Crazing

Crazing is the formation of a network of fine cracks on the surface or within a material, usually caused by internal stresses, thermal gradients, or chemical attack. The resulting pattern may be whitish or cloudy and can alter optical properties and mechanical performance. Crazing is observed in polymers, glass, and ceramic glazes, among other materials.

In polymers, crazing consists of microvoids bounded by stretched polymer fibrils, creating a porous network that can absorb energy but also serve as a path to fracture. It is commonly initiated by tensile stress, impact, or environmental exposure to solvents, heat, or humidity. Polymers such as polycarbonate, PMMA, and other thermoplastics are especially prone. Crazed regions sometimes brighten or whiten and may propagate under continued loading; in some cases, heat treatment can partially anneal or weld craze zones, but this is material dependent.

In glass, crazing describes a network of surface microcracks, especially in tempered or chemically strengthened glass, often caused by thermal shock, surface flaws, or excessive stress. In ceramic art and manufacturing, craze lines refer to cracks in the glaze rather than the body; glaze crazing commonly results from a mismatch between the thermal expansion of glaze and substrate, or from rapid cooling, producing a spiderweb pattern that is typically cosmetic but can affect durability.

Crazing degrades appearance and, depending on material, mechanical properties such as strength, hardness, or barrier integrity. Prevention focuses on controlling processing temperatures and cooling rates, matching thermal expansion, avoiding solvents or aggressive environments, and proper annealing or tempering. Detection relies on visual inspection, microscopy, and optical tests; repairs range from surface sealing to re-glazing or replacement.