grog

In ceramics, clay that has been fired and ground down into fine granules. Grog may be used as an ingredient in a new clay item, raising the overall firing temperature that it can withstand, and thus making it more stable and less likely to crack. Adding grog to the new clay can change its appearance after firing. Grog is also used as a base on which new clay pieces can be made or fired. Clay forms can contract in the kiln, which causes cracking. However, a grog base allows the clay to shrink freely without the base of the item sticking to the surface.