1.
PSO-1
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The PSO-1 is a telescopic sight manufactured in Russia by the Novosibirsk instrument-making factory and issued with the Russian military Dragunov sniper rifle. The PSO-1 was, at the time of its introduction around 1964, the PSO-1 was specifically designed for the SVD as a telescopic sight for military designated marksman activities. The current version of the sight is the PSO-1M2 and this telescopic sight is different from the original PSO-1 only in that it lacks the now obsolete infrared detector. The metal body of the PSO-1 is made from a magnesium alloy, the PSO-1 features a battery-powered red illuminated reticle with light provided by a simple diode bulb. It features professionally ground, fully multi-coated optical elements, an enamel finish for scratch protection. The scope body is sealed and filled with nitrogen, which prevents fogging of optics and was designed to function within a -50 °C to 50 °C temperature range. For zeroing the sight the reticle can be adjusted by manipulating the elevation. Considered the higher end of Soviet military side-mount telescopic sights, the quality of the PSO-1 is higher than most other PSO-style telescopic sights, the PSO-1 has neither a focus adjustment nor a parallax compensation control. Most modern military tactical scopes with lower power fixed magnification such as the ACOG, modern fixed magnification military high-end-grade sniper telescopic sights scopes intended for long-range shooting usually offer one or both of these features. The positioning of the body to the left of the bore’s center line may not be comfortable to all shooters. The PSO-1 elevation turret features bullet drop compensation in 50 m or 100 m increments for engaging point, at longer distances the shooter must use the chevrons that would shift the trajectory by 100 m per each chevron. The BDC feature must be tuned at the factory for the ballistic trajectory of a particular combination of rifle. Inevitable BDC-induced errors will occur if the environmental and meteorological circumstances deviate from the circumstances the BDC was calibrated for, marksmen can be trained to compensate for these errors. The PSO-1 features a reticle with floating elements designed for use in range estimation and bullet drop, the top center chevron is used as the main aiming mark. The horizontal hash marks are for windage and lead corrections and can be used for ranging purposes as well, to the left is a stadiametric rangefinder that can be used to determine the distance from a 1.7 meters tall object/person from 200 m to 1000 m. For this the lowest part of the target is lined up on the horizontal line. Where the top of the target touches the top curved line the distance can be determined and this reticle lay out is also used in several other telescopic sights produced and used by other former Warsaw Pact member states. The three lower chevrons in the center are used as hold over points for engaging targets beyond 1,000 meters
2.
Designated marksman rifle
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A designated marksman rifle is the weapon used by soldiers in the designated marksman role. DMRs have been developed with this ground in mind. DMRs often share some characteristics with sniper rifles when compared to the weapons carried by others in the DMs unit. DMRs may have a telescopic sight, quickly deployed stabilizing bipod to allow optimized accuracy. Most designated marksman rifles are based on a rifle that is currently issued by a nations military. A battle rifle is a semi-automatic or full-automatic rifle that fires 7. 62mm NATO or similar full-power rounds, classic examples include the M14, FN FAL, AR-10 and Heckler & Koch G3. These rifles were replaced by assault rifles firing the 5. 56mm NATO cartridge during the 1980s and 1990s. Some nations have also built rifles that were designed for the designated marksman from the ground up, all designated marksman rifles will have some type of optical sight with a higher magnification level than the standard issue rifle. For example, the SDM-R issued to the United States Army is fitted with a Trijicon 4× ACOG, while the standard-issue M4 carbine is equipped with an unmagnified Aimpoint CompM2 or CompM4. Sometimes, the system will be the only difference between the standard rifle and the designated marksman rifle, as is the case with the F88S DMR issued to the Australian Army. Sniper rifles often have even greater magnification than designated marksman rifles, for example, however, some designated marksman rifles, such as the Mk 12 Special Purpose Rifle or the USMC Squad Advanced Marksman Rifle are fitted with scopes with similar magnification. In some cases, the designated marksman rifle will have a longer barrel than the standard issued rifle, however, this is not universally true. In fact, up until recently, the M16A4 rifle was standard issue throughout the United States Marine Corps. The barrel on the Mk 12 Special Purpose Rifle, the current rifle used by the designated marksman in the USMC, is only 500 mm long -50 mm shorter than the barrel on the standard rifle. Also, some rifles, such as the F88S Austeyr, have a barrel that is the length as the standard service rifle. The FD-200 has a barrel, also found on designated marksman rifles. Most sniper rifles, such as the Accuracy International Arctic Warfare have a barrel with a length of 600 mm or greater, only the SVD and similar designated marksman rifles have a barrel of this length. The designated marksman rifles based on the M14 have barrels 460-560 mm long, in most cases, a designated marksman rifle will share the caliber and possibly even the ammunition type used by standard issue rifles
3.
Bell & Howell
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Bell & Howell is a U. S. -based former manufacturer of motion picture machinery, founded in 1907 by two projectionists, and headquartered in Wheeling, Illinois. The company now provides inserting and finishing solutions for letters and parcels, document processing, microfilmers, scanners, the Bell & Howell trademark is also licensed to makers of various electronic consumer products. According to its charter, the Bell & Howell Company was incorporated on February 17,1907 and it was duly recorded in the Cook County Record Book eight days later. The first meeting of stockholders took place in the office of Attorney W. G, strong on February 19 at 10 a. m. The first board of directors was chosen for a term of one year, Donald Joseph Bell, chairman, Albert Summers Howell, secretary, austin Delaney was president of Bell and Howell in Canada in the 1960s and 1970s before moving with his family from England. Historically, Bell & Howell Co. was an important supplier of many different media technologies, the firm dropped the production of movie cameras in the early 1970s. Bell & Howell is a supplier of equipment for schools. The film laboratory line is now a company, BHP Inc. The firm added microfilm products in 1946 and it purchased University Microfilms International in the 1980s. UMI produced a product called ProQuest, in the 2000s, Bell and & Howell decided to focus on their information technology businesses. The imaging business was sold to Eastman Kodak and the mail business was sold to Pitney Bowes. On June 6,2001 Bell & Howell became ProQuest Company, which was then a publicly traded company, in September 2001, the remaining industrial businesses, along with the Bell & Howell name, were sold to private equity firm Glencoe Capital. The company merged with the North American arm of Böwe Systec Inc, in 2003, Böwe Systec later acquired the entire company. It was known as Böwe Bell & Howell until 2011, when Versa Capital Management bought the company from bankruptcy and they also had an Electronics and Instrumentation Division on Lennox Road, Basingstoke, UK. This facility produced several different types of transducers for applications such as North Sea oil platforms, the modified Apple had additional security elements for classroom use such as a tamper-proof cover. The case color was black but the inside was a standard Apple II Plus, Bell & Howell founded an Education Group within their company in 1907. This Education Group created Bell & Howell Schools in 1966, in that same year, the Education Group purchased a controlling share of DeVry Institute of Technology. Two years later in 1968, Bell & Howell’s Education Group, via a controlling interest in DeVry, acquired Ohio Institute of Technology in Columbus, over the years, the Education Group has bought and sold large interests in a variety of educational organizations and institutions
4.
Telescopic sight
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A telescopic sight, commonly called a scope, is a sighting device that is based on an optical refracting telescope. They are equipped with some form of graphic image pattern mounted in an appropriate position in their optical system to give an accurate aiming point. Telescopic sights are used all types of systems that require accurate aiming but are most commonly found on firearms. Other types of sights are iron sights, reflector sights, the optical components may be combined with optoelectronics to form a night scope. The first experiments directed to give shooters optical aiming aids go back to the early 17th century, for centuries different optical aiming aids and primitive predecessors of telescopic sights were created that had practical or performance limitations. The first documented telescopic rifle sight was invented between 1835 and 1840, in 1855, William Malcolm of Syracuse, NY began producing his own sight. Malcolm used a design incorporating achromatic lenses like those used in telescopes. They were between three and twenty magnification, malcolms and those made by L. M. Amidon of Vermont were the standard during the Civil War. Still other telescopic sights of the same period were the Davidson. An early practical refractor telescope based telescopic sight was built in 1880 by August Fiedler, later telescopic sights with extra long eye relief became available for handgun and scout rifle use. A historic example of a sight with a long eye relief is the German ZF41 which was used during World War II on Karabiner 98k rifles. An early example of a man portable telescopic sight for low visibility/night use is the Zielgerät 1229, the ZG1229 Vampir was a Generation 0 active infrared night vision device developed for the Wehrmacht for the StG44 assault rifle, intended primarily for night use. The issuing of the ZG1229 Vampir system to the military started in 1944, Telescopic sights are classified in terms of the optical magnification and the objective lens diameter, e. g. 10×50. This would denote 10 times magnification with a 50 mm objective lens, in general terms, larger objective lens diameters, due to their ability to gather larger amounts of light, provide a larger exit pupil and hence provide a brighter image at the eyepiece. On fixed magnification sights the magnification power and objective diameter should be chosen on the basis of the intended use, there are also telescopic sights with variable magnification. The magnification can be varied by manually operating a zoom mechanism, variable sights offer more flexibility regarding shooting at varying ranges, targets and light conditions and offer a relative wide field of view at lower magnification settings. The syntax for variable sights is the following, minimal magnification – maximum magnification × objective lens, for example, 3–9×40. Confusingly, some older telescopic sights, mainly of German or other European manufacture, have a different classification where the part of the designation refers to light gathering power
5.
Oscilloscope
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Other signals can be converted to voltages and displayed. Oscilloscopes are used to observe the change of a signal over time, such that voltage. The observed waveform can be analyzed for such properties as amplitude, frequency, rise time, time interval, distortion, modern digital instruments may calculate and display these properties directly. Originally, calculation of these values required manually measuring the waveform against the scales built into the screen of the instrument, the oscilloscope can be adjusted so that repetitive signals can be observed as a continuous shape on the screen. A storage oscilloscope allows single events to be captured by the instrument and displayed for a long time. Oscilloscopes are used in the sciences, medicine, engineering, automotive, general-purpose instruments are used for maintenance of electronic equipment and laboratory work. Special-purpose oscilloscopes may be used for purposes as analyzing an automotive ignition system or to display the waveform of the heartbeat as an electrocardiogram. Early oscilloscopes used cathode ray tubes as their display element and linear amplifiers for signal processing, storage oscilloscopes used special storage CRTs to maintain a steady display of a single brief signal. CROs were later superseded by digital storage oscilloscopes with thin panel displays, fast analog-to-digital converters. DSOs without integrated displays are available at lower cost and use a digital computer to process. The basic oscilloscope, as shown in the illustration, is divided into four sections. The display is usually a CRT or LCD panel which is out with both horizontal and vertical reference lines referred to as the graticule. In addition to the screen, most display sections are equipped with three controls, a focus knob, an intensity knob and a beam finder button. The vertical section controls the amplitude of the displayed signal and this section carries a Volts-per-Division selector knob, an AC/DC/Ground selector switch and the vertical input for the instrument. Additionally, this section is equipped with the vertical beam position knob. The horizontal section controls the base or sweep of the instrument. The primary control is the Seconds-per-Division selector switch, also included is a horizontal input for plotting dual X-Y axis signals. The horizontal beam position knob is located in this section
6.
Microscope slide
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A microscope slide is a thin flat piece of glass, typically 75 by 26 mm and about 1 mm thick, used to hold objects for examination under a microscope. Typically the object is placed or secured on the slide, and this arrangement allows several slide-mounted objects to be quickly inserted and removed from the microscope, labeled, transported, and stored in appropriate slide cases or folders. Microscope slides are used together with a cover slip or cover glass. These sliders were popular in Victorian England until the Royal Microscopical Society introduced the standardized glass microscope slide, a standard microscope slide measures about 75 mm by 25 mm and is about 1 mm thick. A range of sizes are available for various special purposes, such as 75 x 50 mm and for geological use,46 x 27 mm for petrographic studies. Slides are usually made of glass and their edges are often finely ground or polished. Microscope slides are made of optical quality glass, such as soda lime glass or borosilicate glass. Fused quartz slides are used when ultraviolet transparency is important. While plain slides are the most common, there are specialized types. A concavity slide or cavity slide has one or more shallow depressions, designed to hold slightly thicker objects, if this system were used with a slide which did not incorporate these cut-off corners, the corners would chip and the slide could shatter. A graticule slide is marked with a grid of lines that allows the size of objects seen under magnification to be easily estimated, sometimes one square of the grid will itself be subdivided into a finer grid. Slides for specialized applications, such as counting, may have various reservoirs, channels. Various permanent markings or masks may be printed, sand-blasted, or deposited on the surface by the manufacturer, some slides have a frosted or enamel-coated area at one end, for labeling with a pencil or pen. Slides may have special coatings applied by the manufacturer, e. g. for chemical inertness or enhanced cell adhesion, the coating may have a permanent electric charge to hold thin or powdery samples. Common coatings include poly-L-lysine, silanes, epoxy resins, or even gold, the mounting of specimens on microscope slides is often critical for successful viewing. The problem has given much attention in the last two centuries and is a well-developed area with many specialized and sometimes quite sophisticated techniques. In a dry mount, the simplest kind of mounting, the object is placed on the slide. A cover slip may be placed on top to protect the specimen and this mounting can be successfully used for viewing specimens like pollen, feathers, hairs, etc
7.
Firearm
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A firearm is a portable gun - a barreled weapon that launches one or more projectiles, often driven by the action of an explosive force. The first primitive firearms originated in 13th-century China when the fire lance was combined with projectiles. The technology gradually spread through the rest of East Asia, South Asia, older firearms typically used black powder as a propellant, but modern firearms use smokeless powder or other propellants. Most modern firearms have rifled barrels to impart spin to the projectile for improved flight stability, modern firearms can be described by their caliber or in the case of shotguns their gauge, by the type of action employed together with the usual means of deportment. The word firearms usually is used in a sense restricted to small arms, shooters aim firearms at their targets with hand-eye co-ordination, using either iron sights or optical sights. The accurate range of pistols generally does not exceed 100 yards, while most rifles are accurate to 550 yards using iron sights, some purpose-built sniper rifles are accurate to ranges of more than 2,200 yards. The smallest of all firearms is the handgun, there are three common types of handguns, single-shot pistols, revolvers, and semi-automatic pistols. Revolvers have a number of firing chambers or charge holes in a revolving cylinder, semi-automatic pistols have a single fixed firing chamber machined into the rear of the barrel, and a magazine so they can be used to fire more than one round. Each press of the fires a cartridge, using the energy of the cartridge to activate the mechanism so that the next cartridge may be fired immediately. This is opposed to double-action revolvers which accomplish the end using a mechanical action linked to the trigger pull. Prior to the 19th century, virtually all handguns were single-shot muzzleloaders, with the invention of the revolver in 1818, handguns capable of holding multiple rounds became popular. Certain designs of auto-loading pistol appeared beginning in the 1870s and had largely supplanted revolvers in military applications by the end of World War I. By the end of the 20th century, most handguns carried regularly by military, police and civilians were semi-automatic, both designs are common among civilian gun owners, depending on the owners intention. A long gun is any firearm that is larger than a handgun and is designed to be held. Early long arms, from the Renaissance up to the century, were generally smoothbore firearms that fired one or more ball shot. Most modern long guns are either rifles or shotguns, both are the successors of the musket, diverging from their parent weapon in distinct ways. A rifle is so named for the spiral fluting machined into the surface of its barrel. Shotguns are predominantly smoothbore firearms designed to fire a number of shot, shotguns are also capable of firing single slugs, or specialty rounds such as bean bags, tear gas or breaching rounds
8.
Robert Hooke
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Robert Hooke FRS was an English natural philosopher, architect and polymath. Allan Chapman has characterised him as Englands Leonardo, Robert Gunthers Early Science in Oxford, a history of science in Oxford during the Protectorate, Restoration and Age of Enlightenment, devotes five of its fourteen volumes to Hooke. Hooke studied at Wadham College, Oxford during the Protectorate where he became one of a tightly knit group of ardent Royalists led by John Wilkins. Here he was employed as an assistant to Thomas Willis and to Robert Boyle and he built some of the earliest Gregorian telescopes and observed the rotations of Mars and Jupiter. In 1665 he inspired the use of microscopes for scientific exploration with his book, based on his microscopic observations of fossils, Hooke was an early proponent of biological evolution. Much of Hookes scientific work was conducted in his capacity as curator of experiments of the Royal Society, much of what is known of Hookes early life comes from an autobiography that he commenced in 1696 but never completed. Richard Waller mentions it in his introduction to The Posthumous Works of Robert Hooke, the work of Waller, along with John Wards Lives of the Gresham Professors and John Aubreys Brief Lives, form the major near-contemporaneous biographical accounts of Hooke. Robert Hooke was born in 1635 in Freshwater on the Isle of Wight to John Hooke, Robert was the last of four children, two boys and two girls, and there was an age difference of seven years between him and the next youngest. Their father John was a Church of England priest, the curate of Freshwaters Church of All Saints, Robert Hooke was expected to succeed in his education and join the Church. John Hooke also was in charge of a school, and so was able to teach Robert. He was a Royalist and almost certainly a member of a group who went to pay their respects to Charles I when he escaped to the Isle of Wight, Robert, too, grew up to be a staunch monarchist. As a youth, Robert Hooke was fascinated by observation, mechanical works and he dismantled a brass clock and built a wooden replica that, by all accounts, worked well enough, and he learned to draw, making his own materials from coal, chalk and ruddle. Hooke quickly mastered Latin and Greek, made study of Hebrew. Here, too, he embarked on his study of mechanics. It appears that Hooke was one of a group of students whom Busby educated in parallel to the work of the school. Contemporary accounts say he was not much seen in the school, in 1653, Hooke secured a choristers place at Christ Church, Oxford. He was employed as an assistant to Dr Thomas Willis. There he met the natural philosopher Robert Boyle, and gained employment as his assistant from about 1655 to 1662, constructing, operating and he did not take his Master of Arts until 1662 or 1663
9.
Film
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A film, also called a movie, motion picture, theatrical film or photoplay, is a series of still images which, when shown on a screen, creates the illusion of moving images due to the phi phenomenon. This optical illusion causes the audience to perceive continuous motion between separate objects viewed rapidly in succession, the process of filmmaking is both an art and an industry. The word cinema, short for cinematography, is used to refer to the industry of films. Films were originally recorded onto plastic film through a photochemical process, the adoption of CGI-based special effects led to the use of digital intermediates. Most contemporary films are now fully digital through the process of production, distribution. Films recorded in a form traditionally included an analogous optical soundtrack. It runs along a portion of the film exclusively reserved for it and is not projected, Films are cultural artifacts created by specific cultures. They reflect those cultures, and, in turn, affect them, Film is considered to be an important art form, a source of popular entertainment, and a powerful medium for educating—or indoctrinating—citizens. The visual basis of film gives it a power of communication. Some films have become popular worldwide attractions by using dubbing or subtitles to translate the dialog into the language of the viewer, some have criticized the film industrys glorification of violence and its potentially negative treatment of women. The individual images that make up a film are called frames, the perception of motion is due to a psychological effect called phi phenomenon. The name film originates from the fact that film has historically been the medium for recording and displaying motion pictures. Many other terms exist for a motion picture, including picture, picture show, moving picture, photoplay. The most common term in the United States is movie, while in Europe film is preferred. Terms for the field, in general, include the big screen, the screen, the movies, and cinema. In early years, the sheet was sometimes used instead of screen. Preceding film in origin by thousands of years, early plays and dances had elements common to film, scripts, sets, costumes, production, direction, actors, audiences, storyboards, much terminology later used in film theory and criticism apply, such as mise en scène. Owing to the lack of any technology for doing so, the moving images, the magic lantern, probably created by Christiaan Huygens in the 1650s, could be used to project animation, which was achieved by various types of mechanical slides
10.
FN P90
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The FN P90, also known as the FN Project 1990, is a personal defense weapon designed and manufactured by FN Herstal in Belgium. Featuring a compact design with an integrated reflex sight and fully ambidextrous controls. Its design incorporates several innovations such as a unique top-mounted magazine and FNs small-caliber, high-velocity 5. 7×28mm ammunition. The P90 is currently in service with military and police forces in over 40 nations, such as Austria, Brazil, Canada, France, Greece, India, Malaysia, Poland, and the United States. In the United States, the P90 is in use with over 200 law enforcement agencies, while developed and initially marketed as a PDW, it can also be considered a submachine gun or compact assault rifle. The standard selective fire P90 is restricted to military and law enforcement customers, but since 2005, the P90 and its 5. 7×28mm ammunition were developed by FN Herstal in response to NATO requests for a replacement for the 9×19mm Parabellum cartridge and associated pistols and submachine guns. NATO called for two types of weapons chambered for a new cartridge—one a shoulder-fired weapon, and the other a handheld weapon. According to NATO, these new weapons, termed personal defense weapons, were to provide protection in last-resort situations when the user is directly endangered by the enemy. Additionally, it was to be capable of penetrating body armor, the shoulder-fired personal defense weapon was to weigh less than 3 kg, with a magazine capacity of at least 20 rounds. The handheld personal defense weapon was to weigh less than 1 kg, although a weight of 700 g was deemed desirable, the original 5. 7×28mm cartridge, called the SS90, went into production with the P90 in 1990. The SS90 propelled a 1.5 g plastic-core projectile from the P90 at a velocity of roughly 850 m/s. Shortly after its introduction, the P90 was adopted and used in service with the Belgian special forces group in the 1991 Gulf War, following the P90s introduction, FN revised the 5. 7×28mm ammunition. The new variation, designated the SS190, used a projectile 2.7 mm shorter in length than that of the SS90 and this allowed it to be used more conveniently in the 5. 7×28mm FN Five-seven pistol, which was under development at that time. The SS190 projectile had a weight, and a more conventional construction with an aluminium. The first prototypes of the SS190 were created in 1992, a modified version of the P90, with a magazine adapted to use the shortened ammunition, was then introduced in the same year. Several special cartridge variations were developed, such as the L191 tracer round, in 2002 and 2003, NATO conducted a series of tests with the intention of standardizing a PDW cartridge as a replacement for the 9×19mm Parabellum cartridge. The tests compared the merits of the FN5. 7×28mm cartridge and the HK4. 6×30mm cartridge. However, the German delegation and others rejected the NATO recommendation that 5. 7×28mm be standardized, as a result, both the 4. 6×30mm and 5
11.
Diamond
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Diamond is a metastable allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the rate from diamond to graphite is negligible at standard conditions. Diamond is renowned as a material with superlative physical qualities, most of which originate from the covalent bonding between its atoms. In particular, diamond has the highest hardness and thermal conductivity of any bulk material and those properties determine the major industrial application of diamond in cutting and polishing tools and the scientific applications in diamond knives and diamond anvil cells. Because of its extremely rigid lattice, it can be contaminated by very few types of impurities, such as boron, small amounts of defects or impurities color diamond blue, yellow, brown, green, purple, pink, orange or red. Diamond also has relatively high optical dispersion, most natural diamonds are formed at high temperature and pressure at depths of 140 to 190 kilometers in the Earths mantle. Carbon-containing minerals provide the source, and the growth occurs over periods from 1 billion to 3.3 billion years. Diamonds are brought close to the Earths surface through deep volcanic eruptions by magma, Diamonds can also be produced synthetically in a HPHT method which approximately simulates the conditions in the Earths mantle. An alternative, and completely different growth technique is chemical vapor deposition, several non-diamond materials, which include cubic zirconia and silicon carbide and are often called diamond simulants, resemble diamond in appearance and many properties. Special gemological techniques have developed to distinguish natural diamonds, synthetic diamonds. The word is from the ancient Greek ἀδάμας – adámas unbreakable, the name diamond is derived from the ancient Greek αδάμας, proper, unalterable, unbreakable, untamed, from ἀ-, un- + δαμάω, I overpower, I tame. Diamonds have been known in India for at least 3,000 years, Diamonds have been treasured as gemstones since their use as religious icons in ancient India. Their usage in engraving tools also dates to early human history, later in 1797, the English chemist Smithson Tennant repeated and expanded that experiment. By demonstrating that burning diamond and graphite releases the same amount of gas, the most familiar uses of diamonds today are as gemstones used for adornment, a use which dates back into antiquity, and as industrial abrasives for cutting hard materials. The dispersion of light into spectral colors is the primary gemological characteristic of gem diamonds. In the 20th century, experts in gemology developed methods of grading diamonds, four characteristics, known informally as the four Cs, are now commonly used as the basic descriptors of diamonds, these are carat, cut, color, and clarity. A large, flawless diamond is known as a paragon and these conditions are met in two places on Earth, in the lithospheric mantle below relatively stable continental plates, and at the site of a meteorite strike. The conditions for diamond formation to happen in the mantle occur at considerable depth corresponding to the requirements of temperature and pressure
12.
Glass
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Glass is a non-crystalline amorphous solid that is often transparent and has widespread practical, technological, and decorative usage in, for example, window panes, tableware, and optoelectronics. The most familiar, and historically the oldest, types of glass are silicate glasses based on the chemical compound silica, the primary constituent of sand. The term glass, in usage, is often used to refer only to this type of material. Many applications of silicate glasses derive from their optical transparency, giving rise to their use as window panes. Glass can be coloured by adding metallic salts, and can also be painted and printed with vitreous enamels and these qualities have led to the extensive use of glass in the manufacture of art objects and in particular, stained glass windows. Although brittle, silicate glass is extremely durable, and many examples of glass fragments exist from early glass-making cultures, because glass can be formed or moulded into any shape, it has been traditionally used for vessels, bowls, vases, bottles, jars and drinking glasses. In its most solid forms it has also used for paperweights, marbles. Some objects historically were so commonly made of glass that they are simply called by the name of the material, such as drinking glasses. Porcelains and many polymer thermoplastics familiar from everyday use are glasses and these sorts of glasses can be made of quite different kinds of materials than silica, metallic alloys, ionic melts, aqueous solutions, molecular liquids, and polymers. For many applications, like glass bottles or eyewear, polymer glasses are a lighter alternative than traditional glass, silica is a common fundamental constituent of glass. In nature, vitrification of quartz occurs when lightning strikes sand, forming hollow, fused quartz is a glass made from chemically-pure SiO2. It has excellent resistance to shock, being able to survive immersion in water while red hot. However, its high melting-temperature and viscosity make it difficult to work with, normally, other substances are added to simplify processing. One is sodium carbonate, which lowers the transition temperature. The soda makes the glass water-soluble, which is undesirable, so lime, some magnesium oxide. The resulting glass contains about 70 to 74% silica by weight and is called a soda-lime glass, soda-lime glasses account for about 90% of manufactured glass. Most common glass contains other ingredients to change its properties, lead glass or flint glass is more brilliant because the increased refractive index causes noticeably more specular reflection and increased optical dispersion. Adding barium also increases the refractive index, iron can be incorporated into glass to absorb infrared energy, for example in heat absorbing filters for movie projectors, while cerium oxide can be used for glass that absorbs UV wavelengths
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