The Polariscope is an essential tool for determining strain patterns developed during fabrication and manufacturing. It permits immediate determination of strains in most transparent materials. It is valuable in production or as a laboratory tool wherever glass is fabricated, welded or bent. Check liquid in glass thermometers for stress and strains.
As polarized light travels through strained glass or plastic, it undergoes a retardation proportional to the amount of stress. A Polariscope is an instrument which can be used to qualitatively view this retardation.