Sunday, June 1, 2008

How to Differentiate Different Kinds of Pottery

The term pottery that we commonly use is a catch all phrase for the ceramic work that many various peoples throughout the world have done. As ceramic work was developed simultaneously throughout the world, many different regions have their own unique styles determined by the type of clay they use, decoration, glazing, and how their ceramics are fired. This spotter's guide will teach you how to differentiate between the many different types of pottery as well as their individual merits and uses.

The Four Main Kinds of Pottery

Earthenware is usually made from natural clay, fired to some temperature between 1742 degrees Fahrenheit and 2129 degrees Fahrenheit. Most of it is fired in the area of 1940 degrees. The body of earthenware is nonvitreous; that is relatively soft and porous. It will not hold liquids unless it is glazed. Its color is usually buff or red, often quite dark. For this reason it is sometimes covered with a white or colored slip called engobe before glazes or decorations are applied. An unglazed piece will often have a rough, chalk-like texture than can be scratched with a fingernail. They are also much lighter than stoneware.

Stoneware is sometimes made from natural clay and sometimes from prepared clays that are store bought combinations of natural clays. It is fired to higher temperatures than earthenware- usually between 2246 and 2300 degrees Fahrenheit- and as a result is hard and vitreous, able to hold water even when unglazed. Not all natural clays can be used for stoneware, for many of them, especially the red ones, would melt at stoneware temperatures. Pieces of sculpture or tiles made from natural clay, and fired, but not glazed, are sometimes called terra cotta. The term means baked earth. Stoneware pieces are typically hard and smooth, rarely requiring a glaze unless it’s for decoration. They are heavy and very durable, able to be dropped with little or no damage.

There is little common agreement on the dividing line between china and porcelain. In general the term China refers to a type of ware made of a clay body composed of kaolin, ball clay, feldspar, and flint plus a flux (something to lower the melting point). The flux may be a natural ingredient such as tale or a prepared one such as ground glass. China is never made out of natural clay alone. It is produced in two or more firings at different temperatures. The ware is formed and fired to bisque at a high temperature of about 2,381 degrees Fahrenheit. The bisque ware is then glazed with a lower temperature glaze and fired again to roughly 2,129 degrees. After the second firing, china is sometimes decorated with overglaze painting or printed designs and fired a third time in a decorating kiln at a very low temperature, about 1, 481 degrees. Some china is fired even more often than this for special decorative effects. The color of the body is usually white, although specially colored bodies are produced. To the eye it will be opaque, but solid and always glazed. It will be strong, but much more delicate and lightweight than either earthenware or stoneware.

Porcelain requires the hottest fire among all pottery. It is always made from a specially prepared body compound of kaolin, ball clay, feldspar, and flint. True porcelain such as this is also known as hard paste. Porcelain is made in only one firing, the body and glaze maturing together at about 2,462 degrees Fahrenheit. The product of such a fire, as you might expect, is extremely hard and vitreous. As a result porcelain is inordinately strong for how thin and slender such pieces typically are. One way to recognize true porcelain is to hold it to the light. Light should be slightly visible through the porcelain.

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