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I had made a set of plates (from slab) with the Plainsman’s coffee clay and glazed it with John Britts’ 3M4 glaze (dipped half in 3M4 base and other half 3M4 +2.5% rutile). I’ve been using them for weeks with hot and cold food, in the dishwasher and everything. Tonight when I put hot food on one, it cracked through the glaze and the clay. Is this problem due to the clay and glaze not fitting together? And how do I go about fixing it?

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It is the glaze and the lack of annealing the piece. In lampworking, glass needs to be annealed to decrease any stress in the glass so it will not crack. Ceramics that are glazed are glass covering the ceramics, so it also needs to be annealed, with a slow cooling of the piece when fired.

It would also help if you find out the COE of the glaze if you can so you can hold the temperature of the kiln at the best temperature to reduce the stress of the glaze.

I personally do not know what that would be. Possibly, just slowing down the firing process; reducing the temperature very slowly to say twice what you did before.

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  • And do you know how it could be possible that the plate only cracked after weeks of putting hot and cold food on it?
    – Joachim
    Dec 5 '20 at 8:58

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