How should the coefficient of expansion be interpreted?

Unit 5 Topic 10
The Unity Formula

The coefficient of expansion is of value as an indicator of crazing tendency when comparing glazes which are fired on the same clay body under similar firing conditions.

Finding a Crazing Benchmark

After firing a number of glazes on a particular clay body under similar application and firing conditions, they can be examined for crazing to determine how low the coefficient of expansion must be for crazing to disappear.

This expansion value may then be considered as a "crazing benchmark" for that clay body, application and firing conditions.

For example after firing a number of glazes on the same body at the same temperature, you find some of the glazes have not crazed. Next check out the coefficients of expansion for those glazes using glaze calculation software. You may find that the values for the glazes that have not crazed might average say 7.5 (depending on what expansion factors your software uses). This value of 7.5 becomes your guide for glazes on the same clay body, applied similarly and fired at that temperature. You can use it to check unfired glazes for their potential to craze and you can also use it to change glazes to reduce (or increase) crazing.

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