|Monthly Tech-Tip |
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.
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.
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.
Silica, sold as a white powder, is pure quartz mineral. Quartz is the most abundant mineral, it is pure SiO2 silicon dioxide.
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.