A mirror is any smooth superficies which reflects more light rays than it absorbs.
The earliest mirrors were pieces of polished stone such as volcanic obsidian.
All mirrors absorb some light, but the more highly polished they are, the more they will reflect. Even a highly polished sheet of glass will act as a mirror, to an extent, although it allows most of the rays to pass through. The condition of being opaque and the smoothness of surface determine the quality of reflection.
Good mirrors are made of polished glass with a silvery back surface.
The angle between a light ray striking a mirror and the normal (perpendicular) to the mirror is the angle of incidence. The angle between the normal and the ray reflecting off the mirror is the angle of reflection. These two angles are always equal.
Mirrors are of 3 kinds: Plane, or flat, concave, and convex. A concave mirror is one whose surface is like the inside of a hollow ball. It will reflect a larger or smaller image depending on the object's distance from it. If the object is further away, the image will appear upside down. A convex mirror always shows an image smaller than the object. Concave mirrors are used in reflecting telescopes.
The most common kind of mirror is the plane mirror, which has a flat surface.
German chemist Justus von Liebig invented the silvered-glass mirror in 1835.
