This mug 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 the coefficient of thermal expansion (COE) of the glaze is too low compared to that of this low-fire talc body. Simplistically, it is a size 6 glaze stuck onto a size 5 body! The glaze needs its COE increased without too much impact on its other properties (e.g. melting range, surface character, durability, color response) and the least impactful way to do that is by substituting some of the existing CaO, MgO, Li2O, SrO or ZnO for super-high-expansion Na2O. That can be done using glaze chemistry or by substituting some of and existing frit in the recipe for one like Ferro 3110 (it contains lots of Na2O).
Ask the right questions to analyse the real cause of glaze shivering. Do not just treat the symptoms, the real cause is thermal expansion mismatch with the body.