Chapter III
DIRECT COTTON OR SALT COLORS
Among the many changes made in the art of dyeing since the introduction of the coal-tar dyestuffs, perhaps the most important has been the gradual overcoming of the necessity for mordanting the textiles before coloring them in the dye-bath. Almost all of the old vegetable dyes were mordant dyes; that is, the color could not be fastened to the fibre, whether wool, cotton, linen, or even silk, unless the latter had been impregnated with some chemical which would act as amordant to—(i.e., would combine with and hold) the color. These mordants were, in general, the salts of some metal, aluminium, tin, chromium, and iron salts being the ones in common use; and the processes involved in properly mordanting the goods were in many cases—notably in the case of madder and the Turkey red process—far more difficult and tedious and expensive than the actual dyeing.
The first dyestuffs discovered, the true aniline dyes, which were manufactured directly from aniline and from substances strongly resembling aniline in chemical composition, were at once found to act in a different manner on textile fibres. Animal fibres like wool and silk, fur and leather, were dyed by them directly, without the use of any mordant at all. If the dyestuff were dissolved in water (the addition of a little acid makes the color dissolve more readily, but is without other effect) and a wet skein of wool or silk were immersed in it, and a little heat applied, the color would leave the liquid, and fasten itself firmly on to the goods.
But with cotton and linen and other vegetable fibres, these dyes would not work so well. When these materials are warmed in such a dye-bath, the color does not adhere to the fibres, but washes off directly in a hot soap bath, if not, indeed, under a stream of clear hot water. This was noticed by Perkin very soon after his famous discovery, and, wishing to use his new color for dyeing cotton and linen as well as silk and wool, he set to work to discover how to prepare these materials; in short, how to mordant them so that they too would take firm hold of the color. As will be described later in the chapter on Basic colors, his experiments soon led to the introduction and the use of tannic acid and tartar emetic combined, in a process widely used to this day.
The next class of dyestuffs discovered were the so-called acid colors, thus named because they all exhibited distinctly acid properties—that is, they would form salts with the substances known as bases (of which last, by the way, aniline is an important member). These colors, like the earlier ones, would dye the animal fibres directly, but would not color the vegetable fibres, unless the latter were carefully mordanted with alumina, or iron oxide, or some similar metallic base. And even this treatment does not give colors that are fast to washing, so these acid colors are never used on cotton or linen.
After this came the discovery of alizarine, and an important series of very fast and very valuable dyes, all of which were characteristic mordant colors. Even wool and silk, as well as every other textile, must be carefully mordanted with aluminium, chromium, or iron salts, in order to have any coloring effect produced by these dyestuffs. This is the chief reason why, in spite of their beauty and great permanence, the alizarine and other mordant colors are being less used every year. At the end of some twelve or thirteen years after the discovery of the aniline colors, therefore, it was still impossible to dye cotton with them without a more or less elaborate mordanting process. And yet the problem did not seem to be an impossible one. One of the natural dyes, the safflower, already mentioned, has the property of dyeing cotton pretty, and not very fugitive, shades of pink and rose colors, directly, without the necessity for any mordant; and if a natural dyestuff could do that why could not some artificial ones?
Some thirty years ago, a chemist (one story says that it was a laboratory boy) while experimenting with a dyestuff which was then a recent discovery—Congo red, a very brilliant but fugitive and unstable scarlet color—noticed that while filtering a hot solution of it through filter paper, the paper was stained deeply, and, which was more important, the color was not easily washed out with hot water. This excited his curiosity, and after following the matter up a little, he found that not only this Congo red, but a whole series of dyestuffs formed in the same general way, had the power of dyeing cotton directly. This discovery has practically revolutionized the whole art of cotton dyeing. From these few bright and pretty, but distinctly untrustworthy dyes, which were at once named and advertised as “direct cotton colors,” have sprung great numbers of dyestuffs—several hundreds at least—of every conceivable shade, and of late years of every conceivable degree of fastness to light. All resemble the original Congo red in that they will dye cotton and linen, if not absolutely fast, at any rate very fairly fast to washing, in one bath, without the need of any mordants.
This, of course, means that the cost of dyeing cloth with these dyes is very much less than with the other classes mentioned. And, by the way, it also explains why, under the name of Turkey red, so many extremely bad colors have been sold. To dye Turkey red on cotton, using alizarine, and with the most improved and simplified methods, necessitates at least six or seven different steps, each of which requires not only time and expense, but great skill and care; and any one of them, if carelessly performed, may spoil the goods. On the other hand, a mere beginner, by using one of the early, bright, direct colors (quite cheap in itself, because the patents have expired) can, by boiling the goods for half an hour in a dye-bath with a little soap and salt in it, produce a piece of cloth dyed almost the exact shade of the old Turkey red, for probably one-third, or one-quarter of the price. It will look the same on the shop counter; will probably sell just as well to the average, or even to the painstaking customer; but when exposed to air and light for a few weeks, perhaps even for a few days, will lose its brilliancy, and turn some queer, dull shade, probably of purple.
Indeed this particular substitution has been going on for some years on a large scale; and at one time promised to be of some international importance. The Turkey red dyers in Manchester, a few years ago, complained bitterly to the English Government that their market in India was falling off very seriously; and they demanded an investigation, to know what was the matter.
After careful inquiry by the local officials, word came back that there was no difference in the taste of the people for bright scarlet clothes and headgear. Just as much red was worn as ever before. But active agents of the large German color houses had been going through the country, introducing some of these cheap direct cotton scarlets and showing the natives how to use them. And in consequence, up and down India in all the little towns, even in the villages, local dyers were at work who, for a few cents, would dye up an old piece of calico bright red. When it became faded again in a few weeks, they would dye it over again for a very small sum, thus renewing the same piece whenever it was desirable to appear in bright, new clothes.