Heat-strengthened glasses do not suffer spontaneous breakage due to nickel sulphide inclusions. Heat-strengthened glasses do not need to be heat-soaked in advance.
The thermal toughening process causes the surface of the glass to distort in two ways:
- overall bend of 3 mm/m*
- localised bend of 0.3 mm/300 mm*
* values for heat-strengthened glass using the horizontal process
Heat-strengthened glasses cause interference in the same way as thermally toughened glass.