Example of a severely dunted cone 6 stoneware tile. This problem was deliberately created by stacking several tiles on top of this one. This set up a temperature gradient across it so that different parts passed through quartz inversion at different times.
Dunting generally refers to cracking that occurs in ceramic ware as it is cooled in the kiln. The reasons for that cracking can be many.
In ceramics, this refers to the sudden volume change in crystalline quartz particles experience as they pass up and down through 573C. Fired cracks are often related to this.