Stress Testing Polarity Film

Take some of the guesswork out of the kiln.

This simple testing tool helps you spot stress in fused glass before it becomes an unpleasant surprise. Place your glass in front of a light source and hold one sheet of polarity film on each side. As you turn the pieces of film, areas of stress may appear as small, bright starbursts, helping you evaluate your finished piece or investigate possible compatibility concerns.

Each set includes two 3" × 3" sheets—small enough to keep near your kiln and wonderfully handy when something in the glass doesn’t look quite right.

A helpful little window into what your glass may be trying to tell you!

This tool can reveal signs of stress, but it does not replace proper compatibility testing or guarantee that a piece will remain free from cracking.