These DFAC test disks (drying performance) show that minor additions of grog do not reduce the fired shrinkage of this medium fire stoneware much. Nor do they improve its drying performance. In this example, a 10% addition has not reduced shrinkage appreciably nor has it improved drying performance. The 20% addition has reduced the shrinkage and narrowed the crack, but it is still there and resembles the zero-grog version.
In ceramics, drying performance is very important to optimizing production. More plastic clays shrink more and crack more, but they are also better to work with.
Grog is a term used in ceramics to describe crushed brick (or other fired ceramic) aggregate that is added to sculpture and structural clays to improve drying properties.