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clayshapes

Cracked Underglaze

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I'm not sure you can see the problem in the attachment I'm sending with this, but this bowl is earthenware with several layers of commercial underglaze and 2 coats of clear glaze. As you can see, the finish has cracked, as opposed to crackled in many places. Do you think this is a function of too much underglaze -- and possibly not having dried it properly between coats? The underglaze was applied after the bowl was bisque fired, and it was glaze fired to cone 04 (for both underglaze and glaze, this was the recommended cone to fire to). I'm wondering if it's better to decorate with underglaze at the greenware stage so that the underglaze gets fired once before clear glaze is applied, and if that might avoid this cracking. I put three coats of the base (dark blue) underglaze

before applying the other colours. Too much underglaze??? I fired another piece with similar treatment (on a higher shelf) and it didn't crack at all.... Any ideas about what went wrong -- and also -- should I refire in the hope the glaze and underglaze with "melt" more. When I refire bubbled glaze, it is remedied. Although I understand underglaze is a different story....

I'd appreciate any ideas and remedies from more experienced potters!

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Glaze cracking can occur when the glaze layer is applied to thick.Painting in thinner layers and firing layers seperately can solve this problem, but this is lengthy and more expensive.Applying the underglaze when the piece in greenware stage and the covering glaze at a later firing might help.Some clay/glazes combinations are tend to give more cracks then others combinations.Firing biscuitware higher then the glaze could also a help in reducing cracks.Keeping the covering glaze as thin as possible is another option.Avoid cooling too fast after firing.

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