How is the coefficient of expansion helpful in glaze development?

Unit 5 Topic 11
The Unity Formula

When trying to control crazing in a glaze the levels of various oxides in the glaze may be adjusted by altering the materials in the recipe or changing the unity formula in order to lower the coefficient of expansion.
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Computer programmes such as MATRIX calculate the coefficient of expansion for a glaze using the expansion factors for each oxide and the values for that oxide in the unity formula for the glaze. The individual oxide expansions are then totalled to find the coefficient of expansion for the whole glaze.

These calculations are performed automatically in computer programmes so that you can instantly see the new expansion factor for a glaze as you make changes to either the recipe or the unity formula.

A unity formula or a recipe may be manipulated to lower the coefficient of expansion using the 'no crazing' benchmark for the clay body as a guide. Even without such a benchmark a series of glazes (line blended) with gradually lowering expansions can be created for testing to eradicate crazing.
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