The difference between these low fire transparents: Gerstley Borate vs. Ulexite

Tuesday 18th March 2014

Left: Worthington Clear cone 04 glaze (A) uses Gerstley Borate to supply the B2O3 and CaO. Right: A substitute using Ulexite and 12% calcium carbonate (B). The degree of melting is the same but the gassing of the calcium carbonate has disrupted the flow of B. Gerstley Borate gasses also, but does so at a stage in the firing that does not disrupt this recipe. However, as a glaze, B does not gel and produces a clearer glass. A further adjustment to source CaO from non-gassing wollastonite would likely improve it.

Pages that reference this post in the Digitalfire Reference Database:

Gerstley Borate, Calcium Carbonate, Ulexite, Decomposition

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