backsilvered

Backsilvered, also called second-surface, describes a mirror in which the reflective coating is applied to the rear surface of a transparent substrate, typically glass. The front surface remains clear, allowing light to pass through the glass, strike the back coating, and return through the glass to the observer.

Construction and materials: The reflective layer is usually a thin film of silver, sometimes with copper or other metals to improve adhesion, deposited by chemical silvering or vacuum deposition. After silvering, a protective layer—often a coating of copper, nickel, or paint—is applied to shield the silver from tarnish and mechanical damage.

Advantages and characteristics: Because the reflective surface is on the back, the coating is protected by the glass, making the mirror more resistant to scratches in certain environments. Backsilvered mirrors require the light to pass through the glass twice, which can slightly reduce brightness and may introduce minor optical effects compared with first-surface mirrors in some applications.

Applications and usage: Backsilvered mirrors are common in household mirrors and various window-mirror assemblies. They are also used in certain optical instruments where protection of the reflective layer is important or where viewing through the glass is desirable.

History: The technique of silvering glass for mirrors was developed in the 19th century and became widely adopted for consumer and scientific use, leading to the prevalent back-silvered mirror formats seen in many applications today.