Toughened glass can break spontaneously due to the presence of nickel sufide. To avoid this, a Heat Soak treatment can be requested.
The thermal toughening process causes the surface of the glass to distort in two ways:
- Overall bend of 3 mm/m*
- Localised bend of 0.5 mm/300 mm*
* Values for Planibel heat-strengthened glass using the horizontal process
This phenomenon may be more visible in coated glasses.
Anisotropy is caused by compression of the surface of the thermally toughened glass. Under natural lighting conditions, the reflection characteristics vary from one point to another and differently coloured patterns known as "leopard spots" may be seen on the glass.
This particular aspect is inherent to thermally toughened glass.