In external applications, degradation is evidenced by cracks and crazing. The change in temperature and in the redox sometimes cause cracking or crazing. This puts the glazes into compression and so helps prevent crazing. This arcing causes an effect called "crazing" on the interior glass of the X-ray window. In low-fire art-ware bodies, it imparts whiteness and increases thermal expansion to resist crazing. Vinyl polymers like polystyrene and styrene-acrylonitrile tend to fail by crazing. The matrix crazing theory focuses on explaining the toughening effects of crazing. Rather, crazing will occur homogeneously throughout the material. These formulas form the base of crazing theory, shear-yielding theory, and damage competition theory. In some cases, the crazing can gain a more uniform appearance. Crazing frequently precedes fracture in some glassy thermoplastic polymers. Crazing is a glaze defect of glazed pottery. Crazing can take place in glassy polymers under environmental effects. Therefore, the growth of crazing has a critical distance from the tip.