Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/61

Rh The indigo plant, in its general appearance, is not unlike the lucerne of our fields. The seed is sown in drills, about 18 inches apart, and soon makes its appearance above the ground, when it requires incessant care to keep the weeds down, which would otherwise soon choke so tender a crop. In about two months the plants begin to flower, and are then cut down, but shoot up again and give two or three more crops in the same year. Formerly indigo was carefully dried after being cut, and even fire heat was sometimes used for the purpose; but now, at least in India, the practice is abandoned, and it is found in every respect better to use the plant whilst fresh and green. The first process is to place in a shallow wooden vat as much as will loosely cover the bottom of it; water is then let in so as to cover the plants about three inches, and heavy wooden frames are put on the top to prevent them from floating. Being left in this state for from fifteen to twenty hours, fermentation is set up, and much gas is disengaged, the water becoming a light green color. The green liquor is then run off into the second vat, which is placed below the level of the first, in which, whilst the fermentation process is being repeated upon a fresh supply in the first vat, it is violently agitated by being beaten with poles; this causes the grain, as it is called, to separate, and the green matter suspended in the liquor becomes blue and granular, and this change is promoted by the addition of a little lime-water from time to time. When this operation is sufficiently advanced the contents of the vat are allowed to settle, and in a short time the now intensely blue granular matter has sunk to the bottom, leaving the supernatant liquor almost as clear as water; this is then run off nearly to the bottom, and the sediment is run into the third vat, which is below the level of the second; here it awaits several other additions from successive operations, and, a sufficient quantity being accumulated in the third vat, it is suffered to subside and when thoroughly settled the clear liquor is drawn off,