Normally, tempered glass has completely smooth edges due to the extra processing it goes through, while other types of glass usually have scuffed or ridged edges. If the edges of the glass are exposed, run your fingers along them. So you have to watch out for other clues. If you notice any warping, bending, or dimples on the glass, then it is most likely toughened glass.
These imperfections typically occur during the heating process. Because the glass undergoes extreme heat, the tongs used to handle it often leave a slight impression on the surface that you may be able to identify if you look closely enough.
Toughened glass or tempered glass is glass that has undergone processes of controlled thermal treatment to increase its strength. It is four times stronger than normal annealed glass. Due to the increased heat treatment and rapid cooling of the glass, the treatment produces different physical properties. This results in compressive stress on the surface and improved bending strength of glass. Before toughening, the glass must be cut to size or pressed to shape. Toughening does not alter the basic characteristics of glass like light transmission and solar radiant heat properties of normal glass.
It can neither be cut, nor altered. A safety glass, toughened glass is difficult to break but in the event of a breakage, disintegrates into small globules. However, it is prone to very rare spontaneous breakage, a condition that occurs when the repeated heating and cooling cause the nickel sulfide stones to increase in size. First, the glass is carried by rollers and goes through the furnace.
The glass is much stronger under compression as in order to break it, the compressive force must first be exceeded. So a toughened piece of glass is up to four times stronger than standard, annealed or float glass. The process also has the added benefit of forming the differential stress patterns within the glass.
Now when the glass breaks, it will shatter into lots of small, blunt pieces. So toughened glass is strong and safer to use in the windows and doors that are in vulnerable areas around your home. Once the glass has been fitted in a window, then toughened glass and normal float glass are indistinguishable. If you look for a quality mark, then that might give an indication of it the glass is toughened. For example, a British Standard Kitemark in one of the corners of the unit.
If no mark is present, there is really no visual way of checking that the glass is toughened without removing the glass unit. If you removed the unit, you could look to see if the edges are smooth.
The heat from sunlight can make glass expand and contract at inconsistent rates. This creates stress in the glass and can lead to breakage. But the risk of thermal damage can be prevented by using toughened glass. Toughened glass also has an excellent heat-withstanding capacity. Toughened glass is physically as well as thermally solid, and research shows that it can withstand surface compression of at least 10,lbs per square inch, which is why toughened glass is considered to be safety glass.
They are also known to be four to five times stronger than annealed glass and three times stronger than heat-strengthened glass. As these glasses are robust, they reduce the risk of damage if they come in contact with a calamity or disaster.
Toughened glass is manufactured when regular glass is exposed to extreme heat and then cooled rapidly. Due to this excessive heating and cooling process, the chemical composition of the glass goes through an alteration making it more resilient.
If toughened glass comes in contact with some harsh impact, instead of breaking into sharp, jagged shards, it breaks into harmless circular chunks. Thus, these glasses reduce the risk of injury. If toughened glass breaks, it is also more comfortable for you to clean them than the jagged shards of glass. The small chunks can easily be swept up by a broom and then thrown in the garbage without the fear of any jagged shards hurting anyone.
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