(1) Preparation of the indigo solution, or, as it is called,
setting the dye vat. (2) Steeping the cotton in this vat. (3)
Exposing to the air.
FIG. 30.—Indigo Dye-vat for Cloth.
There are several methods of preparing, or setting the dye vat, and of each of these modifications are in use in every indigo dye-house:—
(1) With lime and copperas. (2) Zinc and lime vat. (3) Zinc and
bisulphite of soda.
In all cases it is necessary for the indigo to be ground to the form of a fine paste with water; this is usually done in what is known as the ball-grinding mill. The finer it is ground the more easy is it to make the dye-vats.