The clay body selected for throwing is as important as the type of wheel and wheel head used. There are three general groups of clay bodies - red or white earthenware, stoneware, and porcelain. Stoneware usually has the best working properties. Because it is not always as workable as an earthenware body, porcelain is generally considered a poor clay to use when learning to throw.
Porcelain is composed of a blend of kaolins, china clays, ball clays and feldspars
What is Agate ware.
Agate ware is a decorative ware made from partially blended dark and light clays which give striations. The effect is sometimes created with surface slips. The name comes from the semi-precious agate stone, a form of crypto-crystalline quartz with striated markings.