_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Silk, etc._—For animal fibres, such as wool, silk, furs, feathers, etc., the Basic colors have been almost entirely superseded, in commerce, by the class of dyestuffs known as the Acid colors.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. By using some of the methods of the calico printer, it is possible to employ these dyes, with some success, for stencilling. But even for this purpose, excepting, perhaps, on silk, the modern Vat colors are more convenient, as well as being infinitely more permanent to light. _Disadvantages._—The chief drawback to the use of these dyes is that they are not fast to light. Several of them—Methylene Blue, for instance, and Methylene Heliotrope O (_Metz_)—are fairly fast, but the rest, especially in light shades, and on transparent or translucent fabrics, are liable, when exposed to sunlight for any length of time, to alter their shade to a very marked degree. For dark shades this is not so noticeable, for, when goods are strongly colored, the effect of the sunlight on at least the deeper portions of the fibre is largely counteracted by the color of the goods themselves. So, too, an opaque material, like leather, will hold the same shade of color distinctly longer than silk or, especially, artificial silk, where the sunlight strikes through and through the fibre, without any protection at all. But, generally speaking, these dyes will not stand strong sunlight.