Refiring a cone 6 stoneware mug ruins the glassy surface with blisters
The body is pure Lincoln fireclay. It matures fully by about cone 8. The first firing (left), was to cone 6. The second firing, right, was to cone 7. The higher temperature, theoretically should have given the glaze additional opportunity to smooth out. It is not always logical why this happens, especially with a melt-fluid glaze like this. It appears the re-melting glaze formed blisters on the heat-up and the molten glass had sufficient surface tension to maintain these throughout the cycle. They only broke when increasing viscosity of the cooling melt overcame the surface tension.