Indigo.

The Textile Mercury, 12.3.1892

The chief source of natural indigo is the various species of Indigofera, especially Indigofera tinctoria, which are cultivated in India, China, and South America. It is also contained in European woad, "Isatis tinctoria," and a few other plants, the cultivation of which for the production of indigo was a flourishing industry from the ninth to the 16th centnry, and further, one which, thanks to the decrees of the ruling powers in England. France, and Germany, was the cause of delaying the introduction of the "devouring devil's colour," as the Indian indigo blue was formerly called. The cultivation of European woad is to-day almost an extinct industry, although up to the commencement of the 17th century it was a source of considerable revenue both in France and Germany.

The colour is not contained in the free state in these plants, but as what is called a glucoside, to which the name of "Indican" has been given. In this glucoside the indigo is held in combination with a kind of sugar-glucoside — which former undergoes decomposition under certain well-defined conditions, with the separation of indigo blue.

It is the Indigofera plants of India, China, and South America, especially the first of these, from which the colour is now prepared. The method of its preparation is very simple, although considerable attention is paid to the treatment of the soil previous to the planting of the seeds. Ten to 14 days suffice for the first appearance of the shoots above the soil, after which they continue to grow rapidly. Shortly before flowering, or about three months after sowing, the plants are cut off close to the ground, and are then ready for the extraction of the colour. After cropping, the plants are again allowed to grow, until they are sufficiently mature to admit of a second cutting. Occasionally a third and even a fourth crop is made, but each of these contains successively less and less of the indican. The cut plants are at once placed in large stone cisterns, or fermenting vats, called "steepers," where they arc covered with water and kept in position by means of boards and heavy stones.