Porcelain in China was usually formed of two materials, of which one--Pe-tun-tze--resembles our China stone. It is a white fusible material, a mixture of felspar and quartz, obtained from pounded rock and formed into cakes or bricks, hence its Chinese name.
The other material is named Kaolin, or China clay. It is infusible, and is derived from the decomposed felspar of granite. This is also formed into cakes. When these two materials, China rock and China clay, have been thoroughly ground, cleansed, sifted and refined into an impalpable powder, they are kneaded together in varying proportions to form a clay ready for the potter. The wet clay is turned on the potter's wheel or table, then is passed through the hands of various workmen who add handles and other decorations made in moulds, who smooth the surface and so work upon it that the next process--the drying process--is preparatory to the under-glaze decoration. In this semi-soft state the foot remains a solid mass. Any decorations in blue or red or other colours which can be applied under the glaze are then used for painting the under-glaze decoration. The glaze is next applied in various ways by dipping, by blowing on with a tube, by sprinkling, and so on. When these processes have been completed it only remains for the potter to fashion the foot upon the wheel and to inscribe any mark which may be adopted. These being then coated with glaze, the piece is ready for the furnace.
Porcelain placed in the kiln to be fired has to be protected in strong clay vessels called seggars, which admit the heat but protect it from injury. Every piece is placed in the kiln according to the temperature which is necessary for its complete firing. Some pieces would be placed at the top of the kiln, other pieces at the tip-top of the kiln, very much in accordance with the practice in our English potteries at the present time. The furnace when full is entirely bricked up and the whole contents of the kiln are kept at a great heat, usually for a night and a day, after which the kiln is allowed to cool off, and in due time the porcelain is removed. In speaking of white porcelain, or porcelain decorated under the glaze, the process is now complete, but if enamel colours are used further burnings in a kiln take place. After the enamel decoration has been applied over the glaze--and the painters who use the enamel colours may take long weeks or months in decorating a single piece--and until the whole is finished, the piece is fired again and again in a kiln at a much lower temperature, the process being quite similar to the previous one, although the heat is much less. Colours which are applied with the glaze, as we shall see later--self-colours, such as the Celadons--pass only through the first process and need no second firing.