Diffraction of light from the sides of the craze enable them to be observed in transparent polymers with the use of backlighting Visual inspection is the most commonly used technique for the early detection of crazing in polymers and composites and its importance should not be overlooked. Increasingly visual inspection may involve the use of CCTV or video cameras to aid access and enable a permanent record of the inspection to be made. For the best results visual inspection of transparent or translucent polymers should be conducted using backlighting. This causes diffraction of light from the sides of the craze allowing them to be observed more clearly. However, this technique does depend on whether access can be gained to both sides of the component to allow backlighting to be installed. If backlighting cannot be installed subsurface defects are extremely difficult to observe.

Red dye penetrant used to expose hairline cracking around bolthole in a plastic moulding Enhanced visual inspection of surface cracks can be achieved by the use of dye penetrants. This involves applying a brightly coloured liquid penetrant to the surface of the polymer and allowing capillary action to draw the liquid into the cracks. Excess penetrant can then be removed and a developer applied. The developer draws the dye out of the cracks on to the surface. As the dye covers a larger area of the surface than the actual flaw it is considerably easier to see the defects. Dye penetrants are widely used for failure analysis. However, care should be taken when using them for monitoring a component that is to remain in service as the penetrant can act as an ESC agent.