The Saint-Gobain factory, founded by royal initiative in France, was an important manufacturer, and Bohemian and German glass, often rather cheaper, was also important. Glass mirrors from this period were extremely expensive luxuries. The exact date and location of the discovery is unknown, but in the 16th century, Venice, a city famed for its glass-making expertise, became a centre of mirror production using this new technique. Some time during the early Renaissance, European manufacturers perfected a superior method of coating glass with a tin-mercury amalgam
His process involved the deposition of a thin layer of metallic silver onto glass through the chemical reduction of silver nitrate. The invention of the silvered-glass mirror is credited to German chemist Justus von Liebig in 1835. Nowadays, mirrors are often produced by the vacuum deposition of aluminium directly onto the glass substrate. This silvering process was adapted for mass manufacturing and led to the greater availability of affordable mirrors
By the 11th century, clear glass mirrors were being produced in Moorish Spain. Ibn al-Haytham discussed concave and convex mirrors in both cylindrical and spherical geometries, described spherical and parabolic mirrors, carried out a number of experiments with mirrors, and solved the problem of finding the point on a convex mirror at which a ray coming from one point is reflected to another point. Refracting parabolic mirrors were first described by the Arabian physicist Ibn Sahl in the 10th century, and was later described again by Ibn al-Haytham in his famous Book of Optics
The substrate is shaped, polished and cleaned, and is then coated. Glass mirrors are most often coated with silver or aluminium, implemented by a series of coatings:
Mirrors are also used in scientific apparatus such as telescopes and lasers, cameras, and industrial machinery. Mirrors are most commonly used for personal grooming , decoration, and architecture. Most mirrors are designed for visible light; however, mirrors designed for other types of waves or other wavelengths of electromagnetic radiation are also used, especially in optical instruments
Spherical concave and convex mirrors do not focus parallel rays to a single point due to spherical aberration. Lastly, there are convex mirrors, where a parallel beam becomes divergent, with the rays appearing to diverge from a common intersection “behind” the mirror. Parabolic reflectors resolve this, allowing incoming parallel rays to be focused to a small spot; almost an ideal point. In a plane mirror, a parallel beam of light changes its direction as a whole, while still remaining parallel; the images formed by a plane mirror are virtual images, of the same size as the original object . There are also concave mirrors, where a parallel beam of light becomes a convergent beam, whose rays intersect in the focus of the mirror. Parabolic reflectors are not suitable for imaging nearby objects because the light rays are not parallel. However, the ideal of focusing to a point is a commonly-used approximation
A mirror is an object with a surface that has good specular reflection; that is, it is smooth enough to form an image. Curved mirrors are also used, to produce magnified or diminished images or focus light or simply distort the reflected image. The most familiar type of mirror is the plane mirror, which has a flat surface
In some applications, generally those that are cost-sensitive or that require great durability, mirrors are instead made from a single, bulk material such as polished metal
A beam of light reflects off a mirror at an angle of reflection that is equal to its angle of incidence . That is, if the beam of light is shining on a mirror’s surface at a 30° angle from vertical, then it reflects from the point of incidence at a 30° angle from vertical in the opposite direction
Most mirrors are made by applying a reflective coating to a suitable substrate. The most common such substrate is glass, due to its ease of fabrication, its rigidity, and its ability to take a smooth finish. The reflective coating is typically applied to the back surface of the glass, so that it is protected from corrosion and accidental damage.
In China, bronze mirrors were manufactured from around 2000 BC. Examples of obsidian mirrors found in Anatolia have been dated to around 6000 BC. The earliest manufactured mirrors were pieces of polished stone such as obsidian, a naturally occurring volcanic glass. Mirrors of polished copper were crafted in Mesopotamia from 4000 BC, and in ancient Egypt from around 3000 BC. Polished stone mirrors from central and south America date from around 2000 BC onwards
Copper is added for long-term durability. The tin is applied because the silver will not bond with the glass. The paint protects the coating on the back of the mirror from scratches and other accidental damage. The activator causes the tin/silver to harden
Metal-coated glass mirrors are said to have been invented in Sidon in the first century AD, and glass mirrors backed with gold leaf are mentioned by the Roman author Pliny in his Natural History, written in about 77 AD. The Romans also developed a technique for creating crude mirrors by coating blown glass with molten lead
This law mathematically follows from the interference of a plane wave on a flat boundary
This eliminates double reflections and reduces absorption of light in the mirror. Applications requiring higher reflectivity or greater durability use dielectric coatings, which can achieve reflectivities as high as 99. Cheaper technical mirrors use a silver, aluminium, or gold coating , and achieve reflectivities of 90–95% when new. 999% over a narrow range of wavelengths. A protective overcoat may be applied to prevent oxidation of the reflective layer. For technical applications such as laser mirrors, the reflective coating is typically applied by vacuum deposition on the front surface of the substrate