After this came the discovery of alizarine, and an important series of very fast and very valuable dyes, all of which were characteristic mordant colors. Even wool and silk, as well as every other textile, must be carefully mordanted with aluminium, chromium, or iron salts, in order to have any coloring effect produced by these dyestuffs. This is the chief reason why, in spite of their beauty and great permanence, the alizarine and other mordant colors are being less used every year. At the end of some twelve or thirteen years after the discovery of the aniline colors, therefore, it was still impossible to dye cotton with them without a more or less elaborate mordanting process. And yet the problem did not seem to be an impossible one. One of the natural dyes, the safflower, already mentioned, has the property of dyeing cotton pretty, and not very fugitive, shades of pink and rose colors, directly, without the necessity for any mordant; and if a natural dyestuff could do that why could not some artificial ones? Some thirty years ago, a chemist (one story says that it was a laboratory boy) while experimenting with a dyestuff which was then a recent discovery—Congo red, a very brilliant but fugitive and unstable scarlet color—noticed that while filtering a hot solution of it through filter paper, the paper was stained deeply, and, which was more important, the color was not easily washed out with hot water. This excited his curiosity, and after following the matter up a little, he found that not only this Congo red, but a whole series of dyestuffs formed in the same general way, had the power of dyeing cotton directly. This discovery has practically revolutionized the whole art of cotton dyeing. From these few bright and pretty, but distinctly untrustworthy dyes, which were at once named and advertised as “direct cotton colors,” have sprung great numbers of dyestuffs—several hundreds at least—of every conceivable shade, and of late years of every conceivable degree of fastness to light. All resemble the original Congo red in that they will dye cotton and linen, if not absolutely fast, at any rate very fairly fast to washing, in one bath, without the need of any mordants.