These changes, and one or two others, however, did little towards revolutionising the art; that revolution was left for our own days, and resulted from the discovery of what are known as the Aniline dyes, deduced by a long process from the plants of the coal-measures. Of these dyes it must be enough to say that their discovery, while conferring the greatest honour on the abstract science of chemistry, and while doing great service to capitalists in their hunt after profits, has terribly injured the art of dyeing, and for the general public has nearly destroyed it as an art. Henceforward there is an absolute divorce between the _commercial process_ and the _art_ of dyeing. Anyone wanting to produce dyed textiles with any artistic quality in them must entirely forgo the modern and commercial methods in favour of those which are at least as old as Pliny, who speaks of them as being old in his time.
Now, in order to dye textiles in patterns or otherwise, we need four colours to start with--to wit, blue, red, yellow, and brown; green, purple, black, and all intermediate shades can be made from a mixture of these colours.
Blue is given us by indigo and woad, which do not differ in colour in the least, their chemical product being the same. Woad may be called northern indigo; and indigo tropical or sub-tropical woad.
Note that until the introduction of Prussian blue about 1810 there was _no_ other blue dye except this indigotine that could be called a dye; the other blue dyes were mere stains which would not bear the sun for more than a few days.
Red is yielded by the insect dyes kermes, lac-dye, and cochineal, and by the vegetable dye madder. Of these, kermes is the king; brighter than madder and at once more permanent and more beautiful than cochineal: the latter on an aluminous basis gives a rather cold crimson, and on a tin basis a rather hot scarlet (_e.g._ the dress-coat of a line officer). Madder yields on wool a deep-toned blood-red, somewhat bricky and tending to scarlet. On cotton and linen, all imaginable shades of red according to the process. It is not of much use in dyeing silk, which it is apt to "blind"; _i.e._ it takes off the gloss. Lac-dye gives a hot and not pleasant scarlet, as may be noted in a private militiaman's coat. The French liners' trousers, by the way, are, or were, dyed with madder, so that their countrymen sometimes call them the "Madder-wearers"; but their cloth is somewhat too cheaply dyed to do credit to the drysaltery.