FLOU
Calcium fluoride — the mineral fluorite, ground to a powder · A source of calcium and a strong flux, where a more fusible glaze is wanted · Goes into frits and low-fire enamels as well as glazes · The fluorine gasses off above about 1000°C, which can blister a glaze
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Fluorspar is calcium fluoride, the mineral fluorite, ground to a powder. It can serve as a source of calcium and as a strong flux, where a more fusible melt is wanted, and above about 1000°C the fluorine in it leaves as gas.
Fluorspar can go into a glaze as a source of calcium and as a strong flux. It melts at around 1418°C, well beyond any pottery kiln, so it never melts on its own — it works by dissolving into the glaze around it, where the fluoride breaks up the silicate network and brings the melting point down sharply. A glaze takes it in place of whiting where a more fusible melt is wanted, and it goes into frits and low-fire enamels as well. Above about 1000°C the fluorine leaves as gas, which blisters and pinholes a glaze; used deliberately, that is one route to a crater surface. The gas is also hard on kiln elements.
