Stress Induced Birefringence: Photoelasticity - perpendicular polarization

Using my laptop's display as a source for polarized light, a polystyrene CD jewel case top was photographed using an analyzing polarizer in front of the camera lens.

The polystyrene top was briefly heated in the center with a propane torch causing the plastic to warp. The upper left corner curled up about an inch compared to the rest of the piece.

The color patterns are due to interference caused by retardation of the light going through the plastic. Internal stresses were frozen when the plastic cooled creating a stress tensor field that resulted in a varying birefringence which is seen by a spectral color pattern.

See: en.wikipedia.org/wiki/Photoelasticity

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