Alumina is used for glaze and frit applications. Al2O3 is the main glass stabiliser and opacifier.
Al2O3 is capable of combining with both basic oxides and silica. It hardens the glaze surface.
Used for tiles porcelain applications, Alumina allows a white firing colour (for unglazed/super white body) that can reduce the use of whitening agents or zircon silicate.