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by Robert Playoll

Pottery clay is the clay used to make the three categories of pottery: earthenware, stoneware, and porcelain. Clay is baked in a kiln under intense heat, a process known as firing, and becomes solid. Firing is used both to harden the clay and to adhere glaze to it or color it. In this article, I will give a brief introduction as to the different types of clay available for pottery.

1. Earthenware - This type of clay is very common, and generally contains a fair amount of iron and is made from porous pottery clay fired at low temperatures. Because it is fired at low heat, the pottery clay retains its porous nature. Faience, delft, and majolica are all types of earthenware clays.
2. Stoneware - Stoneware is a clay that is generally a mixture of other clays. It has a high degree of plasticity which means it is very easy to manipulate, and is fired at a high temperature, and so becomes nonporous. You have probably eaten off dinner plates made of stoneware.
3. Porcelain - This pottery is actually made with a mixture of several other types of clay and minerals. It is generally composed of kaolin, ball clay, feldspar and flint. Porcelain, also called china, is fired using very high heat, resulting in a white, nonporous, translucent pottery. It does not have much plasticity and can be a challenge to work with.
4. Ball clay - Ball clay is a rare mineral found in few places around the world. Its name dates back to the early methods of mining when specialized hand tools were used to extract the clay in rough cube shapes. As the corners were knocked through handling and storage, these cubes became rounded and 'ball' shaped. This clay has a finer grain than fire clay, and shrinks a great deal during the firing process. For this reason, it is usually mixed with kaolin, as kaolin clay has a low degree of shrinkage.
5. Fire clay- There are two types of fire clay: flint clay and plastic fire clay. Because of its stability during firing, it can be used to make complex items such as pipes and sanitary ware. Fire clay can be easy to work with or not, as its degree of plasticity is variable. It usually has a very rough texture, and is often added to stoneware.
6. Kaolin- Kaolinite is a clay mineral and is very pure, with a white color. It does not shrink much when fired, and must be fired at a very high temperature. As it does not have a high degree of "plasticity," it is usually used in conjunction with other clays.

Article Source: EzineArticles.com