A metal mirror is a mirror with a thin metal coating, which can be made by evaporation or sputtering technology. As for the bottom, the metal coating is usually glass or metal. Common metallic coatings include aluminum, silver, or gold; Copper, chromium or other nichrome alloys are not commonly used.

The metal coating is usually coated with one or more thin layers of dielectric material, such as amorphous silicon dioxide (SiO2) or silicon nitride (Si3N4), which is used to protect the metal coating from oxidation or scratching. These protective coatings are more wear-resistant than uncoated ones and more sensitive than dielectric mirrors. The contact surface between metal and optical devices needs to be carefully cleaned. And metal mirrors are sensitive to humidity and corrosive gases.