Dissolve 5 ounces of prussiate of potash, in 25 gallons of water heated to 90° or 100°, adding 2 ounces of sulphuric acid; afterwards rinse, and brighten in a very dilute sulphuric acid.
10. Green is given by padding goods, previously dyed in the indigo vat, in a solution of acetate of lead containing a little glue; and then padding them in a warm solution of bichromate of potash; finally rinsing and drying.
III. Resist pastes or reserves; these are subservient to the cold indigo vat, and they may be distributed under four heads; 1. fat reserves; 2. reserves with bases of metallic salts; 3. coloured reserves capable of assuming different tints in the dyeing; 4. reserves with mordants, for the cloth to be afterwards subjected to a dyeing bath, whereby variously coloured figures are brought up on a blue ground, so as to resemble the mineral called lazulite; whence the name lapis or lapis lazuli.
1. The fatty resists are employed in the printing of silk; which see [infra].
2. With regard to reserves the following general observations may be made. After printing-on the paste, the goods must be hung up in a chamber, rather humid than too dry, and left there for a certain time, more or less, according to the nature of the reserve. In dipping them into the blue vat, if the reserve be too dry, it is apt to swell, scale off, and vitiate the pattern. This accident is liable to happen also when the vat is deficient in lime, especially with deep blues.
1. Simple white resist paste for a full body of blue.
Take 1 gallon of water, in which are to be dissolved,
1 pound of binacetate of copper (distilled verdigris), and 3 libs. of sulphate of copper.
This solution is to be thickened with
2 libs. of gum senegal, 1 lib. of British gum, and 4 libs. of pipe-clay; adding afterwards, 2 ounces of nitrate of copper—as a deliquescent substance.
2. White reserve for light blues.