Glass, chrome and aluminum are the materials commonly used to create typical mirrors. Specialty mirrors are made from a slightly different type of glass and coated with other materials.
While glass is the major component of mirrors, it is actually a poor reflector. Since glass possesses the property of uniformity, especially when it is polished, it is an ideal material for mirrors. Furthermore, glass is transparent, rigid and malleable. Mirrors that must withstand extreme temperatures are made from glass composed of boron and silica.
Nearly one hundred years ago, silver was the most common metal coating, leading manufacturers to coin the term” silvering.” Before 1940, mercury was the most popular metallic coating for mirrors because it did not tarnish and spread evenly over the surface of glass. Eventually, manufacturers abandoned this practice due to the toxicity of this liquid. Today most mirrors are coated with chrome or aluminum.
Mirrors used for scientific purposes are often coated with other material, such as silicon nitrides and silicon oxides. These types of coatings serve as protective finishes on the metallic coatings as they are scratch resistant. They are also better reflectors than metallic coatings. Scientific mirrors are sometimes coated with gold and silver to reflect light of different wavelengths and produce a desired effect.
Shatter-resistant mirrors are made from an optically perfect acrylic sheet, which is protected on the back with a durable scratch-resistant coating and with clear polyethylene film on the front.