POTTERY IS THE PROCESS AND THE PRODUCTS OF FORMING VESSELS AND OTHER OBJECTS WITH CLAY AND OTHER RAW MATERIALS, WHICH ARE FIRED AT HIGH TEMPERATURES TO GIVE THEM A HARD AND DURABLE FORM.
EARTHENWARE CLAYS
Earthenware clays were some of the earliest clays used by potters, and it is the most common type of clay found. These clays are highly plastic, or easily worked, and can be sticky. Earthenware clays contain iron and other mineral impurities which cause the clay to reach its optimum hardness at lower temperatures, between 1745 F and 2012 F (950 C and 1100 C).
Typical colors for moist earthenware clays are red, orange, yellow, and light gray. Colors for fired earthenware includes brown, red, orange, buff, medium grey, and white.
STONEWARE CLAYS
Stoneware clays are plastic and are often grey when moist. Their fired colors range from light grey and buff to medium grey and brown. Fired colors are greatly affected by the type of firing.
Mid-fire stoneware clay bodies are formulated to fire to maturity between 2150 F and 2260 F (1160 C and 1225 C). High-fire stoneware clay bodies fire to their mature hardness between 2200 F and 2336 F (1200 C and 1300 C).
BALL CLAYS
Ball clays are highly plastic and contain few mineral impurities. They fire to their mature hardness at about 2336 F (1300 C). When moist they are dark grey and when fired they are either light grey or light buff.
Ball clays do have a serious drawback. They cannot be used by themselves due to their excessive shrinkage during drying and firing. They are extremely useful, however, when added to other clays to increase workability and plasticity.
