An extreme example of blistering in a piece fired at cone 03. The glaze is Ferro Frits 3195 and 3110 with 15% ball clay applied to a bisque piece. Is LOI the issue? No, this glaze has a low LOI. Low bisque? No, it was bisqued at cone 04. Thick glaze layer? Yes, partly. Holding the firing longer at temperature? No, I could hold this all night and the glaze would just percolate the whole time. Slow cooling? Close, but not quite. The secret I found to fix this was to apply the glaze in a thinner layer and drop-and-hold the temperature for 30 minutes at 100F below cone 03. Doing that increased the viscosity of the glaze melt to the point that it could break the blisters (held by surface tension) while still being fluid enough to smooth out the surface.
Questions and suggestions to help you reason out the real cause of ceramic glaze blistering and bubbling problems and work out a solution
Blistering is a common surface defect that occurs with ceramic glazes. The problem emerges from the kiln and can occur erratically in production. And be difficult to solve.
A kiln firing schedule where temperature is eased to the top, then dropped quickly and held at a temperature 100-200F lower.
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