The indigo of the Indigof era tinctoria is obtained by subjecting the plant to a fermentive process, in large masses, iu tanks. After its removal, the water is stirred and beaten by paddles, its colour passes to a blue, and the suspended particles settle to the bottom, forming a blue sediment, which, after the water is drawn off, is dried in the sun and cut up into cakes. The time for sowing varies in Bengal proper, Tirhut, and the several districts of the N.W. Provinces. In Bengal, sowings prevail in the month Kartik (October), hence called Kartiki. In Tirhut, Sarun, and Champarum, in which there is rich alluvial land and a natural moisture, the sowings are in February (Phalgun), and the factories are known as Phalguni. The preparation of the land in Tirhut is much more elaborate than in Bengal proper or the N.W. Provinces, and altogether a more advanced system prevails there, and the work is regularly spread over the whole year. In the N.W. Provinces and in Oudh, the sowings chiefly take place on the first fall of rain in June (Asarh), hence the factories are known as Asarhi, but these have sowings also called Jamowa, which is a sort of compromise between the Phalguni and Asarhi periods. An artificial moisture is secured in February and March by irrigation, and small patches of indigo are sown near every available well.
In the N. TV. Provinces the planter's work comes on him all in a heap in June or July (Asarh and Sawan). He has sowing, cutting the stumps left of the past year's crop, manufacture of the new crop, packing and despatch of the indigo. The fresh plant is filled into steeper vats, and pressed down with beams of wood interlaced with bam boos ; water is then let in from the reservoir, and steeping or fermentation allowed to go on for ten or twelve hours, according to the state of the atmosphere. After fermentation is complete, the liquor is drawn off into a lower beating vat (hauz mahye). Ten or twelve men now enter the vat with shovels ; they are called mahunean or beaters ; they beat (mahye) from one and a half to two hours, and by this means a great quantity of carbonic acid gas is disengaged, and the particles of indigo get thoroughly exposed to the atmo sphere, and obtain their requisite supply of oxygen, after which they granulate. The vat is now allowed to settle, the indigo gradually sub sides, and the water, which separates, is drawn off, and is of the colour of dark sherry. A sediment is left at the bottom of the vat, which is collected and discharged into a cistern alongside, and runs through a strainer (channah) into the boiler (karah), when it is heated to boiling point. From the boiler the liquid indigo (mal) is run on a table on which is spread a sheet, and allowed to filter through until the liquid runs clear. The day following, the indigo, fully drained, is of the consistency of curds, when it is removed to the press-house, put into presses, and subjected to severe pressure. With the aid of nuts and screws, a solid mass is thus obtained, which is taken to the drying-house (bari khana), placed on a cutting frame, and cut with brass wire into cubes or cakes (goti or bari). The cakes are placed on wicker-work frames to dry. A whitish efflores cence soon covers the cakes, and a strong smell of ammonia prevails throughout the drying-house.
When quite dry, the cakes are taken down, brushed, assorted according to colour and quality (rang milan), and packed into boxes for export, after which the N.W. planter has nothing to do till the following June.
In Tirhut the preparation of the land is com menced in October. All the old stumps are dug out, the land is twice ploughed (somra or docha), and a flat roller (henga) passed over, to break the clods and keep in the moisture. If the sith or jhuthi, or refuse indigo stalks (a rich manure), has not already been spread on the land, and allowed to decompose, it is now spread, and, to save time, set fire to, and the ashes well ploughed in ; then all the smaller clods are pulverized, and all grass and refuse removed. The land is then finally ploughed and rolled, and allowed to rest till the end of January. In the beginning of February, sowings begin and last to the end of March. In April and May, the young plant is weeded. About the middle of June or first week in July, manufacturing begins, and lasts without interruption till the end of September. In October the cakes are taken down from the shelves where they have been drying, brushed, packed in boxes weighing about three factory maunds each, marked and numbered, and finally sent down to Calcutta for sale and shipment to Europe, China, Persia, and America.
In Bengal proper, indigo is cultivated at a season when nothing else is on the ground. It occurs intermediately between the two great crops of the year, and it has puzzled Boards of Revenue before now to decide whether it is a rabi or kharif crop. It is cleared off the ground in time for another crop, and it is far from being an exhausting crop. The ryots know this well, and all they get for their indigo is additional to their income, though, at a strict calculation, it would not cover the expense of the cultivation.
After having ploughed the ground in October, November, and the beginning of December, they sow the seed in the last half of March and the beginning of April, while the soil, being neither too hot nor too dry, is most propitious to its germination. A light mould answers best, and sunshine, with occasional light showers, are most favourable to its growth. Twelve pounds of seed are sufficient for sowing an acre of land. The plants grow rapidly, and will bear to be cut for the first time at the beginning of July ; nay, in some districts so early as the middle of June. The indications of maturity are the bursting forth of the flower - buds and the expansion of the blossoms, at which period the plant abounds most in the dyeing principle. Another indication is taken from the leaves, which, if they break across when doubled flat, denote a state of maturity. But this character is somewhat fallaci ous, and depends upon the poverty or richness of the soil. When much rain falls, the plants grow too rapidly, and do not sufficiently elaborate the blue pigment. Bright sunshine is most ad vantageous to its production. The first cropping of the plants is the best ; after two months a second is made, after another interval a third, and even a fourth ; but each of these is of dimin ished value.