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This blistering problem is common in rutile blue glazes, especially high-temperature - this is not saleable. The reason relates to what it takes to create this kind of vibrant variegated aesthetic: Melting the crap out of the glaze and cooling it just right. This particular one is being fired to cone 11 down to get enough melt fluidity to make it crystallize and phase separate. It seems logical that if the glaze is melting so well it should be able to heal any bubbles that form and break (these are more than usual because the body is being overfired and generating gases). However, the fluidity comes with surface tension that can hold the bubbles intact. Each of these holes in the glaze is a product of that - plus another factor: Cooldown is rapid enough that the melt is not sufficiently fluid to heal after bubble breakage. The potter has been using this glaze for many years with success, but a small change in process or materials has occurred to push it past a tipping point. Solutions? A drop and hold firing. Add a flux (e.g. a little lithium or a frit) to make it melt fluid at cone 10R (where the body generates less gasses of decomposition). Replace any high LOI materials in the glaze itself with other materials to source the same oxides.
Troubles |
Glaze Blisters
Questions and suggestions to help you reason out the real cause of ceramic glaze blistering and bubbling problems and work out a solution |
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Glossary |
Drop-and-Soak Firing
A kiln firing schedule where temperature is eased to the top, then dropped quickly and held at a temperature 100-200F lower. |
Glossary |
Rutile Blue Glazes
A type of ceramic glaze in which the surface variegates and crystallizes on cooling in the presence of titanium and iron (usually sourced by rutile) |
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