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Typical zero-boron high-temperature glazes will not soften in a 1500F decal firing. But low-temperature glazes will (especially those high in boron). Even middle-temperature ones, especially those having significant B2O3, can soften. G3806C (right), for example, is reactive and fluid, it certainly will. Even G2926B, which has high Al2O3 and SiO2, has tiny pits (because of the amount of B2O3 in contains). In serious cases, they can bubble like the mug on the right. What happened to this one? Steam. It was in use and had been absorbing water in the months since it was first glaze-fired at cone 03. The one on the left was not used, but it did have some time to absorb water from the air, it is showing tiny pits in the surface. Even if moisture is not present, on refire low fire bodies continue to generate gases of decomposition that affect glazes. Each decal manufacturer has a recommended firing temperature, that is for their decals, not your glaze.
Troubles |
Glaze Pinholes, Pitting
Analyze the causes of ceramic glaze pinholing and pitting so your fix is dealing with the real issues, not a symptom. |
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Glossary |
Borate
Borate glazes, those fluxed with the oxide B2O3, are the most common type used in ceramic industry and hobby for low and medium temperatures. |
Glossary |
Ceramic Decals
This process of printing a design (using ceramic inks) onto film-coated paper to create a waterslide transfer. On wetting, the film decal can slide off the backing on to the glazed ware. |
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