Grog, also known as firesand and chamotte, is a raw material usually made from crushed and ground potsherds, reintroduced back into crude clay to temper it before making ceramic ware. It has a high percentage of silica and alumina. It is normally available as a powder or chippings, and is an important ingredient in Coade stone. Production It can be produced by firing selected fire clays to high temperature before grinding and screening to specific particle sizes. Another method makes it from pitchers. The particle size distribution is generally coarser in size than the other raw materials used to prepare clay bodies. It tends to be porous and have low density. Properties Grog is composed of 40% minimum alumina, 30% minimum silica, 4% maximum iron(III) oxide, up to 2% calcium oxide and magnesium oxide combined. Its melting point is approximately . Its boiling point is over . Its water absorption is maximum 7%. Its thermal expansion coefficient is 5.2 mm/m and thermal conductivity is 0.8 W/(m·K) at 100 °C and 1.0 W/(m·K) at 1000 °C. It is not easily wetted by steel. Applications Grog is used in pottery and sculpture to add a gritty, rustic texture called "tooth"; it reduces shrinkage and aids even drying. This prevents defects such as cracking, crows feet patterning, and lamination. The coarse particles open the green clay body to allow gases to escape. Grog adds structural strength to hand-built and thrown pottery during shaping, although it can diminish fired strength. The finer the particles, the closer the clay bond, and the denser and stronger the fired product. "The strength in the dry state increases with grog down as fine as that passing the 100-mesh sieve, but decreases with material passing the 200-mesh sieve." About 20% grog is added to crude clay (in the dry form) before mixing with water. Adding grog to clay serves two primary functions: 1) It helps prevent cracking of the clay when the ceramic piece is being worked and when it dries, by reducing its plasticity; 2) it protects the ceramic piece from thermal shock while firing, particularly, at the sudden rise or lowering of temperature, and which, if not added, can cause breakage. Substitutes for grog used in pottery are dried and sifted horse manure, or sand collected from dry riverbeds (which has been sifted through a screen), or finely ground schist. Others make use of volcanic ash. In