Toughened glass
Toughened glass, also called tempered glass, is glass that has been heated and then cooled very quickly. This leaves the outer surface in compression and the core in tension, which makes the glass several times stronger than ordinary glass of the same thickness. If it does break, it crumbles into small, blunt pieces and not sharp shards.
Building regulations require safety glass in doors, side panels next to doors and low windows, so toughened or laminated glass is used in front doors and sidelights. Toughened glass cannot be cut, drilled or edge-worked after toughening, so every hole and shape must be finished first.
Decorative glass that must meet these rules is usually made on a toughened or laminated base, with the decoration bonded to the surface or encapsulated inside a sealed unit.