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It would craze glazes! Really badly (this is fired at cone 6). One might think that there is adequate quartz in this high of a percentage of ball clay to at least minimize crazing, even causing shivering. At cone 10 oxidation this has about 5% porosity (the ball clay contributes enough iron that porosity drops to 2% in reduction). While an addition of feldspar would cut this somewhat, only more silica will increase thermal expansion enough to put the squeeze on glazes to prevent crazing like this.
Glossary |
Cristobalite Inversion
In ceramics, cristobalite is a form (polymorph) of silica. During firing quartz particles in porcelain can convert to cristobalite. This has implications on the thermal expansion of the fired matrix. |
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Glossary |
Quartz Inversion
In ceramics, this refers to the sudden volume change in crystalline quartz particles experience as they pass up and down a temperature window centering on 573C. |
Materials |
Silica
Silica, sold as a white powder, is pure quartz mineral. Quartz is pure SiO2 silicon dioxide. It is the most abundant mineral on earth and most used in ceramics. |
Materials |
Ball Clay
A fine particled highly plastic secondary clay used mainly to impart plasticity to clay and porcelain bodies and to suspend glaze, slips and engobe slurries. |
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