These are fired at cone 10R. The kaolin bowl on the left survived 2 seconds! The ball clay next to it: 4 seconds. The Helmer clay (halloysite/kaolin) next to that: 8 seconds. The white stoneware piece: 14 seconds. A commercial stoneware mug could survive for 50 seconds or better. Thermal shock resistance is a complex subject. Of course, the size, thickness and contour of the ware are important. But many other factors come into play: quartz particle content and size, degree of maturity, thermal expansion of the matrix, homogeneity of the matrix, presence and fit of the glaze, internal structure of the mineral species (if the ware is not vitreous), their particles sizes and shapes, presence and type of aggregate (or grog), brittleness of the matrix, and more.
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