This mug is in the bottom of a plastic bucket. It has been pinging every few minutes. For days. Razor-sharp chips of the dark blue glaze on the outside are popping off. This is happening because its thermal expansion is too low compared to this low fire talc body. It needs a frit having a higher co-efficient of thermal expansion (typically having more K2O and Na2O).
Shivering is a ceramic glaze defect that results in tiny flakes of glaze peeling off edges of ceramic ware. It happens because the thermal expansion of the body is too much higher than the glaze.