A temperature shift causes a reduction in size. It is not to be confused with shrinking, which is a permanent condition. With a change in temperature, contraction can be reversed. A chunk of ceramic expands and compresses as it heats and cools. A glaze’s rate of expansion and contraction must be consistent with that of the clay body; otherwise, the glaze may flake off or separate. When it comes to glaze fit and ovenware in pottery, this is something to think about.