Another extremely powerful and brilliant color of this class, used considerably to this day although discovered nearly fifty years ago, is the dye often called, from its origin, Aniline Red. It was, however, named by the German manufacturers, Fuchsine, from its rich, full, crimson shades, resembling the deep tints of the flower, fuchsia, while the French, who discovered and manufactured it soon after the close of Louis Napoleon’s Italian campaign, called it Magenta, after the famous victory of that name.
About this time some German chemists discovered and introduced a full, rich, brown dye, still largely used for dyeing leather (kid gloves and the like), and, naturally enough, gave it the name of Bismarck Brown. And at approximately the same date was discovered the very valuable blue dyestuff, perhaps the best of the whole class, with quite a range of full, deep shades, and with considerable fastness to light, called Methylene Blue.
General Properties.—The early colors of this group are the dyestuffs properly known as the “Aniline Colors” because of their origin; although this name has been applied, loosely, to all of the thousands of artificial dyestuffs without regard to their source of composition. To the chemist, their chemical structure and their behavior toward reagents, such as acids and alkalies, naturally suggested the name “Basic Colors.” This means that they are substances with strong affinity for all sorts of acids, with which they form more or less stable salts, while they can be liberated from these salts by the action of stronger bases, such as ammonia, or the fixed alkalies, soda and potash.
Application.—These facts were discovered by Perkin while trying to introduce his Mauveine into the dyeing industry, and he discovered the methods, used to this day, for applying these dyes to the different textile materials. He found that the dyes of this class have a strong affinity for the different animal fibres, such as wool, silk, leather, etc., all of which seem to possess some acid properties of their own; but pure vegetable materials, like cotton, linen, and paper, from which all impurities such as vegetable acids, gums, etc., have been removed, have no affinity at all for even the most powerful of the Basic dyes. A cotton handkerchief, boiled for hours in a strong solution of Methyl Violet, can be washed in a few minutes clear of every particle of color, while a piece of silk or wool, soaked for an instant in the same dye-bath, will be permanently stained, deep and full.
Cotton, Linen, etc.—In order to fasten these dyes to vegetable fibre it is necessary to give the latter a distinctly acid character, and this was done by Perkin in a manner still used. He steeped the material for several hours in a hot bath of the acid vegetable compound, tannic acid or tannin, found so largely in hemlock and chestnut bark, sumac leaves, nut-galls, and the like; and then loosely fixed the tannin, thus absorbed, by a weak bath of tartar emetic. Cotton or linen fabrics, thus “mordanted,” will combine with the Basic dyes as readily and as firmly as any animal fibre, and the resulting colors, while not, as a rule, fast to light, are extremely fast to washing.
Since the introduction of the direct cotton dyes, both Salt colors and Sulphur colors, this method of dyeing, for skeins or piece goods, has been largely discontinued; but, by using a modification of this process, enormous quantities of Basic colors are still employed, on cotton and linen, in the manufacture of calicoes, organdies, and other printed fabrics.
Curiously enough the Salt and the Sulphur colors, in almost every instance, possess sufficient acid properties of their own to act as very fair mordants for the Basic colors. Accordingly, it is not uncommon for dyers to “top,” with Basic colors, cotton or linen goods dyed directly. In the case of the Salt colors, this increases their fastness to washing, and with Sulphur colors it makes the shades more brilliant.
Most vegetable materials that are used in a more or less natural condition, like straw, raffia, grass, wood-shavings, jute, and the like, contain enough of this natural tannic acid to act as a mordant for the Basic colors, which may in this direction be used as direct dyes.
Wool, Silk, etc.—For animal fibres, such as wool, silk, furs, feathers, etc., the Basic colors have been almost entirely superseded, in commerce, by the class of dyestuffs known as the Acid colors. These occur in much greater abundance and variety, and can be applied with less danger of spoiling the goods by uneven results. For leather, on the other hand, the Basic colors are still largely used, especially for dark shades, or when fastness to light is not particularly desired. On bark-tanned leather, which is full of tannic acid, they take hold particularly well, and are often more convenient to work with than the Acid colors, although they do not, as a rule, give such even results.
Uses.—On a small scale it is hardly worth while for the amateur to try to use these Basic colors for dyeing either cotton or linen. The difficulty of correctly and evenly mordanting the goods is quite as great as that of applying the dyes afterward. And the Sulphur colors and Vat colors will be found quite as fast to washing as the best mordanted Basic colors, with the additional advantage of being very much faster to light, as well as easier of application.