These mugs have experienced very serious shivering. This is an Albany Slip glaze with 10% lithium carbonate, it is known to have a very low thermal expansion. This problem can be solved by reducing the amount of lithium or adding high-expansion sodium or potassium. However these fixes will likely affect the appearance.
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.
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.
GA6-G - Alberta Slip Lithium Brown Cone 6
Plainsman Cone 6 Alberta Slip based glaze. It can be found among others at http://albertaslip.com.
Ceramic Tile Clay Body Formulation
An overview of the technical challenges a technician in the tile industry faces in making good tiles from the least expensive materials and process possible.