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.
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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.
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