This mordant is employed for uniform yellow grounds.
4. Aluminous mordant.
This is made by adding potash to a solution of alum, till its earth begins to be separated, then boiling the mixture to precipitate the subsulphate of alumina, which is to be strained upon a filter, and dissolved in acetic acid of moderate strength with the aid of heat. This mordant is very rich in alumina, and marks 20° B.
5. Aluminous mordant.
5. Take 121⁄2 gallons of water.
5. Take 100 lbs. of alum.
5. Take 150 lbs. of liquid pyrolignite of lime at 111⁄2° Baumé.
This mordant is made with heat like the first; after cooling, some alum crystallizes, and it marks only 121⁄2° B.
A mordant is made by solution of alum in potash, commonly called—
6. Aluminate of potash. The caustic lye is prepared by boiling together for an hour 100 gallons of water, 200 lbs. of potash, and 80 lbs. of quicklime; the mixture is then allowed to settle, the supernatant liquor is decanted, and evaporated till its density be 35° B. In 30 gallons of that lye at a boiling heat, 100 lbs. of ground alum are to be dissolved. On cooling, crystals of sulphate of potash separate. The clear liquor is to be decanted off, and the crystals being washed with a little water, this is to be added to the lye. About 33 gallons of mordant should be obtained.
Mordant for Black.
The pyrolignite of iron called iron liquor in this country, is the only mordant used in calico-printing for black, violet, puce, and brown colours. The acetate of alumina, prepared from pyrolignous acid, is much used by the calico-printers under the name of red or yellow liquor, being employed for these dyes.