Cristobalite is a crystalline form of silica. Silica normally exists in nature as quartz. But cristobalite is available as a powder, it is manufactured by mixing quartz with the right fluxes/catalysts and calcined to the necessary temperature (1100C+), then cooling it quickly. But such a material is not useful in traditional ceramics since it would convert back to quartz on heating. However, quartz particles in a clay body, such as a whiteware that does not fire too vitreous, find themselves in a mix of clays and fluxes that provides an ideal environment for the conversion to cristobalite. The firing temperature, fineness of the quartz particles (finer is better) and soaking time determine the completeness of the conversion.
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