natanata Posted May 15, 2014 Report Share Posted May 15, 2014 Hello everyone, I have a little disaster happened at my shared studio and I wonder if a more experienced potter can comment on that. So, 3 cup out of 7 just melted in the kiln, sticking to the shelve and clay looks like lava, having bubbles inside. No one really knows why did it happen, while 4 other cups survived and another one, made by another potter (no grog, no glaze) looks perfect. I have used so called "Irish clay" (dark brown), adding handmade grog (bisqued porcelain and terracota) and firing it to 1200 C. The only thing I know is that this clay should have been fired at lower temperatures. Those three cups that melted where staying in the side, closer to the heat, the others in the middle, they are fine, but still have something like bubbles on them, so they were starting to melt or so too. Just don't understand why did it happen, could it be that grog caused it.? The one without grog and glaze was even located in a more hotter place, but nothing happened to it. Do you have any idea? Thank you! Link to comment Share on other sites More sharing options...
JLowes Posted May 15, 2014 Report Share Posted May 15, 2014 I think you are correct that the clay should have been fired at a lower temperature. It is unlikely that the porcelain grog would have had a part, but terra cotta is usually a lower firing clay and could have melted and caused an issue. John Link to comment Share on other sites More sharing options...
Wyndham Posted May 15, 2014 Report Share Posted May 15, 2014 You may have intended to go to 05 instead of cone 5 Is that possible? Terra Cotta is a low firing 06-05 range clay. Wyndham Link to comment Share on other sites More sharing options...
Mark C. Posted May 15, 2014 Report Share Posted May 15, 2014 You have mixed two different clays that fire at different temps in a fire made for hotter clays. Whenever you have a lower temperature clay in studios with higher temp bodies then its what I call a disaster waiting to occur-its not if but when. looks like it melted onto an element-Any studio that allows diffent temp clays will sooner than later get this same result-its human nature Bust out the chisel and grinder and make a new rule that no low temp clay be allowed in the doorotherwise you will see this again. Mark Link to comment Share on other sites More sharing options...
natanata Posted May 16, 2014 Author Report Share Posted May 16, 2014 oh! thank you everyone! it was so stupid to fire terracota grogged clay at this high temperature. at least i know the reason now! thank you very very much! Link to comment Share on other sites More sharing options...
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