Originally posted by Benny D
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Generally the higher you fire the body the stronger it will be, but the higher you fire it the less will be its thermal shock capability. Unfired clay(cob) and low fired (<800C) have good thermal shock characteristics. Earthenware and stoneware bodies and temperatures have poor thermal shock, while porcelain bodies and temperatures have good thermal shock. If you want to fire it to 1250 C, you will need a stoneware clay body. Unless you are glazing the dome there is no advantage in firing it twice.
A one inch thick pot will take at least two weeks to dry, maybe more and will need a very slow firing for the first 300 C, and a large kiln to fire it. Personally I think you'd be better off using a castable refractory with stainless steel needles.
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