CaO×3B2O3—traditional important LT alkaline flux, but is no longer being mined. Replace with Ferro 3134 for LT glazes, commercial Gerstley borate substitutes for HT glazes. Test all substitutes. Source: Clay: A Studio Handbook
Sign up for your FREE subscription to the Ceramic Arts Daily Newsletter and we will give you How to Select Raku Clays, Glazes, Kilns and Combustibles Free!