioned wheel and the wheel and the axis of c, and gears into each. The roller A may be lifted out of the forks by the lever 1. To the roller c is fastened a piece of cloth of the width of the goods to be dyed ; this cloth passes over the rollers 6 and 1, under 2 and 3, and over 4 : a similar piece of cloth is wound round the roller b, the end of which is brought up and hung over the roller 5. The cloth or web to be dyed is attached by a long skewer to the cloth of .c, hanging over the roller 4 : the wheel b being now unpinned, and set in motion by a band wheel, or other means, the web is wound upon c, passing under the roller, as before described, until the outer end arrives at the roller 4, when it is attached to the cloth of b by a skewer, and the wheel turned until the cloth on b is unwound. The wheel on c is next thrown out of gear, and that on the axis of b is pinned to its axis, when the wheel being again set in motion, the cloth is unwound from c and wound upon b; and it is thus wound alternately upon each of the rollers b and c, until it is deemed sufficiently dyed. It must then be wound upon the roller b, and the cloth, being detached from the web c, is passed between the rollers e and f, and made fast to the roller h. The wheel on b is then unpinned, and being set in motion, turns A by means of the wheel on c, and the small wheel k; the piece is thus wound upon the roller h, and deprived of a great portion of mois ture by the pressure of the rollers e f When the end appears above the roller 5, the skewer attaching it to the cloth of b is withdrawn, and the roller A is lifted out of the forks by the lever 1, and replaced by a similar one.