Metallic Mirrors

Metal coated mirrors are mirrors (optical reflectors) based on a thin metal coating, produced with an evaporation or sputtering technique. The metallic coating is placed on a substrate, which is often consisting of a glass, or possibly also of a metal. Common metal coatings consist of aluminum, silver or gold; less common are copper, chrome and various nickel/chrome alloys.

Often, the metal layer is covered with a thin layer or multiple layers of a dielectric material such as amorphous SiO2(silica) or Si3N4(silicon nitride),which protects the coating against oxidation(tarnish) and scratches. Such protected coatings are definitely more abrasion-resistant than uncoated ones, but still they tend to be more sensitive than dielectric mirrors. This implies that greater care is required for cleaning of meta-coated optics. Also, metallic mirrors are more or lenss sensitive to humidity and corrosive gases.

Multilayer protection coatings can also be used to enhance the reflectivity(see below):

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