COTTON DYEING

( Teinture de Coton , Fr.; Baumwollenfärberei , Germ.) Cotton and linen yarns and cloths have nearly the same affinity for dyes, and may therefore with propriety be treated, in this respect, together. After they have acquired the proper degree of whitene (see Bleaching ) they are still unfit to receive and retain the dyes in a permanent manner. It is nece ary, before dipping them into the dye-bath, to give them a tendency to condense the colouring particles within their cavities or pores, and to communicate such chemical properties as will fix these particles so that they will not separate, to whatever ordinary trial they may be subjected. All the colours which it would be desirable to transfer to these stuffs unfortunately do not po e this permanence. Men of science engaged in this important art have constantly aimed at the discovery of some new proce es which may transfer into the cla of fast colours those dyes which are at present more or le fugitive. Almost all the goods manufactured of cotton, flax, or hemp, are intended to be washed, and ought, therefore, to be so dyed as to resist the alkaline and soapy solutions commonly used in the laundry. Vital is distinguished dyed cottons into three cla es; 1. the fugitive , or fancy-coloured ( petit teint ), which change their hue or are destroyed by one or two boils with soap; 2. those which resist five or six careful washings with soap, are good dyes, ( bon teint ); and those which were still more durable, such as Turkey reds, may be called fast colours ( grand teint ). The colours of Brazil wood, logwood, an not to, safflower, ., are fugitive ; those made with madder without an oily base, are good ; and those of madder with an oily mordant, are fast . It is, however, po ible to point out certain proce es for giving these different orders of dyes a greater degree of fixity. I shall describe, in the five following paragraphs, the operations conducive to the fixation of colours upon cotton and linen. 1. Galling. Either gall nuts alone, or sumach alone, or these two substances united, are employed to give to cotton the fast dye preparation. 2 or 3 ounces of galls for every pound of cotton, being coarsely pounded, are to be put into a copper containing about 30 gallons of water for every 100 pounds of cotton, and the bath is to be boiled till the bits of galls feel pasty between the fingers. The fire being withdrawn, when the bath becomes moderately cool, it is pa ed through a hair-cloth sieve. If during this operation the liquor should become cold, it must be made once more as hot as the hand can bear. A portion of it is now transferred into another ve el, called a back , in which the cotton is worked till it be well penetrated with the decoction. It is then taken out, wrung at the peg or squeezed in a pre , and straightway hung up in the drying house. Some more of the fresh decoction being added to the partially exhausted liquor in the back, the proce is resumed upon fresh goods. The manipulation is the same with sumach, but the bath is somewhat differently made; because the quantity of sumach must be double that of galls, and must be merely infused in very hot water, without boiling. When galls and sumach are both prescribed, their baths should be separately made and mixed together. 2. Aluming. Alum is a salt which serves to prepare cotton for receiving an indefinite variety of dyes. Its bath is made as follows: For 100 pounds of scoured cotton, about 30 gallons of water being put into the copper, are heated to about 122° F., when 4 ounces of alum, coarsely pounded, are thrown in for every pound of cotton, and instantly di olved. Whenever the heat of the bath has fallen to about 98° F., the cotton is well worked in it, in order that the solution may thoroughly penetrate all its pores. It is then taken out, wrung at the peg or squeezed in the pre , and dried in the shade. The solution of alum is of such constant employment in this kind of dyeing, that it should be made in large quantities at a time, kept in the alum tun, where it can suffer no deterioration, and drawn off by a spigot or stop-cock as wanted. There are certain colours which require alum to be deprived of a portion of its acid exce , as a supersalt; which may be done by putting 1 ounce of crystals of soda into the tun for every pound of alum. But so much soda should never be used as to cause any permanent precipitation of alumina. When thus prepared, it is called saturated alum , though it is by no means neutral to litmus paper; but it crystallizes differently from ordinary alum. Cotton does not take up at the first aluming a sufficient quantity of alum; but it must receive a second, or even a third immersion. In every case the stuff should be thoroughly dried, with an interval of one or two days between each application; and it may even be left for 10 or 12 hours moist with the alum bath before being hung in the air. When the cotton is finally dry, it must be washed before being plunged into the dye bath; otherwise, the portion of alum, not intimately combined with the cotton, but adhering externally to its filaments, would come off by the heat, mix with the bath, alter the colour by di olving in it, and throw it down to the bottom of the copper, in the form of a lake, to the great lo of the dyer. Madder reds, weld yellows, and some other colours, are more brilliant and faster when acetate of alumina, prepared with acetate of lead, alum, and a little potash, is used, than even saturated alum. This mordant is employed cold, and at 4° Baumé. 3. Mordants . See this article in its alphabetical place. 4. Dye baths , are distinguished into two cla es; the colouring bath, and the dyeing bath. The former serves to extract the colouring matters of the different substances, with the exception of madder, which is always used in substance, and never as an extract, infusion, or decoction. In all these cases, when the colour is extracted, that is, when the dye bath is completed by the degree of heat suited to each substance, it is then allowed to cool down a certain way, and the cotton is worked or winced through it, to get the wished-for tint. This is what is called the dye bath. Several colouring baths are made in the cold; and they serve to dye also in the cold; but the greater part require a heat of 90° or 100° to facilitate the penetration of the stuffs by the colouring particles. The description of the several dye baths is given under the individual dyes. 5. Of the washing after the dyeing. —The washing of the cottons after they have received the dyes, is one of the most important operations in the busine . If it is not carefully performed, the exce of colour not combined with the fibres, is apt to stain whatever it touches. This inconvenience would be of little consequence, if the friction carried off the colour equally from all the points; but it does not do so, and hence the surface appears mottled. A well-planned dye house should be an oblong gallery, with a stream of water flowing along in an open conduit in the middle line, a series of dash wheels arranged against the wall, at one side, and of dyeing coppers, furnished with self-acting winces or reels, against the other. In such a gallery, the washing may be done either by hand, by the rinsing machine, or by the dash wheel, according to the quality of the dye, and the texture of the stuffs. And they may be stripped of the water either by the jack and pin, by the squeezing roller, or by the pre . Wooden pins are placed in some dye-houses on each side of the wash cistern or pool. They are somewhat conical, 1 1 ⁄ 2 foot high, 3 1 ⁄ 2 inches in diameter at the base, 1 1 ⁄ 2 at the top, are fixed firmly upright, and at a level of about 3 feet above the bottom of the cistern, so as to be handy for the workmen. See Brazil wood , Fustic , Madder , Black Dye , Brown Dye , ., as also Bleaching , Bran , Calico Printing , Dunging , Dyeing , .