Glasses

A pair of eyeglasses

Glasses, spectacles, or eyeglasses are frames bearing lenses worn in front of the human eyes, sometimes for purely aesthetic reasons but normally for vision correction or eye protection. Special glasses are used for viewing three-dimensional images or experiencing virtual reality.

Modern glasses are typically supported by pads on the bridge of the nose and by temples placed over the ears. Historical types include the pince nez, monocle, and lorgnette.

Glasses are more often called eyeglasses in North American English, occasionally spectacles in British English, and (rarely) frames or lenses. Spectacles is often shortened to specs. In hipster slang they are cheaters.

Glasses were originally made from glass, but many are now made from plastic (often polycarbonate or CR-39) due to the danger of breakage and the greater weight of glass lenses. Some plastics also have more advantageous optical properties than glass, such as better transmission of visible light and greater absorption of ultraviolet light. Some plastics have a greater index of refraction than most types of glass, allowing thinner lenses for a given prescription. Scratch-resistant coatings can be applied to most plastic lenses giving them similar scratch resistance to glass. Hydrophobic coatings designed to ease cleaning are also available, as are anti-reflective coatings intended to improve night vision and make the wearer's eyes more visible.

Corrective spectacles have lenses shaped to correct vision abnormalities, such as myopia.

Safety glasses are a kind of eye protection against flying debris or visible and near visible light or radiation.

Sunglasses protect against high levels of visible and ultraviolet light.

History

Detail of a portrait of Hugh de Provence, painted by Tomasso da Modena in 1352

Glasses were possibly invented in northern Italy, most likely in the late 1280s. The identity of the original inventor is unknown, although a possible source is the Arabs, who may have had magnifying lenses in the 10th century. In 1676, Franciscus Redi, a professor of medicine at the University of Pisa, wrote that he possessed a 1289 manuscript whose author complains that he would be unable to read or write were it not for the recent invention of glasses, and a record of a sermon given in 1305, in which the speaker, a Dominican monk named Fra Giordano da Rivalto, remarked that glasses had been invented less than twenty years previously, and that he had met the inventor. Based on this evidence, Redi credited another Dominican monk, Fra Alessandro da Spina of Pisa, with the re-invention of glasses after their original inventor kept them a secret, a claim contained in da Spina's obituary record. In 1738, a Florentine historian named Domenico Manni reported that a tombstone in Florence credited one Salvino d'Armato (died 1317) with the invention of glasses. Other stories, possibly legendary, credit Roger Bacon with the invention. Bacon's published writings describe the magnifying glass (which he did not invent), but make no mention of glasses.

These early spectacles had convex lenses that could correct the farsightedness (presbyopia) that commonly develops as a symptom of aging. Nicholas of Cusa is believed to have discovered the benefits of concave lens in the treatment of myopia (nearsightedness). However, it was not until 1604 that Johannes Kepler published in his treatise on optics and astronomy, the first correct explanation as to why convex and concave lenses could correct presbyopia and myopia. The American scientist Benjamin Franklin, who suffered from both myopia and presbyopia, invented bifocals in 1784 to avoid having to regularly switch between two pairs of glasses. The first lenses for correcting astigmatism were constructed by the British astronomer George Airy in 1827.

Over time, the construction of spectacle frames also evolved. Early eyepieces were designed to be either held in place by hand or by exerting pressure on the nose (pince-nez). Girolamo Savonarola suggested that eyepieces could be held in place by a ribbon passed over the wearer's head, this in turn secured by the weight of a hat. The modern style of glasses, held by temples passing over the ears, was developed in 1727 by the British optician Edward Scarlett. These designs were not immediately successful, however, and various styles with attached handles such as scissors glasses and lorgnettes remained fashionable throughout the 18th and into the early 19th century.

Despite the increasing popularity of contact lenses and laser corrective eye surgery, glasses remain very common and their technology has not stood still. For instance, it is now possible to purchase frames made of special memory metal alloys that return to their correct shape after being bent. Other frames have spring-loaded hinges. Either of these designs offers dramatically better ability to withstand the stresses of daily wear and the occasional accident.

Corrective glasses

Corrective lenses modify the focal length of the eye to alleviate the effects of shortsightedness (myopia), longsightedness (hyperopia) or astigmatism. The power of a lens is generally measured in diopters. Over-the-counter reading glasses are typically rated at +1.00 to +3.00 diopters. Glasses correcting for myopia will have negative diopter strengths. Lenses made to conform to the prescription of an ophthalmologist or optometrist are called prescription lenses and are used to make prescription glasses.

Safety glasses

Safety glasses with side shields Wraparound safety glasses

Safety glasses are usually made with shatter-resistant plastic lenses to protect the eye from flying debris. Although safety lenses may be constructed from a variety of materials that vary in impact resistance, certain standards suggest that they maintain a minimum 1mm thickness at the thinest point regardless of material. Safety glasses can vary in the level of protection they provide. For example, those used in medicine may be expected to protect against blood splatter while safety glasses in a factory might have stronger lenses and a stronger frame with additional shields at the temples. The lenses of safety glasses can also be shaped for correction. Some safety glasses are designed to fit over corrective glasses or sunglasses. They may provide less eye protection than goggles, face shields or other forms of eye protection, but their light weight increases the likelihood that they will actually be used. Recent safety glasses have tended to be given a more stylish design, in order to encourage their use. The pictured wraparound safety glasses are evidence of this style change with the close fitting nature of the wraparound dispensing with the need for side shields.

Corrective glasses with plastic lenses can often be used in the place of safety glasses in many environments; this is one advantage that they have over contact lenses.

Sunglasses

Scratch-resistant sunglasses made using a NASA developed coating

Main article: Sunglasses

Sunglasses may be made with either prescription or non-prescription (i.e. plano) lenses that are darkened to provide protection against bright visible light. Good sunglasses should also protect against ultraviolet light. Due to changes in the atmosphere, ultraviolet levels are much higher than in the past and ultraviolet protection for eyes and skin is even more important. It is possible to have lenses that look very dark and yet offer little ultraviolet protection. Sunglasses vary greatly and many offer more style than protection.

Glasses with photosensitive lenses, called photochromic lenses, become darker in the presence of UV light. Unfortunately, many car windshields protect the passengers from UV light, while not shielding from bright visible light, making photochromic lenses ineffective where they are most needed. Still, they offer the convenience of not having to carry both clear glasses and sunglasses to those who frequently go indoors and outdoors during the course of a day.

Light polarization is an added feature that can be applied to sunglass lenses. Polarization filters remove horizontal rays of light, which can cause glare. Popular among fishermen and hunters, polarized sunglasses allow wearers to see into water when normally glare or reflected light would be seen. Polarized sunglasses may present some difficulties for pilots in that reflections from water and other structures often used to gauge altitude may be removed, or instrument readings on liquid crystal displays may be blocked.

Special glasses

The illusion of three dimensions on a two dimensional surface can be created by providing each eye with different visual information. Classic 3D glasses create the illusion of three dimensions when viewing specially prepared images. The classic 3D glasses have one red lens and one blue lens. 3D glasses made of cardboard and plastic are distributed at 3D movies. Another kind of 3D glasses uses polarized filters. One kind of electronic 3D spectacles uses electronic shutters.

Virtual reality glasses and helmets have separate video screens for each eye and a method for determining the direction the head is turned.

Conditions glasses are used to correct

Glasses fitted with corrective lenses are a common means of correcting focus problems such as myopia (nearsightedness, short-sightedness) and hyperopia (farsightedness, long-sightedness). Emmetropia, the condition of ideal focus is described as two parallel rays of light entering the eye and converging on or at the retina. Myopia is a condition in which parallel rays of light entering the eye converge before reaching to retina. Hyperopia is a condition in which parallel rays of light entering the eye do not converge prior to reaching the retina. Some would say "the rays of light converge at an imaginary point behind the retina." Astigmatism is a condition in which parallel rays of light entering the eye converge at two separate locations, either before and/or after the retina. As most people age the crystalline lens of the eye loses elasticity resulting in presbyopia, which limits their ability to focus on nearby objects. None of these conditions is considered a disease.

Variation in glasses

Glasses can be very simple. Magnifying lenses for reading that are used to treat mild hypermetropia and presbyopia can be bought off the shelf, but most glasses are made to a particular prescription, based on degree of myopia or hypermetropia combined with astigmatism. Lenses can be ground to specific eyes, but in most cases standard off-the-shelf prescriptions suffice, but require custom-fitting to particular frames.

As people age, their ability to focus is lessened and many decide to use multiple-focus lenses, bifocal or even trifocal to cover all the situations in which they use their sight. Traditional multifocal lenses have two or three distinct viewing areas, each requiring a conscious effort of refocusing. These were originally separate lenses, as invented by Benjamin Franklin. Some modern multifocal lenses give a smooth transition between these lenses, unnoticeable by most wearers. Others have lenses specifically intended for use with computer monitors at a fixed distance. Many people have several pairs of glasses, one for each task or distance, with specific glasses for reading, computer use, and television watching.

Glasses as a fashion accessory

Buddy Holly's thick-rimmed glasses were part of his all-American image.

Glasses are often regarded as unattractive, and many people prefer to wear contact lenses for that reason. Contact lenses also provide much improved peripheral vision.

On the other hand, many people are attracted to people who wear glasses, and glasses are available in a wide range of styles, materials, and even designer labels.

Glasses can be a major part of personal expression, from the extravagance of Elton John and Dame Edna Everage, from Groucho Marx to John Denver to Lisa Loeb all the way to the varied professional personas of eyeglass-wearing knowledge workers.

For some celebrities, glasses form part of their identity. American Senator Barry Goldwater continued to wear lensless horn-rimmed spectacles after being fitted with contact lenses because he was not recognizable without his trademark glasses. British soap star Anne Kirkbride had the same problem: her character on Coronation Street, Deirdre Barlow, became so well-known for her big frames that she was expected to wear them at social gatherings and in international tours, even though Kirkbride has always worn contact lenses. Drew Carey continued to wear glasses for the same reason after getting corrective laser eye surgery. British comedic actor Eric Sykes, who became profoundly deaf as an adult, wears glasses that contain no lenses, but are in fact a bone-conducting hearing aid. Masaharu Morimoto wears glasses to separate his professional persona as a chef from his stage persona as Iron Chef Japanese. And of course John Lennon wore his round "granny glasses" from some of his time with the Beatles to his assassination in 1980.

In popular culture, glasses were all the disguise Superman and Wonder Woman needed to hide in plain view as alter egos Clark Kent and Diana Prince, respectively.

An example of halo effect is seen in the stereotype that those who wear glasses are intelligent or, especially in teen culture, even geeks and nerds. This conception probably comes from an era when most people were illiterate and the first people to wear glasses were those who did a lot of reading. Some people who find that wearing glasses may look nerdy turn to contact lenses instead, especially under peer pressure.

Another unpopular aspect of glasses is their inconvenience. Even though the late-20th century saw the creation of light frames, such as those made of titanium, very flexible frames, and new lens materials and optical coatings, glasses can still cause problems during rigorous sports. The lenses themselves can also become greasy or trap vapour when eating hot food or swimming or walking in rain, reducing visibility significantly. Scraping, fracturing, or breakage of the lenses require time-consuming and costly professional repair, though modern plastic lenses are almost indestructible and very scratch-resistant.

Other names for glasses

  • Pair of glasses (or just glasses) is commonly used in Britain and in North America. Compare with other meanings of the word glass.
  • Spectacles is widely used in Britain and occasionally in the US, in addition to use by professional opticians. Also in frequent use is the shortened form, specs.
  • Eye glasses or eyeglasses is a word used in North American English. In contrast, glass eye refers to a cosmetic prosthetic artificial eye that replaces a missing eye.
  • Frames is sometimes used to refer to framed eyepieces, although it is not common.
  • Lenses is also sometimes used to refer to framed eyepieces, although it is not common.
  • Cheaters is used in the hipster argot. Eyeglasses were a common part of the hipster persona, for example Dizzy Gillespie.

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Scraping, fracturing, or breakage of the lenses require time-consuming and costly professional repair, though modern plastic lenses are almost indestructible and very scratch-resistant. For example, gold is quite common in Turkey but considered a most valuable gift in Sicily. The lenses themselves can also become greasy or trap vapour when eating hot food or swimming or walking in rain, reducing visibility significantly. The symbolic value of gold varies wildly around the world, even within geographic regions. Even though the late-20th century saw the creation of light frames, such as those made of titanium, very flexible frames, and new lens materials and optical coatings, glasses can still cause problems during rigorous sports. In Orthodox Christianity, the wedded couple is adorned with a golden crown during the ceremony, an amalgamation of symbolic rites. Another unpopular aspect of glasses is their inconvenience. Wedding rings are traditionally made of gold; since it is long-lasting and unaffected by the passage of time, it is considered a suitable material for everyday wear as well as a metaphor for the relationship.

Some people who find that wearing glasses may look nerdy turn to contact lenses instead, especially under peer pressure. Medieval kings were inaugurated under the signs of sacred oil and a golden crown, the latter symbolizing the eternal shining light of heaven and thus a Christian king's divinely inspired authority. This conception probably comes from an era when most people were illiterate and the first people to wear glasses were those who did a lot of reading. Winners of races and prizes are usually awarded the gold medal (such as the Olympic Games and the Nobel Prize), while many award statues are depicted in gold (such as the Academy Awards, the Emmy Awards and the British Academy Film Awards). An example of halo effect is seen in the stereotype that those who wear glasses are intelligent or, especially in teen culture, even geeks and nerds. Great human achievements are frequently rewarded with gold, in the form of medals and decorations. In popular culture, glasses were all the disguise Superman and Wonder Woman needed to hide in plain view as alter egos Clark Kent and Diana Prince, respectively. Gold is associated with notable anniversaries, particularly in a 50 year cycle, such as a golden wedding anniversary, golden jubilee, etc.

And of course John Lennon wore his round "granny glasses" from some of his time with the Beatles to his assassination in 1980. On the other hand, eminent orators such as John Chrysostom were said to have a mouth of gold with a silver tongue. Masaharu Morimoto wears glasses to separate his professional persona as a chef from his stage persona as Iron Chef Japanese. American Indians of the Sioux tribe called it "The yellow metal that makes the white man crazy". British comedic actor Eric Sykes, who became profoundly deaf as an adult, wears glasses that contain no lenses, but are in fact a bone-conducting hearing aid. In Communist propaganda, the golden pocket watch and its fastening golden chain were the characteristic accessories of the class enemy, the bourgeois and the industrial tycoons. Drew Carey continued to wear glasses for the same reason after getting corrective laser eye surgery. The Golden Calf is a widely-recognised symbol of idolatry and revolt against God.

British soap star Anne Kirkbride had the same problem: her character on Coronation Street, Deirdre Barlow, became so well-known for her big frames that she was expected to wear them at social gatherings and in international tours, even though Kirkbride has always worn contact lenses. Gold has been associated with the extremities of utmost evil and great sanctity throughout history. American Senator Barry Goldwater continued to wear lensless horn-rimmed spectacles after being fitted with contact lenses because he was not recognizable without his trademark glasses. Gold used in dentistry is widely regarded as the safest form of restorative material, as well as the most successful. For some celebrities, glasses form part of their identity. Liver and kidney damage has, however, been reported for up to 50% of arthritis patients treated with gold-containing drugs. Glasses can be a major part of personal expression, from the extravagance of Elton John and Dame Edna Everage, from Groucho Marx to John Denver to Lisa Loeb all the way to the varied professional personas of eyeglass-wearing knowledge workers. The human body does not absorb gold very well, thus compounds of gold are not normally very toxic.

On the other hand, many people are attracted to people who wear glasses, and glasses are available in a wide range of styles, materials, and even designer labels. There is only one stable isotope of gold, and 18 radioisotopes with Au-195 being the most stable with a half-life of 186 days. Contact lenses also provide much improved peripheral vision. Gold also forms:. Glasses are often regarded as unattractive, and many people prefer to wear contact lenses for that reason. Such compounds containing the Au- anion are called aurides and include caesium auride, CsAu, rubidium auride, RbAu, and tetramethylammonium auride, (CH3)4N+ Au-. Many people have several pairs of glasses, one for each task or distance, with specific glasses for reading, computer use, and television watching. Gold also can under extreme conditions form a +5 state with fluorine (gold pentafluoride, AuF5), as well as (unusually for a metal), a -1 state.

Others have lenses specifically intended for use with computer monitors at a fixed distance. Gold compounds can be aurous (univalent, +1) or auric (trivalent, +3). Some modern multifocal lenses give a smooth transition between these lenses, unnoticeable by most wearers. Although gold is a noble metal, it can form many compounds, auric chloride (AuCl3) and chlorauric acid (HAuCl4) being the most common. These were originally separate lenses, as invented by Benjamin Franklin. Roosevelt expropriated gold by Executive Order 6102, and President Richard Nixon closed the gold window by which foreign countries could exchange American dollars for gold at a fixed rate. Traditional multifocal lenses have two or three distinct viewing areas, each requiring a conscious effort of refocusing. President Franklin D.

As people age, their ability to focus is lessened and many decide to use multiple-focus lenses, bifocal or even trifocal to cover all the situations in which they use their sight. Within the United States, the private possession of gold except as jewelry and coin collecting was banned between 1933 and 1975. Lenses can be ground to specific eyes, but in most cases standard off-the-shelf prescriptions suffice, but require custom-fitting to particular frames. Because of its use as a reserve store of value, the possession of gold is sometimes restricted or banned. Magnifying lenses for reading that are used to treat mild hypermetropia and presbyopia can be bought off the shelf, but most glasses are made to a particular prescription, based on degree of myopia or hypermetropia combined with astigmatism. Prices have risen to the $570/oz ($18,300/kg) mark in early 2006 [3]. Glasses can be very simple. Since 1968 the price of gold on the open market has ranged widely, with a record high of $850/oz ($27,300/kg) on 21 January 1980, to a low of $252.90/oz ($8,131/kg) on 21 June 1999 (London Fixing).

None of these conditions is considered a disease. Federal Reserve Bank, in New York. As most people age the crystalline lens of the eye loses elasticity resulting in presbyopia, which limits their ability to focus on nearby objects. The largest gold depository in the world is that of the U.S. Some would say "the rays of light converge at an imaginary point behind the retina." Astigmatism is a condition in which parallel rays of light entering the eye converge at two separate locations, either before and/or after the retina. Central banks still hold historical gold reserves as a store of value although the level has generally been declining. Hyperopia is a condition in which parallel rays of light entering the eye do not converge prior to reaching the retina. On March 17, 1968, economic circumstances caused the collapse of the gold pool, and a two-tiered pricing scheme was established whereby gold was still used to settle international accounts at the old $35.00 per troy ounce ($1.13/g) but the price of gold on the private market was allowed to fluctuate; this two-tiered pricing system was abandoned in 1975 when the price of gold was left to find its free-market level.

Myopia is a condition in which parallel rays of light entering the eye converge before reaching to retina. By 1961 it was becoming hard to maintain this price, and a pool of US and European banks began to act together to defend the price against market forces. Emmetropia, the condition of ideal focus is described as two parallel rays of light entering the eye and converging on or at the retina. For a long period the United States government set the price of gold at $20.67 per troy ounce ($664.56/kg) but in 1934 the price of gold was set at $35.00 per troy ounce ($1125.27/kg). Glasses fitted with corrective lenses are a common means of correcting focus problems such as myopia (nearsightedness, short-sightedness) and hyperopia (farsightedness, long-sightedness). As part of this system, governments and central banks attempted to control the price of gold by setting values at which they would exchange it for currency. Virtual reality glasses and helmets have separate video screens for each eye and a method for determining the direction the head is turned. Historically gold was used to back currency in an economic system known as the gold standard in which one unit of currency was equivalent to a certain weight of gold.

One kind of electronic 3D spectacles uses electronic shutters. The price of gold is determined on the open market, but a procedure known as the Gold Fixing in London, originating in 1919, provides a twice-daily benchmark figure to the industry. Another kind of 3D glasses uses polarized filters. The purity of a gold bar can also be expressed as a decimal figure ranging from 0 to 1, known as the millesimal fineness, such as 0.995. 3D glasses made of cardboard and plastic are distributed at 3D movies. When it is alloyed with other metals the term carat or karat is used to indicate the amount of gold present, with 24 carats being pure gold and lower ratings proportionally less. The classic 3D glasses have one red lens and one blue lens. Like other precious metals, gold is measured by troy weight and by grams.

Classic 3D glasses create the illusion of three dimensions when viewing specially prepared images. No commercially viable mechanism for performing gold extraction from sea water has yet been identified. The illusion of three dimensions on a two dimensional surface can be created by providing each eye with different visual information. The effort produced little gold and cost the German government far more than the commercial value of the gold recovered. Polarized sunglasses may present some difficulties for pilots in that reflections from water and other structures often used to gauge altitude may be removed, or instrument readings on liquid crystal displays may be blocked. Unfortunately, his assessment of the concentration of gold in sea water was unduly high, probably due to sample contamination. Popular among fishermen and hunters, polarized sunglasses allow wearers to see into water when normally glare or reflected light would be seen. Fritz Haber (the German inventor of the Haber process) attempted commercial extraction of gold from sea water in an effort to help pay Germany's reparations following the First World War.

Polarization filters remove horizontal rays of light, which can cause glare. The world's oceans hold a vast amount of gold, but in very low concentrations (perhaps 1-2 parts per billion). Light polarization is an added feature that can be applied to sunglass lenses. The possibility of cheap man-made gold would have unforeseen economic and political consequences. Still, they offer the convenience of not having to carry both clear glasses and sunglasses to those who frequently go indoors and outdoors during the course of a day. No economically feasible method to manufacture gold artificially has been found and published yet. Unfortunately, many car windshields protect the passengers from UV light, while not shielding from bright visible light, making photochromic lenses ineffective where they are most needed. However, it is possible to obtain infinitesimally small amounts of gold by artificial nuclear transformations in particle accelerators The gold isotopes produced would likely be radioactive.

Glasses with photosensitive lenses, called photochromic lenses, become darker in the presence of UV light. Modern science has since proven the impossibility of making gold from other elements via chemical reactions. Sunglasses vary greatly and many offer more style than protection. porcelain), while searching in vain for the philosopher's stone, which was supposed to turn mercury into gold. It is possible to have lenses that look very dark and yet offer little ultraviolet protection. Scientists, kings and charlatans obsessed with the secret art of alchemy accidentally invented practically useful materials (e.g. Due to changes in the atmosphere, ultraviolet levels are much higher than in the past and ultraviolet protection for eyes and skin is even more important. The idea of producing gold out of lesser metals or other cheap substances has fascinated people throughout the centuries.

Good sunglasses should also protect against ultraviolet light. Other methods of assaying and purifying smaller amounts of gold include parting and inquartation as well as cuppelation, or refining methods based on the dissolution of gold in aqua regia. plano) lenses that are darkened to provide protection against bright visible light. After initial production, gold is often subsequently refined industrially by the Wohlwill process or the Miller process. Sunglasses may be made with either prescription or non-prescription (i.e. In South America, the controversial project Pascua Lama aims at exploitation of rich fields in the high mountains of Atacama, at the border between Chile and Argentina. Main article: Sunglasses. Kolar Gold Fields in India is another example of a city being built on the greatest gold deposits in India.

Corrective glasses with plastic lenses can often be used in the place of safety glasses in many environments; this is one advantage that they have over contact lenses. Siberian regions of the USSR also used to be significant in the global gold mining industry. The pictured wraparound safety glasses are evidence of this style change with the close fitting nature of the wraparound dispensing with the need for side shields. Mines in South Dakota and Nevada supply two-thirds of gold used in the United States. Recent safety glasses have tended to be given a more stylish design, in order to encourage their use. Other major producers are Canada, United States and Western Australia. They may provide less eye protection than goggles, face shields or other forms of eye protection, but their light weight increases the likelihood that they will actually be used. The Second Boer War of 1899–1901 between the British Empire and the white Boers was at least partly over the rights of miners and possession of the gold wealth in South Africa.

Some safety glasses are designed to fit over corrective glasses or sunglasses. Gold fields in the Orange Free State and the Transvaal are deep and require the world's deepest mines. The lenses of safety glasses can also be shaped for correction. The city of Johannesburg was built atop the world's greatest gold finds. For example, those used in medicine may be expected to protect against blood splatter while safety glasses in a factory might have stronger lenses and a stronger frame with additional shields at the temples. This decline was due to the increasing difficulty of extraction and changing economic factors affecting the industry in South Africa. Safety glasses can vary in the level of protection they provide. Production in 1970 accounted for 79% of the world supply, producing about 1,000 tonnes, however production in 2004 was 342 tonnes.

Although safety lenses may be constructed from a variety of materials that vary in impact resistance, certain standards suggest that they maintain a minimum 1mm thickness at the thinest point regardless of material. Since the 1880s South Africa has been the source for a large proportion of the world's gold supply. Safety glasses are usually made with shatter-resistant plastic lenses to protect the eye from flying debris. It is claimed, that all the gold that has been mined throughout the history of mankind could be incorporated in a solid ball with a diameter of 27 metres. Lenses made to conform to the prescription of an ophthalmologist or optometrist are called prescription lenses and are used to make prescription glasses. Ore grades of 30 g/1000 kg (30 ppm) are usually needed before gold is visible to the naked eye, therefore in most gold mines you will not see any gold. Glasses correcting for myopia will have negative diopter strengths. Economic gold extraction can be achieved from ore grades as little as 0.5 g/1000 kg (0.5 ppm) on average in large easily mined deposits, typical ore grades in open-pit mines are 1–5 g/1000 kg (1-5 ppm), ore grades in underground or hard rock mines are usually at least 3 g/1000 kg (3 ppm) on average.

Over-the-counter reading glasses are typically rated at +1.00 to +3.00 diopters. Gold occurs in sea water at 0.1 to 2 mg/t (0.1 to 2 ppb by weight) depending on sample location. The power of a lens is generally measured in diopters. Another important ore type is in sedimentary black shale and limestone deposits containing finely disseminated gold and other platinum group metals. Corrective lenses modify the focal length of the eye to alleviate the effects of shortsightedness (myopia), longsightedness (hyperopia) or astigmatism. In all these deposits the gold is in its native form. Either of these designs offers dramatically better ability to withstand the stresses of daily wear and the occasional accident. Primary deposits can be weathered and eroded, with most of the gold being transported into stream beds where it congregates with other heavy minerals to form placer deposits.

Other frames have spring-loaded hinges. There are several primary deposit types, common ones are termed reef or vein. For instance, it is now possible to purchase frames made of special memory metal alloys that return to their correct shape after being bent. A deposit usually needs some form of secondary enrichment to form an economically viable ore deposit: either chemical or physical processes like erosion or solution or more generally metamorphism, which concentrates the gold in sulfide minerals or quartz. Despite the increasing popularity of contact lenses and laser corrective eye surgery, glasses remain very common and their technology has not stood still. The primary source of gold is usually igneous rocks or surface concentrations. These designs were not immediately successful, however, and various styles with attached handles such as scissors glasses and lorgnettes remained fashionable throughout the 18th and into the early 19th century. Hydrothermal ore deposits of gold occur in metamorphic rocks and igneous rocks; alluvial deposits and placer deposits originate from these sources.

The modern style of glasses, held by temples passing over the ears, was developed in 1727 by the British optician Edward Scarlett. Gold is widely distributed in the Earth's crust at a background level of 0.03 g/1000 kg (0.03 ppm by weight). Girolamo Savonarola suggested that eyepieces could be held in place by a ribbon passed over the wearer's head, this in turn secured by the weight of a hat. Rarer mineral associations are petzite, calaverite, sylvanite, muthmannite, nagyagite and krennerite. Early eyepieces were designed to be either held in place by hand or by exerting pressure on the nose (pince-nez). The most common sulfide associations are pyrite, chalcopyrite, galena, sphalerite, arsenopyrite, stibnite and pyrrhotite. Over time, the construction of spectacle frames also evolved. Common gold associations are quartz often as veins and sulfide minerals.

The first lenses for correcting astigmatism were constructed by the British astronomer George Airy in 1827. These grains occur between mineral grain boundaries or as inclusions within minerals. The American scientist Benjamin Franklin, who suffered from both myopia and presbyopia, invented bifocals in 1784 to avoid having to regularly switch between two pairs of glasses. Occasionally large accumulations of native gold (also known as nuggets) occur but usually gold occurs as minute grains. However, it was not until 1604 that Johannes Kepler published in his treatise on optics and astronomy, the first correct explanation as to why convex and concave lenses could correct presbyopia and myopia. Due to its relative chemical inertness gold is usually found as the native metal or alloy. Nicholas of Cusa is believed to have discovered the benefits of concave lens in the treatment of myopia (nearsightedness). Because of its historically high value, much of the gold mined throughout history is still in circulation in one form or another.

These early spectacles had convex lenses that could correct the farsightedness (presbyopia) that commonly develops as a symptom of aging. During the 19th century, gold rushes occurred whenever large gold deposits were discovered, including the California, Colorado, Otago, Australia, Witwatersrand, Black Hills, and Klondike gold rushes. Bacon's published writings describe the magnifying glass (which he did not invent), but make no mention of glasses. For modern attempts to produce artificial gold, see gold synthesis. Other stories, possibly legendary, credit Roger Bacon with the invention. Their symbol for gold was the circle with a point at its center (☉), which was also the astrological symbol, the Egyptian hieroglyph and the ancient Chinese character for the Sun (now 日). In 1738, a Florentine historian named Domenico Manni reported that a tombstone in Florence credited one Salvino d'Armato (died 1317) with the invention of glasses. Although they never succeeded in this attempt, the alchemists promoted an interest in what can be done with substances, and this laid a foundation for today's chemistry.

Based on this evidence, Redi credited another Dominican monk, Fra Alessandro da Spina of Pisa, with the re-invention of glasses after their original inventor kept them a secret, a claim contained in da Spina's obituary record. The primary goal of the alchemists was to produce gold from other substances, such as lead — presumably by the interaction with a mythical substance called the philosopher's stone. In 1676, Franciscus Redi, a professor of medicine at the University of Pisa, wrote that he possessed a 1289 manuscript whose author complains that he would be unable to read or write were it not for the recent invention of glasses, and a record of a sermon given in 1305, in which the speaker, a Dominican monk named Fra Giordano da Rivalto, remarked that glasses had been invented less than twenty years previously, and that he had met the inventor. Gold in antiquity was relatively easy to obtain geologically; however, 75% of all gold ever produced has been extracted since 1910.[2] It has been estimated that all the gold in the world that has ever been refined would form a single cube 20 m (66 ft) a side. The identity of the original inventor is unknown, although a possible source is the Arabs, who may have had magnifying lenses in the 10th century. Gold has been used as a symbol for purity, value, royalty, and particularly roles that combine these properties (see gold album). Glasses were possibly invented in northern Italy, most likely in the late 1280s. Gold has long been considered one of the most precious metals, and its value has been used as the standard for many currencies (known as the gold standard) in history.

. The European exploration of the Americas was fueled in no small part by reports of the gold ornaments displayed in great profusion by Native American peoples, especially in Central America, Peru, and Colombia. Sunglasses protect against high levels of visible and ultraviolet light. Exploitation is said to date from the time of Midas, and this gold was important in the establishment of what is probably the world's earliest coinage in Lydia between 643 and 630 BC. Safety glasses are a kind of eye protection against flying debris or visible and near visible light or radiation. The south-east corner of the Black Sea was famed for its gold. Corrective spectacles have lenses shaped to correct vision abnormalities, such as myopia. Gold is also mentioned several times in the Old Testament.

Hydrophobic coatings designed to ease cleaning are also available, as are anti-reflective coatings intended to improve night vision and make the wearer's eyes more visible. Egypt and Nubia had the resources to make them major gold-producing areas for much of history. Scratch-resistant coatings can be applied to most plastic lenses giving them similar scratch resistance to glass. Egyptian hieroglyphs from as early as 2600 BC describe gold, which king Tushratta of the Mitanni claimed was as "common as dust" in Egypt. Some plastics have a greater index of refraction than most types of glass, allowing thinner lenses for a given prescription. It may have been the first metal used by humans and was valued for ornamentation and rituals. Some plastics also have more advantageous optical properties than glass, such as better transmission of visible light and greater absorption of ultraviolet light. Gold ( Sanskrit jval, Greek χρυσóς [khrisós], Latin aurum for "shining dawn", Anglo-Saxon gold, Chinese 金 [jīn],Japanese 金 [kin] ) has been known and highly valued since prehistoric times.

Glasses were originally made from glass, but many are now made from plastic (often polycarbonate or CR-39) due to the danger of breakage and the greater weight of glass lenses. Because of its high electrical conductivity and resistance to corrosion and other desirable combinations of physical and chemical properties, gold also emerged in the late 20th century as an essential industrial metal. In hipster slang they are cheaters. Gold and its many alloys are most often used in jewelry, coinage and as a standard for monetary exchange in many countries. Spectacles is often shortened to specs. Pure gold is too soft for ordinary use and is hardened by alloying with silver, copper, and other metals. Glasses are more often called eyeglasses in North American English, occasionally spectacles in British English, and (rarely) frames or lenses. [1].

Historical types include the pince nez, monocle, and lorgnette. Recent research undertaken by Frank Reith of the Australian National University shows that microbes play an important role in the formation of gold deposits, transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits. Modern glasses are typically supported by pads on the bridge of the nose and by temples placed over the ears. The added metal is oxidized and dissolves allowing the gold to be displaced from solution and be recovered as a solid precipitate. Special glasses are used for viewing three-dimensional images or experiencing virtual reality. Gold ions in solution are readily reduced and precipitated out as gold metal by the addition of virtually any other metal as the reducing agent. Glasses, spectacles, or eyeglasses are frames bearing lenses worn in front of the human eyes, sometimes for purely aesthetic reasons but normally for vision correction or eye protection. Common oxidation states of gold include +1 (gold(I) or aurous compounds) and +3 (gold(III) or auric compounds).

Eyeglasses were a common part of the hipster persona, for example Dizzy Gillespie. Heat, moisture, oxygen, and most corrosive agents have very little chemical effect on gold, making it well-suited for use in coins and jewelry; conversely, halogens will chemically alter gold, and aqua regia dissolves it. Cheaters is used in the hipster argot. Gold is a good conductor of heat and electricity, and is not affected by air and most reagents. Lenses is also sometimes used to refer to framed eyepieces, although it is not common. As the amount of silver increases, the color becomes whiter and the specific gravity lower. Frames is sometimes used to refer to framed eyepieces, although it is not common. Native gold contains usually eight to ten per cent silver, but often much more — alloys with a silver content over 20% are called electrum.

In contrast, glass eye refers to a cosmetic prosthetic artificial eye that replaces a missing eye. Adding copper yields a redder metal, iron blue, Silver produces green, aluminium purple, platinum metals white, and natural bismuth together with silver alloys produce black. Eye glasses or eyeglasses is a word used in North American English. This can be done to increase its strength, or create several exotic colors, sold for instance in the western United States to the tourist trade as "Black Hills" gold. Also in frequent use is the shortened form, specs. A soft metal, gold will readily form alloys with many other metals. Spectacles is widely used in Britain and occasionally in the US, in addition to use by professional opticians. It is the most malleable and ductile metal known; a single gram can be beaten into a sheet of one square metre, or an ounce into 300 square feet.

Compare with other meanings of the word glass. Only silver colloids exhibit the same interactions with light, albeit at a shorter frequency, making silver colloids yellow in color. Pair of glasses (or just glasses) is commonly used in Britain and in North America. These colors are the result of gold's plasmon frequency lying in the visible range, which causes red and yellow light to be reflected, and blue light to be absorbed. Gold is a metallic element with a characteristic yellow color, but can also be black or ruby when finely divided, while colloidal solutions are intensely colored and often purple. .

Its ISO currency code is XAU. Gold forms the basis for a monetary standard used by the International Monetary Fund (IMF) and the Bank for International Settlements (BIS). For millennia, gold has served as money and is also used in jewelry, dentistry, and in electronics. The metal occurs as nuggets or grains in rocks and in alluvial deposits and is one of the coinage metals.

A soft, shiny, yellow, dense, malleable, ductile (trivalent and univalent) transition metal, gold does not react with most chemicals but is attacked by chlorine, fluorine and aqua regia. Gold is a chemical element in the periodic table that has the symbol Au (from the Latin aurum) and atomic number 79. The Columbia Electronic Encyclopedia, 6th ed. Los Alamos National Laboratory – Gold.

Gold hydrazide: an olive-green powder, AuN2H3, one of several explosive compounds known archaically as aurum fulminans. Gold cluster compounds. Gold chalcogenides (O, S, Se,Te). Gold halides (F,Cl,Br,I).

The AuCl4- ion after dissolving in aqua regia. Green gold (a gold/silver alloy) is used in specialized jewelry while gold alloys with copper (reddish color) are more widely used for that purpose (rose gold)*. White gold (an alloy of gold with platinum, palladium, nickel, and/or zinc) serves as a substitute for platinum. Only the salts and radioisotopes (mentioned above) have any evidence of medicinal value.

For similar reasons, it also used as the basis for some superstitious, over the top, health claims. Some use it as an excuse to create super-expensive delicacies ($1,000 cocktails). Having no reactivity it adds no taste but is taken as a delicacy. Called varak or (varaq) in India.

Gold flake is used on and in some gourmet sweets and drinks. The gold isotope Au-198, (half-life: 2.7 days) is used in some cancer treatments and for treating other diseases. However, it can also cause photosensitive rashes, gastrointestinal disturbance, and kidney damage. It inhibits lymphocyte proliferation, lysosomal enzyme release, the release of reactive oxygen species from macrophages, and IL-1 production.

Disodium aurothiomalate is a treatment for rheumatoid arthritis (administered intramuscularly). Since it is a good reflector of both infrared and visible light, it is used for the protective coatings on many artificial satellites. Many competitions and honors, such as the Olympics and the Nobel Prize, award a gold medal to the winner (with silver to the second-place finisher, and bronze to the third.). Gold is used as a coating enabling biological material to be viewed under a scanning electron microscope.

It is also the usual starting point for making other gold compounds. Gold(III) chloride is used as a catalyst in organic chemistry. Chlorauric acid is used in photography for toning the silver image. It is also the form used as gold paint on ceramics prior to firing.

Colloidal gold (a gold nanoparticle) is an intensely colored solution that is currently studied in many labs for medical, biological and other applications. Gold is used in restorative dentistry especially in tooth restorations such as crowns and bridges. The resistance to oxidation of gold has led to its widespread use as thin layers electroplated on the surface of electrical connectors to ensure a good connection. Gold performs critical functions in computers, communications equipment, spacecraft, jet aircraft engines, and a host of other products.

Gold can be made into thread and used in embroidery.

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