An example of how much Gerstley Borate LOI can affect a glaze

Tuesday 20th February 2018

Fired at cone 6. The samples on the bottom tiles are from ten-gram balls that have melted down. These glazes have the same chemistry, but the one of the left sources its B2O3 from Gerstley Borate (which has a high LOI). The one on the right gets it from a frit. Because the fritted version has less gases of decomposition to expel, the glass is much smoother. Curiously, the fritted version is flowing less and the red color has been lost. Why? This could be because the Al2O3, which stabilizes glazes against excessive fluidity, is being dissolved into the melt better and more available for glass building.

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