mirror

A mirror is a smooth, highly reflective surface that forms images through specular reflection of light. When light encounters the surface, rays are reflected at angles equal to the angles at which they arrived, producing an image that for a plane mirror is upright, laterally inverted, and located behind the mirror at a distance equal to the object’s distance in front of it. The term can also apply to devices that use curved reflective surfaces to modify light paths.

Most everyday mirrors are plane mirrors made of glass with a reflective metal coating on the back, traditionally silver and more recently aluminum. The coating is protected by a layer of paint or epoxy. Front-surface mirrors place the reflective coating on the outer surface to avoid the faint ghosting that can occur with back coatings. Curved mirrors—concave and convex—alter image size and focus. Concave mirrors can form real images when objects are near the focal point and virtual images when farther away; convex mirrors always form diminished virtual images and are common in vehicle rear views for broad field visibility. Parabolic and other aspheric shapes are used in telescopes and lighting.

Historically, mirrors have evolved from polished metals and natural obsidian to glass mirrors with silvering in the early modern period, refinements in production spreading in the 17th century. Modern manufacturing includes protective coatings, anti-corrosion layers, and high-precision coatings for scientific and industrial use.

Culturally, mirrors appear as symbols of truth, self-knowledge, and reflection in myths, literature, and art. They also serve practical roles in grooming, architecture, optics, photography, and surveillance.