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A mirror, also known as a looking glass, is an object that reflects an
image An image or picture is a visual representation. An image can be Two-dimensional space, two-dimensional, such as a drawing, painting, or photograph, or Three-dimensional space, three-dimensional, such as a carving or sculpture. Images may be di ...
. Light that bounces off a mirror forms an image of whatever is in front of it, which is then focused through the lens of the eye or a camera. Mirrors reverse the direction of light at an angle equal to its incidence. This allows the viewer to see themselves or objects behind them, or even objects that are at an angle from them but out of their field of view, such as around a corner. Natural mirrors have existed since
prehistoric Prehistory, also called pre-literary history, is the period of human history between the first known use of stone tools by hominins  million years ago and the beginning of recorded history with the invention of writing systems. The use o ...
times, such as the surface of water, but people have been manufacturing mirrors out of a variety of materials for thousands of years, like stone, metals, and glass. In modern mirrors, metals like
silver Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...
or
aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
are often used due to their high
reflectivity The reflectance of the surface of a material is its effectiveness in Reflection (physics), reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the respon ...
, applied as a thin coating on
glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...
because of its naturally smooth and very hard surface. A mirror is a
wave In physics, mathematics, engineering, and related fields, a wave is a propagating dynamic disturbance (change from List of types of equilibrium, equilibrium) of one or more quantities. ''Periodic waves'' oscillate repeatedly about an equilibrium ...
reflector.
Light Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...
consists of waves, and when light waves reflect from the flat surface of a mirror, those waves retain the same degree of curvature and
vergence A vergence is the simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision. When a creature with binocular vision looks at an object, the eyes must rotate around a vertical axis so that the proj ...
, in an equal yet opposite direction, as the original waves. This allows the waves to form an image when they are focused through a lens, just as if the waves had originated from the direction of the mirror. The light can also be pictured as rays (imaginary lines radiating from the light source, that are always perpendicular to the waves). These rays are reflected at an equal yet opposite angle from which they strike the mirror (incident light). This property, called
specular reflection Specular reflection, or regular reflection, is the mirror-like reflection (physics), reflection of waves, such as light, from a surface. The law of reflection states that a reflected ray (optics), ray of light emerges from the reflecting surf ...
, distinguishes a mirror from objects that diffuse light, breaking up the wave and scattering it in many directions (such as flat-white paint). Thus, a mirror can be any surface in which the texture or roughness of the surface is smaller (smoother) than the
wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
of the waves. When looking at a mirror, one will see a
mirror image A mirror image (in a plane mirror) is a reflection (physics), reflected duplication of an object that appears almost identical, but is reversed in the direction perpendicular to the mirror surface. As an optical phenomenon, optical effect, it r ...
or reflected image of objects in the environment, formed by light emitted or scattered by them and reflected by the mirror towards one's eyes. This effect gives the illusion that those objects are behind the mirror, or (sometimes) in front of it. When the surface is not flat, a mirror may behave like a reflecting
lens A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...
. A plane mirror yields a real-looking undistorted image, while a curved mirror may distort, magnify, or reduce the image in various ways, while keeping the lines, contrast, sharpness, colors, and other image properties intact. A mirror is commonly used for inspecting oneself, such as during
personal grooming Grooming (also called preening) is the art and practice of cleaning and maintaining parts of the body. It is a species-typical behavior. In animals Individual animals regularly clean themselves and put their fur, feathers or other skin c ...
; hence the old-fashioned name "looking glass". This use, which dates from prehistory, overlaps with uses in decoration and
architecture Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and construction, constructi ...
. Mirrors are also used to view other items that are not directly visible because of obstructions; examples include
rear-view mirror A rear-view mirror (or rearview mirror) is a, usually plane mirror, flat, mirror in automobiles and other vehicles, designed to allow the driver to see rearward through the vehicle's rear window (rear windshield). In cars, the rear-view mirror ...
s in vehicles, security mirrors in or around buildings, and dentist's mirrors. Mirrors are also used in optical and scientific apparatus such as
telescope A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...
s,
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...
s,
camera A camera is an instrument used to capture and store images and videos, either digitally via an electronic image sensor, or chemically via a light-sensitive material such as photographic film. As a pivotal technology in the fields of photograp ...
s,
periscope A periscope is an instrument for observation over, around or through an object, obstacle or condition that prevents direct line-of-sight observation from an observer's current position. In its simplest form, it consists of an outer case with ...
s, and industrial machinery. According to
superstition A superstition is any belief or practice considered by non-practitioners to be irrational or supernatural, attributed to fate or magic (supernatural), magic, perceived supernatural influence, or fear of that which is unknown. It is commonly app ...
s breaking a mirror is said to bring seven years of bad luck. The terms "mirror" and "reflector" can be used for objects that reflect any other types of waves. An acoustic mirror reflects sound waves. Objects such as walls, ceilings, or natural rock-formations may produce echos, and this tendency often becomes a problem in
acoustical engineering Acoustical engineering (also known as acoustic engineering) is the branch of engineering dealing with sound and vibration. It includes the application of acoustics, the science of sound and vibration, in technology. Acoustical engineers are typical ...
when designing houses, auditoriums, or recording studios. Acoustic mirrors may be used for applications such as parabolic microphones, atmospheric studies, sonar, and
seafloor mapping The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as seabeds. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...
. An atomic mirror reflects matter waves and can be used for atomic
interferometry Interferometry is a technique which uses the ''interference (wave propagation), interference'' of Superposition principle, superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important inves ...
and atomic
holography Holography is a technique that allows a wavefront to be recorded and later reconstructed. It is best known as a method of generating three-dimensional images, and has a wide range of other uses, including data storage, microscopy, and interfe ...
.


History


Prehistory

The first mirrors used by humans were most likely pools of still water, or shiny stones. The requirements for making a good mirror are a surface with a very high degree of flatness (preferably but not necessarily with high
reflectivity The reflectance of the surface of a material is its effectiveness in Reflection (physics), reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the respon ...
), and a surface roughness smaller than the wavelength of the light. The earliest manufactured mirrors were pieces of polished stone such as
obsidian Obsidian ( ) is a naturally occurring volcanic glass formed when lava extrusive rock, extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. Produced from felsic lava, obsidian is rich in the lighter element ...
, a naturally occurring volcanic glass. Examples of obsidian mirrors found at Çatalhöyük in
Anatolia Anatolia (), also known as Asia Minor, is a peninsula in West Asia that makes up the majority of the land area of Turkey. It is the westernmost protrusion of Asia and is geographically bounded by the Mediterranean Sea to the south, the Aegean ...
(modern-day Turkey) have been dated to around 6000 BCE. Mirrors of polished copper were crafted in
Mesopotamia Mesopotamia is a historical region of West Asia situated within the Tigris–Euphrates river system, in the northern part of the Fertile Crescent. Today, Mesopotamia is known as present-day Iraq and forms the eastern geographic boundary of ...
from 4000 BCE, and in ancient Egypt from around 3000 BCE. Polished stone mirrors from Central and South America date from around 2000 BCE onwards.


Bronze Age to Early Middle Ages

By the
Bronze Age The Bronze Age () was a historical period characterised principally by the use of bronze tools and the development of complex urban societies, as well as the adoption of writing in some areas. The Bronze Age is the middle principal period of ...
most cultures were using mirrors made from polished discs of
bronze Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals (such as phosphorus) or metalloid ...
,
copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
,
silver Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...
, or other metals. The people of Kerma in
Nubia Nubia (, Nobiin language, Nobiin: , ) is a region along the Nile river encompassing the area between the confluence of the Blue Nile, Blue and White Nile, White Niles (in Khartoum in central Sudan), and the Cataracts of the Nile, first cataract ...
were skilled in the manufacturing of mirrors. Remains of their bronze
kiln A kiln is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or Chemical Changes, chemical changes. Kilns have been used for millennia to turn objects m ...
s have been found within the temple of Kerma. In China, bronze mirrors were manufactured from around 2000 BC, some of the earliest bronze and copper examples being produced by the Qijia culture. Such metal mirrors remained the norm through to Greco-Roman Antiquity and throughout the
Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the 5th to the late 15th centuries, similarly to the post-classical period of global history. It began with the fall of the Western Roman Empire and ...
in
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
. During the
Roman Empire The Roman Empire ruled the Mediterranean and much of Europe, Western Asia and North Africa. The Roman people, Romans conquered most of this during the Roman Republic, Republic, and it was ruled by emperors following Octavian's assumption of ...
silver mirrors were in wide use by servants. Speculum metal is a highly reflective
alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...
of copper and tin that was used for mirrors until a couple of centuries ago. Such mirrors may have originated in China and India. Mirrors of speculum metal or any precious metal were hard to produce and were only owned by the wealthy. Common metal mirrors tarnished and required frequent polishing. Bronze mirrors had low reflectivity and poor
color rendering The color rendering of a light source refers to its ability to reveal the colors of various objects faithfully (i.e. to produce Metamerism (color), illuminant metamerism) in comparison with an ideal or natural light source. Light sources with good ...
, and stone mirrors were much worse in this regard. These defects explain the
New Testament The New Testament (NT) is the second division of the Christian biblical canon. It discusses the teachings and person of Jesus in Christianity, Jesus, as well as events relating to Christianity in the 1st century, first-century Christianit ...
reference in 1 Corinthians 13 to seeing "as in a mirror, darkly." The Greek
philosopher Philosophy ('love of wisdom' in Ancient Greek) is a systematic study of general and fundamental questions concerning topics like existence, reason, knowledge, Value (ethics and social sciences), value, mind, and language. It is a rational an ...
Socrates Socrates (; ; – 399 BC) was a Ancient Greek philosophy, Greek philosopher from Classical Athens, Athens who is credited as the founder of Western philosophy and as among the first moral philosophers of the Ethics, ethical tradition ...
urged young people to look at themselves in mirrors so that, if they were beautiful, they would become worthy of their beauty, and if they were ugly, they would know how to hide their disgrace through learning.
Glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...
began to be used for mirrors in the 1st century CE, with the development of soda-lime glass and glass blowing. The Roman scholar
Pliny the Elder Gaius Plinius Secundus (AD 23/24 79), known in English as Pliny the Elder ( ), was a Roman Empire, Roman author, Natural history, naturalist, and naval and army commander of the early Roman Empire, and a friend of the Roman emperor, emperor Vesp ...
claims that artisans in
Sidon Sidon ( ) or better known as Saida ( ; ) is the third-largest city in Lebanon. It is located on the Mediterranean Sea, Mediterranean coast in the South Governorate, Lebanon, South Governorate, of which it is the capital. Tyre, Lebanon, Tyre, t ...
(modern-day
Lebanon Lebanon, officially the Republic of Lebanon, is a country in the Levant region of West Asia. Situated at the crossroads of the Mediterranean Basin and the Arabian Peninsula, it is bordered by Syria to the north and east, Israel to the south ...
) were producing glass mirrors coated with
lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...
or gold leaf in the back. The metal provided good reflectivity, and the glass provided a smooth surface and protected the metal from scratches and tarnishing. However, there is no archeological evidence of glass mirrors before the third century. These early glass mirrors were made by blowing a glass bubble, and then cutting off a small circular section from 10 to 20 cm in diameter. Their surface was either concave or convex, and imperfections tended to distort the image. Lead-coated mirrors were very thin to prevent cracking by the heat of the molten metal. Due to the poor quality, high cost, and small size of glass mirrors, solid-metal mirrors (primarily of steel) remained in common use until the late nineteenth century. Silver-coated metal mirrors were developed in China as early as 500 CE. The bare metal was coated with an amalgam, then heated until the mercury boiled away.


Middle Ages and Renaissance

The evolution of glass mirrors in the
Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the 5th to the late 15th centuries, similarly to the post-classical period of global history. It began with the fall of the Western Roman Empire and ...
followed improvements in glassmaking technology. Glassmakers in
France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
made flat glass plates by blowing glass bubbles, spinning them rapidly to flatten them, and cutting rectangles out of them. A better method, developed in
Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...
and perfected in
Venice Venice ( ; ; , formerly ) is a city in northeastern Italy and the capital of the Veneto Regions of Italy, region. It is built on a group of 118 islands that are separated by expanses of open water and by canals; portions of the city are li ...
by the 16th century, was to blow a cylinder of glass, cut off the ends, slice it along its length, and unroll it onto a flat hot plate. Venetian glassmakers also adopted
lead glass Lead glass, commonly called crystal, is a variety of glass in which lead replaces the calcium content of a typical potash glass. Lead glass contains typically 18–40% (by mass) lead(II) oxide (PbO), while modern lead crystal, historically a ...
for mirrors, because of its crystal-clarity and its easier workability. During the early European
Renaissance The Renaissance ( , ) is a Periodization, period of history and a European cultural movement covering the 15th and 16th centuries. It marked the transition from the Middle Ages to modernity and was characterized by an effort to revive and sur ...
, a fire-gilding technique developed to produce an even and highly reflective tin coating for glass mirrors. The back of the glass was coated with a tin-mercury amalgam, and the mercury was then evaporated by heating the piece. This process caused less
thermal shock Thermal shock is a phenomenon characterized by a rapid change in temperature that results in a transient mechanical load on an object. The load is caused by the differential expansion of different parts of the object due to the temperature chang ...
to the glass than the older molten-lead method. The date and location of the discovery is unknown, but by the 16th century Venice was a center of mirror production using this technique. These Venetian mirrors were up to square. For a century, Venice retained the monopoly of the tin amalgam technique. Venetian mirrors in richly decorated frames served as luxury decorations for palaces throughout Europe, and were very expensive. For example, in the late seventeenth century, the Countess de Fiesque was reported to have traded an entire wheat farm for a mirror, considering it a bargain. However, by the end of that century the secret was leaked through industrial espionage. French workshops succeeded in large-scale industrialization of the process, eventually making mirrors affordable to the masses, in spite of the
toxicity Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacteria, bacterium, or plant, as well as the effect o ...
of mercury's vapor.


Industrial Revolution

The invention of the ribbon machine in the late
Industrial Revolution The Industrial Revolution, sometimes divided into the First Industrial Revolution and Second Industrial Revolution, was a transitional period of the global economy toward more widespread, efficient and stable manufacturing processes, succee ...
allowed modern glass panes to be produced in bulk. The Saint-Gobain factory, founded by royal initiative in France, was an important manufacturer, and
Bohemia Bohemia ( ; ; ) is the westernmost and largest historical region of the Czech Republic. In a narrow, geographic sense, it roughly encompasses the territories of present-day Czechia that fall within the Elbe River's drainage basin, but historic ...
n and German glass, often rather cheaper, was also important. The invention of the silvered-glass mirror is credited to German chemist
Justus von Liebig Justus ''Freiherr'' von Liebig (12 May 1803 – 18 April 1873) was a Germans, German scientist who made major contributions to the theory, practice, and pedagogy of chemistry, as well as to agricultural and biology, biological chemistry; he is ...
in 1835. His wet deposition process involved the deposition of a thin layer of metallic silver onto glass through the chemical reduction of silver nitrate. This silvering process was adapted for mass manufacturing and led to the greater availability of affordable mirrors.


Contemporary technologies

Mirrors are often produced by the wet deposition of silver, or sometimes nickel or chromium (the latter used most often in automotive mirrors) via
electroplating Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal coating on a solid substrate through the redox, reduction of cations of that metal by means of a direct current, direct electric cur ...
directly onto the glass substrate. Glass mirrors for optical instruments are usually produced by vacuum deposition methods. These techniques can be traced to observations in the 1920s and 1930s that metal was being ejected from
electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...
s in gas discharge lamps and condensed on the glass walls forming a mirror-like coating. The phenomenon, called sputtering, was developed into an industrial metal-coating method with the development of
semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...
technology in the 1970s. A similar phenomenon had been observed with incandescent light bulbs: the metal in the hot filament would slowly sublimate and condense on the bulb's walls. This phenomenon was developed into the method of evaporation coating by Pohl and Pringsheim in 1912. John D. Strong used evaporation coating to make the first
aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
-coated telescope mirrors in the 1930s. The first
dielectric mirror A dielectric mirror, also known as a Bragg mirror, is a type of mirror composed of multiple thin film, thin layers of dielectric material, typically deposited on a substrate of glass or some other optical material. By careful choice of the type a ...
was created in 1937 by Auwarter using evaporated
rhodium Rhodium is a chemical element; it has symbol Rh and atomic number 45. It is a very rare, silvery-white, hard, corrosion-resistant transition metal. It is a noble metal and a member of the platinum group. It has only one naturally occurring isot ...
. The metal coating of glass mirrors is usually protected from abrasion and corrosion by a layer of paint applied over it. Mirrors for optical instruments often have the metal layer on the front face, so that the light does not have to cross the glass twice. In these mirrors, the metal may be protected by a thin transparent coating of a non-metallic (
dielectric In electromagnetism, a dielectric (or dielectric medium) is an Insulator (electricity), electrical insulator that can be Polarisability, polarised by an applied electric field. When a dielectric material is placed in an electric field, electric ...
) material. The first metallic mirror to be enhanced with a dielectric coating of
silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...
was created by Hass in 1937. In 1939 at the Schott Glass company, Walter Geffcken invented the first dielectric mirrors to use multilayer coatings.


Burning mirrors

The Greek in
Classical Antiquity Classical antiquity, also known as the classical era, classical period, classical age, or simply antiquity, is the period of cultural History of Europe, European history between the 8th century BC and the 5th century AD comprising the inter ...
were familiar with the use of mirrors to concentrate light. Parabolic mirrors were described and studied by the mathematician Diocles in his work ''On Burning Mirrors''.
Ptolemy Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...
conducted a number of experiments with curved polished iron mirrors, and discussed plane, convex spherical, and concave spherical mirrors in his ''Optics''. Parabolic mirrors were also described by the
Caliphate A caliphate ( ) is an institution or public office under the leadership of an Islamic steward with Khalifa, the title of caliph (; , ), a person considered a political–religious successor to the Islamic prophet Muhammad and a leader of ...
mathematician Ibn Sahl in the tenth century.


Types of mirrors

Mirrors can be classified in many ways; including by shape, support, reflective materials, manufacturing methods, and intended application.


By shape

Typical mirror shapes are planar and curved mirrors. The surface of curved mirrors is often a part of a
sphere A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...
. Mirrors that are meant to precisely concentrate parallel rays of light into a point are usually made in the shape of a
paraboloid of revolution In geometry, a paraboloid is a quadric surface that has exactly one axial symmetry, axis of symmetry and no central symmetry, center of symmetry. The term "paraboloid" is derived from parabola, which refers to a conic section that has a similar p ...
instead; they are used in telescopes (from radio waves to X-rays), in antennas to communicate with broadcast satellites, and in
solar furnace A solar furnace is a structure that uses concentrated solar power to produce high temperatures, usually for industry. Parabolic mirrors or heliostats concentrate light ( Insolation) onto a focal point. The temperature at the focal point may ...
s. A segmented mirror, consisting of multiple flat or curved mirrors, properly placed and oriented, may be used instead. Mirrors that are intended to concentrate sunlight onto a long pipe may be a circular cylinder or of a parabolic cylinder.


By structural material

The most common structural material for mirrors is glass, due to its transparency, ease of fabrication, rigidity, hardness, and ability to take a smooth finish.


Back-silvered mirrors

The most common mirrors consist of a plate of transparent glass, with a thin reflective layer on the back (the side opposite to the incident and reflected light) backed by a coating that protects that layer against abrasion, tarnishing, and
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
. The glass is usually soda-lime glass, but lead glass may be used for decorative effects, and other transparent materials may be used for specific applications. A plate of transparent
plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...
may be used instead of glass, for lighter weight or impact resistance. Alternatively, a flexible transparent plastic film may be bonded to the front and/or back surface of the mirror, to prevent injuries in case the mirror is broken. Lettering or decorative designs may be printed on the front face of the glass, or formed on the reflective layer. The front surface may have an anti-reflection coating.


Front-silvered mirrors

Mirrors which are reflective on the front surface (the same side of the incident and reflected light) may be made of any rigid material. The supporting material does not necessarily need to be transparent, but telescope mirrors often use glass anyway. Often a protective transparent coating is added on top of the reflecting layer, to protect it against abrasion, tarnishing, and corrosion, or to absorb certain wavelengths.


Flexible mirrors

Thin flexible plastic mirrors are sometimes used for safety, since they cannot shatter or produce sharp flakes. Their flatness is achieved by stretching them on a rigid frame. These usually consist of a layer of evaporated aluminium between two thin layers of transparent plastic.


By reflective material

In common mirrors, the reflective layer is usually some metal like silver, tin,
nickel Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...
, or
chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...
, deposited by a wet process; or aluminium, deposited by sputtering or evaporation in vacuum. The reflective layer may also be made of one or more layers of transparent materials with suitable indices of refraction. The structural material may be a metal, in which case the reflecting layer may be just the surface of the same. Metal concave dishes are often used to reflect infrared light (such as in space heaters) or
microwave Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...
s (as in satellite TV antennas). Liquid metal telescopes use a surface of liquid metal such as mercury. Mirrors that reflect only part of the light, while transmitting some of the rest, can be made with very thin metal layers or suitable combinations of dielectric layers. They are typically used as beamsplitters. A dichroic mirror, in particular, has surface that reflects certain wavelengths of light, while letting other wavelengths pass through. A cold mirror is a dichroic mirror that efficiently reflects the entire visible light spectrum while transmitting
infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
wavelengths. A hot mirror is the opposite: it reflects infrared light while transmitting visible light. Dichroic mirrors are often used as filters to remove undesired components of the light in cameras and measuring instruments. In X-ray telescopes, the
X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
s reflect off a highly precise metal surface at almost grazing angles, and only a small fraction of the rays are reflected. In flying relativistic mirrors conceived for X-ray lasers, the reflecting surface is a spherical shockwave (wake wave) created in a low-density plasma by a very intense laser-pulse, and moving at an extremely high velocity.


Nonlinear optical mirrors

A phase-conjugating mirror uses
nonlinear optics Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in Nonlinearity, nonlinear media, that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity ...
to reverse the phase difference between incident beams. Such mirrors may be used, for example, for coherent beam combination. The useful applications are self-guiding of laser beams and correction of atmospheric distortions in imaging systems.


Physical principles

When a sufficiently narrow beam of light is reflected at a point of a surface, the surface's normal direction \vec n will be the bisector of the angle formed by the two beams at that point. That is, the direction vector \vec u towards the incident beams's source, the normal vector \vec n, and direction vector \vec v of the reflected beam will be coplanar, and the angle between \vec n and \vec v will be equal to the angle of incidence between \vec n and \vec u, but of opposite sign. This property can be explained by the physics of an
electromagnetic In physics, electromagnetism is an interaction that occurs between particles with electric charge via electromagnetic fields. The electromagnetic force is one of the four fundamental forces of nature. It is the dominant force in the interacti ...
plane wave that is incident to a flat surface that is
electrically conductive Electrical resistivity (also called volume resistivity or specific electrical resistance) is a fundamental specific property of a material that measures its electrical resistance or how strongly it resists electric current. A low resistivity in ...
or where the
speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant exactly equal to ). It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time i ...
changes abruptly, as between two materials with different indices of refraction. * When parallel beams of light are reflected on a plane surface, the reflected rays will be parallel too. * If the reflecting surface is concave, the reflected beams will be convergent, at least to some extent and for some distance from the surface. * A convex mirror, on the other hand, will reflect parallel rays towards divergent directions. More specifically, a concave parabolic mirror (whose surface is a part of a paraboloid of revolution) will reflect rays that are parallel to its
axis An axis (: axes) may refer to: Mathematics *A specific line (often a directed line) that plays an important role in some contexts. In particular: ** Coordinate axis of a coordinate system *** ''x''-axis, ''y''-axis, ''z''-axis, common names ...
into rays that pass through its focus. Conversely, a parabolic concave mirror will reflect any ray that comes from its focus towards a direction parallel to its axis. If a concave mirror surface is a part of a prolate ellipsoid, it will reflect any ray coming from one focus toward the other focus. A convex parabolic mirror, on the other hand, will reflect rays that are parallel to its axis into rays that seem to emanate from the focus of the surface, behind the mirror. Conversely, it will reflect incoming rays that converge toward that point into rays that are parallel to the axis. A convex mirror that is part of a prolate ellipsoid will reflect rays that converge towards one focus into divergent rays that seem to emanate from the other focus. Spherical mirrors do not reflect parallel rays to rays that converge to or diverge from a single point, or vice versa, due to spherical aberration. However, a spherical mirror whose diameter is sufficiently small compared to the sphere's radius will behave very similarly to a parabolic mirror whose axis goes through the mirror's center and the center of that sphere; so that spherical mirrors can substitute for parabolic ones in many applications. A similar aberration occurs with parabolic mirrors when the incident rays are parallel among themselves but not parallel to the mirror's axis, or are divergent from a point that is not the focus – as when trying to form an image of an object that is near the mirror or spans a wide angle as seen from it. However, this aberration can be sufficiently small if the object image is sufficiently far from the mirror and spans a sufficiently small angle around its axis.


Mirror images

Mirrors reflect an image to the observer. However, unlike a projected image on a screen, an image does not actually exist on the surface of the mirror. For example, when two people look at each other in a mirror, both see different images on the same surface. When the light waves converge through the lens of the eye they interfere with each other to form the image on the surface of the
retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...
, and since both viewers see waves coming from different directions, each sees a different image in the same mirror. Thus, the images observed in a mirror depend upon the angle of the mirror with respect to the eye. The angle between the object and the observer is always twice the angle between the eye and the normal, or the direction perpendicular to the surface. This allows animals with
binocular vision Binocular vision is seeing with two eyes. The Field_of_view, field of view that can be surveyed with two eyes is greater than with one eye. To the extent that the visual fields of the two eyes overlap, #Depth, binocular depth can be perceived. Th ...
to see the reflected image with
depth perception Depth perception is the ability to perceive distance to objects in the world using the visual system and visual perception. It is a major factor in perceiving the world in three dimensions. Depth sensation is the corresponding term for non-hum ...
and in three dimensions. The mirror forms a ''virtual image'' of whatever is in the opposite angle from the viewer, meaning that objects in the image appear to exist in a direct line of sight—behind the surface of the mirror—at an equal distance from their position in front of the mirror. Objects behind the observer, or between the observer and the mirror, are reflected back to the observer without any actual change in orientation; the light waves are simply reversed in a direction perpendicular to the mirror. However, when viewer is facing the object and the mirror is at an angle between them, the image appears inverted 180° along the direction of the angle.''Mastering Physics for ITT-JEE, Volume 2'' By S. Chand & Co. 2012 Er. Rakesh Rathi Page 273--276 Objects viewed in a (plane) mirror will appear laterally inverted (e.g., if one raises one's right hand, the image's left hand will appear to go up in the mirror), but not vertically inverted (in the image a person's head still appears above their body). However, a mirror does not actually "swap" left and right any more than it swaps top and bottom. A mirror swaps front and back. To be precise, it reverses the object in the direction perpendicular to the mirror surface (the normal), turning the three dimensional image inside out (the way a glove stripped off the hand can be turned inside out, turning a left-hand glove into a right-hand glove or vice versa). When a person raises their left hand, the actual left hand raises in the mirror, but gives the illusion of a right hand raising because the imaginary person in the mirror is literally inside-out, hand and all. If the person stands side-on to a mirror, the mirror really does reverse left and right hands, that is, objects that are physically closer to the mirror always appear closer in the virtual image, and objects farther from the surface always appear symmetrically farther away regardless of angle. Looking at an image of oneself with the front-back axis flipped results in the perception of an image with its left-right axis flipped. When reflected in the mirror, a person's right hand remains directly opposite their real right hand, but it is perceived by the mind as the left hand in the image. When a person looks into a mirror, the image is actually front-back reversed (inside-out), which is an effect similar to the hollow-mask illusion. Notice that a mirror image is fundamentally different from the object (inside-out) and cannot be reproduced by simply rotating the object. An object and its mirror image are said to be
chiral Chirality () is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek language, Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is dist ...
. For things that may be considered as two-dimensional objects (like text), front-back reversal cannot usually explain the observed reversal. An image is a two-dimensional representation of a three-dimensional space, and because it exists in a two-dimensional plane, an image can be viewed from front or back. In the same way that text on a piece of paper appears reversed if held up to a light and viewed from behind, text held facing a mirror will appear reversed, because the image of the text is still facing away from the observer. Another way to understand the reversals observed in images of objects that are effectively two-dimensional is that the inversion of left and right in a mirror is due to the way human beings perceive their surroundings. A person's reflection in a mirror appears to be a real person facing them, but for that person to really face themselves (i.e.: twins) one would have to physically turn and face the other, causing an actual swapping of right and left. A mirror causes an illusion of left-right reversal because left and right were ''not'' swapped when the image appears to have turned around to face the viewer. The viewer's egocentric navigation (left and right with respect to the observer's point of view; i.e.: "my left...") is unconsciously replaced with their allocentric navigation (left and right as it relates another's point of view; "...your right") when processing the virtual image of the apparent person behind the mirror. Likewise, text viewed in a mirror would have to be physically turned around, facing the observer and away from the surface, actually swapping left and right, to be read in the mirror.


Optical properties


Reflectivity

The reflectivity of a mirror is determined by the percentage of reflected light per the total of the incident light. The reflectivity may vary with wavelength. All or a portion of the light not reflected is absorbed by the mirror, while in some cases a portion may also transmit through. Although some small portion of the light will be absorbed by the coating, the reflectivity is usually higher for first-surface mirrors, eliminating both reflection and absorption losses from the substrate. The reflectivity is often determined by the type and thickness of the coating. When the thickness of the coating is sufficient to prevent transmission, all of the losses occur due to absorption. Aluminium is harder and more resistant to tarnishing than silver, and will reflect 85 to 90% of the light in the visible to near-ultraviolet range, but experiences a drop in its reflectance between 800 and 900 nm. Gold is very soft and easily scratched, but does not tarnish. Gold is greater than 96% reflective to near and far-infrared light between 800 and 12000 nm, but poorly reflects visible light with wavelengths shorter than 600 nm (yellow). Silver is expensive, soft, and quickly tarnishes, but has the highest reflectivity in the visual to near-infrared of any metal. Silver can reflect up to 98 or 99% of light to wavelengths as long as 2000 nm, but loses nearly all reflectivity at wavelengths shorter than 350 nm. Dielectric mirrors can reflect greater than 99.99% of light, but only for a narrow range of wavelengths, ranging from a bandwidth of only 10 nm to as wide as 100 nm for
tunable laser A tunable laser is a laser whose wavelength of operation can be altered in a controlled manner. While all active laser medium, laser gain media allow small shifts in output wavelength, only a few types of lasers allow continuous tuning over a sign ...
s. However, dielectric coatings can also enhance the reflectivity of metallic coatings and protect them from scratching or tarnishing. Dielectric materials are typically very hard and relatively cheap, however the number of coats needed generally makes it an expensive process. In mirrors with low tolerances, the coating thickness may be reduced to save cost, and simply covered with paint to absorb transmission.


Surface quality

Surface quality, or surface accuracy, measures the deviations from a perfect, ideal surface shape. Increasing the surface quality reduces distortion, artifacts, and aberration in images, and helps increase coherence, collimation, and reduce unwanted
divergence In vector calculus, divergence is a vector operator that operates on a vector field, producing a scalar field giving the rate that the vector field alters the volume in an infinitesimal neighborhood of each point. (In 2D this "volume" refers to ...
in beams. For plane mirrors, this is often described in terms of flatness, while other surface shapes are compared to an ideal shape. The surface quality is typically measured with items like
interferometer Interferometry is a technique which uses the '' interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...
s or optical flats, and are usually measured in wavelengths of light (λ). These deviations can be much larger or much smaller than the surface roughness. A normal household-mirror made with float glass may have flatness tolerances as low as 9–14λ per inch (25.4 mm), equating to a deviation of 5600 through 8800 nanometers from perfect flatness. Precision ground and polished mirrors intended for lasers or telescopes may have tolerances as high as λ/50 (1/50 of the wavelength of the light, or around 12 nm) across the entire surface. The surface quality can be affected by factors such as temperature changes, internal stress in the substrate, or even bending effects that occur when combining materials with different coefficients of
thermal expansion Thermal expansion is the tendency of matter to increase in length, area, or volume, changing its size and density, in response to an increase in temperature (usually excluding phase transitions). Substances usually contract with decreasing temp ...
, similar to a bimetallic strip.


Surface roughness

Surface roughness describes the texture of the surface, often in terms of the depth of the microscopic scratches left by the polishing operations. Surface roughness determines how much of the reflection is specular and how much diffuses, controlling how clear or cloudy the image will be. For perfectly specular reflection, the surface roughness must be kept smaller than the wavelength of the light. Microwaves, which sometimes have a wavelength greater than an inch (~25 mm) can reflect specularly off a metal screen-door, continental ice-sheets, or desert sand, while visible light, having wavelengths of only a few hundred nanometers (a few hundred-thousandths of an inch), must meet a very smooth surface to produce specular reflection. For wavelengths that are approaching or are even shorter than the diameter of the atoms, such as
X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
s, specular reflection can only be produced by surfaces that are at a grazing incidence from the rays. Surface roughness is typically measured in microns, wavelength, or grit size, with ~80,000–100,000 grit or ~½λ–¼λ being "optical quality".


Transmissivity

Transmissivity is determined by the percentage of light transmitted per the incident light. Transmissivity is usually the same from both first and second surfaces. The combined transmitted and reflected light, subtracted from the incident light, measures the amount absorbed by both the coating and substrate. For transmissive mirrors, such as one-way mirrors,
beam splitter A beam splitter or beamsplitter is an optical instrument, optical device that splits a beam of light into a transmitted and a reflected beam. It is a crucial part of many optical experimental and measurement systems, such as Interferometry, int ...
s, or laser output couplers, the transmissivity of the mirror is an important consideration. The transmissivity of metallic coatings are often determined by their thickness. For precision beam-splitters or output couplers, the thickness of the coating must be kept at very high tolerances to transmit the proper amount of light. For dielectric mirrors, the thickness of the coat must always be kept to high tolerances, but it is often more the number of individual coats that determine the transmissivity. For the substrate, the material used must also have good transmissivity to the chosen wavelengths. Glass is a suitable substrate for most visible-light applications, but other substrates such as zinc selenide or synthetic sapphire may be used for infrared or ultraviolet wavelengths.


Wedge

Wedge errors are caused by the deviation of the surfaces from perfect parallelism. An optical wedge is the angle formed between two plane-surfaces (or between the principle planes of curved surfaces) due to manufacturing errors or limitations, causing one edge of the mirror to be slightly thicker than the other. Nearly all mirrors and optics with parallel faces have some slight degree of wedge, which is usually measured in
seconds The second (symbol: s) is a unit of time derived from the division of the day first into 24 hours, then to 60 minutes, and finally to 60 seconds each (24 × 60 × 60 = 86400). The current and formal definition in the International System of ...
or minutes of arc. For first-surface mirrors, wedges can introduce alignment deviations in mounting hardware. For second-surface or transmissive mirrors, wedges can have a prismatic effect on the light, deviating its trajectory or, to a very slight degree, its color, causing chromatic and other forms of aberration. In some instances, a slight wedge is desirable, such as in certain laser systems where stray reflections from the uncoated surface are better dispersed than reflected back through the medium.


Surface defects

Surface defects are small-scale, discontinuous imperfections in the surface smoothness. Surface defects are larger (in some cases much larger) than the surface roughness, but only affect small, localized portions of the entire surface. These are typically found as scratches, digs, pits (often from bubbles in the glass), sleeks (scratches from prior, larger grit polishing operations that were not fully removed by subsequent polishing grits), edge chips, or blemishes in the coating. These defects are often an unavoidable side-effect of manufacturing limitations, both in cost and machine precision. If kept low enough, in most applications these defects will rarely have any adverse effect, unless the surface is located at an image plane where they will show up directly. For applications that require extremely low scattering of light, extremely high reflectance, or low absorption due to high energy levels that could destroy the mirror, such as lasers or Fabry-Perot interferometers, the surface defects must be kept to a minimum.


Manufacturing

Mirrors are usually manufactured by either polishing a naturally reflective material, such as speculum metal, or by applying a reflective coating to a suitable polished substrate. In some applications, generally those that are cost-sensitive or that require great durability, such as for mounting in a prison cell, mirrors may be made from a single, bulk material such as polished metal. However, metals consist of small crystals (grains) separated by grain boundaries that may prevent the surface from attaining optical smoothness and uniform reflectivity.


Coating


Silvering

The coating of glass with a reflective layer of a metal is generally called " silvering", even though the metal may not be silver. Currently the main processes are
electroplating Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal coating on a solid substrate through the redox, reduction of cations of that metal by means of a direct current, direct electric cur ...
, "wet" chemical deposition, and vacuum deposition. Front-coated metal mirrors achieve reflectivities of 90–95% when new.


Dielectric coating

Applications requiring higher reflectivity or greater durability, where wide bandwidth is not essential, use dielectric coatings, which can achieve reflectivities as high as 99.997% over a limited range of wavelengths. Because they are often chemically stable and do not conduct electricity, dielectric coatings are almost always applied by methods of vacuum deposition, and most commonly by evaporation deposition. Because the coatings are usually transparent, absorption losses are negligible. Unlike with metals, the reflectivity of the individual dielectric-coatings is a function of
Snell's law Snell's law (also known as the Snell–Descartes law, the ibn-Sahl law, and the law of refraction) is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing th ...
known as the
Fresnel equations The Fresnel equations (or Fresnel coefficients) describe the reflection and transmission of light (or electromagnetic radiation in general) when incident on an interface between different optical media. They were deduced by French engineer and ...
, determined by the difference in
refractive index In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...
between layers. Therefore, the thickness and index of the coatings can be adjusted to be centered on any wavelength. Vacuum deposition can be achieved in a number of ways, including sputtering, evaporation deposition, arc deposition, reactive-gas deposition, and ion plating, among many others.


Shaping and polishing


Tolerances

Mirrors can be manufactured to a wide range of engineering tolerances, including
reflectivity The reflectance of the surface of a material is its effectiveness in Reflection (physics), reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the respon ...
, surface quality, surface roughness, or transmissivity, depending on the desired application. These tolerances can range from wide, such as found in a normal household-mirror, to extremely narrow, like those used in lasers or telescopes. Tightening the tolerances allows better and more precise imaging or beam transmission over longer distances. In imaging systems this can help reduce anomalies ( artifacts), distortion or blur, but at a much higher cost. Where viewing distances are relatively close or high precision is not a concern, wider tolerances can be used to make effective mirrors at affordable costs.


Applications


Personal grooming

Mirrors are commonly used as aids to
personal grooming Grooming (also called preening) is the art and practice of cleaning and maintaining parts of the body. It is a species-typical behavior. In animals Individual animals regularly clean themselves and put their fur, feathers or other skin c ...
. They may range from small sizes (portable), to full body sized; they may be handheld, mobile, fixed or adjustable. A classic example of an adjustable mirror is the cheval glass, which the user can tilt.


Safety and easier viewing

;Convex mirrors Convex mirrors provide a wider
field of view The field of view (FOV) is the angle, angular extent of the observable world that is visual perception, seen at any given moment. In the case of optical instruments or sensors, it is a solid angle through which a detector is sensitive to elec ...
than flat mirrors, and are often used on vehicles, especially large trucks, to minimize blind spots. They are sometimes placed at
road junction A junction is where two or more roads meet. History Roads are a means of transport, historically linking locations such as towns, forts and geographic features such as river fords. Where roads met outside of an existing settlement, these junct ...
s, and at corners of sites such as parking lots to allow people to see around corners to avoid crashing into other vehicles or
shopping cart A shopping cart (American English), trolley (British English, Australian English), or buggy (Southern American English, Appalachian English), also known by a variety of #Name, other names, is a wheeled cart supplied by a Retail#Types of ret ...
s. They are also sometimes used as part of security systems, so that a single video camera can show more than one
angle In Euclidean geometry, an angle can refer to a number of concepts relating to the intersection of two straight Line (geometry), lines at a Point (geometry), point. Formally, an angle is a figure lying in a Euclidean plane, plane formed by two R ...
at a time. Convex mirrors as decoration are used in interior design to provide a predominantly experiential effect. ; Mouth mirrors or "dental mirrors" :Dentists use mouth mirrors or "dental mirrors" to allow indirect vision and lighting within the mouth. Their reflective surfaces may be either flat or curved. Mouth mirrors are also commonly used by mechanics to allow vision in tight spaces and around corners in equipment. ;
Rear-view mirror A rear-view mirror (or rearview mirror) is a, usually plane mirror, flat, mirror in automobiles and other vehicles, designed to allow the driver to see rearward through the vehicle's rear window (rear windshield). In cars, the rear-view mirror ...
s :Rear-view mirrors are widely used in and on vehicles (such as automobiles, or bicycles), to allow drivers to see other vehicles coming up behind them. On rear-view sunglasses, the left end of the left glass and the right end of the right glass work as mirrors.


One-way mirrors and windows

;One-way mirrors :One-way mirrors (also called two-way mirrors) work by overwhelming dim transmitted light with bright reflected light. A true one-way mirror that actually allows light to be transmitted in one direction only without requiring external energy is not possible as it violates the
second law of thermodynamics The second law of thermodynamics is a physical law based on Universal (metaphysics), universal empirical observation concerning heat and Energy transformation, energy interconversions. A simple statement of the law is that heat always flows spont ...
. ;One-way windows :One-way windows can be made to work with polarized light in the laboratory without violating the second law. This is an apparent paradox that stumped some great physicists, although it does not allow a practical one-way mirror for use in the real world. Optical isolators are one-way devices that are commonly used with lasers.


Signalling

With the sun as the light source, a mirror can be used to signal by variations in the orientation of the mirror. The signal can be used over long distances, possibly up to on a clear day. Native American tribes and numerous militaries used this technique to transmit information between distant outposts. Mirrors can also be used to attract the attention of search-and-rescue parties. Specialized types of mirrors are available and are often included in military
survival kit A survival kit is a package of basic tools and supplies prepared as an aid to survival skills, survival in an emergency. Civil and military aircraft, lifeboat (shipboard), lifeboats, and spacecraft are equipped with survival kits. Survival ki ...
s.


Technology


Televisions and projectors

Microscopic mirrors are a core element of many of the largest high-definition televisions and
video projector A video projector is an image projector that receives a video signal and projects the corresponding image onto a projection screen using a lens system. Video projectors use a very bright ultra-high-performance lamp (a special mercury arc l ...
s. A common technology of this type is
Texas Instruments Texas Instruments Incorporated (TI) is an American multinational semiconductor company headquartered in Dallas, Texas. It is one of the top 10 semiconductor companies worldwide based on sales volume. The company's focus is on developing analog ...
' DLP. A DLP chip is a postage stamp-sized microchip whose surface is an array of millions of microscopic mirrors. The picture is created as the individual mirrors move to either reflect light toward the projection surface (
pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a Raster graphics, raster image, or the smallest addressable element in a dot matrix display device. In most digital display devices, p ...
on), or toward a light-absorbing surface (pixel off). Other projection technologies involving mirrors include LCoS. Like a DLP chip, LCoS is a microchip of similar size, but rather than millions of individual mirrors, there is a single mirror that is actively shielded by a
liquid crystal Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal can flow like a liquid, but its molecules may be oriented in a common direction as i ...
matrix with up to millions of pixels. The picture, formed as light, is either reflected toward the projection surface (pixel on), or absorbed by the activated LCD pixels (pixel off). LCoS-based televisions and projectors often use 3 chips, one for each primary color. Large mirrors are used in rear-projection televisions. Light (for example from a DLP as discussed above) is "folded" by one or more mirrors so that the television set is compact.


Optical discs

Optical disc An optical disc is a flat, usuallyNon-circular optical discs exist for fashion purposes; see shaped compact disc. disc-shaped object that stores information in the form of physical variations on its surface that can be read with the aid o ...
s are modified mirrors which encode binary data as a series of physical pits and lands on an inner layer between the metal backing and outer plastic surface. The data is read and decoded by observing distortions in a reflected laser beam caused by the physical variations in the inner layer. Optical discs typically use aluminum backing like conventional mirrors, though ones with silver and
gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...
backings also exist.


Solar power

Mirrors are integral parts of a
solar power Solar power, also known as solar electricity, is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Solar panels use the photovoltaic effect to c ...
plant. The one shown in the adjacent picture uses concentrated solar power from an array of parabolic troughs.


Instruments

Telescope A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...
s and other precision instruments use ''front silvered'' or first surface mirrors, where the reflecting surface is placed on the front (or first) surface of the glass (this eliminates reflection from glass surface ordinary back mirrors have). Some of them use silver, but most are aluminium, which is more reflective at short wavelengths than silver. All of these coatings are easily damaged and require special handling. They reflect 90% to 95% of the incident light when new. The coatings are typically applied by vacuum deposition. A protective overcoat is usually applied before the mirror is removed from the vacuum, because the coating otherwise begins to corrode as soon as it is exposed to oxygen and humidity in air. ''Front silvered'' mirrors have to be resurfaced occasionally to maintain their quality. There are optical mirrors such as mangin mirrors that are ''second surface mirrors'' (reflective coating on the rear surface) as part of their optical designs, usually to correct optical aberrations. The reflectivity of the mirror coating can be measured using a reflectometer and for a particular metal it will be different for different wavelengths of light. This is exploited in some optical work to make cold mirrors and hot mirrors. A cold mirror is made by using a transparent substrate and choosing a coating material that is more reflective to visible light and more transmissive to
infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
light. A hot mirror is the opposite, the coating preferentially reflects infrared. Mirror surfaces are sometimes given thin film overcoatings both to retard degradation of the surface and to increase their reflectivity in parts of the spectrum where they will be used. For instance, aluminium mirrors are commonly coated with silicon dioxide or magnesium fluoride. The reflectivity as a function of wavelength depends on both the thickness of the coating and on how it is applied. For scientific optical work,
dielectric mirror A dielectric mirror, also known as a Bragg mirror, is a type of mirror composed of multiple thin film, thin layers of dielectric material, typically deposited on a substrate of glass or some other optical material. By careful choice of the type a ...
s are often used. These are glass (or sometimes other material) substrates on which one or more layers of dielectric material are deposited, to form an optical coating. By careful choice of the type and thickness of the dielectric layers, the range of wavelengths and amount of light reflected from the mirror can be specified. The best mirrors of this type can reflect >99.999% of the light (in a narrow range of wavelengths) which is incident on the mirror. Such mirrors are often used in
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...
s. In astronomy,
adaptive optics Adaptive optics (AO) is a technique of precisely deforming a mirror in order to compensate for light distortion. It is used in Astronomy, astronomical telescopes and laser communication systems to remove the effects of Astronomical seeing, atmo ...
is a technique to measure variable image distortions and adapt a deformable mirror accordingly on a timescale of milliseconds, to compensate for the distortions. Although most mirrors are designed to reflect visible light, surfaces reflecting other forms of electromagnetic radiation are also called "mirrors". The mirrors for other ranges of
electromagnetic waves In physics, electromagnetic radiation (EMR) is a self-propagating wave of the electromagnetic field that carries momentum and radiant energy through space. It encompasses a broad spectrum, classified by frequency or its inverse, wavelength, ran ...
are used in optics and
astronomy Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest includ ...
. Mirrors for radio waves (sometimes known as reflectors) are important elements of
radio telescope A radio telescope is a specialized antenna (radio), antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the r ...
s. Simple
periscope A periscope is an instrument for observation over, around or through an object, obstacle or condition that prevents direct line-of-sight observation from an observer's current position. In its simplest form, it consists of an outer case with ...
s use mirrors.


Face-to-face mirrors

Two or more mirrors aligned exactly parallel and facing each other can give an infinite regress of reflections, called an
infinity mirror The infinity mirror (also sometimes called an infinite mirror) is a configuration of two or more Parallel (geometry), parallel or angled mirrors, which are arranged to create a series of further and further reflections that appear to recede to inf ...
effect. Some devices use this to generate multiple reflections: *
Fabry–Pérot interferometer In optics, a Fabry–Pérot interferometer (FPI) or etalon is an optical cavity made from two parallel reflecting surfaces (i.e.: thin mirrors). Optical waves can pass through the optical cavity only when they are in resonance with it. It is ...
*
Laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...
(which contains an
optical cavity An optical cavity, resonating cavity or optical resonator is an arrangement of mirrors or other optical elements that confines light waves similarly to how a cavity resonator confines microwaves. Optical cavities are a major component of lasers, ...
) * 3D kaleidoscope to concentrate light * momentum-enhanced solar sail


Military applications

Tradition states that
Archimedes Archimedes of Syracuse ( ; ) was an Ancient Greece, Ancient Greek Greek mathematics, mathematician, physicist, engineer, astronomer, and Invention, inventor from the ancient city of Syracuse, Sicily, Syracuse in History of Greek and Hellenis ...
used a large array of mirrors to burn Roman ships during an attack on Syracuse. This has never been proven or disproved. On the TV show ''
MythBusters ''MythBusters'' is a science entertainment television series created by Peter Rees (producer), Peter Rees and produced by Beyond International in Australia. The series premiered on the Discovery Channel on January 23, 2003. It was broadcast in ...
'', a team from MIT tried to recreate the famous "Archimedes Death Ray". They were unsuccessful at starting a fire on a ship. Previous attempts to set a boat on fire using only the bronze mirrors available in Archimedes' time were unsuccessful, and the time taken to ignite the craft would have made its use impractical, resulting in the ''MythBusters'' team deeming the myth "busted". It was however found that the mirrors made it very difficult for the passengers of the targeted boat to see; such a scenario could have impeded attackers and have provided the origin of the legend. (See solar power tower for a practical use of this technique.) Periscopes were used to great effect in war, especially during the World Wars where they were used to peer over the parapet of trenches to ensure that the soldier using the periscope could see safely without the risk of incoming direct fire from other small arms.


Seasonal lighting

Due to its location in a steep-sided valley, the Italian town of Viganella gets no direct sunlight for seven weeks each winter. In 2006 a €100,000 computer-controlled mirror, 8×5 m, was installed to reflect sunlight into the town's piazza. In early 2007 the similarly situated village of Bondo, Switzerland, was considering applying this solution as well. In 2013, mirrors were installed to reflect sunlight into the town square in the Norwegian town of Rjukan. Mirrors can be used to produce enhanced lighting effects in greenhouses or conservatories.


Architecture

Mirrors are a popular design-theme in architecture, particularly with late modern and post-modernist high-rise buildings in major cities. Early examples include the Campbell Center in
Dallas Dallas () is a city in the U.S. state of Texas and the most populous city in the Dallas–Fort Worth metroplex, the List of Texas metropolitan areas, most populous metropolitan area in Texas and the Metropolitan statistical area, fourth-most ...
, which opened in 1972, and the John Hancock Tower (completed in 1976) in Boston. More recently, two skyscrapers designed by architect Rafael Viñoly, the Vdara in Las Vegas and 20 Fenchurch Street in London, have experienced unusual problems due to their concave curved-glass exteriors acting as respectively cylindrical and spherical reflectors for sunlight. In 2010, the ''Las Vegas Review Journal'' reported that sunlight reflected off the Vdara's south-facing tower could singe swimmers in the hotel pool, as well as melting plastic cups and shopping bags; employees of the hotel referred to the phenomenon as the "Vdara death ray", aka the " fryscraper." In 2013, sunlight reflecting off 20 Fenchurch Street melted parts of a Jaguar car parked nearby and scorching or igniting the carpet of a nearby barber-shop. This building had been nicknamed the "walkie-talkie" because its shape was supposedly similar to a certain model of two-way radio; but after its tendency to overheat surrounding objects became known, the nickname changed to the "walkie-scorchie".


Fine art


Paintings

Painters depicting someone gazing into a mirror often also show the person's reflection. This is a kind of abstraction—in most cases the angle of view is such that the person's reflection should not be visible. Similarly, in movies and still photography an actor or actress is often shown ostensibly looking at him- or herself in a mirror, and yet the reflection faces the camera. In reality, the actor or actress sees only the camera and its operator in this case, not their own reflection. In the psychology of perception, this is known as the Venus effect. The mirror is the central device in some of the greatest of European paintings: *
Édouard Manet Édouard Manet (, ; ; 23 January 1832 – 30 April 1883) was a French Modernism, modernist painter. He was one of the first 19th-century artists to paint modern life, as well as a pivotal figure in the transition from Realism (art movement), R ...
's ''
A Bar at the Folies-Bergère ''A Bar at the Folies-Bergère'' () is a painting by Édouard Manet, considered to be his last major work. It was painted in 1882 and exhibited at the Paris Salon of that year. It depicts a scene in the Folies Bergère nightclub in Paris. The pa ...
'' (1882) *
Titian Tiziano Vecellio (; 27 August 1576), Latinized as Titianus, hence known in English as Titian ( ), was an Italian Renaissance painter, the most important artist of Renaissance Venetian painting. He was born in Pieve di Cadore, near Belluno. Ti ...
's '' Venus with a Mirror'' *
Jan van Eyck Jan van Eyck ( ; ; – 9 July 1441) was a Flemish people, Flemish painter active in Bruges who was one of the early innovators of what became known as Early Netherlandish painting, and one of the most significant representatives of Early Nort ...
's '' Arnolfini Portrait'' *
Pablo Picasso Pablo Diego José Francisco de Paula Juan Nepomuceno María de los Remedios Cipriano de la Santísima Trinidad Ruiz y Picasso (25 October 1881 – 8 April 1973) was a Spanish painter, sculptor, printmaker, Ceramic art, ceramicist, and Scenic ...
's '' Girl before a Mirror'' (1932) *
Diego Velázquez Diego Rodríguez de Silva y Velázquez (baptised 6 June 15996 August 1660) was a Spanish painter, the leading artist in the Noble court, court of King Philip IV of Spain, Philip IV of Spain and Portugal, and of the Spanish Golden Age. He i ...
's '' Rokeby Venus'' *
Diego Velázquez Diego Rodríguez de Silva y Velázquez (baptised 6 June 15996 August 1660) was a Spanish painter, the leading artist in the Noble court, court of King Philip IV of Spain, Philip IV of Spain and Portugal, and of the Spanish Golden Age. He i ...
's '' Las Meninas'' (wherein the viewer is both the watcher - of a self-portrait in progress - and the watched) and the many adaptations of that painting in various media * Veronese's ''Venus with a Mirror'' Artists have used mirrors to create works and to hone their craft: * Filippo Brunelleschi discovered linear perspective with the help of the mirror. *
Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 1452 - 2 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially rested o ...
called the mirror the "master of painters". He recommended, "When you wish to see whether your whole picture accords with what you have portrayed from nature take a mirror and reflect the actual object in it. Compare what is reflected with your painting and carefully consider whether both likenesses of the subject correspond, particularly in regard to the mirror." * Many self-portraits are made possible through the use of mirrors, such as great self-portraits by Dürer, Frida Kahlo,
Rembrandt Rembrandt Harmenszoon van Rijn (; ; 15 July 1606 – 4 October 1669), mononymously known as Rembrandt was a Dutch Golden Age painter, printmaker, and Drawing, draughtsman. He is generally considered one of the greatest visual artists in ...
, and Van Gogh. M. C. Escher used special shapes of mirrors in order to achieve a much more complete view of his surroundings than by direct observation in '' Hand with Reflecting Sphere'' (1935; also known as ''Self-Portrait in Spherical Mirror''). Mirrors are sometimes necessary to fully appreciate art work: * István Orosz's
anamorphic Anamorphic format is a cinematography technique that captures widescreen images using recording media with narrower native Aspect ratio (image), aspect ratios. Originally developed for 35 mm movie film, 35 mm film to create widescreen pres ...
works are images distorted such that they only become clearly visible when reflected in a suitably shaped and positioned mirror.


Sculpture

*
Anamorphosis Anamorphosis is a distorted projection that requires the viewer to occupy a specific vantage point, use special devices, or both to view a recognizable image. It is used in painting, photography, sculpture and installation, toys, and film speci ...
projecting sculpture into mirrors Contemporary anamorphic artist Jonty Hurwitz uses cylindrical mirrors to project distorted sculptures. * Sculptures comprised entirely or in part of mirrors include: ** '' Infinity Also Hurts'', a mirror, glass and
silicone In Organosilicon chemistry, organosilicon and polymer chemistry, a silicone or polysiloxane is a polymer composed of repeating units of siloxane (, where R = Organyl group, organic group). They are typically colorless oils or elastomer, rubber ...
sculpture by artist Seth Wulsin ** '' Sky Mirror'', a public sculpture by artist Anish Kapoor


Other artistic mediums

Some other contemporary artists use mirrors as the material of art: * A Chinese magic mirror is a device in which the face of the bronze mirror projects the same image that was cast on its back. This is due to minute curvatures on its front. * Specular holography uses a large number of curved mirrors embedded in a surface to produce three-dimensional imagery. * Paintings on mirror surfaces (such as silkscreen printed glass mirrors) * Special mirror installations: ** ''Follow Me'', a mirror labyrinth by artist Jeppe Hein (see also, Entertainment: Mirror mazes, below) ** ''Mirror Neon Cube'' by artist Jeppe Hein


Religious function of the real and depicted mirror

In the
Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the 5th to the late 15th centuries, similarly to the post-classical period of global history. It began with the fall of the Western Roman Empire and ...
, mirrors existed in various shapes for multiple uses. Mostly they were used as an accessory for personal hygiene but also as tokens of courtly love, made from
ivory Ivory is a hard, white material from the tusks (traditionally from elephants) and Tooth, teeth of animals, that consists mainly of dentine, one of the physical structures of teeth and tusks. The chemical structure of the teeth and tusks of mamm ...
in the ivory-carving centers in Paris, Cologne and the Southern Netherlands. They also had their uses in religious contexts as they were integrated in a special form of pilgrim badges or pewter/lead mirror boxes From the late 14th century. Burgundian ducal inventories show us that the dukes owned a mass of mirrors or objects with mirrors, not only with religious iconography or inscriptions, but combined with reliquaries, religious paintings or other objects that were distinctively used for personal piety. Considering mirrors in paintings and book illumination as depicted artifacts and trying to draw conclusions about their functions from their setting, one of these functions is to be an aid in personal prayer to achieve self-knowledge and knowledge of God, in accord with contemporary theological sources. For example, the famous Arnolfini Wedding by
Jan van Eyck Jan van Eyck ( ; ; – 9 July 1441) was a Flemish people, Flemish painter active in Bruges who was one of the early innovators of what became known as Early Netherlandish painting, and one of the most significant representatives of Early Nort ...
shows a constellation of objects that can be recognized as one which would allow a praying man to use them for his personal piety: the mirror surrounded by scenes of the Passion to reflect on it and on oneself, a
rosary The Rosary (; , in the sense of "crown of roses" or "garland of roses"), formally known as the Psalter of Jesus and Mary (Latin: Psalterium Jesu et Mariae), also known as the Dominican Rosary (as distinct from other forms of rosary such as the ...
as a device in this process, the veiled and cushioned bench to use as a prie-dieu, and the abandoned shoes that point in the direction in which the praying man kneeled. The metaphorical meaning of depicted mirrors is complex and many-layered, e.g. as an attribute of Mary, the "speculum sine macula" (mirror without blemish), or as attributes of scholarly and theological wisdom and knowledge as they appear in book illuminations of different evangelists and authors of theological treatises. Depicted mirrors – orientated on the physical properties of a real mirror – can be seen as metaphors of knowledge and reflection and are thus able to remind beholders to reflect and get to know themselves. The mirror may function simultaneously as a symbol and as a device of a moral appeal. That is also the case if it is shown in combination with virtues and vices, a combination which also occurs more frequently in the 15th century: the moralizing layers of mirror metaphors remind the beholder to examine themself thoroughly according to their own virtuous or vicious life. This is all the more true if the mirror is combined with iconography of death. Not only is Death as a corpse or skeleton holding the mirror for the still-living personnel of paintings, illuminations and prints, but the skull appears on the convex surfaces of depicted mirrors, showing the painted and real beholders their future face.


Decoration

Mirrors are frequently used in interior decoration and as ornaments: * Mirrors, typically large and unframed, are frequently used in interior decoration to create an illusion of space and to amplify the apparent size of a room. They come also framed in a variety of forms, such as the pier glass and the overmantel mirror. * Mirrors are used also in some schools of
feng shui Feng shui ( or ), sometimes called Chinese geomancy, is a traditional form of geomancy that originated in ancient China and claims to use energy forces to harmonize individuals with their surrounding environment. The term ''feng shui'' mean ...
, an ancient Chinese practice of placement and arrangement of space to achieve harmony with an environment. * The softness of old mirrors is sometimes replicated by contemporary artisans for use in
interior design Interior design is the art and science of enhancing the interior of a building to achieve a healthier and more aesthetically pleasing environment for the people using the space. With a keen eye for detail and a Creativity, creative flair, an ...
. These reproduction antiqued mirrors are works of art and can bring color and texture to an otherwise hard, cold reflective surface. * A decorative reflecting
sphere A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...
of thin metal-coated glass, working as a reducing wide-angle mirror, is sold as a Christmas ornament called a ''bauble''. * Some pubs and bars hang mirrors depicting the logo of a brand of liquor, beer or drinking establishment.


Entertainment

* Illuminated rotating disco balls covered with small mirrors are used to cast moving spots of light around a dance floor. * The
hall of mirrors The Hall of Mirrors () is a grand Baroque architecture, Baroque style gallery and one of the most emblematic rooms in the royal Palace of Versailles near Paris, France. The grandiose ensemble of the hall and its adjoining salons was intended to ...
, commonly found in
amusement park An amusement park is a park that features various attractions, such as rides and games, and events for entertainment purposes. A theme park is a type of amusement park that bases its structures and attractions around a central theme, often fea ...
s, is an attraction in which a number of distorting mirrors produce unusual reflections of the visitor. * Mirrors are employed in kaleidoscopes, personal entertainment devices invented in
Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...
by Sir
David Brewster Sir David Brewster Knight of the Royal Guelphic Order, KH President of the Royal Society of Edinburgh, PRSE Fellow of the Royal Society of London, FRS Fellow of the Society of Antiquaries of Scotland, FSA Scot Fellow of the Scottish Society of ...
. * Mirrors are often used in magic to create an
illusion An illusion is a distortion of the senses, which can reveal how the mind normally organizes and interprets sensory stimulation. Although illusions distort the human perception of reality, they are generally shared by most people. Illusions may ...
. One effect is called Pepper's ghost. * Mirror
maze A maze is a path or collection of paths, typically from an entrance to a goal. The word is used to refer both to branching tour puzzles through which the solver must find a route, and to simpler non-branching ("unicursal") patterns that lead ...
s, often found in
amusement park An amusement park is a park that features various attractions, such as rides and games, and events for entertainment purposes. A theme park is a type of amusement park that bases its structures and attractions around a central theme, often fea ...
s, contain large numbers of mirrors and sheets of glass. The idea is to navigate the disorientating array without bumping into the walls. Mirrors in attractions like this are often made of
Plexiglas Poly(methyl methacrylate) (PMMA) is a synthetic polymer derived from methyl methacrylate. It is a transparent thermoplastic, used as an engineering plastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and bra ...
to prevent breakages.


Film and television

Mirrors appear in many movies and TV shows: *''
Black Swan The black swan (''Cygnus atratus'') is a large Anatidae, waterbird, a species of swan which breeds mainly in the southeast and southwest regions of Australia. Within Australia, the black swan is nomadic, with erratic migration patterns dependent ...
'' is a
psychological horror Psychological horror is a genre, subgenre of horror fiction, horror and psychological fiction with a particular focus on mental, emotional, and Mental state, psychological states to frighten, disturb, or unsettle its audience. The subgenre freque ...
film that frequently incorporates mirrors. Fractured mirrors are prominent in the film, and the character Nina stabs herself with a broken piece of mirror. * ''Candyman'' is a horror film about a malevolent spirit summoned by speaking its name in front of a mirror. * '' Conan the Destroyer'' features a mirror-embedded chamber deep within Thoth-Amon's castle. The mirrors are first used in an illusory fashion to deceive Conan once he is separated by his companions, and during a battle sequence it is discovered that by breaking the mirrors he is able to damage and eventually defeat the otherwise-invulnerable wizard Thoth-Amon. *'' Dead of Night'' is an
anthology In book publishing, an anthology is a collection of literary works chosen by the compiler; it may be a collection of plays, poems, short stories, songs, or related fiction/non-fiction excerpts by different authors. There are also thematic and g ...
horror film with one segment titled "The Haunted Mirror," in which a mirror casts a murderous spell. *''
Doctor Strange Dr. Stephen Vincent Strange is a fictional character appearing in American comic books published by Marvel Comics. Created by Steve Ditko, the character first appeared in ''Strange Tales'' #110 (cover-dated July 1963). Doctor Strange serves as ...
'', '' Doctor Strange in the Multiverse of Madness'', and '' Spider-Man: No Way Home'' feature the fictional mirror dimension, a parallel dimension in the
Marvel Universe The Marvel Universe is a fictional shared universe where the stories in most American comic book titles and other media published by Marvel Comics take place. Superhero teams such as the Avengers, the X-Men, the Fantastic Four, the Guardia ...
that reflects objects like a mirror, but in different directions. *'' Enter the Dragons iconic and final fight scene occurs in a mirrored room. The mirrors create multiple reflections of the fight movements but are eventually smashed. *'' The Floorwalker'' and '' Duck Soup'' contain a mirror scene in which one person comically pretends to be the mirror reflection of someone else. This mirror scene has been imitated in other comedy films and TV shows. *''
Hamlet ''The Tragedy of Hamlet, Prince of Denmark'', often shortened to ''Hamlet'' (), is a Shakespearean tragedy, tragedy written by William Shakespeare sometime between 1599 and 1601. It is Shakespeare's longest play. Set in Denmark, the play (the ...
'' has a throne room with mirrored walls. Hamlet, played by
Kenneth Branagh Sir Kenneth Charles Branagh ( ; born 10 December 1960) is a British actor and filmmaker. Born in Belfast and raised primarily in Reading, Berkshire, Branagh trained at RADA in London and served as its president from 2015 to 2024. List of award ...
, gives his famous speech with the words "to be or not to be," looking into these mirrors. * ''Harry Potter and the Philosopher's Stone'' includes the magical Mirror of Erised. *'' Inception'' contains mirrors created in a dream sequence. Ariadne creates two mirrors facing each other that form an infinite number of reflected mirrors. *'' Lady in the Lake'', a 1947
film noir Film noir (; ) is a style of Cinema of the United States, Hollywood Crime film, crime dramas that emphasizes cynicism (contemporary), cynical attitudes and motivations. The 1940s and 1950s are generally regarded as the "classic period" of Ameri ...
, was shot from the point of view of the protagonist, who is seen only when a mirror is included in the shot. *'' Last Night in Soho'' is a psychological horror movie with several mirror scenes. The character Ellie occasionally sees her mother's ghost in mirrors. *''
The Matrix ''The Matrix'' is a 1999 science fiction film, science fiction action film written and directed by the Wachowskis. It is the first installment in the The Matrix (franchise), ''Matrix'' film series, starring Keanu Reeves, Laurence Fishburne, Ca ...
'' uses various reflections and mirrors throughout the film. Neo watches a broken mirror mend itself, and different objects create reflections. * ''
Mirror A mirror, also known as a looking glass, is an object that Reflection (physics), reflects an image. Light that bounces off a mirror forms an image of whatever is in front of it, which is then focused through the lens of the eye or a camera ...
'' is a drama film by Andrei Tarkovsky that includes several scenes with mirrors and several scenes shot in reflection. *'' Mirror Mirror'' is a fantasy comedy film based on Snow White that features a Mirror House and Mirror Queen. * ''Mirrors'' is a horror film about haunted mirrors that reflect different scenes than those in front of them. *''
Persona A persona (plural personae or personas) is a strategic mask of identity in public, the public image of one's personality, the social role that one adopts, or simply a fictional Character (arts), character. It is also considered "an intermediary ...
'' relies on mirror sequences to show how the two women, Bibi and Liv, reflect each other and become more alike. * '' Poltergeist III'' features mirrors that do not reflect reality and which can be used as portals to an afterlife. *'' Psycho'' by Alfred Hitchock has several shots with mirrors that reflect characters. * ''Oculus'' is a horror film about a haunted mirror that causes people to hallucinate and commit acts of violence. *''
Orpheus In Greek mythology, Orpheus (; , classical pronunciation: ) was a Thracians, Thracian bard, legendary musician and prophet. He was also a renowned Ancient Greek poetry, poet and, according to legend, travelled with Jason and the Argonauts in se ...
'' includes an important theme of mirrors in connection to aging and death. *''
Sailor Moon is a Japanese manga series written and illustrated by Naoko Takeuchi. It was originally serialized in Kodansha's Shōjo manga, ''shōjo'' manga magazine ''Nakayoshi'' from 1991 to 1997; the 60 individual chapters (later reorganized into ...
'' in the fourth story arc has a major theme pertaining to mirrors, which entrap several of the Sailor Senshi, the fiancée of the protagonist, and the villain in the arc. *''
Taxi Driver ''Taxi Driver'' is a 1976 American neo-noir psychological drama film directed by Martin Scorsese and written by Paul Schrader. Set in a morally decaying New York City following the Vietnam War, it stars Robert De Niro as veteran Marine and ...
'' has a notable scene with a mirror in which the character Travis, played by
Robert De Niro Robert Anthony De Niro ( , ; born August 17, 1943) is an American actor, director, and film producer. He is considered to be one of the greatest and most influential actors of his generation. De Niro is the recipient of List of awards and ...
, asks himself the famous line, "You talkin' to me?" *'' The Lady from Shanghai'' has a climatic hall of mirrors scene that has become a trope in cinema narratives. *'' Raging Bull'' ends with the character Jake talking to himself in a mirror, a scene that was reused in '' Boogie Nights''. *'' The Shining'' is a horror movie that includes several scenes with mirrors. Every time the character Jack encounters a ghost, a mirror is present. * '' The 10th Kingdom''
miniseries In the United States, a miniseries or mini-series is a television show or series that tells a story in a predetermined, limited number of episodes. Many miniseries can also be referred to, and shown, as a television film. " Limited series" is ...
requires the characters to use a magic mirror to travel between New York City (the 10th Kingdom) and the Nine Kingdoms of
fairy tale A fairy tale (alternative names include fairytale, fairy story, household tale, magic tale, or wonder tale) is a short story that belongs to the folklore genre. Such stories typically feature magic, enchantments, and mythical or fanciful bei ...
. *'' The Twilight Zone'' episode " The Mirror" features a mirror that the character Clemente believes can provide visions and information about enemies. *'' Us'' is a horror film that includes a girl seeing a
doppelgänger A doppelgänger ( ), sometimes spelled doppelgaenger or doppelganger, is a ghostly double of a living person, especially one that haunts its own fleshly counterpart. In fiction and mythology, a doppelgänger is often portrayed as a ghostly or p ...
of herself in a house of mirrors in a
funhouse A funhouse or fun house is an attraction found in amusement parks and funfair midways, equipped with various devices designed to surprise, challenge, or amuse visitors. Unlike thrill rides or dark rides, fun houses are participatory attractio ...
. The mirror images reflect the similarities in the clones throughout the film. *''
Vertigo Vertigo is a condition in which a person has the sensation that they are moving, or that objects around them are moving, when they are not. Often it feels like a spinning or swaying movement. It may be associated with nausea, vomiting, perspira ...
'' includes several appearances of mirrors with both Scottie and Madeleine in the frame.


Literature

Mirrors featured in literature: *
Christian Bible The Bible is a collection of religious texts that are central to Christianity and Judaism, and esteemed in other Abrahamic religions such as Islam. The Bible is an anthology (a compilation of texts of a variety of forms) biblical languages ...
passages, 1 Corinthians 13:12 (" Through a Glass Darkly") and 2 Corinthians 3:18, reference a dim mirror-image or poor mirror-reflection. * Narcissus of
Greek mythology Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of ancient Greek folklore, today absorbed alongside Roman mythology into the broader designation of classical mythology. These stories conc ...
wastes away while gazing, self-admiringly, at his reflection in water. * Elsewhere in Greek Mythology,
Perseus In Greek mythology, Perseus (, ; Greek language, Greek: Περσεύς, Romanization of Greek, translit. Perseús) is the legendary founder of the Perseid dynasty. He was, alongside Cadmus and Bellerophon, the greatest Greek hero and slayer of ...
is said to have defeated the
Gorgon The Gorgons ( ; ), in Greek mythology, are three monstrous sisters, Stheno, Euryale, and Medusa, said to be the daughters of Phorcys and Ceto. They lived near their sisters the Graeae, and were able to turn anyone who looked at them to sto ...
Medusa with the aid of a mirrored shield which allowed him to avoid the petrifying effect of her visage by only viewing her reflection. * The Song dynasty history ''
Zizhi Tongjian The ''Zizhi Tongjian'' (1084) is a chronicle published during the Northern Song dynasty (960–1127) that provides a record of Chinese history from 403 BC to 959 AD, covering 16 dynasties and spanning almost 1400 years. The main text is ...
'' ''Comprehensive Mirror in Aid of Governance'' by Sima Guang is so titled because "mirror" (鑑, jiàn) is used metaphorically in Chinese to refer to gaining insight by reflecting on past experience or history. * In the late 6th century Chinese folktale '' The Broken Mirror Restored'' two lovers who are separated by war break a mirror in two so that they might find each other again by identifying the other half of the mirror. The phrase "broken mirror restored", or "broken mirror joined together" has been used as an idiom to suggests the happy reunion of a separated couple. * In the European
fairy tale A fairy tale (alternative names include fairytale, fairy story, household tale, magic tale, or wonder tale) is a short story that belongs to the folklore genre. Such stories typically feature magic, enchantments, and mythical or fanciful bei ...
, '' Snow White'' (collected by the Brothers Grimm in 1812), the evil queen asks, "
Mirror A mirror, also known as a looking glass, is an object that Reflection (physics), reflects an image. Light that bounces off a mirror forms an image of whatever is in front of it, which is then focused through the lens of the eye or a camera ...
, mirror, on the wall... who's the fairest of them all?" * In the Aarne-Thompson-Uther Index tale type ATU 329, "Hiding from the Devil (Princess)", the protagonist must find a way to hide from a princess, who, in many variants, owns a magical mirror that can see the whole world. * In
Tennyson Alfred Tennyson, 1st Baron Tennyson (; 6 August 1809 – 6 October 1892) was an English poet. He was the Poet Laureate of the United Kingdom, Poet Laureate during much of Queen Victoria's reign. In 1829, Tennyson was awarded the Chancellor's ...
's famous poem '' The Lady of Shalott'' (1833, revised in 1842), the titular character possesses a mirror that enables her to look out on the people of Camelot, as she is under a curse that prevents her from seeing Camelot directly. *
Hans Christian Andersen Hans Christian Andersen ( , ; 2 April 1805 – 4 August 1875) was a Danish author. Although a prolific writer of plays, travelogue (literature), travelogues, novels, and poems, he is best remembered for his literary fairy tales. Andersen's fai ...
's fairy tale ''
The Snow Queen "The Snow Queen" () is an 1844 original fairy tale by Danish author Hans Christian Andersen. It was first published 21 December 1844 in ''New Fairy Tales. First Volume#New Fairy Tales. First Volume. Second Collection, New Fairy Tales. First Vo ...
'', features the devil, in a form of an evil troll, who made a magic mirror that distorts the appearance of everything that it reflects. *
Lewis Carroll Charles Lutwidge Dodgson (27 January 1832 – 14 January 1898), better known by his pen name Lewis Carroll, was an English author, poet, mathematician, photographer and reluctant Anglicanism, Anglican deacon. His most notable works are ''Alice ...
's ''
Through the Looking-Glass ''Through the Looking-Glass, and What Alice Found There'' is a novel published in December 1871 by Lewis Carroll, the pen name of Charles Lutwidge Dodgson, a mathematics lecturer at Christ Church, Oxford, Christ Church, University of Oxford. I ...
and What Alice Found There'' (1871) has become one of the best-loved exemplars of the use of mirrors in literature. The text itself utilizes a narrative that mirrors that of its predecessor, ''
Alice's Adventures in Wonderland ''Alice's Adventures in Wonderland'' (also known as ''Alice in Wonderland'') is an 1865 English Children's literature, children's novel by Lewis Carroll, a mathematics university don, don at the University of Oxford. It details the story of a ...
''. * In
Oscar Wilde Oscar Fingal O'Fflahertie Wills Wilde (16 October 185430 November 1900) was an Irish author, poet, and playwright. After writing in different literary styles throughout the 1880s, he became one of the most popular and influential playwright ...
's novel, ''
The Picture of Dorian Gray ''The Picture of Dorian Gray'' is an 1890 philosophical fiction and Gothic fiction, Gothic horror fiction, horror novel by Irish writer Oscar Wilde. A shorter novella-length version was published in the July 1890 issue of the American period ...
'' (1890), a
portrait A portrait is a painting, photograph, sculpture, or other artistic representation of a person, in which the face is always predominant. In arts, a portrait may be represented as half body and even full body. If the subject in full body better r ...
serves as a magical mirror that reflects the true visage of the perpetually youthful protagonist, as well as the effect on his soul of each sinful act. * W. H. Auden's villanelle "Miranda" repeats the refrain: "My dear one is mine as mirrors are lonely". * The short story '' Tlön, Uqbar, Orbis Tertius'' (1940) by
Jorge Luis Borges Jorge Francisco Isidoro Luis Borges Acevedo ( ; ; 24 August 1899 – 14 June 1986) was an Argentine short-story writer, essayist, poet and translator regarded as a key figure in Spanish literature, Spanish-language and international literatur ...
begins with the phrase "I owe the discovery of Uqbar to the conjunction of a mirror and an encyclopedia" and contains other references to mirrors. * ''The Trap'', a short story by H.P. Lovecraft and Henry S. Whitehead, centers around a mirror. "It was on a certain Thursday morning in December that the whole thing began with that unaccountable motion I thought I saw in my antique Copenhagen mirror. Something, it seemed to me, stirred—something reflected in the glass, though I was alone in my quarters." * Magical objects in the ''Harry Potter'' series (1997–2011) include the Mirror of Erised and two-way mirrors. * Under ''Appendix: Variant Planes & Cosmologies'' of the ''
Dungeons & Dragons ''Dungeons & Dragons'' (commonly abbreviated as ''D&D'' or ''DnD'') is a fantasy tabletop role-playing game (TTRPG) originally created and designed by Gary Gygax and Dave Arneson. The game was first published in 1974 by TSR (company)#Tactical ...
'' '' Manual of the Planes'' (2000), is The Plane of Mirrors (page 204). It describes the Plane of Mirrors as a space existing behind reflective surfaces, and experienced by visitors as a long corridor. The greatest danger to visitors upon entering the plane is the instant creation of a mirror-self with the opposite alignment of the original visitor. * ''The Mirror Thief'', a novel by Martin Seay (2016), includes a fictional account of industrial espionage surrounding mirror-manufacturing in 16th-century Venice. * '' The Glass Floor'', a short story by
Stephen King Stephen Edwin King (born September 21, 1947) is an American author. Dubbed the "King of Horror", he is widely known for his horror novels and has also explored other genres, among them Thriller (genre), suspense, crime fiction, crime, scienc ...
, concerns a mysterious and deadly mirrored floor. * '' The Reaper's Image'', a short story by
Stephen King Stephen Edwin King (born September 21, 1947) is an American author. Dubbed the "King of Horror", he is widely known for his horror novels and has also explored other genres, among them Thriller (genre), suspense, crime fiction, crime, scienc ...
, concerns a rare Elizabethan mirror that displays the Reaper's image when viewed, which symbolises the death of the viewer. * Kilgore Trout, a protagonist of
Kurt Vonnegut Kurt Vonnegut ( ; November 11, 1922 – April 11, 2007) was an American author known for his Satire, satirical and darkly humorous novels. His published work includes fourteen novels, three short-story collections, five plays, and five nonfict ...
's novel '' Breakfast of Champions'', believes that mirrors are windows to other universes, and refers to them as "leaks", a recurring motif in the book. *In ''
The Fellowship of the Ring ''The Fellowship of the Ring'' is the first of three volumes of the epic novel ''The Lord of the Rings'' by the English author J. R. R. Tolkien; it is followed by ''The Two Towers'' and ''The Return of the King''. The action takes place in th ...
'' by
J. R. R. Tolkien John Ronald Reuel Tolkien (, 3 January 1892 – 2 September 1973) was an English writer and philologist. He was the author of the high fantasy works ''The Hobbit'' and ''The Lord of the Rings''. From 1925 to 1945, Tolkien was the Rawlinson ...
, the Mirror of Galadriel allows one to see things of the past, present and possible future. The mirror additionally appears in the movie adaptation.


Mirror test

Only a few animal species have been shown to have the ability to recognize themselves in a mirror, most of them
mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...
s. Experiments have found that the following animals can pass the mirror test: *
Human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...
s. Humans tend to fail the mirror test until they are about 18 months old, or what psychoanalysts call the " mirror stage". * All
great ape The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); '' Gorilla'' (the ...
s: **
Bonobo The bonobo (; ''Pan paniscus''), also historically called the pygmy chimpanzee (less often the dwarf chimpanzee or gracile chimpanzee), is an endangered great ape and one of the two species making up the genus ''Pan (genus), Pan'' (the other bei ...
s **
Chimpanzee The chimpanzee (; ''Pan troglodytes''), also simply known as the chimp, is a species of Hominidae, great ape native to the forests and savannahs of tropical Africa. It has four confirmed subspecies and a fifth proposed one. When its close rel ...
s **
Orangutan Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genus ...
s **
Gorilla Gorillas are primarily herbivorous, terrestrial great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or five su ...
s. Initially, it was thought that gorillas did not pass the test, but there are now several well-documented reports of gorillas (such as Koko) passing the test. * Bottlenose dolphins * Orcas *
Elephants Elephants are the Largest and heaviest animals, largest living land animals. Three living species are currently recognised: the African bush elephant (''Loxodonta africana''), the African forest elephant (''L. cyclotis''), and the Asian ele ...
* European magpies


See also

* Anish Kapoor (artist working with mirrors) * Aranmula kannadi *
Chirality (mathematics) In geometry, a figure is chiral (and said to have chirality) if it is not identical to its mirror image, or, more precisely, if it cannot be mapped to its mirror image by Rotation (mathematics), rotations and Translation (geometry), translations a ...
* Corner reflector * Curved mirror * Deformable mirror * Digital micromirror device * Heliotrope (instrument) * Honeycomb mirror * List of telescope parts and construction * '' Melong'' * Mirror armour * Non-reversing mirror *
Mirror writing Mirror writing is formed by writing in the direction that is the reverse of the natural way for a given language, such that the result is the mirror image of normal writing: it appears normal when reflected in a mirror. It is sometimes used as ...
* Mirrors in Mesoamerican culture * Perfect mirror *
Periscope A periscope is an instrument for observation over, around or through an object, obstacle or condition that prevents direct line-of-sight observation from an observer's current position. In its simplest form, it consists of an outer case with ...
* Selfie * Spectrophobia * TLV mirror * Venus effect *


References


Further reading

* ''Le miroir: révélations, science-fiction et fallacies. Essai sur une légende scientifique'', Jurgis Baltrušaitis, Paris, 1978. . * ''On reflection'',
Jonathan Miller Sir Jonathan Wolfe Miller CBE (21 July 1934 – 27 November 2019) was an English theatre and opera director, actor, author, television presenter, comedian and physician. After training in medicine and specialising in neurology in the late 19 ...
, National Gallery Publications Limited (1998). . * ''Lo specchio, la strega e il quadrante. Vetrai, orologiai e rappresentazioni del 'principium individuationis' dal Medioevo all'Età moderna'', Francesco Tigani, Roma, 2012. . *Shrum, Rebecca K. 2017.
In the Looking Glass: Mirrors and Identity in Early America
''. Johns Hopkins University Press.


External links

* * * *
How Mirrors Are Made (video)
Glass Association of North America (GANA)
July 2019 "The Ugly History of Beautiful Things: Mirrors" by Katy Kelleher for Longreads
{{Authority control Fiction about mirrors Glass applications Reflective building components Wallcoverings