Architectural glass light in industrial factories. Annealed glass is glass without internal stresses caused by heat treatment, i.e., rapid cooling, or by toughening or heat strengthening. Glass becomes annealed if it is heated above a transition point then allowed to cool slowly, without being quenched. Float glass is annealed during the process of manufacture. However, most toughened glass is made from float glass that has been specially heat-treated. Annealed glass breaks into large, jagged shards that can cause serious injury and is considered a hazard in architectural applications. Building codes in many parts of the world restrict the use of annealed glass
Heated glass 350 degrees Fahrenheit (177 degrees Celsius). The standard desirable temperature range in buildings is between 104 and 113 degrees Fahrenheit (40 to 44 degrees Celsius). For industrial purposes higher temperatures may be warranted. The first heated glass was created in 1931 by Protes Glass Company, offered for cars. Their product was not a success. Heated glass was first used on a wide scale in World War II to prevent aircraft windshields from frosting over in cold weather and high altitudes. It is still used in aviation for this purpose. Heated glass has been used in architectural applications for the past