Toughening process,
• Involves heating and cooling treatment whereby high compressive stresses are set up at the surfaces with balancing tensile stresses in the center.
• Improves the glass strength against impact and thermal stress loads.
• Keeps the original volume, chemical composition, color and clarity of the glass.
Tempered Glass is approximately 5 times stronger than annealed glass against impact. Tempered Glass is appropriate for using as safety glass because it matters into small, blunt edged fragments, which reduce the risk of injury.
Certain "tempering patterns" which are only visible under some lighting conditions and distorsions within allowable bow&warp tolerances are normally accepted as an inherent and unavoidable characteristic of heat treatment and not a defect.
Heat soaking can also be specified with fully tempered panels to eliminate those prone to "spontaneous breakage" in certain occasions.