Tempered glass is one of the most common and safest types of glazing available. It is recommended for commercial and some residential settings, especially in wet areas such as bathrooms, showers and tub enclosures. It is also used for doors, patio doors and escalator and stairway balustrades. This type of glass shatters into small, rounded chunks rather than sharp jagged shards, making it safer for people to walk through.

Glass that has been tempered is also more durable, as it resists the deformation caused by direct impact and can take several blows before breaking. It is also more resistant to thermal stress, as it has been heated to high temperatures before cooling rapidly.

The process of tempering glass, also called toughening or heat-strengthening, takes only about a minute. It involves heating annealed glass in a special furnace to an extremely high temperature, then immediately cooling it through a quick process known as quenching. This causes the outer layer of the glass to become compressed while the inner core remains in tension, making it up to four times stronger than annealed glass.

After the glass is quenched, it must be cooled quickly and evenly to prevent distortion. This is accomplished by blasting it with cool air from a number of nozzles. This sudden change in temperature puts the glass into a state of compression, allowing it to absorb more energy without breaking. If the glass is not sufficiently cooled it may develop cracks and pitting on the surface. This is known as white haze, and while not dangerous, can detract from the appearance of your glass.

While tempered glass is very strong, it can still be damaged or broken by abuse during installation and use. During installation it is common for fasteners such as nails or screws to nick the edges of a piece of glass, creating concentrations of stresses around these defects. Over time, these stresses can build up to the point where the glass breaks. In most cases, this happens only in a short distance from the point of damage, but occasionally an entire sheet of glass can break due to these concentrated stresses.

Another problem with tempered glass occurs when small nickel sulfide inclusions are present in the glass. These can form as a result of the stainless steel machinery used in the manufacturing and handling processes. These tiny shards of nickel will change structure over time and grow until the internal stresses exceed the glass’ strength, leading to spontaneous breakage years after the glass was manufactured.

To prevent these types of problems, all cutting and edgework must be completed prior to the tempering process. GTI will process the glass with ground or polished edges, and offer a variety of decorative profiled edgework. Holes and notches can be tempered, however holes must be the same size as or bigger than the glass thickness, and a minimum diameter of 3/16” is required for 1/8” glass. The tolerances for hole dimensions are slightly different for different laminations, and can be discussed with a GTI sales representative.