Glass used in architecture today commonly includes clear and tinted glass substrates, low-emissivity and solar-control coatings, decorative ceramic-frit patterns and safety glazing considerations that require glass to be heat-treated. Heat-strengthened and fully tempered glass is designed to meet increased thermal and mechanical stresses, or other specified physical criteria. As a result of the heat-treating fabrication process, quench patterns/marks or what is often referred to as a "strain pattern," may become visible in heat-strengthened and fully tempered glass under certain natural or polarized lighting conditions. This document discusses these patterns. This document was originally published in January 2008, and was republished in 2017.