Stress during the fire and chilling process causes cracking in ceramics. Clay goes through a “silica inversion” at just over 400 degrees Fahrenheit and then again at slightly over 1000 degrees Fahrenheit during the fire process. The clay is put under a lot of strain throughout this process. Another factor might be the difference in clay and glaze contraction. Although all pottery is subjected to this stress, the majority of it is able to tolerate it.
Dunting isn’t usually visible right after the kiln is turned off. It can take up to a month or more for it to appear, but it should not be mistaken with cracks caused by “thermal shock.”