The Polaroid filter set contains two (2), Polaroid filters and is used to test for stress in fused or lampworked glass pieces.
Each filter measures 3" x 3", and is protected on one side with a thin, protective film, which should be carefully removed for best visibility.
TO TEST FOR STRESS:
Place one filter over a light source (a flashlight works well).
Sandwich the glass between it and the second filter.
Rotate this filter until it blocks out the light.
At this point, (if stress is present), a halo or flare should appear around the perimeter or areas of attached glass.