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This is a buff stoneware body, Plainsman M340. A L3954F black engobe was applied inside and upper outside at leather hard. The piece was fired at cone 6 using the PLC6DS schedule. The inside, totally clouded glaze is G2926B. Outside is GA6-B Alberta Slip amber clear. Normally that inside glaze is crystal-clear on other bodies, but this black engobe is generating tiny gas bubbles at the exact wrong time during the firing and the melt is unable to pass them. The black stain thus seems implicated as the gas generator or catalyst. The outside glaze, although amber rather than completely transparent, demonstrates here its ability to clear micro-bubble clouding in spite of this issue.
Glaze clouding is a universal issue in ceramics. Terra cotta bodies demonstrate this best. Pretty well all transparent glazes, even commercially available ones, can cloud. This example is G2931K, it can be beautifully crystal clear. But the thickness of application is the key to achieving that (as thickness increases this happens). We ball milled it to see if that would help, but as you can see, that has not impacted the problem. This is a dipping version so that is part of the reason why it is easy to get it on too thick. One of the advantages of brushing glazes is the ability to carefully control thickness,
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Troubles |
Clouding in Ceramic Glazes
There a many factors to deal with in your ceramic process to achieve transparent glazes that actually fire to a crystal-clear glass |
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