The chemical strengthening process of glass is used to improve the physical characteristics of glass, increasing its resistance to mechanical stresses and to thermal shocks.
The process is achieved with long bath in potassium salts, during which the glass exchanges the sodium ions in the surface layer sheet with those of the potassium.
Once the sheet of glass is taken out of the bath, the superficial layers will have a permanent pre-stressing state compensated by a traction tension in the inner layers.
This state of tension affords the glass mechanical characteristics of up to 2 and half times superior in comparison to the same glass with the thermal toughening process and up to 6 times the overlaid glass.
The chemical hardening process by its nature does not involve any kind of optical distortion and imprint on the treated glass; thanks to the perfect balance of the tension state, the birefringence effect (anisotropy) is also absent.
Chemically strengthened glass is not subject to spontaneous rupture by nickel sulphide inclusions and therefore does not require Heat Soak Test treatments.
Today, Viraver is the company which produces the biggest sheets of chemically toughened glass in the world: 8 m x 3,21.