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A mirror, reflecting a vase.

A mirror is an object with at least one 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 non-optical instruments.

Contents

History

A sculpture of a lady looking into a mirror, India

The first mirrors used by people were most likely pools of dark, still water, or water collected in a primitive vessel of some sort. The earliest manufactured mirrors were pieces of polished stone such as obsidian, a naturally occurring volcanic glass. Examples of obsidian mirrors found in Anatolia (modern-day Turkey) have been dated to around 6000 BC. Polished stone mirrors from central and south America date from around 2000 BC onwards.[1] Mirrors of polished copper were crafted in Mesopotamia from 4000 BC,[1] and in ancient Egypt from around 3000 BC.[2] In China, bronze mirrors were manufactured from around 2000 BC,[3] some of the earliest bronze and copper examples being produced by the Qijia culture. Mirrors made of other metal mixtures (alloys) such as copper and tin speculum metal may have also been produced in China and India.[4] Mirrors of speculum metal or any precious metal were hard to produce and were only owned by the wealthy.[5]

Metal-coated glass mirrors are said to have been invented in Sidon (modern-day Lebanon) in the first century AD,[6] and glass mirrors backed with gold leaf are mentioned by the Roman author Pliny in his Natural History, written in about 77 AD.[7] The Romans also developed a technique for creating crude mirrors by coating blown glass with molten lead.[8]

Parabolic mirrors were described and studied in classical antiquity by the mathematician Diocles in his work On Burning Mirrors.[9] Ptolemy conducted a number of experiments with curved polished iron mirrors,[10] and discussed plane, convex spherical, and concave spherical mirrors in his Optics.[11] Parabolic mirrors were also described by the physicist Ibn Sahl in the 10th century,[12] and Ibn al-Haytham discussed concave and convex mirrors in both cylindrical and spherical geometries,[13] 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.[14] By the 11th century, clear glass mirrors were being produced in Moorish Spain.[15]

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.[16] 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.[17] 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.

Manufacturing

Mirrors are manufactured by applying a reflective coating to a suitable substrate. The most common such substrate is glass, due to its transparency, ease of fabrication, rigidity, hardness, and ability to take a smooth finish. The reflective coating ("silver") is typically applied to the back surface of the glass, so that the reflecting side of the coating is protected from corrosion and accidental damage by the glass on one side and the coating itself and optional paint for further protection on the other.

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).[citation needed]

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[18] or aluminium, implemented by a series of coatings:[citation needed]

  1. Tin(II) chloride
  2. Silver
  3. Chemical activator
  4. Copper
  5. Paint

The Tin(II) chloride 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.[19] The paint protects the coating on the back of the mirror from scratches and other accidental damage.[citation needed]

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.[citation needed]

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.[citation needed]

Types of Glass Mirror

There are many types of glass mirrors, each of them representing a different manufacturing process and reflection type.

An aluminum glass mirror is made of a float glass manufactured using vacuum coating, i.e. aluminum is spread over the glass in the vacuum chamber and then coated with two or more layers of waterproof protective paint. Aluminum glass mirror provides an actual and accurate reflection.

Silver Glass Mirror is an ordinary mirror coated on its back surface with silver that produces images by reflection. This kind of glass mirror is produced by coating a silver, copper film and two or more layers of waterproof paint on the back surface of float glass, which perfectly resists acid and moisture. Silver glass mirror provides clear and actual images, is quite durable and is widely used for furniture, bathroom and other decoration purposes.

Low Aluminum Glass Mirror is manufactured by coating silver and two layers of protective paint on the back surface of glass. Low aluminum glass mirror is very clear, light transmissive, smooth, and reflects accurate natural colors. This type of glass is widely used for framing presentations and exhibitions in which a precise color representation of the artwork is truly essential or when the background color of the frame is predominantly white.

Safety Glass Mirror is made of a glass silver mirror by sticking a special protective film in the back surface of the mirror, which prevents injuries in case the mirror is broken. This kind of mirror is used for furniture, doors, glass walls, commercial shelves, or public areas.

Silkscreen Printed Glass Mirror is produced using inorganic color ink that prints patterns through a special screen onto glass. Various colors, patterns, and glass shapes are available. Such glass mirror is durable and more moisture resistant than an ordinary printed glass and can server for over 20 years. This type of glass is widely used for decoration purposes (mirrors, table tops, doors, windows, kitchen chop boards, etc.)

Decorative Glass Mirrors are usually handcrafted. Different shades, shapes and glass thickness are often available.

Effects

In a plane mirror, a parallel beam of light changes its direction as a whole, while still remaining parallel; the images formed by a plane mirror are virtual images, of the same size as the original object (see mirror image). There are also concave mirrors, where a parallel beam of light becomes a convergent beam, whose rays intersect in the focus of the mirror. Lastly, there are convex mirrors, where a parallel beam becomes divergent, with the rays appearing to diverge from a common intersection "behind" the mirror. Spherical concave and convex mirrors do not focus parallel rays to a single point due to spherical aberration. However, the ideal of focusing to a point is a commonly-used approximation. Parabolic reflectors resolve this, allowing incoming parallel rays (for example, light from a distant star) to be focused to a small spot; almost an ideal point. Parabolic reflectors are not suitable for imaging nearby objects because the light rays are not parallel. If you look in a mirror, your image reverses, (e.g. if you raise your right hand, your left hand will go up in the mirror)

A beam of light reflects off a mirror at an angle of reflection that is equal to its angle of incidence (if the size of a mirror is much larger than the wavelength of light). That is, if the beam of light is shining on a mirror's surface at a θ° angle vertically, then it reflects from the point of incidence at a θ° angle from vertically in the opposite direction.

This law mathematically follows from the interference of a plane wave on a flat boundary (of much larger size than the wavelength).

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.[2] 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

A two-way mirror is a sheet of glass coated with a layer of metal only a few dozen atoms thick, which reflects some percentage of the light incident on it and transmits the remainder to the other side.

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.[20][21] Optical isolators are one-way devices that are commonly used with lasers.

Signalling

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 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. 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.[3] [4][5]

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.

A dielectric coated mirror used in a dye laser. The mirror is over 99% reflective at 550 nanometers, (yellow), but will allow most other colors to pass through.

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.

Face-to-face mirrors
A dielectric mirror used in lasers.

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

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.[22][23] 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 in attractions like this are often made of plexiglass as to assure that they do not break.

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, Titian's Venus with a mirror, Veronese's Venus with a mirror, 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 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 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. In the European fairy-tale Snow White, the evil queen 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.[24] 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.[25] 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.[citation needed]

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.[26]

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.[27]

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

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.[28] 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.[29] 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.[30]

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.[31] See also X-ray optics.

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

See also

Notes

  1. ^ a b History of Mirrors Dating Back 8000 Years, Jay M. Enoch, School of Optometry, University of California at Berkeley
  2. ^ The National Museum of Science and Technology, Stockholm
  3. ^ Chinavoc.com
  4. ^ Google Books Search, by Joseph Needham, Gwei-djen Lu, Science and civilisation in China, Volume 5, page 238
  5. ^ Books Search, Albert Allis, The Scientific American cyclopedia of formulas, page 89
  6. ^ Mirrors in Egypt, Digital Egypt for Universities
  7. ^ Wondrous Glass: Images and Allegories, Kelsey Museum of Archaeology
  8. ^ The Book of the Mirror, Cambridge Scholars Publishing, edited by Miranda Anderson
  9. ^ pp. 162–164, Apollonius of Perga's Conica: text, context, subtext, Michael N. Fried and Sabetai Unguru, Brill, 2001, ISBN 9004119779.
  10. ^ p. 64, Mirror mirror: a history of the human love affair with reflection, Mark Pendergrast, Basic Books, 2004, ISBN 0465054714
  11. ^ pp. 38 ff., Ptolemy's Theory of Visual Perception: An English Translation of the "Optics" with Introduction and Commentary, A. Mark Smith, Transactions of the American Philosophical Society, new series 86, #2 (1996), pp. iii–300.
  12. ^ pp. 465, 468, 469, A Pioneer in Anaclastics: Ibn Sahl on Burning Mirrors and Lenses, Roshdi Rashed, Isis, 81, #3 (September 1990), pp. 464–491, doi:10.1086/355456.
  13. ^ R. S. Elliott (1966). Electromagnetics, Chapter 1. McGraw-Hill.
  14. ^ Dr. Mahmoud Al Deek. "Ibn Al-Haitham: Master of Optics, Mathematics, Physics and Medicine, Al Shindagah, November-December 2004.
  15. ^ Dr. Kasem Ajram (1992). The Miracle of Islam Science (2nd Edition ed.). Knowledge House Publishers. ISBN 0-911119-43-4. 
  16. ^ The Tin-Mercury Mirror: Its Manufacturing Technique and Deterioration Processes, Per Hadsund, Studies in Conservation, Vol. 38, No. 1 (Feb., 1993)
  17. ^ Liebig, Justus (1856). "Ueber Versilberung und Vergoldung von Glas". Annalen der Chemie und Pharmacie 98 (1): 132–139. doi:10.1002/jlac.18560980112. 
  18. ^ [1]
  19. ^ Episode 305 of How It's Made, filmed at verrerie-walker.com in Anjou, Quebec, Canada
  20. ^ Mungan, C.E. (1999). "Faraday Isolators and Kirchhoff’s Law: A Puzzle" (pdf). http://www.usna.edu/Users/physics/mungan/Scholarship/FaradayIsolators.pdf. Retrieved 2006-07-18. 
  21. ^ Rayleigh, On the magnetic rotation of light and the second law of thermodynamics, Nature (London), Vol. 64, p. 577 (Oct. 10, 1901).
  22. ^ BBC NEWS | Europe | Italy village gets 'sun mirror'
  23. ^ Swiss Officials Want to Spread Sunshine, Swiss Officials May Build Giant Mirror to Give Light to Sunless Village - CBS News
  24. ^ Milkinson, David; Barbara (2009). "Breaking a Mirror". Urban Legends Reference Pages. Snopes.com. p. 1. http://www.snopes.com/luck/superstition/breakmirror.asp. Retrieved 2009-08-29. 
  25. ^ www.mirrorsmyth.com
  26. ^ www.answers.com/topic/mirrors-4
  27. ^ "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 2007-05-24. 
  28. ^ 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. 
  29. ^ 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. 
  30. ^ 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. 
  31. ^ 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. 

References

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


Study guide

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An electron microscope image of a tiny piece of dielectric mirror being cut out from a larger substrate. The periodic structure of the mirror is clearly visible on the bottom edge.

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1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

MIRROR (through O. Fr. mirour, mod. miroir, from a supposed Late Lat. miratorium, from mirari, to admire), an optical instrument which produces images of objects by reflection. In its usual forms it is simply a highly polished sheet of metal or of glass (which may or may not be covered, either behind or before, with a metallic film); a metallic mirror is usually termed a speculum. The laws relating to the optical properties of mirrors are treated in the article Reflection Of Light.

Ancient Mirrors

The mirror (thr07rrpov, g aoirTpov, gv07rrpov, speculum) of the Etruscans, Greeks and Romans consisted of a thin disk of metal (usually bronze) slightly convex and polished on one side, the other being left plain or having a design incised upon it. A manufactory of mirrors of glass at Sidon is mentioned by Pliny (Nat. Hist. xxxvi. 66, 193), but they appear to have been little used (one has been found at San Remo). Glass mirrors were coated, but with tin; some silver mirrors have also been found. They are said to have been in use as early as the time of Pompey, and were common under the empire. Homer knows nothing of mirrors, but they are frequently mentioned in the tragedians and onwards. The usual size was that of an ordinary hand-mirror, but in imperial times some appear to have been large enough to take in the whole figure (Seneca, Nat. quaest., i. 17, 8), being either fixed to the wall or working up and down like a window sash. The first specimen of a Greek mirror was not discovered till 1867, at Corinth, and the number extant is comparatively small. They are usually provided with a handle, which sometimes took the form of a statuette (especially of Aphrodite) supported on a pedestal, or consist of two metallic circular disks (the "box" mirrors) fitting in to each other, and sometimes fastened together by a hinge. The upper disk or cover was ornamented on the outside with a design in low relief; inside it was polished to reflect the face. The lower disk was decorated inside with engraved figures. The best specimens of both kinds of mirrors date from a little before 400 B.C. and last for some time after that. Of the reliefs, one of the best examples is "Ganymede carried away by the eagle"; amongst the incised mirrors may be mentioned one representing Leucas and Corinthus, inscribed with their names (both the above in Collignon, L'Archeologie grecque, 1907, figs. 212, 213); the Genius of the Cock-fights (Revue archeologique, new ser. xvii., 1868, Pl. 13). A bronze mirror-case, found at Corinth, has attached on the outside a relief representing an Eros with two girls; on the inside is incised a design of a nymph seated on a bench and playing with Pan at a game resembling the Italian mora (Classical Review, Feb. 1889, p. 86). On the back of another mirror in the British Museum (Gazette archeologique, ii. Pl. 27) is a figure of Eros which has been silvered over. With this was found the bronze case used to contain it, on the back of which is a group of Aphrodite and Eros in repousse. It was found in Crete; but most of the Greek mirrors and mirror-cases having designs are from Corinth.

The principal feature of the Etruscan mirrors, the extant examples of which far outnumber the Greek, is the design incised on the back. Belonging chiefly to the 4th and 3rd centuries, they mostly resemble the Greek disk-mirrors in form, box-mirrors being rare. As a rule the subjects incised are taken from Greek mythology and legend (Trojan War, birth of Athena, Aphrodite and Adonis), the names of the persons represented being frequently added in Etruscan letters and orthography (Apul= Apollo, Achle = Achilles, Achmemrum = Agamemn.on). Scenes from daily life, the toilet, the bath, the palaestra, also occur. In most cases the style of drawing, the types of the figures, and the manner of composing the groups are true to the characteristics of Greek art. Some may have been imported from Greece, but the greater number appears to have been more or less faithfully imitated from such designs as occurred on the Greek vases which the Etruscans obtained from Greece. Even where distinctly Etruscan figures are introduced, such as the, heroes Aelius and Caelius Vibenna on a mirror in the British Museum, Greek models are followed. Although the work is frequently rough and careless, certain very fine and beautiful specimens have been found: the famous Semele-mirror, and the healing of Telephus, in which Achilles is shown scraping the healing rust from the lance with a crescent-shaped knife (Baumeister, Denkmaler, figs. 557, 1 774). Roman mirrors are usually disk-mirrors, the back of the disk, if engraved, being generally ornamented with decorative patterns, not with any subject design.

Plain mirrors are found wherever Greek and Roman civilization spread, and a specimen found in Cornwall (now in the British Museum) shows that the Celtic population of England had adopted the form and substance of the mirror from their conquerors. This specimen is enriched with a Celtic pattern incised. The shape of the handle exhibits native originality. Mirrors were sometimes used in Greece for purposes of divination (Pausanias vii. 21, 5). The mirror was let down into a well by means of a string until it grazed the surface of the water with the rim; after a little while it was pulled up, and when looked into showed the face of the sick person, alive or dead, on whose behalf the ceremony had been performed. This took place at Patrae.

See J. J. de Witte, "Les miroirs chez les anciens," in Extrait des annales de l'academie, xxviii. (Antwerp, 1872); Mylonas, `EXXnvcKa KiTO rTpa (Athens, 1876); M. Collignon, L'Arche'ologie grecque (new ed., 1907; Eng. tr. by J. H. Wright, 1886); E. Gerhard, Etruskische Spiegel (1840-1867), continued by K. Klugmann and G. Kurte (1884-1897); article in Smith's Dictionary of Greek and Roman Antiquities (3rd ed., 1891). (J. H. F.) Medieval and Modern Mirrors. - Small metallic mirrors with a highly polished surface were largely used during the middle ages: pocket mirrors or small hand mirrors carried at the girdle being indispensable adjuncts to ladies' toilets. The pocket mirrors consisted of small circular plaques of polished metal, usually steel or silver, fixed in a shallow circular box covered with a lid. Mirror-cases were chiefly made of ivory, carved with relief representations of love or domestic scenes, hunting and games, and sometimes illustrations of popular poetry or romance. Gold and silver, enamels, ebony and other costly materials were likewise used for mirror cases, on which were lavished the highest decorative efforts of art workmanship and costly jewelling. The mirrors worn at the girdle had no cover, but were furnished with a short handle. In 625 Pope Bonif ace IV. sent Queen Ethelberga of Northumbria a present of a silver mirror; and in early Anglo-Saxon times mirrors were well known in England. It is a remarkable fact that on many of the sculptured stones of Scotland, belonging probably to the 7th, 8th or 9th century, representations of mirrors, mirror-cases and combs occur.

The method of backing glass with thin sheets of metal for mirrors was well known in the middle ages, at a time when steel and silver mirrors were almost exclusively employed. Vincent of Beauvais, writing about 1250, says that the mirror of glass and lead is the best of all, "quia vitrum propter transparentiam melius recipit radios"; and a verre d mirer is mentioned in the inventories of the dukes of Burgundy, dating from the 15th century. A gild of glass-mirror makers existed at Nuremberg in 1373, and small convex mirrors were commonly made in southern Germany before the beginning of the 16th century; and these continued to be in demand, under the name of bull'seyes (Ochsen-Augen), till comparatively modern times. They were made by blowing small globes of glass into which while still hot was passed through the pipe a mixture of tin, antimony and resin or tar. When the globe was entirely coated with the metallic compound and cooled it was cut into convex lenses, which formed small but well-defined images. As early as 1317 a "Magister de Alemania," who knew how to work glass for mirrors, broke an agreement he had made to instruct three Venetians, leaving in their hands a large quantity of mixed alum and soot for which they could find no use. It was, however, in Venice that the making of glass mirrors on a commercial scale was first developed; and the republic enjoyed a muchprized monopoly of the manufacture for about a century and a half. In 1507 two inhabitants of Murano, representing that they possessed the secret of making perfect mirrors of glass, a knowledge hitherto confined to one German glass-house, obtained an exclusive privilege of manufacturing mirrors for a period of twenty years. In 1564 the mirror-makers of Venice, who enjoyed peculiar privileges, formed themselves into a corporation. The products of the Murano glass-houses quickly supplanted the mirrors of polished metal, and a large and lucrative trade in Venetian glass mirrors sprang up. They were made from blown cylinders of glass, which were slit, flattened on a stone, carefully polished, the edges frequently bevelled, and the backs "silvered" by an amalgam. The glass was remarkably pure and uniform, the "silvering" bright, and the sheets sometimes of considerable dimensions. In the inventory of his effects, made on the death of the French minister Colbert, a Venetian mirror, 46 by 26 in., in a silver frame, is valued at 8016 livres, while a picture by Raphael is put down at 3000 livres.

The manufacture of glass mirrors, with the aid of Italian workmen, was practised in England by Sir Robert Mansel early in the 17th century, and about 1670 the duke of Buckingham was concerned in glass-works at Lambeth where flint glass was made for looking-glasses. These old English mirrors, with bevelled edges in the Venetian fashion, are still well known. The Venetians guarded with the utmost jealousy the secrets of their manufactures, and gave exceptional privileges to those engaged in such industries. By their statutes any glass-maker carrying his art into a foreign state was ordered to return on the pain of imprisonment of his nearest relatives, and should he disobey the command emissaries were delegated to slay him. In face of such a statute Colbert attempted in 1664 to get Venetian artists transported to France to develop the two great industries of mirror-making and point-lace working. The ambassador, the bishop of Beziers, pointed out that this was to court the risk of being thrown into the Adriatic, and, further, that Venice was selling to France mirrors to the value of ioo,000 crowns and lace to three or four times that value. Nevertheless, twenty Venetian glass-mirror makers were sent to France in 1665, and the manufacture was begun in the Faubourg St Antoine, Paris. But previous to this the art of blowing glass for mirrors had been practised at Tour-la-Ville, near Cherbourg, by Richard Lucas, Sieur de Nehou, in 1653; and by the subsequent combination of skill of both establishments French mirrors soon excelled in quality those of Venice. The art received a new impulse in France on the introduction of the making of plate glass in 1691. The St Gobain Glass Company attribute the discovery to Louis Lucas of Nehou, and over the door of the chapel of St Gobain they have placed an inscription in memory of "Louis Lucas qui inventa en 1691 le methode de couler les glaces et installa la manufacture en 1695 dans le château de Saint Gobain." Manufacture. - The term "silvering," as applied to the formation of a metallic coating on glass for giving it the properties of a mirror, was till quite recently a misnomer, seeing that till about 1840 no silver, but a tin amalgam, was used in the process. Now, however, a large proportion of mirrors are made by depositing on the glass a coating of pure silver, and the old amalgamation process is comparatively little used.

The process of amalgamation consists in applying a thin amalgam of tin and mercury to the surface of glass. A sheet of thin tin-foil, somewhat larger than the glass to be operated on, is spread out on a flat table, and after all folds and creases have been completely removed a small quantity of mercury is rubbed lightly and quickly over the whole surface, and the scum of dust, impure tin and mercury is taken off. Mercury is then poured upon the "quickened" foil until there is a body of it sufficient to float the glass to be silvered (about h in. deep), and the glass (scrupulously cleaned simultaneously with the above operations) is slid over the surface of the mercury. Weights are placed over the surface until the greater part of the amalgamated mercury is pressed out, and the table is then tilted so that all superfluous mercury finds its way to the gutter. The glass is left twenty-four hours under weights; it is then turned over, silvered side up and removed to a drainer, where it dries and hardens. This process, when elaborated, yields excellent results, producing a brilliant silver-white metallic lustre, which is only subject to alteration by exposure to high temperatures or by contact with damp surfaces; but the mercurial vapours to which the workmen are exposed give rise to the most distressing and fatal affections.

The "silver on glass" mirror may be regarded as a discovery of J. von Liebig, who in 1835 observed that by heating aldehyde with an ammoniacal solution of silver nitrate in a glass vessel a brilliant deposit of metallic silver was formed on the surface of the glass. In practice the process was introduced about 1840; and it is now carried on, with several modifications, in two distinct ways, called the hot and the cold process respectively. In the former method there is employed a horizontal double-bottomed metallic table, which is heated with steam to from 35° to 40° C., and the reduction of the ammoniacal silver solution is effected with tartaric acid.

In silvering by the cold process advantage is taken of the power of sugar to reduce the silver nitrate. This method has been generally adopted for the silvering of mirrors for astronomical telescopes. G. W. Ritchey ("The Modern Reflecting Telescope," Smithsonian Contributions to Knowledge, xxxiv. 40) used the process devised by Brashear in 1884. The glass disk is mounted on a rocking-table, and most carefully cleaned with nitric acid, potash, and finally with distilled water. The reducing solution (which improves on keeping) is made up from 200 parts of water, 20 of loaf sugar, 20 of alcohol and 1 of nitric acid (commercial pure). The silver solution is prepared as follows: 2 parts of silver nitrate are dissolved in 20 parts of water, and strong ammonia added until the brown solution becomes clear. A solution of 12 parts of potash (pure by alcohol) in 20 of water is now added, and then ammonia until the solution is again clear. A solution of 4 part of silver nitrate in 16 of water is added until the liquid is straw-coloured; it is then filtered. Quantities of the solutions, such that the sugar equals one half the nitrate, are taken, then diluted, mixed, and poured on to the plate, which is gently rocked. The liquid goes muddy-brown, and in 3 to 4 minutes it begins to clear, a thick deposit being formed in about 5 minutes. The solution is poured off, and water run on, the streaks of precipitate being removed by lightly held cotton wool. The washing is repeated, and then water is allowed to remain on the film for one hour. The water is then run off, and the plate is washed several times with alcohol, and then dried by an air fan. The film is now burnished with a chamois leather pad, and finally with the finest jewellers' rouge, the silver surface being the reflecting surface of the mirror.

The deposit of silver on glass is not so adherent and unalterable under the influence of sunlight and sulphurous fumes as the tinmercury amalgam., and, moreover, real silvered glass has in many cases a slightly yellowish tinge. These defects have been overcome by a process introduced by Lenoir, which consists of brushing over the silvered surface with a dilute solution of cyanide of mercury, which, instantaneously forming a kind of amalgam, renders the deposit at once much whiter and more firmly adherent than before. To protect the thin metallic film from mechanical injury and the chemical action of gases and vapours it is coated with shellac or copal varnish, over which, when dry, are applied two coatings of red-lead paint or an electrolytically-deposited film of copper. This precaution only applies when the silver forms the back of the mirror.

Platinum Mirrors

A cheap process of preparing mirror glass was to some extent prosecuted in France, whereby a thin but very adherent deposit of platinum is formed on the glass. A solution of chloride of platinum with a proportion of litharge and borate of lead dissolved in essential oil of spike is applied with a brush to wellcleaned glass, which is then placed on edge in a muffle furnace, and the platinum is thus burned in, forming an exceedingly thin but brilliant metallic backing having a somewhat grey lustre. It was used only for the lids of cheap boxes, toys, ornamental letters, &c.

Magic Mirrors

Hand mirrors of metal are still in common use in Oriental countries, and in Japan bronze mirrors possess a religious significance. They have been known and used from the most remote period, mention of them being found in Chinese literature of the 9th century. The (reputed) first made Japanese mirror, preserved at Ise, is an object of the highest veneration in Japan, and an ancient mirror, connected with which is a tradition to the effect that it was given by the sun-goddess at the foundation of the empire, is a principal article of the Japanese regalia. The mirrors of Japan in general consist of thin disks, from 3 to 12 in. in diameter, of speculum metal with handles, cast in one piece. The polished face of the mirror is slightly convex in form, so that a reflected image is seen proportionately. reduced in size; the back of the disk is occupied with ornamentation and inscriptions in bold relief, and its rim is also raised to the back. Much attention has been attracted to these mirrors by a singular physical peculiarity which in a few cases they are found to possess. These are known as magic mirrors from the fact that when a strong beam of light is reflected from their smooth and polished surface, and thrown on a white screen, an image of the raised ornaments and characters on the back of the mirror is formed with more or less distinctness in the disk of light on the screen. This peculiarity has at no time been specially observed by the Japan- ese, but in China it attracted attention as early as the IIth century, and mirrors possessed of this property sell among the Chinese at ten or even twenty times the price sought for the ordinary nonsensitive examples. The true explanation of the magic mirror was first suggested by the French physicist Charles Cleophas Person in 1847, who observed that the reflecting surface of the mirrors was not uniformly convex, the portions opposite relief surfaces being plane. Therefore, as he says, "the rays reflected from the convex portion diverge and give but a feebly illuminated image, while, on the contrary, the rays reflected from the plane portions of the mirror preserve their parallelism, and appear on the screen as an image by reason of their contrast with the feebler illumination of the rest of the disk." Such differences of plane in the mirror surface are accidental, being due to the manner in which it is prepared, a process explained by W. E. Ayrton and J. Perry (Proc. Roy. Soc., 1878, vol. xxviii.), by whom ample details of the history, process of manufacture and composition of Oriental mirrors have been published. A preliminary operation in polishing the surface consists of scoring the cast disk in every direction with a sharp tool. The thicker portions with relief ornament offer more resistance to the pressure of the tool than the thin flat portions, which tend to yield and form at first a concave surface, but this by the reaction of its elasticity rises afterwards and forms a slightly convex surface, while the more rigid thick portions are comparatively little affected. This irregularity of surface is inconspicuous in ordinary light, and does not visibly distort images; but when the mirror reflects a bright light on a screen the unequal radiation renders the minute differences of surface obvious.


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Bible wiki

Up to date as of January 23, 2010

From BibleWiki


An object having a nearly perfect reflecting surface. In ancient times mirrors were invariably made of metal; in Egypt, of polished brass. It is no doubt this kind of mirror to which reference is made in Ex 38:8 and in Job 37:18. Reflections might also be seen in still water (Prov 27:19). In the enumeration of women's ornaments in Isa 3:23, hand-mirrors seem to be included; but this is somewhat doubtful. References to mirrors occur in the Apocrypha (Ecclus. [Sirach] xxii. 11) and in the New Testament (1Cor 33:12).

The Rabbis were acquainted with the use of mirrors, sometimes employing metal (Kelim xxx. 2). On the Sabbath it was not allowable to look into a mirror unless it was fixed on a wall (Shab. 149a). It would appear that later there was a tendency to forbid men to view themselves in mirrors, as this was regarded as effeminate (see Levy, "Neuhebr. Wörterb." i. 236). Nevertheless, the members of Rabbi's family were allowed to do so (Yer. Shab. vi. 7) because they were "close to the government."

The modern Jews of eastern Europe have a number of superstitions in regard to mirrors the exact origin of which it is difficult to trace. Mirrors are covered when a person dies. The angel of death will be seen if one looks into a mirror at such a time. If a mirror is broken, seven years of poverty will result; this is a general superstition, and not confined to Jews. In Galicia it is supposed that if one puts a mirror in front of a sleeping man with a candle between them, the sleeper will follow a person whither the latter wills. If the sleeper strikes one under these circumstances, the person stricken will not live more than a year.

This entry includes text from the Jewish Encyclopedia, 1906.
Facts about MirrorRDF feed

Simple English

[[File:|right|thumb|A framed mirror showing a jug.]]

File:Photo of two people reflected in a fish
A fish pond acting as a mirror to reflect views of people.

A mirror or looking-glass is something that reflects light. One common plane mirror is a piece of special flat glass that a person can look into in order to see themselves or what is behind them.

Sometimes, a flat piece of metal or the surface of water can act like a mirror.

The reason you are able to see yourself in a mirror is because light comes in and gets reflected, and that's how you are able to see your reflection. Mirrors can have magnification properties, making images appear smaller or larger than their actual size. They can also be concave (curved inward) or convex (curved outward), making the reflected angle and view to be smaller or larger, respectively.

Special mirrors in a museum are good to check out. Some make a person's appearance look quite strange. Also, in a mirror, writing appears backwards, as a "mirror image" of the original writing.

Mirrors are usually made out of sand, in the manner glass is made, but some mirrors have been made of polished metal to show a nearly clear view.








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