DYEING, the art of imparting colors to textile and other material, such as cotton, silk, wool, and leather. Dyeing has been practiced from time immemo rial. Dyeing with colors obtained from natural products had reached a high state of perfection when Perkin, in 1856, introduced the first of the coal-tar colors. Since that date the progress of artificial color-making has been so rapid, and the application of the new dyes made so simple, that, excepting indigo, logwood and cutch, the old colors and processes are now practically driven out of use.
If the fiber is of animal origin, such as silk or wool, a simple immersion in a bath containing the color will usually dye the fabric; but color so applied to a vegetable substance—as cotton, linen, or jute, is easily washed off, except in the case of the "direct" colors. Vegetable substances are consequently usually treated with mordants (see CALico). Mordants are substances which form in soluble precipitates with the dyes in the body of the fiber. The mordants most largely used are tannic acid, the salts of antimony, aluminum, and chromium.
Dyeing of Cotton.—The following is a brief outline of the processes in use for a few important colors: Black is produced by mordanting the goods with salt of iron and then dyeing in a decoction of logwood or by dyeing in a bath containing logwood, bichromate of potash, and mineral acid. Aniline salts with a suitable oxidizing mixture yield a very fast and valuable black. Eichromates and chlorates are among the substances used as oxidizing agents.
Brown is obtained by working in a catechu or cutch bath and then in a bi chromate bath. Bismarck-brown on a tannin mordant, and direct browns, are also used.
Purples and lilacs are obtained from alizarin on an iron mordant, with basic colors, as methyl or Hofmann's violet, on a tannin mordant, and direct dyes.
Red. The fastest red dye is alizarin or Turkey red. The process is rather com plicated, involving working in a specially prepared oil, aluminum mordant, steam ing, dyeing with alizarin, and dunging. Reds are produced on goods impregnated with an alkaline solution of B naphthol by passing through a bath of diazotized Para, with aniline or naphthylamine.
Blue. The best blue in respect to fast ness is indigo. The coloring constituent of indigo is indigotine.
Dyeing of Wool.—All the coloring mat ters obtained from natural products men tioned in connection with cotton are ap plicable to wool, and in addition cochineal is considerably used. Cochineal with a tin mordant gives a very brilliant scarlet. The basic colors dye wool without the aid of a mordant. Direct colors are appli cable to wool. Aniline black is not applicable.
Dyeing of Silk.—Black is the most im portant color dyed on silk. In dyeing the object is usually to add weight to, or "shiff," the fabric.
Up to the time of the outbreak of the World War, the manufacture of dyes was practically in the hands of Germany or of German controlled organizations. The embargo on the importation of German goods, therefore, created a very serious situation in the United States and Amer ican chemists at once set themselves zealously at work to invent and prepare dyes which should take the place of these formerly obtained in Germany. At first the results were unsatisfactory, but by 1919 the dyestuff industry had reached such a successful basis that it was able to manufacture practically all essential dyes. In that year not less than 1,733 chemists were engaged in research and the industry required the services of over 20,000 employees. The total output of nearly 200 firms was over 50,000,000 pounds, with a value of nearly $70,000, 000. In March, 1918, the American Dyestuff Manufacturing Association was organized. At an exhibition held in New York City in the same year, samples of dyeing from about 50 American dyestuffs were shown. These samples were sub jected to most severe tests, and by com parison with German dyes, established the superiority of the American product. The production of coal tar dyes in the United States in 1918 was about 46,000, 000 pounds. The imports in 1915 amounted to practically the same figure. There were exported in 1918 American dyes to the value of nearly $12,000,000; in 1920 it amounted to $25,792,565.