Crazing is a phenomenon that produces a network of fine cracks on the surface of a material, such as a glaze layer on pottery or ceramic dishes. Crazing generally occurs in amorphous, brittle polymers like polystyrene, acrylic, and polycarbonate, and it is typified by a whitening of the crazed region. Crazes form at highly stressed regions associated with scratches, flaws, stress concentrations, and molecular inhomogeneities, and they generally propagate perpendicular to the applied tension. Crazing is considered a defect in the glaze and can weaken the item, and it may also harbor bacteria. However, there are cases where crazing is a desired effect, such as in pottery or ceramic dishes, where it can be used to create a crackle effect. Crazing can often be eliminated simply by applying a thinner glaze coat, and adding increasing amounts of silica to the glaze can also help to reduce crazing.