These mugs are made from a vitreous cone 10R sculpture clay (Plainsman Native Sculpture). The grog is the lighter colored specks against the background of a quite vitreous dark burning and smooth clay. This body thus has quite a bit more fired strength than the average much more porous sculpture body.
Grog is a term used in ceramics to describe crushed brick (or other fired ceramic) aggregate that is added to sculpture and structural clays to improve drying properties.
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