C Walker Posted October 5, 2023 Report Share Posted October 5, 2023 Some of my stoneware pieces (fired to 1220) have come out with lumps. These seem to be in the clay rather than the glaze. Only 3 out if the 12 pieces have these. These are in different clay bodies and are not in pieces near to the elements. How is it that these do not occur when bisque firing? My clay bodies can be fired higher than 1220 so Im not over firing in that sense. Has anyone ideas about what I can do? Quote Link to comment Share on other sites More sharing options...
Hulk Posted October 5, 2023 Report Share Posted October 5, 2023 Hi C Walker, welcome to the Forum! That looks like "bloat" Clay can puff up like that when whatever it is that's gassing/expanding is trapped. At bisque temps, perhaps the bloating part could still "breathe" and hence doesn't show. When I had some bloating, it was more in the thicker parts, however, I also thought there were problem bits here and there in the clay that were at issue. Trimming down the thicker parts and extra time soaking at about 1500°F in the bisque fire seemed to help, and fire to just cone 5 (it was a cone 5 clay). Watching against thick sections might help. Giving a long bisque fire with plenty of oxygen might help - burn out the gassing bits. Firing just up to maturity and no more could also help, and not too fast at the end. Surely you'll get more input, check back after while. Nice colors, pattern, texture Body Bloating (digitalfire.com) Bloating (digitalfire.com) Pres and Rae Reich 2 Quote Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted October 6, 2023 Report Share Posted October 6, 2023 That definitely looks like bloating to me too. If your clay is rated to higher than 1220*C, I’d contact your supplier. That’s not supposed to happen on an underfired clay body, and you may have a bad batch. Babs and Rae Reich 2 Quote Link to comment Share on other sites More sharing options...
C Walker Posted October 6, 2023 Author Report Share Posted October 6, 2023 12 hours ago, Hulk said: Hi C Walker, welcome to the Forum! That looks like "bloat" Clay can puff up like that when whatever it is that's gassing/expanding is trapped. At bisque temps, perhaps the bloating part could still "breathe" and hence doesn't show. When I had some bloating, it was more in the thicker parts, however, I also thought there were problem bits here and there in the clay that were at issue. Trimming down the thicker parts and extra time soaking at about 1500°F in the bisque fire seemed to help, and fire to just cone 5 (it was a cone 5 clay). Watching against thick sections might help. Giving a long bisque fire with plenty of oxygen might help - burn out the gassing bits. Firing just up to maturity and no more could also help, and not too fast at the end. Surely you'll get more input, check back after while. Nice colors, pattern, texture Body Bloating (digitalfire.com) Bloating (digitalfire.com) Thanks to both of you for your advice. I’ve just double checked and one of my clay bodies has a top temperature of 1220 centigrade so I reckon thats why my tiles are sometimes bloating. The other pieces were made from reclaim clay and have some of the same clay mixed in. Its not happening in any other clay. Mystery solved- so now I wont be wasting so much time decorating pieces that are likely to bloat. Thank you! Hulk, Callie Beller Diesel and Rae Reich 3 Quote Link to comment Share on other sites More sharing options...
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