Polarization Stress Analysis photograph
Many transparent subject, especially those made of plastics, cause certain properties of light to change
in a manner invisible to our eyes. They change the direction of the plane of polarization of light. This
is an effect that can then be visualized by placing the subject between polarizers. Stresses frozen into
these plastic parts during the manufactuing process then give rise to multicolored patterns that
indicate the degree to which the plastic part affects a light beam traveling though it.