Mirrors

Mirrors are smooth, highly reflective surfaces that form images by reflection. Light follows the law of incidence equals reflection, with the image location and orientation depending on surface shape. Plane mirrors produce virtual, upright, same-size images behind the surface. Curved mirrors, either concave or convex, can magnify or reduce images and may form real images in front of the surface (concave) or only virtual images (convex).

Most modern mirrors are glass or plastic substrates coated on the back with a reflective metal such as aluminum or silver. The reflective layer is protected by paint or a clear polymer. Dielectric coatings are used for specialized optical performance. Historically, mirrors used silvering or tin backing; today aluminum dominates, especially for durability and cost.

Early mirrors were polished stones or metals. Glass mirrors with metal backing appeared in antiquity; the modern silvering process emerged in the 19th century, and aluminum coatings became standard in the 20th century.

Mirrors are used in grooming, interior design, and architecture, and play essential roles in optical instruments such as telescopes, cameras, periscopes, laser systems, and solar concentrators by directing and shaping light.