Left: Dry mug. Right: Glazed and fired to cone 6. This is Polar Ice porcelain from Plainsman Clays. It is very vitreous and has the highest fired shrinkage of any body they make (14-15% total). This is the highest firing shrinkage you should ever normally encounter with a pottery clay.
Potters and some manufacturers fire ceramic ware twice, once to prepare it for glazing (call bisquit firing) and the second time to melt the glaze onto it.
Ceramics, by their brittle nature, have high compressive strength. But in functional ceramics we are more concerned about the tensile strength as this relates better to serviceability.
Plainsman Electric Bisque Firing Schedule
Three-step to 1832F