Effects with Cellophane
Safety Warnings
Warning: Overhead Projector Heat
Purpose
Everyday transparent plastic objects placed between crossed polarizers reveal colorful stress and birefringence patterns. Demonstrates photoelasticity — how manufacturing stresses and molecular alignment produce optical anisotropy visible through polarized light.
Figure 1:
Desk tape dispenser between crossed polarizers. Stress concentrations from the molding process produce vivid rainbow interference patterns, especially around curves and mounting points.
Figure 2:
Overhead projector setup with mask, lower polarizer on stage, and upper polarizer (analyzer) mounted on ring stand for easy rotation.
Figure 3:
Corner of a zippy bag between crossed polarizers. The parallel stress fringes from the heat-sealed edge reveal residual manufacturing stresses.
Figure 4:
Cellophane tape strips arranged in an asterisk pattern between crossed polarizers. Overlapping regions show different colors due to increased thickness, and the dark center appears where tape axes align with polarizer axes.
Figure 5:
Plastic container lid between crossed polarizers reveals complex residual stress patterns from injection molding, with radial and circular symmetry.
Equipment
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