Millennium Dome raid
The Millennium Dome raid was an attempted robbery of the Millennium Dome's diamond exhibition in Greenwich, South East London occurring on 7 November 2000. A local gang planned to ram-raid the De Beers diamond exhibition, being held in the dome at the time; the gang had planned to escape via the Thames in a speedboat. The De Beers diamond exhibition had a number of jewels on display, including the Millennium Star, a flawless 203.04 carats gem with an estimated worth of £200 million and considered one of the most perfect gems in the world. On display were priceless blue diamonds; the attempted robbery was foiled by the Flying Squad of the Metropolitan Police Service, as a result of information from Kent Police Serious Crime who had the gang members under surveillance for their suspected roles in a number of unsuccessful armoured vehicle robberies. The operation to foil the robbery was the biggest operation undertaken in the Flying Squad's history and at trial the judge in the case commended the way it was carried out.
If the heist had succeeded with a haul of £350 million worth of diamonds, it would have become one of the biggest robberies in history. In the summer of 2000, the Flying Squad became aware of a major armed robbery plot after a tip-off was received; the location of this robbery was unclear, but the identities of some of the robbers were known to the police. The police spent a number of months developing intelligence on the plot and set up an operation that they codenamed Operation Magician. During the intelligence gathering the location of the robbery was found to be the Millennium Dome in Greenwich. In February 2000, armed men tried to pull off a £10 million raid on a security van in Nine Elms, South London; the gunmen had stopped the security lorry by blocking off both ends of Nine Elms Lane. They had planned to use their own lorry, carrying Christmas trees, as a battering ram; this lorry had a huge metal spike covered by the foliage. The gang planned to split the security lorry's rear doors with the ram.
The gang's plan failed when a motorist, late for work removed the keys from the ignition of the unattended Christmas tree van. The robbers, left with no choice, made their escape in an inflatable speedboat towards Chelsea, it was attempted again on 7 July in Kent. This time, the gang got closer to the cash, with the metal spike being rammed into the van, they were seconds from taking the money. Detective Superintendent Jon Shatford stated that this attempted robbery brought to his attention a gang, capable of carrying out a robbery with this level of planning. Fifteen months after this attempted robbery, there was another case where a gang tried to pull off another robbery using similar techniques; this unsuccessful attack provided the police with important clues and led them to track some of the vehicles that were used in the raid to two isolated farms in rural Kent. After this unsuccessful robbery the police received a tip-off about the Dome raid from an informer. At a meeting between detectives to discuss the Nine Elms Lane attempted robbery and the information that the informer had provided about the Dome raid, one detective who had visited the dome quipped, "Maybe they are after the Millennium jewels?"
It was this comment. On 1 September 2000, the team identified three of the suspected robbers – Lee Wenham, Raymond Betson and William Cockram – at the Dome, it was found that every time they had visited the attraction, the Thames was at high tide. They were observed visiting the exhibition and recording video footage, leading the police to suspect that the exhibition could be a target; the surveillance on the men was increased and the Dome was placed under close watch. The precautions taken by the Flying Squad included replacing the priceless gems with replicas of the same size, allowing the originals to be stored elsewhere, as well as installing a false wall inside the exhibit room, behind which 20 police were waiting in full tactical gear. Due to an increase in surveillance, the police discovered other members of the gang; these included Terry Millman, tasked with obtaining the getaway speedboat, to be used for the escape. Cockram and Betson were observed filming the surrounding river and jetty.
The surveillance on the gang continued and their visits to the Dome became more frequent. In late September a few members of the gang were spotted testing a speedboat in a harbour in Kent; the Metropolitan Police were able to identify the possible days upon which the raid could take place and communicated this information to De Beers and the Dome's management. Two of the days that the police had identified resulted in aborted attempts; the first aborted attempt occurred in early October and was called off due to the malfunctioning of the speedboat, to be used for the getaway. The second aborted attempt occurred one day before the date of the actual raid, but was cancelled upon the gang discovering the tide was too low to ensure a safe getaway. After this attempt the police suspected the raid was imminent and were convinced the raid would take place the following day; the police replaced all Dome staff with armed undercover officers. On a number of days in October, the gang under surveillance looked as if they were about to commence the raid.
Some members were spotted towing a speedboat to Greenwich and placing the boat in the river opposite the Dome. This activity indicated to the Squad; the delay was
Dubai
Dubai is the largest and most populous city in the United Arab Emirates. On the southeast coast of the Persian Gulf, it is the capital of the Emirate of Dubai, one of the seven emirates that make up the country. Dubai is a global business hub of the Middle East, it is a major global transport hub for passengers and cargo. Oil revenue helped accelerate the development of the city, a major mercantile hub, but Dubai's oil reserves are limited and production levels are low: today, less than 5% of the emirate's revenue comes from oil. A growing centre for regional and international trade since the early 20th century, Dubai's economy today relies on revenues from trade, aviation, real estate, financial services. Dubai has attracted world attention through large construction projects and sports events, in particular the world's tallest building, the Burj Khalifa; as of 2012, Dubai was the most expensive city in the Middle East. In 2014, Dubai's hotel rooms were rated as the second most expensive in the world.
Many theories have been proposed as to the origin of the word "Dubai". One theory suggests the word was used to describe the souq, similar to the souq in Ba. An Arabic proverb says "Daba Dubai", meaning "They came with a lot of money." According to Fedel Handhal, a scholar on the UAE's history and culture, the word Dubai may have come from the word daba, referring to the slow flow of Dubai Creek inland. The poet and scholar Ahmad Mohammad Obaid traces it to the same word, but to its alternative meaning of "baby locust" due to the abundant nature of locusts in the area before settlement; the history of human settlement in the area now defined by the United Arab Emirates is rich and complex, points to extensive trading links between the civilisations of the Indus Valley and Mesopotamia, but as far afield as the Levant. Archaeological finds in the emirate of Dubai at Al-Ashoosh, Al Sufouh and the notably rich trove from Saruq Al Hadid show settlement through the Ubaid and Hafit periods, the Umm Al Nar and Wadi Suq periods and the three Iron Ages in the UAE.
The area was known to the Sumerians as Magan, was a source for metallic goods, notably copper and bronze. The area was covered with sand about 5,000 years ago as the coast retreated inland, becoming part of the city's present coastline. Pre-Islamic ceramics have been found from the 4th centuries. Prior to the introduction of Islam to the area, the people in this region worshiped Bajir. After the spread of Islam in the region, the Umayyad Caliph of the eastern Islamic world invaded south-east Arabia and drove out the Sassanians. Excavations by the Dubai Museum in the region of Al-Jumayra found several artefacts from the Umayyad period; the earliest recorded mention of Dubai is in 1095 in the Book of Geography by the Andalusian-Arab geographer Abu Abdullah al-Bakri. The Venetian pearl merchant Gasparo Balbi visited the area in 1580 and mentioned Dubai for its pearling industry. Dubai is thought to have been established as a fishing village in the early 18th century and was, by 1822, a town of some 7–800 members of the Bani Yas tribe and subject to the rule of Sheikh Tahnun bin Shakhbut of Abu Dhabi.
In 1833, following tribal feuding, members of the Al Bu Falasah tribe seceded from Abu Dhabi and established themselves in Dubai. The exodus from Abu Dhabi was led by Obeid bin Saeed and Maktoum bin Butti, who became joint leaders of Dubai until Ubaid died in 1836, leaving Maktum to establish the Maktoum dynasty. Dubai signed the General Maritime Treaty of 1820 along with other Trucial States, following the British punitive expedition against Ras Al Khaimah of 1819, which led to the bombardment of the coastal communities of the Persian Gulf; this led to the 1853 Perpetual Maritime Truce. Dubai – like its neighbours on the Trucial Coast – entered into an exclusivity agreement in which the United Kingdom took responsibility for the emirate's security in 1892. In 1841, a smallpox epidemic broke out in the Bur Dubai locality, forcing residents to relocate east to Deira. In 1896, fire broke out in Dubai, a disastrous occurrence in a town where many family homes were still constructed from barasti - palm fronds.
The conflagration consumed half the houses of Bur Dubai, while the district of Deira was said to have been destroyed. The following year, more fires broke out. A female slave was subsequently put to death. In 1901, Maktoum bin Hasher Al Maktoum established Dubai as a free port with no taxation on imports or exports and gave merchants parcels of land and guarantees of protection and tolerance; these policies saw a movement of merchants not only directly from Lingeh, but those who had settled in Ras Al Khaimah and Sharjah to Dubai. An indicator of the growing importance of the port of Dubai can be gained from the movements of the steamer of the Bombay and Persia Steam Navigation Company, which from 1899 to 1901 paid five visits annually to Dubai. In 1902 the company's vessels made 21 visits to Dubai and from 1904 on, the steamers called fortnightly – in 1906, trading seventy thousand tonnes of cargo; the frequency of these vessels only helped to accelerate Dubai's role as an emerging port and trading hub of preference.
Lorimer notes the transfer from Lingeh'bids fair to become complete and permanent', that the town had by 1906 supplanted Lingeh as the chief entrepôt of the Trucial States. The'great storm' of 1908 struck the pearling boats of Dubai and the coastal emirates t
2009 Graff Diamonds robbery
The Graff Diamonds robbery took place on 6 August 2009 when two men posing as customers entered the premises of Graff Diamonds in New Bond Street and stole jewellery worth nearly £40 million. It was believed to be the largest gems heist in Britain at the time, the second largest British robbery after the £53 million raid on a Securitas depot in Kent in 2006; the thieves' haul totalled 43 items of jewellery, consisting of rings, bracelets and wristwatches. One necklace alone has been reported as being worth more than £3.5m. Britain's previous largest jewellery robbery took place at Graff's, in 2003; as of September 2014, none of the stolen jewels have been recovered. The robbers used the services of a professional make-up artist to alter their skin tones and their features using latex prosthetics and to be fitted with professional wigs; the artist took four hours having been told that it was for a music video. Viewing the results in a mirror, Aman Kassaye commented: "My own mother wouldn't recognise me now," to which his accomplice is reported to have laughed and replied: "That's got to be a good thing, hasn't it?"
The same make-up studio had unwittingly helped disguise members of the gang that robbed the Securitas depot in 2006. On 6 August 2009 at 4:40 pm, two dressed men arrived at the Graff Diamonds jewellery store by taxi and once inside produced two handguns which they used to threaten staff, they made no attempt to conceal their faces from the premises' CCTV cameras due to their elaborate disguises. Though one of the robbers was wearing leather gloves, store security allowed him entry, being used to the eccentric behaviour of some super-wealthy clients. Petra Ehnar, a shop assistant, was forced at gunpoint to empty the store's display cabinets. A total of 43 rings, bracelets and watches were taken, she was held hostage at gunpoint and was forced into the street during the getaway. She testified that the robbers told her that she would be killed if she did not carry out their demands. After releasing the hostage outside the store, one of the robbers fired a shot into the air to create confusion, both escaped the scene in a blue BMW vehicle.
This vehicle was abandoned in nearby Dover Street, where a second gunshot was fired into the ground while the robbers switched to a second vehicle, a silver Mercedes. They again switched vehicles in Farm Street, after which there was no further information regarding their whereabouts. All of the diamonds had been laser-inscribed with the Graff logo and a Gemological Institute of America identification number. Detectives investigating the robbery stated: "They knew what they were looking for and we suspect they had a market for the jewels." The suspects' details were circulated to all ports and airports but police believed they would have an elaborately prepared escape route and had left the country. The robbery was being investigated by Barnes Flying Squad, headed by Detective Chief Inspector Pam Mace; the financial loss to Graff Diamonds was more than US$10 million. The actual value of the pieces for insurance purposes, was put at $39 million, but according to Nicholas Paine, the company secretary, the syndicate that insured Graff was only liable for $28.9 million.
The robbers were caught shortly after police searched one of the getaway cars abandoned by the robbers. A pay-as-you go mobile phone was discovered that robbers Aman Kassaye and Craig Calderwood left in the car after ramming into a black cab. After the collision, in their haste to transfer to a second vehicle, the robbers forgot the mobile phone, wedged between the driver's seat and the handbrake. Anonymous numbers stored on the mobile phone allowed police to discover the identity of the robber. On 20 August 2009, two men, Craig Calderwood, 26, of no fixed abode, Solomun Beyene, 24, of Lilestone Road, London NW8, were charged in connection with the robbery. On 21 August, a third man, Clinton Mogg, 42, of Westby Road, was charged, Calderwood and Beyene were remanded in custody by Westminster Magistrates' Court. On 22 August, Mogg appeared at Westminster Magistrates' Court. All three were remanded in custody to appear at Kingston Crown Court on 1 September. A fourth man, aged 50, bailed. By mid-October, ten male suspects had been arrested in connection with the robbery.
Charges brought against the individuals include conspiracy with others to commit robbery, attempted murder, holding someone hostage, possessing firearms and using a handgun to resist arrest. Aman Kassaye, who planned and executed the heist, was found guilty of conspiracy to rob and possession of a firearm after a three-month trial at Woolwich Crown Court. On 7 August 2010, he was sentenced to 23 years in prison. Three other men – Solomun Beyene, 25, of London, Clinton Mogg, 43, of Bournemouth, Thomas Thomas, 46, of Kingston upon Thames – were each jailed for 16 years after being convicted of conspiracy to rob. Craig Calderwood was jailed for 21 years; as of March 2011, none of the stolen jewellery has been recovered. Experts believe the jewellery has been broken up so the precious stones could be anonymously resold after being recut. List of bank robbers and robberies Major crimes in the United Kingdom List of missing treasure Hunt for £40m jewel heist gang – BBC News Channel report Graff Diamonds – Official site Jewellery worth $65million stolen in armed robbery – Metropolitan Police Bulletin
Synthetic diamond
A synthetic diamond is a diamond produced by a controlled process, as contrasted with a natural diamond created by geological processes or an imitation diamond made of non-diamond material that appears similar to a diamond. Synthetic diamond is widely known as HPHT diamond or CVD diamond, after the two common production methods. While the term synthetic may sometimes be associated by consumers with imitation products, synthetic diamonds are made of the same material as natural diamonds—pure carbon, crystallized in an isotropic 3D form. In the United States, the Federal Trade Commission has indicated that the terms laboratory-grown, laboratory-created, -created "would more communicate the nature of the stone". Numerous claims of diamond synthesis were documented between 1879 and 1928. In the 1940s, systematic research began in the United States and the Soviet Union to grow diamonds using CVD and HPHT processes; the first reproducible synthesis was reported around 1955. Those two processes still dominate the production of synthetic diamond.
A third method, known as detonation synthesis, entered the diamond market in the late 1990s. In this process, nanometer-sized diamond grains are created in a detonation of carbon-containing explosives. A fourth method, treating graphite with high-power ultrasound, has been demonstrated in the laboratory, but has no commercial application; the properties of synthetic diamond depend on the details of the manufacturing processes. Synthetic diamond is used in abrasives, in cutting and polishing tools and in heat sinks. Electronic applications of synthetic diamond are being developed, including high-power switches at power stations, high-frequency field-effect transistors and light-emitting diodes. Synthetic diamond detectors of ultraviolet light or high-energy particles are used at high-energy research facilities and are available commercially; because of its unique combination of thermal and chemical stability, low thermal expansion and high optical transparency in a wide spectral range, synthetic diamond is becoming the most popular material for optical windows in high-power CO2 lasers and gyrotrons.
It is estimated. Both CVD and HPHT diamonds can be cut into gems and various colors can be produced: clear white, brown, blue and orange; the advent of synthetic gems on the market created major concerns in the diamond trading business, as a result of which special spectroscopic devices and techniques have been developed to distinguish synthetic and natural diamonds. After the 1797 discovery that diamond was pure carbon, many attempts were made to convert various cheap forms of carbon into diamond; the earliest successes were reported by James Ballantyne Hannay in 1879 and by Ferdinand Frédéric Henri Moissan in 1893. Their method involved heating charcoal at up to 3500 °C with iron inside a carbon crucible in a furnace. Whereas Hannay used a flame-heated tube, Moissan applied his newly developed electric arc furnace, in which an electric arc was struck between carbon rods inside blocks of lime; the molten iron was rapidly cooled by immersion in water. The contraction generated by the cooling produced the high pressure required to transform graphite into diamond.
Moissan published his work in a series of articles in the 1890s. Many other scientists tried to replicate his experiments. Sir William Crookes claimed success in 1909. Otto Ruff claimed in 1917 to have produced diamonds up to 7 mm in diameter, but retracted his statement. In 1926, Dr. J Willard Hershey of McPherson College replicated Moissan's and Ruff's experiments, producing a synthetic diamond. Despite the claims of Moissan and Hershey, other experimenters were unable to reproduce their synthesis; the most definitive replication attempts. A prominent scientist and engineer known for his invention of the steam turbine, he spent about 40 years and a considerable part of his fortune trying to reproduce the experiments of Moissan and Hannay, but adapted processes of his own. Parsons was known for methodical record keeping, he wrote a number of articles—some of the earliest on HPHT diamond—in which he claimed to have produced small diamonds. However, in 1928, he authorized Dr. C. H. Desch to publish an article in which he stated his belief that no synthetic diamonds had been produced up to that date.
He suggested that most diamonds, produced up to that point were synthetic spinel. In 1941, an agreement was made between the General Electric and Carborundum companies to further develop diamond synthesis, they were able to heat carbon to about 3,000 °C under a pressure of 3.5 gigapascals for a few seconds. Soon thereafter, the Second World War interrupted the project, it was resumed in 1951 at the Schenectady Laboratories of GE, a high-pressure diamond group was formed with Francis P. Bundy and H. M. Strong. Tracy Hall and others joined this project shortly thereafter; the Schenectady group improved
Mohs scale of mineral hardness
The Mohs scale of mineral hardness is a qualitative ordinal scale characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. Created in 1812 by German geologist and mineralogist Friedrich Mohs, it is one of several definitions of hardness in materials science, some of which are more quantitative; the method of comparing hardness by observing which minerals can scratch others is of great antiquity, having been mentioned by Theophrastus in his treatise On Stones, c. 300 BC, followed by Pliny the Elder in his Naturalis Historia, c. 77 AD. While facilitating the identification of minerals in the field, the Mohs scale does not show how well hard materials perform in an industrial setting. Despite its lack of precision, the Mohs scale is relevant for field geologists, who use the scale to identify minerals using scratch kits; the Mohs scale hardness of minerals can be found in reference sheets. Mohs hardness is useful in milling, it allows assessment of.
The scale is used at electronic manufacturers for testing the resilience of flat panel display components. The Mohs scale of mineral hardness is based on the ability of one natural sample of mineral to scratch another mineral visibly; the samples of matter used by Mohs are all different minerals. Minerals are chemically pure solids found in nature. Rocks are made up of one or more minerals; as the hardest known occurring substance when the scale was designed, diamonds are at the top of the scale. The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, or the softest material that can scratch the given material. For example, if some material is scratched by apatite but not by fluorite, its hardness on the Mohs scale would fall between 4 and 5. "Scratching" a material for the purposes of the Mohs scale means creating non-elastic dislocations visible to the naked eye. Materials that are lower on the Mohs scale can create microscopic, non-elastic dislocations on materials that have a higher Mohs number.
While these microscopic dislocations are permanent and sometimes detrimental to the harder material's structural integrity, they are not considered "scratches" for the determination of a Mohs scale number. The Mohs scale is a purely ordinal scale. For example, corundum is twice as hard as topaz; the table below shows the comparison with the absolute hardness measured by a sclerometer, with pictorial examples. On the Mohs scale, a streak plate has a hardness of 7.0. Using these ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale; the table below incorporates additional substances that may fall between levels: Comparison between hardness and hardness: Mohs hardness of elements is taken from G. V. Samsonov in Handbook of the physicochemical properties of the elements, IFI-Plenum, New York, USA, 1968. Cordua, William S. "The Hardness of Minerals and Rocks". Lapidary Digest, c. 1990
Guild
A guild is an association of artisans or merchants who oversee the practice of their craft/trade in a particular area. The earliest types of guild formed as a confraternities of tradesmen, they were organized in a manner something between a professional association, a trade union, a cartel, a secret society. They depended on grants of letters patent from a monarch or other authority to enforce the flow of trade to their self-employed members, to retain ownership of tools and the supply of materials. A lasting legacy of traditional guilds are the guildhalls constructed and used as guild meeting-places. Guild members found guilty of cheating on the public would be banned from the guild. An important result of the guild framework was the emergence of universities at Bologna and Paris. A type of guild was known in Roman times. Known as collegium, collegia or corpus, these were organised groups of merchants who specialised in a particular craft and whose membership of the group was voluntary. One such example is the corpus naviculariorum, the college of long-distance shippers based at Rome's La Ostia port.
The Roman guilds failed to survive the collapse of the Roman Empire. In medieval cities, craftsmen tended to form associations based on their trades, confraternities of textile workers, carpenters, glass workers, each of whom controlled secrets of traditionally imparted technology, the "arts" or "mysteries" of their crafts; the founders were free independent master craftsmen who hired apprentices. There were several types of guilds, including the two main categories of merchant guilds and craft guilds but the frith guild and religious guild. Guilds arose beginning in the High Middle Ages as craftsmen united to protect their common interests. In the German city of Augsburg craft guilds are being mentioned in the Towncharter of 1156; the continental system of guilds and merchants arrived in England after the Norman Conquest, with incorporated societies of merchants in each town or city holding exclusive rights of doing business there. In many cases they became the governing body of a town. For example, London's Guildhall became the seat of the Court of Common Council of the City of London Corporation, the world’s oldest continuously elected local government, whose members to this day must be Freemen of the City.
The Freedom of the City, effective from the Middle Ages until 1835, gave the right to trade, was only bestowed upon members of a Guild or Livery. Early egalitarian communities called "guilds" were denounced by Catholic clergy for their "conjurations" — the binding oaths sworn among the members to support one another in adversity, kill specific enemies, back one another in feuds or in business ventures; the occasion for these oaths were drunken banquets held on December 26, the pagan feast of Jul —in 858, West Francian Bishop Hincmar sought vainly to Christianise the guilds. In the Early Middle Ages, most of the Roman craft organisations formed as religious confraternities, had disappeared, with the apparent exceptions of stonecutters and glassmakers the people that had local skills. Gregory of Tours tells a miraculous tale of a builder whose art and techniques left him, but were restored by an apparition of the Virgin Mary in a dream. Michel Rouche remarks that the story speaks for the importance of transmitted journeymanship.
In France, guilds were called corps de métiers. According to Viktor Ivanovich Rutenburg, "Within the guild itself there was little division of labour, which tended to operate rather between the guilds. Thus, according to Étienne Boileau's Book of Handicrafts, by the mid-13th century there were no less than 100 guilds in Paris, a figure which by the 14th century had risen to 350." There were different guilds of metal-workers: the farriers, knife-makers, chain-forgers, nail-makers formed separate and distinct corporations. In Catalan towns, specially at Barcelona, guilds or gremis were a basic agent in the society: a shoemakers' guild is recorded in 1208. In England in the City of London Corporation, more than 110 guilds, referred to as livery companies, survive today, with the oldest more than a thousand years old. Other groups, such as the Worshipful Company of Tax Advisers, have been formed far more recently. Membership in a livery company is expected for individuals participating in the governance of The City, as the Lord Mayor and the Remembrancer.
The guild system reached a mature state in Germany circa 1300 and held on in German cities into the 19th century, with some special privileges for certain occupations remaining today. In the 15th century, Hamburg had 100 guilds, Cologne 80, Lübeck 70; the latest guilds to develop in Western Europe were the gremios of Spain: Toledo. Not all city economies were controlled by guilds. Where guilds were in control, they shaped labor and trade. In order to become a master, a journeyman would have to go on a three-year voyage called journeyman years; the practice of the journeyman years still exists in France. As production became more specialized, trade guilds were divided and subdivided, eliciting the squabbles over jurisdiction that produced the paperwork by which economic historians trace their development: The
Facet
Facets are flat faces on geometric shapes. The organization of occurring facets was key to early developments in crystallography, since they reflect the underlying symmetry of the crystal structure. Gemstones have facets cut into them in order to improve their appearance by allowing them to reflect light. Of the hundreds of facet arrangements that have been used, the most famous is the round brilliant cut, used for diamond and many colored gemstones; this first early version of what would become the modern Brilliant Cut is said to have been devised by an Italian named Peruzzi, sometime in the late 17th century. On, the first angles for an "ideal" cut diamond were calculated by Marcel Tolkowsky in 1919. Slight modifications have been made since but angles for "ideal" cut diamonds are still similar to Tolkowsky's formula. Round brilliants cut before the advent of "ideal" angles are referred to as "Early round brilliant cut" or "Old European brilliant cut" and are considered poorly cut by today's standards, though there is still interest in them from collectors.
Other historic diamond cuts include the "Old Mine Cut", similar to early versions of the round brilliant, but has a rectangular outline, the "Rose Cut", a simple cut consisting of a flat, polished back, varying numbers of angled facets on the crown, producing a faceted dome. Sometimes a 58th facet, called a culet is cut on the bottom of the stone to help prevent chipping of the pavilion point. Earlier brilliant cuts have large culets, while modern brilliant cut diamonds lack the culet facet, or it may be present in minute size; the art of cutting a gem is an exacting procedure performed on a faceting machine. The ideal product of facet cutting is a gemstone that displays a pleasing balance of internal reflections of light known as brilliance and colorful dispersion, referred to as "fire", brightly colored flashes of reflected light known as scintillation. Transparent to translucent stones are faceted, although opaque materials may be faceted as the luster of the gem will produce appealing reflections.
Pleonaste and black diamond are examples of opaque faceted gemstones. The angles used for each facet play a crucial role in the final outcome of a gem. While the general facet arrangement of a particular gemstone cut may appear the same in any given gem material, the angles of each facet must be adjusted to maximize the optical performance; the angles used will vary based on the refractive index of the gem material. When light passes through a gemstone and strikes a polished facet, the minimum angle possible for the facet to reflect the light back into the gemstone is called the critical angle. If the ray of light strikes a surface lower than this angle, it will leave the gem material instead of reflecting through the gem as brilliance; these lost light rays are sometimes referred to as "light leakage", the effect caused by it is called "windowing" as the area will appear transparent and without brilliance. This is common in poorly cut commercial gemstones. Gemstones with higher refractive indexes make more desirable gemstones, the critical angle decreases as refractive indices increase, allowing for greater internal reflections as the light is less to escape.
This machine uses a motor-driven plate to hold a flat disk for the purpose of cutting or polishing. Diamond abrasives bonded to metal or resin are used for cutting laps, a wide variety of materials are used for polishing laps in conjunction with either fine diamond powder or oxide-based polishes. Water is used for cutting, while either oil or water is used for the polishing process; the machine uses a system called a "mast" which consists of an angle readout, height adjustment and a gear with a particular number of teeth is used as a means of setting the rotational angle. The angles of rotation are evenly divided by the number of teeth present on the gear, though many machines include additional means of adjusting the rotational angle in finer increments called a "cheater"; the stone is bonded to a rod known as a "dop" or "dop stick" and is held in place by part of the mast referred to as the "quill". The dopped stone is ground at precise angles and indexes on cutting laps of progressively finer grit, the process is repeated a final time to polish each facet.
Accurate repetition of angles in the cutting and polishing process is aided by the angle readout and index gear. The physical process of polishing is a subject of debate. One accepted theory is that the fine abrasive particles of a polishing compound produce abrasions smaller than the wavelengths of light, thus making the minute scratches invisible. Since gemstones have two sides, a device called a "transfer jig" is used to flip the stone so that each side may be cut and polished. Cleaving relies on planar weaknesses of the chemical bonds in the crystal structure of a mineral. If a sharp blow is applied at the correct angle, the stone may split cleanly apart. While cleaving is sometimes used to split uncut gemstones into smaller pieces, it is never used to produce facets. Cleaving of diamonds was once common, but as the risk of damaging a stone is too high, undesirable diamond pieces resulted; the preferred method of splitting diamonds into smaller pieces is now sawing. An older and more primitive style of faceting machine called a jamb peg machine used wooden dop sticks of precise length and a "mast" system consisting of a plate with holes placed in it.
By placing the back end of the dop into one of the many holes, the stone could
