Alumina oxide, Al2O3, is a chemical compound of aluminium and oxygen, and is commonly called alumina. Essentially a refractory, it is responsible for the matteness or brilliance of glazes. However, too much alumina can cause a dry appearance. It prevents devitrification and adds strength. Alumina oxide is insoluble in water and has a high melting temperature of 3550° F. Because of this, alumina oxide can lend great strength to clays and glazes and is frequently used in the industrial ceramics industry.es.