What is the significance of the Alumina : Silica ratio?

Unit 5 Topic 8
The Unity Formula

If the level of silica in the unity formula for the glaze is appropriate then the Al : Si ratio indicates the viscosity (fluidity or tendency to run) and the degree to which it may be clear and textured.

For stone ware temperatures the limit formula tables indicate an Al : Si ratio of around 9 - 10.

Assuming that the silica level is appropriate for the temperature then the Al : Si ratio lower than 9 might indicate a move towards a more viscous and perhaps opaque and matt glaze resulting from excessive Al2O3.

The reverse (a higher ratio) might indicate a glaze which tended to move while still showing opacity resulting from excessive SiO2.

Menu of Study Units
Check out >>