The rim was allowed to get ahead of the base. A thinner section (that happened during throwing) was exploited by the stresses and a crack appeared during heatup, likely during the bisque.
Body Cracking and Dunting During Firing
Ceramic industry can fire much faster and deal with much heavier objects than potters can, how do they do it. The answer is they pay more attention to the basics, it is all common sense and good equipment.
Clay Cracking During Drying
The best way to avoid drying cracks when making ceramics or pottery is to avoid doing the things that cause it. Do not just blame the clay, anything can technically be dried.
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