Definition: In pottery, thermal shock (noun) is the fracturing effect that occurs when ceramic objects are rapidly either heated or cooled. In severe cases it can cause the shattering of a pot (such as in the case of removing glowing-hot pots from a kiln and rapidly cooling them to room temperature). In many cases, especially as seen when a pot is heated and cooled repeatedly in every day use, the fracturing or cracking may be at the microscopic level.
Examples:
In Western-style raku, thermal shock is often deliberately used to create crackling in glazes.