Has a high melting point.
oxide second only to silica in importance linking flux and silica
- Most glazes
contain 5-15%. More than this (25%) promotes matt textures and
amount may cause crawling, pin-holing and greyish colours with
viscosity and extends the melt range.
- When introduced
as clay alumina helps keep glaze materials in suspension and acts
as an adhesive binding unfired gaze materials on the surface of
alumina raises the melting point of a glaze (twice as effective
- together with flux oxides and SiO2
- the preferable source of alumina not provided by feldspars or
other sources of flux.
Ball clays or china clays are preferable as they have minimum
iron or manganese impurities.
- Alumina trihydrate
- less desirable but useful where clays are unable to provide
the required ratio with SiO2.
clays - useful for avoiding cracking of glaze surface after application
where clay content of the glaze is high.
- Orange /
pink with copper + high alumina and low silica.