Craze: When Pottery Cracks from Within

In everyday speech, a craze is a temporary obsession, a trend that sweeps through a population before fading away. A craze for vinyl records, a craze for sourdough bread. The word carries a sense of enthusiasm and collective whimsy, something that passes but leaves fond memories.

In industrial ceramics, craze is a defect, and it is permanent. It occurs when the glaze or enamel coating on pottery shrinks more than the body underneath during cooling, or when thermal stress causes uneven contraction. The result is a fine, branching network of cracks that spreads across the surface, typically visible as a web-like pattern. Unlike a single crack that might be dismissed as impact damage, crazing affects the entire piece and signals a failure in material compatibility or firing control.

The distinction matters because crazing looks like it might be intentional aging, a patina that comes with time. Antique dealers and collectors sometimes struggle to tell the difference between genuine age cracks and manufacturing defects. This ambiguity has made craze a persistent problem in quality assurance; pieces rejected from the kiln may later sell as rustic or vintage without anyone knowing the glaze was never fit for purpose.

Crazing happens most often when there is a mismatch between the thermal expansion coefficients of the glaze and the body, or when water penetrates the exposed ceramic beneath cracks and freezes. In functional ware like dinnerware or bathroom tile, it is also a hygiene issue, since the cracks can trap bacteria and become stained. The word itself, older than modern chemistry, captures something true: the piece is fractured, broken into a pattern that resembles, at first glance, the fine lines of age.