Glassmaking starts by melting sand, soda ash and lime together in large furnaces at high temperatures. When the liquid cools, it becomes glass. If the surface becomes scratched, it may be possible to repair it.
Shallow surface scratches are easy to remedy. However, fixing deep scratches that have penetrated the glass surface is impossible. The glass would need to be returned to its liquid state which is not an option. New replacement glass must be fitted.
Australian Standards AS1288 2006 and AS 1288-94 require that safety glass must be installed in locations where accidents are known to occur at greater frequency. Outdoor and indoor glass, doors with glass side panels, bathroom shower screens and low-level glass must be fitted with safety glass due to risk of human impact. In these and other areas, safety glass is installed because it breaks safely on impact.
Toughened glass, sometimes referred to as tempered glass, is heated in a furnace and cooled quickly to harden it. Once the process is complete, the glass cannot be cut even using a diamond blade. However, it is possible to polish the glass surface to a depth of 3mm in the absence of cut outs.
The process of manufacturing toughened or tempered glass creates internal stresses to give the glass strength. Small internal defects resulting from impurities and external defects caused by microscopic scratches, chipping, expansion due to sunlight and other factors can make toughened glass fracture at any time.