Names.—These dyes have long been made by all of the great firms, although two or three have made more of a specialty of them than the rest. It was soon found that the presence of common (table) salt in the dyestuffs was valuable, as lessening the waste of dyestuff in the dye-liquor, and also increasing the fastness to washing of the dyed goods. For this reason the common name given to this class is that of “Salt Colors.” Owing, however, to the fact that Congo red, the first discovered of the whole class, was derived from the chemical known as benzidine, these salt colors are sometimes referred to, in general, as the “Congo,” or as the “benzidine” dyes. Besides this they are frequently known as “cotton colors,” or “direct cotton colors.” The different manufacturers, however, have assigned certain class names to their own dyestuffs, as follows:
Benzo (Elberfeld); Diamine (Cassella); Dianil (Metz); Mikado (Elberfeld); Naphthamine (Kalle); Oxamine (Badische); Phenamine (Badische).
Uses.—These colors are chiefly used for dyeing cotton, linen, and paper. They take particularly well on mercerized cotton, and on some varieties of artificial silk. They can also be used to dye wool and silk, and, indeed, in many cases give colors faster, both to light and to washing, on these fibres than on cotton. As a rule they will not dye animal fibres excepting at a high temperature—near the boiling point—and in an acid bath. Whereas cotton and linen are preferably dyed in an alkaline or at least a neutral bath, and, while they must be boiled in the dye-bath for at all permanent results, will take the color as a stain at quite low temperatures.
For this reason these dyes are often used for dyeing even shades in one bath, upon mixed goods—that is, wool and cotton, cotton and silk, etc. The goods are first dyed in a lukewarm bath till the cotton is nearly the proper shade, and then, on heating, the wool or silk will take up the color and, before long, catch up with the cotton. It must, however, be remembered that on cotton and linen these dyes are not, as a rule, at all fast to washing, unless they have been well boiled with the goods. When dyed on silk at a boil, they are fast to hot soap and water, a fact which, sometimes, is of much importance.
DYEING DIRECTIONS
Dye-bath.—The color must first be dissolved in water, care being taken not to leave any undissolved lumps or specks of color floating around in, or settled at the bottom of, the dye-bath. For this reason it is generally best, in all dyeing operations, first of all to make a decidedly strong solution of the color, by dissolving a considerable quantity of it (depending of course on the amount of goods to be dyed) in hot water, in a pitcher or saucepan. In the dyehouse this would be called a “stock solution,” and would always be made of a definite strength,—say five parts of color to one hundred of water—and kept well covered up. Sometimes in hot weather it would be treated with a little preservative like benzoate of soda, so that it could be used at any time it was needed. When this color solution is added to the dye-bath, it should always be carefully strained through a piece of cheesecloth or any other fine medium that will catch the specks and undissolved lumps. Otherwise spots are liable to appear, on the finished goods, which it is almost impossible to eradicate without stripping off every trace of color from the dyed material.
Water.—The dye-bath is prepared with plain water. The amount necessary for each lot of goods can only be told by experience. For some classes of dyes, like the Acid colors and the Basic colors, to be described later, the quantity of water makes but little difference. But for dark shades with these Salt colors it is best not to have more than enough water to thoroughly soak, and comfortably cover, the wetted goods, with enough room to stir and turn them easily. The dye-bath is now set on the stove to warm up and, when dyeing light or medium shades, some soap is usually dissolved in it. This is not absolutely necessary but helps to make the color go on more evenly, and penetrate the fibres better.
Soap.—For dyeing purposes in general, any pure, carefully made soap acts satisfactorily. For silk dyeing, and especially for silk finishing, it is said that greater lustre can be gained with olive oil (Castile) soap. But when this cannot be obtained, Ivory soap or Pears’ soap or, in fact, any good brand of bath or toilet soap will do almost as well. For the washing and finishing of wool and silk the use of strong laundry soaps should be avoided if possible, because they usually contain alkali, in the form of borax or of carbonate of soda, which is liable to “tender the goods.” For cotton and linen dyeing and finishing, this does not make any difference. The easiest way to add the soap to the dye-bath is to use it in one of the wire soap-shakers, which has a convenient handle, and holds half a cake or even a whole cake of soap at one time.
Even Dyeing.—The goods should be well washed, rinsed, and wrung out, so as to be sure that they are free from dirt and grease, and have been thoroughly and evenly wet. They are then placed in the dye-bath, completely under the liquid, and stirred round and round and turned over and over with the dye-sticks. The chief objects in stirring are, first, to prevent part of the goods from resting on the bottom and then getting more heat than the rest of the material, in which case, naturally, it will become darker when finished; and second, to prevent the outside portion of the goods from getting more color than the inner portions. Accordingly the goods, when placed in the dye-bath, must be well opened up and, excepting when deliberately making patterns by the method described later under the name of “Tied and Dyed Work,” they should not be tied or entangled in knots or bunches. Every part must be equally exposed, by the turning and lifting and stirring, to the action of the color solution.
If only light shades are desired, the goods are heated and turned until the proper shade has been reached—remembering always that, unless the color has been boiled on, it is likely to be only a stain which will wash off easily.