Procelain

Porcelain originates from China and first appeared during the Tang Dynasty (618 – 906 A.D.) Porcelain was developed from stoneware. Unlike stoneware, porcelain requires very high combustion temperatures (starting at 1,200 °C). Hence, porcelain was invented so late, as, in order to produce high combustion temperatures, the fire had to be brought under control, which was very difficult to accomplish with primitive means. Chinese master
craftsmen of pottery were the first who succeeded in doing this.

Components
The components of porcelain are the mineral kaolin (a fire-resistant decomposition product of feldspar), feldspar and quartz.

Processing
The components of porcelain (kaolin approx. 40 – 60 %, feldspar approx. 20 – 30 % and quartz approx. 20 – 40 %) must be carefully processed in order to achieve optimum results. Thus, the raw materials must be carefully freed of dirt. Iron, copper, nickel and manganese must be removed in order to obtain the pure white color.

The components are processed to form a mass by adding water. This then has to rest for a while (up to 2 years). Only then the mass has the right consistency to be shaped by hand, turned on a wheel or poured into a mould. The drying process follows this.

The first firing (biscuit firing in up to 900 °C) removes the water from the porcelain and gives it the stability required for further processing.

After the first firing, the clay is still porous and absorbent. Now it is dipped into the glaze which has a similar chemical composition to that of the porcelain mass.

The porcelain treated in this way is now exposed to the glost firing at a temperature of approx. 1,400 °C. The glaze then becomes permanently attached to the clay; a beautiful, smooth surface is created that is not only very hard, but also immune to attacks by acids, with the exception of fluoric acid. In order to give the porcelain elaborate decorations, the merchandise can now be painted or provided with a transfer picture.
The now following third firing, the so-called over glaze firing, seals the decoration onto the porcelain.