Indigo is a coloring material of vegetable origin, which owes its color and its important applications to a direct blue principle, known under the name of indigotine. It has been used as a dyestuff from time immemorial, by the inhabitants of India; and it is from the East, the cradle of the textile arts, that Europe has derived it. It was probably received from India by the Greeks, among other products first made known to them by the expeditions of Alexander the Great. Dioscorides clearly refers to indigo in mentioning the two coloring matters brought from India. Pliny mentions a coloring material, having an admirable mixture of blue and purple, as coming from India, which he calls _indicum_. That he refers to indigo is curiously manifest by the test which he gives, by which the genuine drug might always and _certainly be distinguished from the spurious_. This is by putting it on live coals, when, says he, “the true _indicum_ will burn with a flame of a most beautiful purple tint.” The purple vapor from burning indigo is still a characteristic test. The Romans, it is apparent, used indigo only as a pigment, not knowing what is still the most important art connected with its use,—how to make it soluble so as to be available in dyeing.
That indigo as a commercial product was first obtained from India is not only proved by the testimony of Pliny, and other ancient writers, but is confirmed by a variety of circumstances, and particularly by its name, which is known to have been _nil_ in the Hindu language, from the earliest times of which there is mention of it. This name is still given by the Hindoos to the color blue, and to all the plants producing indigo. The Arabs and Egyptians, who obtained a knowledge of indigo from India, adopted the Hindu name, the Arabs calling it _nil_ or _nir_, and the Egyptians _nil_ or _niel_. The Portuguese preserved the Indian name, with a slight modification, the substance being called _aniliera_ in their language. The coloring substances afterwards found in coal-tar having been first found in indigo, modern science has adopted for them the name of _aniline_.
It has been asserted that this substance was not known in Europe until the time of the discovery of the passage to India round the Cape of Good Hope. But Dr. Bancroft has shown that indigo was brought by merchants from India to Alexandria, and thence to Venice, when that city was the _entrepôt_ of Europe and the East. It doubtless contributed to the excellence which the Italian states first attained in the wool manufacture. The drug was called _endigo_ in Venice, and it is from that city that we have derived its name and use. It was imperfectly known in England under its Spanish name in the sixteenth century, for we find in Hackluyt “Voyages” his instructions to a traveller who was going to Turkey to ascertain “if _anile_, that coloureth blue, be a natural commodity of those parts, and if it be composed of an herbe.”