"A group of minerals used in proportions up to 25% flux in bodies and up to 100% in glazes. Feldspars contain alkalis plus silica and aluminium oxide and are therefore natural frits or glazes. In fact, they have cooled and crystallized from a molten magma. They contain alkalis, notably postassium and sodium oxdies, which if alone are soluble, but when combined with aluminium oxide and silica in feldspars, these alkalis are reasonably insoluble. The value of feldspar is thus seen as an opportunity to introduce alkalis into a body or glaze without recourse to fritting."
-The Potter's Dictionary of Materials and Techniques

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This Cornish Stone substitute is a calcium feldspar mineral used as a major constituent of glazes, and occasionally as a flux in bodies. Cornwall Stone is partially kaolinized, and can contain between 5-12% Kaolin.

A potash spar used extensively in clay and glaze formulas.

A selected white firing high grade potassium feldspar ground to 200 mesh for ceramic applications. Moderate potash content and low iron oxide.

200 mesh flotation grade soda Feldspar.

A soda spar. It can reduce crazing tendencies when added to a clay body. Also used in glazes where a soda spar is required.

Substitute for Spodumene. A source of lithia, which is a flux, that helps to develop copper blue tone glazes. Can replace feldspar and also reduces the vitrification temperature and shrinkage rate in glazes.