The "basic colors" have a well known type in magenta. They are usually applied to wool and silk in a neutral or slightly alkaline bath; on cotton they are fixed by means of tannate of antimony or tin. The "acid colors" are only suitable for wool and silk, to which they are applied in an acid bath. A typical representative of this group is furnished by any one of the ordinary azo scarlets which in recent years have come into prominence as competitors of cochineal. The "Congo colors" are comparatively new, and are conveniently so named from the first coloring matter of the group which was discovered, viz., Congo red. They are applicable to wool, silk, and cotton, usually in a neutral or slightly alkaline bath. Of the dyes produced directly upon the fiber itself, one may take aniline black and also primulin as a type, the latter a dye somewhat recently introduced by Mr. A.G. Green, of this city.
Our first impression, in looking at these "direct dyes," is that they are more numerous and more brilliant than the "mordant dyes," and that they are for the most part fugitive. Still, if we examine the different series in detail, we shall find here and there, on the different fibers, colors quite equal in fastness to any of the "mordant dyes."
Among the "basic colors" we search in vain, however, for a really fast dye on any fiber. Still, Magdala red, perhaps, appears faster than the rest on silk, and among the greens and blues we find a few dull blues on cotton, which, for this fiber, have been recommended as substitutes for indigo, viz., Indophenin, paraphenylene, blue, cinerein, Meldola's blue, etc. The azine greens, also, appear tolerably fast on cotton and on silk, but although possessing some body of color, after exposure, the original dark green has changed to a decided drab.
When we examine the "acid colors," however, we meet with a number of scarlets, crimsons, and clarets, possessing considerable fastness both on wool and on silk. Some, indeed, appear almost, if not entirely, as fast as cochineal scarlet, e.g., Biebriech scarlet, brilliant crocein, etc.
Among the "acid oranges and yellows," we also find a goodly number which are of medium fastness. About ten, either on wool or on silk, may even be accounted really fast, and are fit, apparently, to rank with alizarin colors. Note, for example, on wool: Crocein orange, aurantia, orange crystal, tartrazin, milling yellow, palatine orange; on silk, acid yellow D, brilliant yellow, azo acid yellow, metanil yellow, curcumin S, etc. I may remark that these are some of the fastest yellows on wool and silk with which we are acquainted. It is interesting to note the decided fugitive character, on silk, of tartrazin, aurantia, orange crystal, etc., compared with their great fastness on wool. Observe, also, how, on wool, the pale lemon yellow of picric acid has changed to a full reddish brown.
Among the "acid greens and blues," all the colors are fugitive, both on wool and on silk. Patent blue appears slightly better than the rest. Of the "acid blacks and violets," a few colors are of medium fastness, both on wool and silk, e.g., naphthol black, naphthylamine, black, resorcinol brown, fast brown, etc.
When we examine the Congo colors, amid a number of very fugitive colors, we find a few which are satisfactorily fast. Among the reds, for example, diamine fast red is quite remarkable for its fastness, both on wool and silk, and may certainly rank with alizarin; but on cotton, it is quite as fugitive as the rest. Of medium fastness on wool are brilliant Congo G and R, Congo G R; and on silk, diamine scarlet B, deltapurpurin 5 B, and brilliant Congo R.
Among the "Congo oranges and yellows," we find some of the fastest on cotton of this class of colors. Still they deserve only the rank of medium fastness. They are Mikado orange 4 R, R, G. Hessian yellow, curcumin S, chrysophenin. On wool, we have about half a dozen of medium fastness, viz., benzo-orange, Congo orange R, chrysophenin G, chrysamin R, brilliant yellow. On silk, however, we find in this group about a dozen of the fastest oranges and yellows with which we are acquainted for this fiber, viz., Congo orange R, chrysophenin G, diamine yellow N, brilliant yellow, curcumin W, benzo orange, Hessian yellow, chrysamin R and G, cresotin yellow R and G, cotton yellow G, and carbazol yellow.
Does it not appear somewhat remarkable that we should find among this generally fugitive group of coloring matters colors which are so eminently fast on silk, and which we entirely fail to meet with among those groups which usually furnish our fast colors, e.g., the alizarin group?
Passing on to the "Congo violets, blues, and purples," we find few colors worthy of particular notice for fastness. Diamine violet N appears, perhaps, of medium fastness on wool and silk, while sulphonazurin, benzo-black blue, and direct gray may claim the same distinction on silk.