Porcelain, an ingenious pottery product first developed during the Shang Dynasty in 1600 BCE, represents both beauty and grace in Chinese pottery. Because of its unique material properties, porcelain has considerable strength, hardness, whiteness, translucence and insulation. By 600 AD, porcelain-making techniques had been perfected, and Chinese porcelain began spreading outside China. European merchants throughout the 17th century prized porcelain.
Forming
In the forming process, the porcelain's body is constructed. There are many methods of forming, such as slip casting, plastic forming and pressing. Each method highlights different desirable qualities of the porcelain, such as surface quality, density and uniformity. The most common method, slip casting, is characterized by pouring slip and liquid clay into a plaster mold. Once the water is drained, a layer of solid porcelain remains for use. As the substance dries, the porcelain layer becomes rigid, and the mold is removed.
Glazing
The glazing technique ensures pottery will be impermeable to liquids. Porcelain pottery is often glazed for decorative purposes, using the glaze's raw materials in varying quantities. Common ingredients for a glaze include alumina, silica and calcia. Glazes are applied to the porcelain body by means of painting, pouring, dipping and spraying. Finally, glazing effectively makes porcelain pottery resistant to dirt and staining.
Decoration
In addition to standard glazing, porcelain can also be decorated using various pigments. These pigments often contain cobalt, copper and colored enamels. Various styles of decoration have suited porcelain in different time periods. Often, porcelain decoration must be combined with glazing and firing techniques to achieve maximum effect. The pigments can function beneath the initial glaze; repeated firing stages can achieve different decoration styles.
Firing
During the firing process, porcelain wares are heated to high temperatures in a kiln to permanently fix their shapes. There are two types of kiln: periodic and tunnel. A periodic kiln fires one batch of porcelain at any time, and firing cycles are adjustable. In the tunnel kiln, the chamber is hundreds of feet long and contains multiple heating zones. After the firing technique, the porcelain obtains its glass-like quality and becomes non-porous.
