What is the Coefficient of Expansion?

Unit 5 Topic 9
The Unity Formula

This value represents the degree to which a glaze will expand and contract in the firing process. It is an indicator of the amount of crazing (or shivering) which might be expected of a glaze fired on a particular clay body.
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The coefficient of expansion reflects the amount of crazing which might be expected of a glaze when fired on a particular clay body in certain firing conditions.

Each oxide in a unity formula has a unique expansion factor allocated to by researchers who have studied and measured the degree to which oxides contribute to the overall expansion of a glaze melt.

As several ceramists have studied glaze expansion there are several different sets of factors which may be used and each of these sets has been named after their originators.

Although some glaze technologists have their own preferences, it does not really matter whose expansion factors are used. It is important to use only one set as the factors are not interchangeable.
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Nicky's Blue Celedon
KNO
CaO
0.3
0.7
Al2O3
0.4
SiO2
2.6
Al : Si
Expan
6.50
12.33

 

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