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 can soften. G3806C, for example, is reactive and fluid, it certainly will. Even G2926B, which has high Al2O3 and SiO2, has enough boron to soften and sometimes create tiny pits. In serious cases they can bubble like the mug on the right. Why? 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, low fire bodies especially may still have some gases of decomposition to affect the glaze. One more thing: Fire the decals at the recommended temperature, often cone 022.
This process of printing a design (using ceramic inks) onto a film coated decal paper, drying it, transferring the film on to the fired ware. But beware of a problem they do not mention.
Borate glazes, those fluxed with the oxide B2O3, are the most common type used in ceramic industry and hobby for low and medium temperatures.
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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