CHAPTER VI THE INDIGO OR VAT COLORS =History.=—Most of the colors of this group have been discovered and put on the market within the last two years. Thus they form the most recent as well as, in many respects, the most interesting and, perhaps, the most important class of modern dyestuffs. On the other hand, to this same group belong not only indigo itself, which has been known and valued in the East from the earliest ages, but also that most famous of all the ancient dyestuffs, Tyrian Purple. Indigo itself does not exist as such in nature; but it is easily formed by oxidation, or the exposure to air, of a substance—Indican—which occurs as such, or can be produced by a simple process of fermentation, in the juices of many widely distributed plants. Accordingly, even quite barbarous races in different parts of the world noticed the deep permanent blue stains formed on their bodies and clothing when they crushed, accidentally or on purpose, the leaves and stems of the various _Indigoferæ_. Gradually they learned to extract the color in a solid and permanent form so that they could dye with it, instead of using the juice of the fresh plant itself—and then they took to cultivating the plants. These plants—_Indigofera Anil_, _I. tinctoria_, and others originally found wild have been, up to the last four or five years, extensively cultivated in many tropical countries, notably in India (some of the best qualities came from the province of Bengal, and hence the common name for the natural dyestuff—Bengal Indigo), Japan, China, Java, South and Central America, and Africa. From these plants the indigo of commerce, in the form of dark blue granular lumps with a characteristic coppery lustre, was prepared by a comparatively simple process of fermentation, extraction, and oxidation. Indigo may also be obtained, although in small quantities only, and in an impure condition, from other plants. Notably among these is _Isatis tinctoria_, or woad, which in early days was extensively cultivated in England and the Continent, and which, even now, is used in small quantities in some processes of indigo dyeing.