A highly plastic clay, usually light in color, which is the basis of many potting bodies. Alone, it tends to be too fine and slippery for use, but additions of sand, grog and coarser and less-plastic clays actually improve workability. Ball clay is a general term for many clays. It comes from the practice of digging the clay out of the open pits in convenient blocks of about 12 kb, called balls. These clays are always plastic, and mostly cream and vitrify in the 1100°C to 1200°C (2012°F to 2192°F) range.