CHAPTER XI
Glost Firing
“When Fortune bringeth thee affliction, console thyself by remembering that one day thou must see prosperity, and another day difficulty.”
—From El Koran.
The hard porous biscuit shape will now need a coat of glaze and a subsequent glost fire.
Raw glazes for green shapes are now seldom used except for the coarser wares or peasant pottery. In commerce it is, however, largely used on tiles, mouldings, and big sanitary appliances. For common cheap crockery a soft lead glaze, often galena, is generally used. It is applied with a brush, or the pot still leathery and tough is dipped in the glaze. Raw glazes have a strong inclination to leave in the firing. They are very difficult to manipulate unless they are of the simplest formula and fired very slowly. The addition of a little clay in the form of slip to the glaze will often counteract the tendency to leave the pot.
The ordinary glazes in dry powder form are mixed with water to the consistency of cream and passed with the aid of a stout brush through a phosphor
bronze sieve into a large basin or tub. The sieves may range from eighty to two hundred mesh, according to the delicacy of the work. For ordinary work No. 100 suffices. The biscuit to receive the glaze should be quite clean and free from dust or dirt with the insides carefully dusted or blown out. Grease will stop absorption, but with opaque glazes discoloration is not of great importance. If the biscuit is hard and inclined to be non-porous, the glaze will need to be mixed fairly thick before it will cling; with soft and porous shapes a comparatively thin mixture will take readily.