Fluorspar supplies CaO.
Fluorspar has a theoretical composition of CaF2. It is produced by the metamorphosis of limestone and dolomite by fluorine-rich gases.
Manufactured in the U.S. by Inverness Mining Co., Cave-In-Rock, IL. Comes from Kentucky and Illinois.
In glazes, usually used in small amounts. Helps to flux the glaze and may produce opacity (fluorite crystals). Silicon tetrafluoride produced by the decomposition of fluorspar may cause blisters and pinholes, and may damage the kiln and the potter. Because silicon is removed, may matt the surface. Can help in the development of unusual blues from cobalt and copper.
(courtesy of glazy.org)
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