Tempered glass, which is single sheet security glass, was presented for the first time in 1933 under the name “Sekurit” by Glaswerke Herzogenrath close to Aix-la-Chapelle. We use tempered glass for many functional tables and almost all of our dining tables. Our table tops made of tempered glass are marked with a special signet on the edge.
In a thermal process, float glass panes are further processed after their production to become tempered glass. The panes are taken through a furnace that heats them to almost 620 °C. The glass is then rapidly cooled with forced drafts of air, so that the surface cools down quicker than the inner portion of the glass, which causes zones of different tension in the glass. These zones characterize tempered glass.
Except for the different tension zones, which might be seen according to the viewing angle, it is not possible to see the difference between tempered glass and normal glass. Small irregularities on the surface like craters, caster marks, pixel, and optical effects caused by the difference in refraction at the tension zones (veils, waves, streaks or rainbow effects) are typical for tempered glass. However, they have enhanced thermal resistance, high flexural strength and high resistance to shocks. Nonethe¬less, a stroke against the pane edge may lead to almost invisible damages, e.g. looking like an air bubble in the glass, or small conchoidal fractures at the edge. After some time, fine fissures may occur, starting from such damages, which can make the entire pane collapse. In general, this happens after some time and seemingly without a reason, as the damage which is the reason and source of this (if ever it was noticed) is not associated with the destruction of the glass pane. In some individual cases, the tempered glass panes may break spontaneously, mainly during the first year of having been produced, due to corroding nickel sulphide inclusions. If tempered glass breaks, it usually shatters into small fragments, partly interlocked cubes and therewith reduces the danger of getting injured.