1.3 Common Clay Body Materials

Stoneware Clay

Kaolin is sedimentary porcelain clay, its name in Chinese means High (“Kao”) Hill (“Lin) where the clay was found. It is a very pure form of white rock, provides a source of alumina and silica for clay and glaze. It is the major component of high-temperature whiteware and porcelain which vitrifies at cone 34 or 1700C. Kaolin itself is hardly used alone as clay body but usually serves as the base with other clays. EPK, Grolleg, Tile#6 ,and Florida kaolin are sedimentary kaolin.

Ball Clay is a sedimentary clay. Its raw color is dark gray, brown, or tan due to the addition of carbonaceous material. It contains more iron and organic material than kaolin. Its particle size is also much finer with high plasticity. However, ball clay is too plastic to be used along. It is used to improve the plasticity and dry strength of the clay body. Due to its high plasticity, the ball clay usually cannot be used a lot. A clay body with 10 to 20 % bally clay will impart the throwing qualities greatly. Its maturing temperature is high and ranges from cone 10-12. Sometimes used as a source of alumina and silica for glaze and improved the strength of glaze coating.

Fire Clay is a sedimentary clay with larger particle size, thus with a lower shrinkage rate. It has a good resistance to head and commonly used for oven pottery, brick, tile, and kiln furniture. Fire clay vitrifies between 1200-1700C. It is served as a source of the clay body to raise the mature temperature.

Stoneware is the flavor to most potters due to its high plasticity and less shrinkage. It maturing temperate is range from 1180-up to 1300C/cone 6 to cone 10. The clays are different in composition, which contain impurities, such as calcium, feldspar, and iron. Its color after firing varies from buff to gray.

Earthenware is low-firing clay that matures at temperatures ranging from 1020-1180C/cone 08 to cone 02, beyond that it will become a glaze. Therefore earthenware is rather fragile and quite porous than stoneware and porcelain. Its porosity is between 5 and 15 percent. It contains a relatively high percentage of iron oxide, which serves as a flux (meter) and gives a red-fired color result.