HT alkaline fluxes—insoluble aluminum silicates of potassium, sodium, calcium, and/or lithium—inexpensive flux for clay and glaze. Substitution of soda spar for potash spar can lower vitrification by 100 degrees. Toxic in inhalation. See Custer feldsparG-200Kona F-4 feldsparnepheline syenitespodumene.  Source: Clay: A Studio Handbook


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