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This is a cone 6 porcelain mug with G2934 matte glaze (with 6% black stain added). We get this satin matte effect in our test kilns using the PLC6DS schedule. Larger kilns cool slower so this glaze turns out too matte in them, we deal with that by increasing the percentage of glossy base (this is a 15:85 blend of G2926B glossy and G2934 matte). The gold decal is from Sanbao Studio. On the left, it has just been applied, other than the glossy finish revealing its location, no gold design is visible. But, after the decal firing, using the MDDCL schedule, we get the result on the right.
The G2934 base matte recipe is good for decals because it has a very low B2O3 content (unlike high boron glazes that can begin to melt very early, even in a decal firing, and alter their degree of matteness or even produce tiny pinholes or blisters). G2934 can tolerate some high-boron G2926B glossy, enough to de-matte it, and still work well with decals.
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A user experienced this issue with five brands of gold luster, making them unusable. Panic ensued as looming orders could not be met. A session with ChatGPT finally provided the answer: Firing schedule. The preprogrammed fast-fire schedule in the electric kiln was too fast. It noted that organic compounds need time to burn out completely before 800°F. When kilns are densely packed, good ventilation is also important. Different vendors recommend different firing temperatures between cone 020-018. Unlike decal firings, the gold can, and even should, be fired while still wet.
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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