mirror

1. A surface capable of reflecting sufficient undiffused light to form an image of an object placed in front of it. Also called looking glass.
2. Something that faithfully reflects or gives a true picture of something else.
3. Something worthy of imitation.

To reflect in or as if in a mirror: “The city mirrors many of the greatest moments of Western culture” (Olivier Bernier).

[Middle English mirour, from Old French mireor, from mirer, to look at, from Latin mīrārī, to wonder at, from mīrus, wonderful.]

Background

From the earliest recorded history, humans have been fascinated by reflections. Narcissus was supposedly bewitched by his own reflection in a pool of water, and magic powers are ascribed to mirrors in fairy tales. Mirrors have advanced from reflective pools and polished metal surfaces to clear glass handheld and bathroom mirrors. They have been used in interior decoration since the 17th century, and reflective surfaces on cars and in hotel lobbies are still popular in modern design. Mirrors are used for practical purposes as well: examining our appearance, examining what is behind us on the road, building skyscrapers, and making scientific research instruments, such as microscopes and lasers.

The nature of modernn mirrors is not fundamentally different from a pool of water. When light strikes any surface, some of it will be reflected. Mirrors are simply smooth surfaces with shiny, dark backgrounds that reflect very well. Water reflects well, glass reflects poorly, and polished metal reflects extremely well. The degree of reflectivity—how much light bounces off of a surface—and the diffusivity of a surface—what direction light bounces off of a surface—may be altered. These alterations are merely refinements, however. In general, all reflective surfaces, and hence, all mirrors, are really the same in character.

Man-made mirrors have been in existence since ancient times. The first mirrors were often sheets of polished metal and were used almost exclusively by the ruling classes. Appearance often reflected, and in some cases determined, position and power in society, so the demand for looking glasses was high, as was the demand for the improvement of mirror-making techniques. Silvering—the process of coating the back of a glass sheet with melted silver—became the most popular method for making mirrors in the 1600s. The glass used in these early mirrors was often warped, creating a ripple in the image. In some severe cases, the images these mirrors reflected were similar to those we'd see in a fun-house mirror today. Modern glassmaking and metallurgical techniques make it easy to produce sheets of glass that are very flat and uniformly coated on the back, improving image clarity tremendously. Still, the quality of a mirror depends on the time and materials expended to make it. A handheld purse mirror may reflect a distorted image, while a good bathroom mirror will probably have no noticeable distortions. Scientific mirrors are designed with virtually no imperfections or distorting qualities whatsoever.

Materials technology drastically affects the quality of a mirror. Light reflects best from surfaces that are non-diffusive, that is, smooth and opaque, rather than transparent. Any flaw in this arrangement will detract from the effectiveness of the mirror. Innovations in mirror making have been directed towards flattening the glass used and applying metal coatings of uniform thickness, because light traveling through different thicknesses of glass over different parts of a mirror results in a distorted image. It is due to these irregularities that some mirrors make you look thinner and some fatter than normal. If the metal backing on a mirror is scratched or thin in spots, the brightness of the reflection will also be uneven. If the coating is very thin, it may be possible to see through the mirror. This is how one-way mirrors are made. Non-opaque coating is layered over the thin, metal backing and only one side of the mirror (the reflecting side) is lit. This allows a viewer on the other side, in a darkened room, to see through.

Raw Materials

Glass, the main component of mirrors, is a poor reflector. It reflects only about 4 percent of the light which strikes it. It does, however, possess the property of uniformity, particularly when polished. This means that the glass contains very few pits after polishing and will form an effective base for a reflective layer of metal. When the metal layer is deposited, the surface is very even, with no bumps or wells. Glass is also considered a good material for mirrors because it can be molded into various shapes for specialty mirrors. Glass sheets are made from silica, which can be mined or refined from sand. Glass made from natural crystals of silica is known as fused quartz. There are also synthetic glasses, which are referred to as synthetic fused silica. The silica, or quartz, is melted to high temperatures, and poured or rolled out into sheets.

A few other types of glass are used for high-quality scientific grade mirrors. These usually contain some other chemical component to strengthen the glass or make it resistant to certain environmental extremes. Pyrex, for example, is a borosilicate glass—a glass composed of silica and boron—that is used when mirrors must withstand high temperatures.

In some cases, a plastic substrate will do as well as a glass one. In particular, mirrors on children's toys are often made this way, so they don't break as easily. Plastic polymers are manufactured from petroleum and other organic chemicals. They can be injection molded into any desired shape, including flat sheets and circles, and can be opaque or transparent as the design requires.

These base materials must be coated to make a mirror. Metallic coatings are the most common. A variety of metals, such as silver, gold, and chrome, are appropriate for this application. Silver was the most popular mirror backing one hundred years ago, leading to the coinage of the term "silvering." Old silver-backed mirrors often have dark lines behind the glass, however, because the material was coated very thinly and unevenly, causing it to flake off, scratch or tarnish. More recently, before 1940, mirror manufacturers used mercury because it spread evenly over the surface of the glass and did not tarnish. This practice was also eventually abandoned, for it posed the problem of sealing in the toxic liquid. Today, aluminum is the most commonly used metallic coating for mirrors.

Scientific grade mirrors are sometimes coated with other materials, like silicon oxides and silicon nitrides, in up to hundreds of layers of, each a 10,000th of an inch thick. These types of coatings, referred to as dielectric coatings, are used both by themselves as reflectors, and as protective finishes on metallic coatings. They are more scratch resistant than metal. Scientific mirrors also use silver coatings, and sometimes gold coatings as well, to reflect light of a particular color of light more or less well.

Design

Surface regularity is probably the most important design characteristic of mirrors. Mirrors for household use must meet roughly the same specifications as window panes and picture frame glass. The glass sheets used must be reasonably flat and durable. The designer need only specify the thickness required; for example, thicker mirrors are more durable, but they are also heavier. Scientific mirrors usually have specially designed surfaces. These surfaces must be uniformly smooth within several lOOOths of an inch, and can be designed with a specific curvature, just like eyeglass lenses. The design principle for these mirrors is the same as that of eyewear: a mirror may be intended to focus light as well as reflect it.

The mirror design will also specify the type of coating to be used. Coating material is chosen based on required durability and reflectivity and, depending on the intended purpose of the mirror, it may be applied on the front or back surface of the mirror. Any subsequent layers of protective coatings must also be specified at this stage. For most common mirrors, the reflective coating will be applied on the back surface of the glass because it is less likely to be harmed there. The back side is then frequently mounted in a plastic or metal frame so as to entirely seal the coating from the air and sharp objects.

For scientific use, the color, or wavelength of light, which the mirror will reflect must be considered. For standard visible light or ultraviolet light mirrors, aluminum coatings are common. If the mirror is to be used with infrared light, a silver or gold coating is best. Dielectric coatings are also good in the infrared range. Ultimately, however, the choice of coating will depend on durability as well as wavelength range, and some reflectivity may be sacrificed for resilience. A dielectric coating, for example, is much more scratch resistant than a metallic coating and, despite the additional cost, these coatings are often added on top of metal to protect it. Coatings on scientific grade mirrors are usually applied on the front surface of the glass, because light which travels through glass will always distort to a small degree. This is undesirable in most scientific applications.

The Manufacturing
Process

Cutting and shaping the glass

• The first step in manufacturing any mirror is cutting the outline of the glass "blank" to suit the application. If the mirror is for an automobile, for example, the glass will be cut out to fit in the mirror mount on the car. Although some mirror manufacturers cut their own glass, others receive glass that has already been cut into blanks. Regardless of who cuts the glass, very hard, finely pointed blades are used to do the cutting. Diamond scribes or saws—sharp metal points or saws with diamond dust embedded in them—are often used because the diamond will wear down the glass before the glass wears down the diamond. The cutting method used depends entirely on the final shape the mirror will take. In one method, the blades or scribes may be used to cut partway through the glass; pressure can then be used to break the glass along the score line. In another method, a machine uses a diamond saw to cut all the way through the glass by drawing the blade back and forth or up and down multiple times, like an automated bandsaw. Cutting is usually done before the metal coating is applied, because the coating may flake off the glass as a result of the cut. An alternative to cutting the glass to form blanks is to mold the glass in its molten state.
• Blanks are then placed in optical grinding machines. These machines consist of large base plates full of depressions that hold the blanks. The blank-filled base is placed against another metal plate with the desired surface shape: flat, convex, or concave. A grinding compound—a gritty liquid—is spread over the glass blanks as they are rubbed or rolled against the curved surface. The action is similar to grinding spices with a mortar and pestle. The grit in the compound gradually wears away the glass surface until it assumes the same shape as the grinding plate. Finer and finer grits are used until the surface is very smooth and even.

  Hand grinding techniques exist as well, but they are extremely time-consuming and difficult to control. They are only used in cases where mechanical grinding would be impossible, as is the case with very large or unusually shaped surfaces. A commercial optical grinder can accommodate 50 to 200 blanks, which are all polished simultaneously. This is much more efficient than hand grinding. Even specialty optics can be made mechanically in adjustable equipment.

Applying the reflective material

• When the glass surfaces are shaped appropriately and polished to a smooth finish, they are coated with whatever reflective material the designer has chosen. Regardless of the coating material, it is applied in an apparatus called an evaporator. The evaporator is a large vacuum chamber with an upper plate for supporting the blank mirrors, and a lower crucible for melting the coating metal. It is so called because metal is heated in the crucible to the point that it evaporates into the vacuum, depositing a coating on the surface of the glass much like hot breath will steam a cold window. Blanks are centered over holes in the upper plate that allow the metal vapor to reach the surface of the glass. Metals can be heated to several hundreds or thousands of degrees (depending on the boiling point of the metal), before they vaporize. The temperature and timing for this procedure are controlled very precisely to achieve exactly the right thickness of metal. This method of coating creates very uniform and highly reflective surfaces.
• The shape of the holes in the upper plate will be transferred to the glass in metal, like paint through a stencil. This effect is often used to intentionally pattern the mirror. Metal stencils, or masks, can be applied to the surface of the glass to create one or more patterns.
• Dielectric coatings—either as reflective layers or as protective layers over metal ones—are applied in much the same way, except that gases are used instead of metal chunks. Silicon oxides and silicon nitrides are typically used as dielectric coatings. When these gases combine in extreme heat, they react to form a solid substance. This reaction product forms a coating just like metal does.
• Several evaporation steps may be combined to make a multiple-layer coating. Clear dielectric materials may be evaporated on top of metal or other dielectrics to change the reflective or mechanical properties of a surface. Mirrors with silvering on the back of the glass, for instance, often have an opaque dielectric layer applied to improve the reflectivity and keep the metal from scratching. One-way mirrors are the exception to this procedure, in which case great care must be taken not to damage the thin metal coating.
• Finally, when the proper coatings have been applied, the finished mirror is mounted in a base or packed carefully in a shock resistant package for shipping.

Quality Control

How good does a mirror have to be? Is it sufficient to have 80 percent of the light bounce off? Does all 80 percent have to bounce in exactly the same direction? The answer is dependent on the application. A purse mirror might only be 80 or 90 percent reflective, and might have some slight irregularity in the thickness of the glass (like ripples on the surface of a pond). The image would be slightly distorted in this case, but the distortion would be barely visible to the naked eye. If, however, a mirror is to be used for a scientific application, for example in a telescope, the shape of the surface and the reflectivity of the coating must be known to a very specific degree, to insure the reflected light goes exactly where the telescope designer wants it, and at the right intensity. The tolerances on the mirror will affect the cost and ease with which it can be manufactured.

Batch mirror uniformity is the first and fore-most job of quality assurance. Mirrors on the edge of a grinding plate or evaporator chamber may not have the same surface or coating as those in the center of the apparatus. If there is a wide range of metal thicknesses or surface flatnesses in a single batch of mirrors, the process must be adjusted to improve uniformity.

Several methods are employed to test the integrity of a mirror. The surface quality is examined first visually for scratches, unevenness, pits, or ripples. This can be done with the unaided eye, with a microscope, or with an infrared photographic process designed to show differences in metal thicknesses.

For more stringent surface control, a profile of the mirror can be measured by running a stylus along the surface. The position of the stylus is recorded as it is dragged across the mirror. This is similar to the way a record player works. Like the record player, the drawback to a mechanical stylus is that it can damage the surface it is detecting. Mirror manufacturers have come to the same solution as the recording industry: use a laser. The laser can be used for non-destructive testing in the same way a compact disc player reads the music from a disc without altering its surface.

In addition to these mechanical tests, mirrors may be exposed to a variety of environmental conditions. Car mirrors, for example, are taken through extremes of cold and heat to insure that they will withstand weather conditions, while bathroom mirrors are tested for water resistance.

The Future

As glassmaking techniques improve, mirrors find a more elaborate place in art and architecture. Stronger, lighter glasses are more attractive to designers. Some one-way mirror manufacturing techniques allow windows to be manufactured that are mirrored on the outside. This creates a distinctive appearance on a building and also makes the building's air conditioning system more efficient by deflecting heat during the summer. This type of mirror is now commonly seen on office buildings.

Mirrors will also continue to be used in sophisticated optical applications, from microscopes and telescopes to laser-based reading systems such as compact disc players and bar code scanners.

Where To Learn More

Books

Hecht, Eugene. Optics. Addison-Wesley Publishing Co., 1974.

Korsch, Dietrich. Reflective Optics. Academic Press, 1991.

Londono, ed. Recent Trends in Optical Systems Design: Computer Lens Design. SPIE-International Society for Optical Engineering, 1987.

Periodicals

Derra, Skip. "Spin Casting Method Makes the Grade for Telescopic Mirrors." Research & Development. August, 1989, p. 24.

Folger, Tim and Roger Ressmeyer. "The Big Eye." Discover. November, 1991, p. 40.

Hogan, Brian J. "Astronomy Gets a Sharper Vision." Design News. August 26, 1991, p. 110.

"Custom Optics." Laser Focus World. December, 1992.

Nash, J. Madeline. "Shoot for the Stars." Time. April 27, 1992, p. 56.

Walker, Jearl. "Wonders with the Retroreflector, a Mirror That Removes Distortion from a Light Beam." Scientific American. April, 1986, p. 118.

[Article by: Leslie G. Melcer]

noun

One that is worthy of imitation or duplication: beau ideal, example, exemplar, ideal, model, paradigm, pattern, standard. See good/bad.

verb

1. To send back or form an image of: image, reflect. See show/hide.
2. To copy (another) slavishly: echo, image, imitate, mimic, parrot, reflect, repeat. See same/different/compare.

A reflective device.

1. A nearly perfect reflecting surface.
2. A small oval ornament surrounded by a molding.

The mirror reflects oneself from the inner depths. If the mirror is clear, one is gazing upon one's true self. This may be a shocking or a pleasant experience, depending upon how many shortcomings or false images the dreamer presents in the real world. A cracked or cloudy mirror reflects the distortions that are projected into the world.

The now-popular idea that vampires cast no reflection in a mirror (and often have an intense aversion to them) seems to have first been put forward in Bram Stoker's novel, Dracula Soon after his arrival at Castle Dracula Jonathan Harker observed that the building was devoid of mirrors. When Dracula silently came into Harker's room while he was shaving, Harker noticed that Dracula, who was standing behind him, did not appear in the shaving mirror as he should have. Dracula complained that mirrors were objects of human vanity, and, seizing the shaving mirror, he broke it. When the novel was brought to the stage and the episode in Castle Dracula deleted, the incident of the mirror was transformed into a confrontation between Dracula and Dr. Abraham Van Helsing

The mirror incident does not seem to have any precedent in either vampire folklore or the earlier vampire short stories and dramas although Stoker seemed to have been aware of folklore about mirrors. Mirrors were seen as somehow revealing a person's spiritual double, the soul. In seeing themselves revealed in a mirror, individuals found confirmation that there was a soul and that hence life went on. They also found in the reflection a new source of anxiety, as the mirror could be used negatively to affect the soul. The notion that the image in the mirror was somehow the soul underlay the idea that breaking a mirror brought seven years' bad luck. Breaking the mirror also damaged the soul.

Thus, one could speculate that the vampire had no soul, had nothing to reflect in the mirror. The mirror forced the vampire to confront the nature of his/her existence as the undead, neither living nor dead. On occasion in both vampire fiction and the cinema, the idea of nonreflection in mirrors has been extended to film, that is, the vampire would not appear in photographs if developed.

In her popular reinterpretation of the vampire myth, Anne Rice dropped Stoker's mirror convention. She argued in part that although vampires have certain "supernatural" attributes, they existed in the same physical universe as mortals and generally had to conform to the same physical laws, including those of optics. Hence, in Interview with the Vampire and Vampire Lestat, Louis and Lestat de Lioncourt respectively, saw themselves in a mirror and experienced a moment of self-revelation about their new vampire image. (Of course, Rice's vampires didn't follow all physical laws since they had the ability to fly.)

Goldberg, Benjamin. The Mirror and Man. Charlottesville, VA: University Press of Virginia, 1985. 260 pp.
Ramsland, Katherine. The Vampire Companion. New York: Ballantine Books, 1993. 507 pp.

This article is about wave reflectors (mainly, specular reflection of visible light). For other uses, see Mirror (disambiguation).

A mirror, reflecting a vase.

A mirror is an object with at least one polished and therefore specularly reflective surface. The most familiar type of mirror is the plane mirror, which has a flat surface. Curved mirrors are also used, to produce magnified or diminished images or focus light or simply distort the reflected image.

Mirrors are commonly used for personal grooming (in which case the old-fashioned term "looking-glass" can be used), decoration, and architecture. Mirrors are also used in scientific apparatus such as telescopes and lasers, cameras, and industrial machinery. Most mirrors are designed for visible light; however, mirrors designed for other types of waves or other wavelengths of electromagnetic radiation are also used, especially in optical instruments.

Metal-coated glass mirrors are said to have been invented in Sidon (modern-day Lebanon) in the first century AD,^[1] and glass mirrors backed with gold leaf are mentioned by the Roman author Pliny the Elder Revolution By Lucio Russo, Silvio Levy Page 331</ref>. Ibn al-Haytham discussed concave and convex mirrors in both cylindrical and spherical geometries,^[2] carried out a number of experiments with mirrors, and solved the problem of finding the point on a convex mirror at which a ray coming from one point is reflected to another point.^[3] By the 11th century, clear glass mirrors were being produced in [[=Ajram>Dr. Kasem Ajram (1992). The Miracle of Islam Science (2nd Edition ed.). Knowledge House Publishers. ISBN 0-911119-43-4. </ref>

Some time during the early Renaissance, European manufacturers perfected a superior method of coating glass with a tin-mercury amalgam. The exact date and location of the discovery is unknown, but in the 16th century, Venice, a city famed for its glass-making expertise, became a centre of mirror production using this new technique. Glass mirrors from this period were extremely expensive luxuries.^[4] The Saint-Gobain factory, founded by royal initiative in France, was an important manufacturer, and Bohemian and German glass, often rather cheaper, was also important.

The invention of the silvered-glass mirror is credited to German chemist Justus von Liebig in 1835.^[5] His 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. Nowadays, mirrors are often produced by the vacuum deposition of aluminium (or sometimes silver) directly onto the glass substrate.

In classical antiquity mirrors were made of solid metal (bronze, later silver) and were too expensive for widespread use, as well as being prone to corrosion. Due to the low reflectivity of polished metal these mirrors also gave a darker image than modern ones, making them unsuitable for indoor use with the artificial lighting of the time (candles or lanterns).

The method of making mirrors out of plate glass was invented by 16th-century Venetian glassmakers on the island of Murano, who covered the back of the glass with mercury, obtaining near-perfect and undistorted reflection. For over one hundred years Venetian mirrors installed in richly decorated frames served as luxury decoration for palaces throughout Europe, but the secret of the mercury process eventually arrived to London and Paris during the 17th century, due to industrial espionage. French workshops succeeded in large scale industrialization of the process, eventually making mirrors affordable to the masses, although mercury's toxicity remained a problem^{[citation needed]}.

In modern times the mirror substrate is shaped, polished and cleaned, and is then coated. Glass mirrors are most often coated with non-toxic silver or aluminium, implemented by a series of coatings:

1. tin
2. silver
3. chemical activator
4. copper
5. paint

The tin is applied because silver will not bond with the glass. The activator causes the tin/silver to harden. Copper is added for long-term durability.^[6] The paint protects the coating on the back of the mirror from scratches and other accidental damage.

In some applications, generally those that are cost-sensitive or that require great durability, mirrors are made from a single, bulk material such as polished metal.

For technical applications such as laser mirrors, the reflective coating is typically applied by vacuum deposition on the front surface of the substrate. This eliminates double reflections (a weak reflection from the surface of the glass, and a stronger one from the reflecting metal) and reduces absorption of light by the mirror. Technical mirrors may use a silver, aluminium, or gold coating (the latter typically for infrared mirrors), and achieve reflectivities of 90–95% when new. A protective transparent overcoat may be applied to prevent oxidation of the reflective layer. Applications requiring higher reflectivity or greater durability where wide bandwidth is not essential use dielectric coatings, which can achieve reflectivities as high as 99.999% over a narrow range of wavelengths.

Contents 1 Applications 1.1 Safety and easier viewing 1.2 Two-way mirrors 1.3 Signalling 1.4 Technology 1.4.1 Televisions and projectors 1.4.2 Instruments 1.4.2.1 Face-to-face mirrors 1.4.3 Military applications 1.4.4 Seasonal lighting 1.5 Leisure 1.5.1 Decoration 1.5.2 Entertainment 1.5.3 Art 1.5.4 Literature 2 Mirrors and superstition 3 Mirrors and animals 4 Unusual types of mirror 5 See also 6 Notes 7 Bibliography 8 External links

Applications

Reflections in a spherical convex mirror. The photographer is seen at top right

Safety and easier viewing

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. Some motorcycle helmets have a built-in so-called MROS (Multiple Reflective Optic System): a set of reflective surfaces inside the helmet that together function as a rear-view mirror.[1] There exist rear view sunglasses, of which the left end of the left glass and the right end of the right glass work as mirrors.

Convex mirrors are used to provide a wider field of view than a flat mirror, and are often used on vehicles, especially large trucks, to minimise blind spots. They are sometimes placed at road junctions, and corners of places such as parking lots to allow people to see around corners to avoid crashing into other vehicles or shopping carts. They are also sometimes used as part of security systems, so that a single video camera can show more than one angle at a time.

Mouth mirrors or "dental mirrors" are used by dentists 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 engineers to allow vision in tight spaces and around corners in equipment.

Two-way mirrors

Main article: Two-way mirror

A two-way mirror (two-way as viewers on both sides use it), sometimes called a one-way mirror or one-way glass (because it is possible to see through it in one direction only), reflects some percentage of the light incident on it and transmits the remainder to the other side. It is a sheet of glass coated with a layer of metal only a few dozen atoms thick, transmitting some light and reflecting the remainder (from both sides).

It is typically used as an apparently normal mirror in a brightly lit room, with a much darker room on the other side. People on the brightly lit side see their own reflection—it looks like a normal mirror. People on the dark side see through it—it looks like a transparent window. The light from the bright room reflected from the mirror back into the room itself is much greater than the light transmitted from the dark room, overwhelming the small amount of light transmitted from the dark to the bright room; conversely, the light reflected back into the dark side is overwhelmed by the light transmitted from the bright side. This allows a viewer in the dark side to observe the bright room covertly.

The reality television program Big Brother makes extensive use of two-way mirrors throughout its set to allow cameramen in special black hallways to use movable cameras to film contestants without being seen.

The same type of mirror, when used in an optical instrument, is called a half-silvered mirror or beam splitter. Its purpose is quite different: to split a beam of light so that part, usually about half, passes straight through, while the other part is reflected. In a typical scientific application the two resulting beams are made to interfere after traversing different paths. An unusual single-lens reflex camera used a half-silvered mirror to create an image of the scene both in the film plane and in the viewfinder.

One-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: if we place a cold object on the transmitting side and a hot one on the blocked side, radiant energy would be transferred from the cold to the hot object.

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. ^[7][8] Optical isolators are one-way devices that are commonly used with lasers.

Signalling

Main article: Heliograph

With the sun as 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 60 kilometres on a clear day. This technique was used by Native American tribes and numerous militaries to transmit information between distant outposts.

Mirrors can also be used for rescue, especially to attract the attention of search and rescue helicopters. Specialised signalling mirrors are available and are often included in military survival kits.

Technology

Televisions and projectors

Microscopic mirrors are a core element of many of the largest high-definition televisions and video projectors. A common technology of this type is Texas Instruments' DLP. A DLP chip is a postage stamp-sized microchip whose surface is comprised of 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 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 matrix with up to millions of pixels. The picture is 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 mentioned above) is "folded" by one or more mirrors so that the television set is compact.

Instruments

Telescopes 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 aluminum, 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 the air. Front silvered mirrors have to be resurfaced occasionally to keep their quality.

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 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, aluminum 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 mirrors 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 lasers.

In astronomy, adaptive optics 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 the most of 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 are used in optics and astronomy. Mirrors for radio waves are important elements of radio telescopes.

A Mangin mirror is a combination lens and concave mirror and is widely used in optical instruments and even sometimes in cameras.[2] [3][4]

Face-to-face mirrors

Two or more mirrors placed exactly face to face give the appearance of an infinite regress. Some devices use this to generate multiple reflections:

• Fabry-Pérot interferometer
• Laser (which contains an optical cavity)
• some types of catoptric cistula
• momentum-enhanced solar sail

Military applications

It has been said that Archimedes used a large array of mirrors to burn Roman ships during an attack on Syracuse. This has never been proven or disproved; however, it has been put to the test. Recently, on a popular Discovery Channel show, MythBusters, a team from MIT tried to recreate the famous "Archimedes Death Ray". They were successful at starting a fire on a ship at 75 feet away; however, previous attempts to light the 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". (See solar power tower for a practical use of this technique.)

Seasonal lighting

A multi-facet mirror in the Kibble Palace conservatory, Glasgow, Scotland.

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.^[9][10] Mirrors can be used to produce enhanced lighting effects in greenhouses or conservatories.

Leisure

Decoration

Mirrors, typically large and unframed, are frequently used in interior decoration to create an illusion of space, and amplify the apparent size of a room.

Mirrors are used also in some schools of feng shui, an ancient Chinese practice of placement and arrangement of space to achieve harmony with the environment.

The softness of old mirrors is sometimes replicated by contemporary artisans for use in interior design. These reproduction antiqued mirrors are works of art and can bring color and texture to an otherwise hard, cold reflective surface. It is an artistic process that has been attempted by many and perfected by few.

A decorative reflecting sphere of thin metal-coated glass, working as a reducing wide-angle mirror, is sold as a Christmas ornament called a bauble.

Entertainment

The hall of mirrors, commonly found in amusement parks, is an attraction in which a number of distorted mirrors are used to produce unusual reflections of the visitor. Mirror mazes, also found in amusement parks, contain large numbers of mirrors and sheets of glass. The idea is to navigate the disorientating array without bumping into the walls.

Mirrors are often used in magic to create an illusion. One effect is called Pepper's ghost. Illuminated rotating disco balls covered with small mirrors are used to cast moving spots of light around a dance floor. Mirrors are employed in kaleidoscopes, personal entertainment devices invented in Scotland by sir David Brewster.

Art

Filippo Brunelleschi discovered linear perspective with the help of the mirror, Leonardo da Vinci 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." The mirror is the central device in some of the greatest of European paintings: Jan Van Eyck's Arnolfini Portrait, Diego Velazquez's Las Meninas and Edouard Manet’s A Bar at the Folies-Bergère. Without a mirror, the great self portraits by Dürer, Rembrandt, Van Gogh and Frida Kahlo could not have been painted. M. C. Escher used special shapes of mirrors in order to have a much more complete view of the surroundings than by direct observation (Hand with Reflecting Sphere). István Orosz’s anamorphic works are images distorted such way that they only become clearly visible when reflected in a suitably-shaped and positioned mirror. Some other contemporary artists use mirrors as the material of art, like in mirror-sculptures and paintings on mirror surfaces. Some artists build special mirror installations as the neon mirror cubes by Jeppe Hein.

Painters depicting someone in front of 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 the 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.

Literature

Mirrors play a powerful role in cultural literature, from the self-loving Narcissus of Greek Mythology to the Biblical reference to Through a Glass Darkly. The evil queen in the European fairy-tale Snow White asked, "Mirror, mirror, on the wall... who's the fairest of them all?" Some of the best-loved uses of mirrors in literature include Lewis Carroll's Through the Looking Glass and the Mirror of Erised in the Harry Potter series. Horror movies about mirrors include Candyman and Mirrors.

Mirrors and superstition

There are many legends and superstitions surrounding mirrors. Mirrors are said to be a reflection of the soul, and they were often used in traditional witchcraft as tools for scrying or performing other spells. It is also said that mirrors cannot lie. They can show only the truth, so it is a very bad omen indeed to see something in a mirror which should not be there. Also there is a legend that a newborn child should not see a mirror until its first birthday as its soul is still developing. If the child sees its reflection it is said that it will die.

It is a common superstition that someone who breaks a mirror will receive seven years of bad luck. One of the many reasons for this belief is that the mirror is believed to reflect part of the soul, therefore, breaking the mirror will break part of the soul. However, the soul is said to regenerate every seven years, thus coming back unbroken. To counter this one of many rituals has to be performed, the easiest of which is to stop the mirror from reflecting the broken soul by grinding it to dust.^[11] The belief might also simply originate from the high cost of mirrors in times gone past. It is also said that tapping the broken mirror on a gravestone seven times will allow the soul to heal. Another option is to bury the mirror, also preventing the mirror from reflecting the broken soul. However, if the mirror is both touched to the gravestone and buried, the bad luck will remain. If you are in this position, the only course of action is to dig up the mirror and grind it to dust. Finally, this dust must be sprinkled around the same gravestone on which the mirror was initially tapped.

In days past it was customary in the southern United States to cover the mirrors in a house where the wake of a deceased person was being held. It was believed that the person's soul would become trapped in a mirror left uncovered. This practice is still followed in other countries (Greece), extending to everything that could reflect the deceased person's face (like TV appliances); another explanation given is that the devil will appear in the reflection of the dead. Mirrors falling from walls or otherwise breaking or cracking mysteriously were said to be haunted.

According to legend, a vampire has no reflection in mirrors because it is an undead creature and has already lost its soul.

Spectrophobia is the fear of mirrors.

Another superstition claims it is bad luck to have two mirrors facing each other.^[12]

A staple of childhood slumber parties is the game Bloody Mary, which involves chanting "Bloody Mary" three times in a darkened room while staring into a mirror. There are many versions of the game, but the general idea is that "Mary" will appear in the mirror and attempt to harm or kill the person who has summoned her. Thanks to a series of popular horror movies based on a supernatural killer who haunted mirrors, the phrase "Candy Man" may be substituted for Mary.

Mirrors and animals

The Asian elephant can recognise its own reflection in a mirror

Experiments have shown that only large-brained social animals are able to recognise that a mirror shows a reflection of themselves.^[13]

Animals that have shown they are able to use a mirror to study themselves:

• Asian elephants
• Bonobos
• Common chimpanzees
• Dolphins
• Magpies
• Orangutans

Unusual types of mirror

Other types of reflecting device are also called "mirrors". For example metallic reflectors are used to reflect infrared light (such as in space heaters), or microwaves.

4.5 metre high acoustic mirror near Kilnsea Grange, East Yorkshire, UK

An acoustic mirror is a passive device used to reflect and perhaps to focus sound waves. Acoustic mirrors were used for selective detection of sound waves, especially during World War II. They were used for detection of enemy aircraft prior to the development of radar. Acoustic mirrors are used for remote probing of the atmosphere; they can be used to form a narrow diffraction-limited beam.^[14] They can also be used for underwater "imaging".

Active mirrors are mirrors that amplify the light they reflect. They are used to make disk lasers.^[15] The amplification is typically over a narrow range of wavelengths, and requires an external source of power.

An atomic mirror is a device which reflects matter waves. Usually, atomic mirrors work at grazing incidence. Such a mirror can be used for atomic interferometry and atomic holography. It has been proposed that they can be used for non-destructive imaging systems with nanometer resolution.^[16]

Cold mirrors are dielectric mirrors that reflect the entire visible light spectrum while efficiently transmitting infrared wavelengths. Conversely, hot mirrors reflect infrared light while allowing visible light to pass. These can be used to separate useful light from unneeded infrared to reduce heating of components in an optical device. They can also be used as dichroic beamsplitters.

Corner reflectors use three flat mirrors to reflect light back towards its source. They are used for emergency location, and even laser ranging to the Moon.

X-ray mirrors produce specular reflection of X-rays. All known types work only at angles near grazing incidence, and only a small fraction of the rays are reflected.^[17]

A non-reversing mirror is a mirror that provides a non-reversed image of its subject.

See also

Look up Mirror in Wiktionary, the free dictionary.

• Anamorphosis
• Aranmula kannadi
• Bronze mirror
• Cold mirror and Hot mirror
• Curved mirror
• Deformable mirror
• Dielectric mirror
• Digital micromirror device
• Home decor
• Honeycomb mirror
• Mirror armour (an oriental partial plate armour from polished metal mirrors)
• Mirror writing
• Perfect mirror
• Periscope
• Rear-view mirror
• Reflectivity
• Silvering
• TLV mirror — An ancient type of Chinese mirror from the Han Dynasty.
• Two-way mirror (Also known as one-way mirror)
• Venus effect

Notes

1. ^ Mirrors in Egypt, Digital Egypt for Universities
2. ^ R. S. Elliott (1966). Electromagnetics, Chapter 1. McGraw-Hill.
3. ^ Dr. Mahmoud Al Deek. "Ibn Al-Haitham: Master of Optics, Mathematics, Physics and Medicine, Al Shindagah, November-December 2004.
4. ^ The Tin-Mercury Mirror: Its Manufacturing Technique and Deterioration Processes, Per Hadsund, Studies in Conservation, Vol. 38, No. 1 (Feb., 1993)
5. ^ Liebig, Justus (1856). "Ueber Versilberung und Vergoldung von Glas". Annalen der Chemie und Pharmacie 98 (1): 132–139. doi:10.1002/jlac.18560980112. 
6. ^ Episode 305 of How It's Made, filmed at La Verrerie Walker Ltée in Ajou, Quebec, Canada
7. ^ Mungan, C.E. (1999). "Faraday Isolators and Kirchhoff’s Law: A Puzzle" (pdf). http://www.usna.edu/Users/physics/mungan/Scholarship/FaradayIsolators.pdf. Retrieved on 2006-07-18. 
8. ^ Rayleigh, On the magnetic rotation of light and the second law of thermodynamics, Nature (London), Vol. 64, p. 577 (Oct. 10, 1901).
9. ^ BBC NEWS | Europe | Italy village gets 'sun mirror'
10. ^ Swiss Officials Want to Spread Sunshine, Swiss Officials May Build Giant Mirror to Give Light to Sunless Village - CBS News
11. ^ www.mirrorsmyth.com
12. ^ www.answers.com/topic/mirrors-4
13. ^ "Elephants see themselves in the mirror". Peter Aldhous. New Scientist. 30 October 2006. http://www.newscientist.com/article/dn10402-elephants-see-themselves-in-the-mirror.html. Retrieved on 2007-05-24. 
14. ^ M. A. Kallistratova (1997). "Physical grounds for acoustic remote sensing of the atmospheric boundary layer". Lecture Notes in Earth Sciences 69: 3–34. doi:10.1007/BFb0009558. http://www.springerlink.com/content/w613354427150024. 
15. ^ K. Ueda; N. Uehara (1993). "Laser-diode-pumped solid state lasers for gravitational wave antenna". Proceedings of SPIE 1837: 336–345. doi:10.1117/12.143686. http://bookstore.spie.org/index.cfm?fuseaction=DetailPaper&ProductId=143686&coden=PSISDG. 
16. ^ D.Kouznetsov; H. Oberst, K. Shimizu, A. Neumann, Y. Kuznetsova, J.-F. Bisson, K. Ueda, S. R. J. Brueck (2006). "Ridged atomic mirrors and atomic nanoscope". Journal of Physics B 39: 1605–1623. doi:10.1088/0953-4075/39/7/005. http://stacks.iop.org/0953-4075/39/1605. 
17. ^ V.V.Protopopov; V.A.Shishkov, and V.A.Kalnov (2000). "X-ray parabolic collimator with depth-graded multilayer mirror". Review of Scientific Instruments 71 (12): 4380–4386. doi:10.1063/1.1327305. 

Bibliography

• Mirror, Mirror: A History of the Human Love Affair with Reflection, Mark Pendergrast. Basic Books (2003). ISBN 0-465-05471-4 .
• On reflection, Jonathan Miller, National Gallery Publications Limited (1998). ISBN 0-300-07713-0 .
• The Mirror: A History, Sabine Melchior-Bonnet, Routledge, 2001, ISBN 0415924480

External links

Wikimedia Commons has media related to: Mirrors

• The Mirror: A History by Sabine Melchior-Bonnet at Google Books
• The Narcissus Syndrome Revisited by Yves Doré
• How Mirrors Are Made (video), Glass Association of North America]
• Knol/Google Mirror page
• How Antique Mirrors can be reproduced

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - spejl
v. tr. - (af)spejle

idioms:

• mirror finish    højglanspolering
• mirror image    spejlbillede
• mirror writing    spejlskrift

Nederlands (Dutch)
spiegel, toonbeeld, weerspiegelen, afspiegelen, navolgen

Français (French)
n. - miroir, glace, (Aut) rétroviseur, (fig) reflet
v. tr. - (lit, fig) refléter, se réfléchir

idioms:

• mirror finish    brillant, peinture brillante
• mirror image    (fig) image inversée
• mirror writing    écriture spéculaire, écriture en miroir

Deutsch (German)
n. - Spiegel
v. - widerspiegeln

idioms:

• mirror finish    Hochglanz
• mirror image    Spiegelbild
• mirror writing    Spiegelschrift

Ελληνική (Greek)
n. - (οπτ.) καθρέφτης, κάτοπτρο, πιστή απομίμηση
v. - καθρεφτίζω, αντικατοπτρίζω, αντανακλώ

idioms:

• mirror finish    αντανακλαστική επιφάνεια
• mirror image    (οπτ.) εναντιόμορφο είδωλο
• mirror writing    κατοπτρική γραφή (από τα δεξιά προς τα αριστερά)

Italiano (Italian)
riflettere, specchio, riflesso

idioms:

• mirror finish    superficie riflettente
• mirror image    immagine a specchio
• mirror writing    scrittura a specchio

Português (Portuguese)
n. - espelho (m), modelo (m)
v. - espelhar

idioms:

• mirror finish    superfície reflexiva (f)
• mirror image    à imagem e semelhança
• mirror writing    escrita espelhada

Русский (Russian)
зеркало, отображение, зеркальная поверхность, отражать

idioms:

• mirror finish    зеркальная полировка
• mirror image    зеркальное отображение
• mirror writing    зеркальное письмо

Español (Spanish)
n. - espejo, retrovisor, reflejo, ejemplo, modelo
v. tr. - reflejar

idioms:

• mirror finish    superficie reflectora
• mirror image    reflejo exacto, contraimagen
• mirror writing    escritura invertida

Svenska (Swedish)
n. - spegel, mönster
v. - återspegla

中文（简体）(Chinese (Simplified))
镜子, 典范, 写真, 反映, 映出

idioms:

• mirror finish    像镜面一样亮的表面
• mirror image    镜像, 映像, 反映, 翻版
• mirror writing    倒写

中文（繁體）(Chinese (Traditional))
n. - 鏡子, 典範, 寫真
v. tr. - 反映, 映出

idioms:

• mirror finish    像鏡面一樣亮的表面
• mirror image    鏡像, 映像, 反映, 翻版
• mirror writing    倒寫

한국어 (Korean)
n. - 거울, 표범
v. tr. - 비추다, 반사하다

日本語 (Japanese)
n. - 鏡, 反射鏡, 写し出すもの
v. - 映す, 反映させる

idioms:

• mirror finish    ぴかぴかの
• mirror image    鏡像
• mirror writing    逆書き
• rear-view mirror    バックミラー

العربيه (Arabic)
‏(الاسم) مرآة (فعل) يعكس صورة‏

עברית (Hebrew)
n. - ‮ראי, מראה, בבואה‬
v. tr. - ‮שיקף בבואה (כמו ראי)‬

If you are unable to view some languages clearly, click here.

To select your translation preferences click here.