A dyestuff; the original blue of blue jeans.

indigo dye

© Shamils | Dreamstime


Indigo is a dye prepared from the leaves and small branches of a plant, of which there are many varieties, the most remarkable of which is the Indigofera Tinctoria, (Nil, Hind. Nili, San.) from which the dye is made. The root of this plant is three or four lines thick, and more than a foot long, of a faint smell, something like parsley; from which issues a single stem nearly of the same thickness, about two feet high, straight, hard, almost woody, covered with a bark slightly split, of a grey ash colour towards the bottom, green in the middle, reddish at the extremity, and without the appearance of pith inside. The leaves are ranged in pairs round the stalk, of an oval form, smooth, soft to the touch, furrowed above, of a deep green on the under side, and connected with a very short penduncle. From about one-third of the stem to the extremity there are ears that are loaded with very small flowers, from 12 to 15, but destitute of smell. The pistil, which is in the middle of each flower, changes into a pod, in which the seeds are enclosed.

leaves and flowers of Indigofera

© Dinesh Gamage | Dreamstime

This plant requires a good soil, well tilled, and not too dry; the seed, which, as to figure and colour, resembles gunpowder, is sown in the broad cast during the latter months of the hot season, or at the commencement of the rains. Continual attention is required to eradicate the weeds; and with no further labour, the early plant is ready for cutting in the beginning of August, and the fields arriving successively at maturity, supply the works until the commencement of October.

pots in which leaves are fermenting

Fermented indigo in China, 21st century

© Nuvisage | Dreamstime

When the plant has been cut, it is placed in layers in a large wooden vessel, and covered with water. It soon ferments, the water becomes opaque, and assumes a green colour. When the fermentation has continued long enough, which is judged of by the paleness of the leaves, and which requires from 6 to 24 hours, according to the temperature of the air, and the state of the plant, the liquid is drawn off into large flat vessels, where it is constantly agitated till the blue floculi begin to make their appearance; fresh water is now poured in, which causes the blue flakes to precipitate. The yellow liquid is then drawn off, and the sediment, when the water is sufficiently drained from it, is formed into small cakes, and dried in the shade.

The indigo imported from India is classed by the trade under the following denominations :— East India, blue, purple, violet, and copper. The chief signs of good indigo are its lightness, and feeling dry between the fingers; its swimming in water; if thrown upon burning coals, its emitting a violet coloured smoke, and leaving but little ashes behind. In chusing indigo, the large regular formed cakes should be preferred, of a fine rich blue colour, externally free from the white adhesive mould, and of a clean neat shape, as it is much depreciated in consequence of an irregular shape in the cakes, and the incrustation of white mould; when broken, it should be of a bright purple cast, of a close and compact texture, free from white specks or sand, and when rubbed with the nail, should have a beautiful shining copper-like appearance; it should swim in water, and when burnt by the candle, it should fly like dust. That which is heavy, dull coloured, and porous, should be rejected; likewise the small and broken pieces, which, though equally good in quality with regular formed cakes, do not obtain an equal price.

This article has attracted much attention, and speculation has urged its production very far. The average crop of nine years, ending 1821-22, was 89,200 maunds; the following year it was 108,904 maunds, whilst that of 1823-24, is said to be but 75,600 maunds. A large supply, it is stated, might be obtained in Bengal : perhaps as much as 150 or 200,000 maunds, little short of 15 millions of pounds. In the last edition of this Work it was observed, that “the demand of all Europe was estimated at 3 millions of pounds per annum; (the demand in peace is estimated at 24,000 chests of 4 factory maunds each, about 3,500,000 lbs.); but supposing it to extend to 4 millions, Bengal could supply the whole!” The quantity of indigo exported from Calcutta in 1821, was 82,887 factory maunds; and the average annual export in 7 years, 63,139 factory maunds. The home (Bengal) consumption is estimated at 4 per cent. of the produce.

Wiliam Milburn.
Revised by Thomas Thornton.
Oriental Commerce, or the East India Trader's Complete Guide; …
London: Printed for Kingsbury, Parbury, and Allen, 1825.
Pages 289-291.

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