Heat Strengthened Glass

When annealed glass is heated up to a temperature range of 600° Celsius to 650° Celsius, for a specified time and then suddenly air-cooled. It gives strength to the glass. The most important factor of heat-strengthened glass is that it has very less wave distortion as compared to fully toughened glass. The glass breaks into slightly bigger pieces and moves towards edges. It is approximately 2-3 times stronger than annealed glass.  The chances of breakage are very little during transportation  and handling. With the probability towards Nickel Sulphite (NiS) inclusions, spontaneous breakage becomes practically non-existent.