Tempered glass is the more popular but there are many uses for simple annealed glass. Tempered glass is valued for its safety and strength, but when neither of those factors is an issue, annealed glass is a good, less expensive choice.
Techniques for annealing and tempering glass have been around for centuries. But the first person to hold a patent for a process to temper glass was a chemist from Austria named Rudolph Seiden.
There are many applications for tempered glass. It is used commercially in glass doors that have no frames. The windows in the passenger sides of cars use tempered glass to increase safety.
Annealed glass can be used in many situations. If a window is in a low-traffic area where safety is not a concern, annealed glass may be the best option because it remains cheaper than tempered glass. But many states have adopted building codes where tempered glass is required. For instance, any glass window within three feet of an open door must be tempered.
When glass is annealed, it is slowly cooled to relieve any internal stresses. When not annealed, glass is more likely to crack when exposed to temperature chances. Unlike tempered glass, traditional annealed glass will break off into large, sharp shards when broken. This can pose obvious safety risks. Care should be taken when choosing locations to instal annealed glass.
Tempered glass is also called toughened glass. Unlike annealed glass, tempered glass breaks into small, square pieces when broken. This makes it less likely to lacerate a person that comes into contact with it. Tempered glass is one of the hardest types of glasses, several times harder than most others, including annealed glass. Creating tempered glass involves the use of chemicals and heat to give it its properties. These treatments balance the internal stress rating of the glass.
Tempered glass is more expensive than annealed glass because it has to go through more processes in its creation. Despite its shortcomings when compared with tempered glass, annealed glass is still widely used because of its low cost.