In many cases, the object is coated with a glassy substance called glaze. Firing at a low temperature produces earthenware, a porous material. Earthenware can be made waterproof by glazing. Firing at a high temperature produces stoneware, a hard, heavy material. Stoneware is nonporous without glazing.
Kaolin is a pure white clay that forms when the mineral feldspar breaks down.
Petuntse is a type of feldspar found only in China. It is ground to a fine powder and mixed with kaolin. The kaolin, which is highly resistant to heat, does not melt and therefore allows the item to hold its shape. The process is complete when the petuntse fuses itself to the kaolin. The differences between these types of porcelain are based on the material from which they are made.