Calcined Alumina – Al2O3 (m.p. 3700oF/2040o C) is produced by calcining hydrated alumina at temperatures of 1200o-1300oC to convert it to alpha-Al2O3. Alpha-alumina is the most stable form of aluminum oxide. Glazes with a moderate alumina content tend to be matt, opaque, and very durable. It also reduces shrinkage, increases thixotropy, minimizes firing warpage, and adds fired strength.