The cullinan diamond was dug out from the ground by a native miner in South Africa's Transvaal Premier Mine in 1905. Weighing 3,106 carats in the rough, this colourless stone is regarded today as one of the greatest diamond discoveries of all time. The Transvall government purchased it and named it after Sir Thomas Cullinan, who had discovered the mine three years earlier. They presented the stone to King Edward 5 in 1907, after which it was brocken up into nine large stones and a hundred smaller ones. The pear-shaped Cullinan-1 piece of 530.2 carats is the largest cut diamond in the world and is presently set into the head of the English sceptre. The Cullinan 2, often referred to as the Star of Africa weighs 317 -carats and is in the Imperial State Crown.
The Centenary diamond weighed 599 carats in the rough and was found in 1988. Under instructions from the De Beers Company, one of the world's most renowned stone cutters, Tolkowsky cut it in the then new brilliant style to a perfectly coloured gem of 273 carats. This largest diamond in the world was presented to Queen Elizabeth 2 to become part of the British Crown Jewels.
The Regent Diamond was found in 1699 in one of the mines on the Krishna River in southern India. William Pitt, Governor of Madras at Fort St.George in Madras, bought the 410-carat stone for 20,400 and brought it to England in 1701. It was then cut and sold to the Duke of Orleans, then Regent of France. Marie Antoinette was seen wearing it, but during the France Revolution it disappeared; later it was located later in a hole in a Paris loft. The French government pawned it once to raise money from a German banker and again to guarantee a loan from Dutch bankers. Napoleon Bonaparte had it set in the hilt of the sword he carried when he was proclaimed Emperor of France, It is now in the Louvre museum in Paris.
The Darya-i-Nur is a flawless, transparent pink stone, of weight between 175 and 195 carats. Nadir Shah captured it along with the Kohinoor when the attacked Delhi in 1739 and was last seen when the Shah Pahlevi of Iran wore it for his coronation in 1967. It is the largest and most remarkable gem in the State Jewels of Iran. Set in a gold frame with other diamonds, it is topped by a crown bearing lions with ruby eyes, holding scimitars.
The Orloff is the largest diamond of the Russian collection. This stone of 195 carats weight is of an almost hemipherical rosette shape and is said to have been stolen from the Srirangam temple near Tiruchirapalli, India. It finally arrived in Amesterdam where the Prince Orloffbought it to give the Empress Catherine 2 of Russia.
The Moon of the Mountains, a diamond of 120 carats, once adorned the throne of Nadir Shah. After his assassination, it was stolen by an Afghan soldier. It finally ended up in the collection of the Russian government.
The hope diamond was also found in the Kollur mines. In 1642, Tavernier seems to have bought it before selling it to Louis 14 in 1668. It is possible that originally it was a beautiful violet blue diamond called the Tavernier, of a mass of 112.2 carats. In 1673, Sieur Pitau, the court jeweler, cut it to a stone of 67.13 carats. Louis 15, in 1749 then had it cut to an oval pice of 45.22 carats. It disappeared for several years after the French Revolution, but reappeared in America when it was bought by Henry Philip Hope, after whom it is named. After Henry Hope died, the diamond passed throught several owners till Evelyn Walsh McLean bought the diamond in 1911. On her death in 1947, Harry Winston, the jeweller bought it and presented it to the Smithsonian Institution where it can be seen today. The Hope diamond known as the most valuable stone in the world.
Tuesday, April 19, 2011
Famous Diamonds
The price per gram of diamond increases with its weight but stones beyond a certain size are so rare that they cannot be valued on this scale. The few very large and spectacular diamonds are priceless and can trace their complex and controversial history through tales of war. intrigue and love. It is, in fact, the story of their passage through the lives of several owners and not their size, lustre or other properties that determines the price that they command.
The kohinoor or the 'Mountain of Light' diamond was found two thousand five hundred years ago by a villager of Matanga in Kollur in Andhra Pradesh. Old palm leaf manuscripts record the weight of the rough stone as 1986 carats. Sanskirt legends report that Karna, the King of Anga, wore this diamond in his crown to give him invincibility during the great Mahabharata war. The stone later came into the possession of Emperor Vikramaditya of Ujjain (60 BC). During the early Persian invasion of India, the diamond was apparently taken to the court of Darius the Great but after the break-up of the Persian Empire, the gem found its way back to India. There is recorded evidence that the Kohinoor was with the family of the Rajah of Malwa in India, for several centuries, having been passed down from generation to generation. When the Moghuls invaded India, Sultan Babar, the first of the Moghuls emperors, acquired the diamond in 1340 AD. It was hidden in the Moghul treasury for about two centuries and in 1526 the diamond was set as one of the peacock's eyes in the famous Peacock Throne of Shah Jahan. In 1739, Nadir Shah of Persia, invaded India and captured Delhi and seized the Peacock Throne but could not find the Kohinoor diamond about which he had heard to much. Nadir Shah later learned from informants that the Moghul emperor had hidden the stone is his turban. During a dinner party Nadir Shah suggested an exchange of turbans, a custom prevalent at the time. The Emperor could not refuse this request and reluctantly undid his silk turban, revealing the gem. Nadir Shah then named it the 'Mountain of Light'. Historians disagree about the source of the name of the stone and insist that the name was a variant on Kollur, where it was found.
When Nadir Shah was murdered, one of his bodyguards took the Kohinoor to Afghanistan. Years later, Maharaja Ranjit Singh of the Punjab acquired it in exchange for military help to Ahmed Shah, the Moghul king. After the British won the war against the Sikhs, they annexed the Punjab and the East India Company claimed the diamond as partial idemnity. To mark the two-hundred and fiftieth anniversary of the Company in 1850, the directors presented the diamond to Queen Victoria who wore it in a brooch after it was cut to 800 carats. It was re-cut to a smaller size of 219 carats and later cut again to a more striking oval cut diamond of 108.93 carats before it was set inn the State Crown, worn by Queen Alexandra and Queen Mary. Queen Elizabeth 2 wore it in 1952 for her coronation. The diamond in now part of the British Crown Jewela. The Indian government has now laid claim to the diamond as it was taken by force from this country.
The Great Moghul was also found in 1650 near Kollur in India, according to the French traveller, Tavenier. In the rough it weighed 787.5 carats. Reports say that it was presented to Emperor Shah Jahanin 1656 by Mir Jumla and so was named after the ruler. The Emperor asked Hortensio Borgis, the Venetian diamond-cutter, a lapidary who at that time was domiciled in India, to cut the stone. The work was done so badly that Borgis was forced to pay a heavy fine. When Tavernier last saw the Great Moghul in the treasury of Emperor Aurangzeb in 1665, he described it as looking like an egg and having the form of a very high and round rosette weighing 280 carats. The stone then disappeared and it is possible that it lies in some secret treasury somewhere.
The excelsior, another very large diamond, flawless with a beautiful blue-white colour weighed 971.75 carats and came from the Jagersfontein mine in South Africa. It was afterwards renamed the 'Jubilee,' to celebrate the sixtieth anniversary of the accession of Queen Victoria. The African who found it in a spade of gravel on June 30, 1893 was rewarded 500 in money and a horse equipped with saddle and bridle. Two years later, its value varied between 1,000,000. The rough stone, however, had a black spot near centre of its mass that was removed by cleaving the stone in two. The larger portion yielded a perfect brilliant weighing 239 carats. A smaller, 18-carat marquise stone was cut from the remaining portion.
The kohinoor or the 'Mountain of Light' diamond was found two thousand five hundred years ago by a villager of Matanga in Kollur in Andhra Pradesh. Old palm leaf manuscripts record the weight of the rough stone as 1986 carats. Sanskirt legends report that Karna, the King of Anga, wore this diamond in his crown to give him invincibility during the great Mahabharata war. The stone later came into the possession of Emperor Vikramaditya of Ujjain (60 BC). During the early Persian invasion of India, the diamond was apparently taken to the court of Darius the Great but after the break-up of the Persian Empire, the gem found its way back to India. There is recorded evidence that the Kohinoor was with the family of the Rajah of Malwa in India, for several centuries, having been passed down from generation to generation. When the Moghuls invaded India, Sultan Babar, the first of the Moghuls emperors, acquired the diamond in 1340 AD. It was hidden in the Moghul treasury for about two centuries and in 1526 the diamond was set as one of the peacock's eyes in the famous Peacock Throne of Shah Jahan. In 1739, Nadir Shah of Persia, invaded India and captured Delhi and seized the Peacock Throne but could not find the Kohinoor diamond about which he had heard to much. Nadir Shah later learned from informants that the Moghul emperor had hidden the stone is his turban. During a dinner party Nadir Shah suggested an exchange of turbans, a custom prevalent at the time. The Emperor could not refuse this request and reluctantly undid his silk turban, revealing the gem. Nadir Shah then named it the 'Mountain of Light'. Historians disagree about the source of the name of the stone and insist that the name was a variant on Kollur, where it was found.
When Nadir Shah was murdered, one of his bodyguards took the Kohinoor to Afghanistan. Years later, Maharaja Ranjit Singh of the Punjab acquired it in exchange for military help to Ahmed Shah, the Moghul king. After the British won the war against the Sikhs, they annexed the Punjab and the East India Company claimed the diamond as partial idemnity. To mark the two-hundred and fiftieth anniversary of the Company in 1850, the directors presented the diamond to Queen Victoria who wore it in a brooch after it was cut to 800 carats. It was re-cut to a smaller size of 219 carats and later cut again to a more striking oval cut diamond of 108.93 carats before it was set inn the State Crown, worn by Queen Alexandra and Queen Mary. Queen Elizabeth 2 wore it in 1952 for her coronation. The diamond in now part of the British Crown Jewela. The Indian government has now laid claim to the diamond as it was taken by force from this country.
The Great Moghul was also found in 1650 near Kollur in India, according to the French traveller, Tavenier. In the rough it weighed 787.5 carats. Reports say that it was presented to Emperor Shah Jahanin 1656 by Mir Jumla and so was named after the ruler. The Emperor asked Hortensio Borgis, the Venetian diamond-cutter, a lapidary who at that time was domiciled in India, to cut the stone. The work was done so badly that Borgis was forced to pay a heavy fine. When Tavernier last saw the Great Moghul in the treasury of Emperor Aurangzeb in 1665, he described it as looking like an egg and having the form of a very high and round rosette weighing 280 carats. The stone then disappeared and it is possible that it lies in some secret treasury somewhere.
The excelsior, another very large diamond, flawless with a beautiful blue-white colour weighed 971.75 carats and came from the Jagersfontein mine in South Africa. It was afterwards renamed the 'Jubilee,' to celebrate the sixtieth anniversary of the accession of Queen Victoria. The African who found it in a spade of gravel on June 30, 1893 was rewarded 500 in money and a horse equipped with saddle and bridle. Two years later, its value varied between 1,000,000. The rough stone, however, had a black spot near centre of its mass that was removed by cleaving the stone in two. The larger portion yielded a perfect brilliant weighing 239 carats. A smaller, 18-carat marquise stone was cut from the remaining portion.
Diamond Mining
In the conventional sawing and drilling of a diamond, diamond particles continuously chip the stone at high speed. There are occasions when this method fails, such as when a hard 'knaat' is encountered, an average packet of rough diamonds contains about three to five per cent knaats. If the knaats are more than about one millimetre in size within the rough stone, they could be seen and so rejected. Smaller inclusions are dangerous, as they could damage the saw blades or the scaifes. Again, a hard inclusion might cause vibration of the thin saw blade and shatter it, unless the cutting is slowed down so much that a five carat knaat takes several weeks to cut. Laser drilling and sawing overcomes these problems. In addition, unlike the conventional saw or drill, there is no physical contact between the laser hardware and the stone. Consequently, oil residues or material of the saw blade do not contaminate the stone.
When the focused laser beam hits the stone at a very small spot and the beam energy is absorbed, the temperature at the target spot shoots up to more than 3000C. The heating is extremely fast and so is the cooling, beacuse of the pulsed nature of the laser light. Consequently, the rest of the stone is not heated by the laser beam. To increase the absorption of the laser light by the diamond, a spot of graphite is first apllied to the entrance point of the desired hole. As the beam hits the stone this graphite spot absorbs all the energy of the laser and evaporates. The diamond below the spot becomes graphite locally because of the high temperature and, in turn, provides an absorptive spot. The diamond is therefore cut by evaporation and not by abrasion. The hole produced by the beam is V shaped and as it gets deeper, it becomes wider. However, good design of the optics of the laser system can narroe the diameter of the hole to less than ten microns. The weight loss of the diamond by laser sawing is therefore much less than by conventional sawing, provided special care is taken. Twinned or grained crystals of diamond are cut in a few hours instead of the weeks required by conventional sawing.
Laser sawing is therefore superior to conventional methods, as the cuts can be made irrespective of crystallographic direction. Accuracies of twenty-five microns are routine, limited only by the movement of the holder and vibrations of the table. When a laser is employed for kerfing, the kerf can be as thin as 0.3 micron. Kerf depths of four-hundred micron are achieved in about twenty-five seconds.
The laser beam is produced by flashing light from xenon flash tubes on to a rod of laser material. The rod absorbs this energy and emits it as an exceedingly parallel and coherent beam. The laser material is a solid rod of ruby, Neodymium glass (Nd glass) or Neodymium aluminum garnet (NdYGA,) with accurately parallel and polished faces. Carbon dioxide gas in a quartz tube also acts as a laser material but the focusing is not as fine as with a solid rod. A serious problem in all high power lasers is the overheating of the laser material and the choice of the laser equipment depends on the use that is made of the system.
A typical laser drilling or cutting machine used for diamond processing would have a pulsed NdYAG emitting light of wavelength of 1060 nm, with a peak power one to twenty five kilowatt and a pulse width of 0.2 microseconds. The repetition rate of the pulses is ten to ten housand per second. Other factors affect laser drilling, of holes than the minimal requirements of power density. Not only are the diameter and the depth of the hole dependent on the wavelength of the laser light, but they are also determined by the mode of the laser output. The lowest order mode and the shortest wavelength give the sharpest focussed spot.
When the focused laser beam hits the stone at a very small spot and the beam energy is absorbed, the temperature at the target spot shoots up to more than 3000C. The heating is extremely fast and so is the cooling, beacuse of the pulsed nature of the laser light. Consequently, the rest of the stone is not heated by the laser beam. To increase the absorption of the laser light by the diamond, a spot of graphite is first apllied to the entrance point of the desired hole. As the beam hits the stone this graphite spot absorbs all the energy of the laser and evaporates. The diamond below the spot becomes graphite locally because of the high temperature and, in turn, provides an absorptive spot. The diamond is therefore cut by evaporation and not by abrasion. The hole produced by the beam is V shaped and as it gets deeper, it becomes wider. However, good design of the optics of the laser system can narroe the diameter of the hole to less than ten microns. The weight loss of the diamond by laser sawing is therefore much less than by conventional sawing, provided special care is taken. Twinned or grained crystals of diamond are cut in a few hours instead of the weeks required by conventional sawing.
Laser sawing is therefore superior to conventional methods, as the cuts can be made irrespective of crystallographic direction. Accuracies of twenty-five microns are routine, limited only by the movement of the holder and vibrations of the table. When a laser is employed for kerfing, the kerf can be as thin as 0.3 micron. Kerf depths of four-hundred micron are achieved in about twenty-five seconds.
The laser beam is produced by flashing light from xenon flash tubes on to a rod of laser material. The rod absorbs this energy and emits it as an exceedingly parallel and coherent beam. The laser material is a solid rod of ruby, Neodymium glass (Nd glass) or Neodymium aluminum garnet (NdYGA,) with accurately parallel and polished faces. Carbon dioxide gas in a quartz tube also acts as a laser material but the focusing is not as fine as with a solid rod. A serious problem in all high power lasers is the overheating of the laser material and the choice of the laser equipment depends on the use that is made of the system.
A typical laser drilling or cutting machine used for diamond processing would have a pulsed NdYAG emitting light of wavelength of 1060 nm, with a peak power one to twenty five kilowatt and a pulse width of 0.2 microseconds. The repetition rate of the pulses is ten to ten housand per second. Other factors affect laser drilling, of holes than the minimal requirements of power density. Not only are the diameter and the depth of the hole dependent on the wavelength of the laser light, but they are also determined by the mode of the laser output. The lowest order mode and the shortest wavelength give the sharpest focussed spot.
World Diamond Trade
Europeans once believed that the cutting or alteration of a diamond would destroy its magical properties, but sometime after 1330 AD, cutters in Venice learned how to shape polish a diamond with an iron wheel coated with diamond dust to produce greater brilliance. The city then became the first centre for diamond trading. Over the next century, diamond traders, mainly Jews escaping from persecution, shifted to Bruges and Paris, and laser to Antwerp. They marketed their diamonds to European jewellers, who began to set diamonds in jewels and royal regalia during the thirteenth and fourteenth centuries.
The diamonds came from Indian mines. Among the merchants who sailed east seeking to profit from the sale of diamonds and spices was the great Portuguese navigator Vasco da Gama. He was one of the first to sail via the Cape of Good Hope, hoping to avoid the Arab pirates who roved the Arabian Sea. He landed near Goa and this port became the Portuguese trading centre in India, and a flourishing trade in diamonds developed from Goa to Lisbon and then on to Antwerp.
The discovery of diamonds in Brazil caused the collapse of the diamond market in 1725 although it was initially advertised that these diamonds came from India. India and Brazil were the main sources of diamond up until 1851. Fifteen years later, the children of an African farmer picked up a white pebble that turned out to be a 21-carat diamond. This was followed soon afterwards by the discovery of another stone of 83 carats. These finds triggered a major diamond rush in South Africa and Rhodesia that later expanded into mining for gold and copper. Deep volcanic pipes that were apparently an inexhaustible source of diamond were then located, mined and factories started production.
In 1908, diamonds were found near the sea shore in South West Africa and by 1925, the stones that were found below thirty feet of sand on the coast of Namaqualand as well as north of the Orange River, proved to be the richest source of high quality gems. An unbelievable twenty-five per cent of the gathered stones were of the finest quality. Prospecting then began in the Belgian Congo; now Congo provides sixty per cent of world diamond output. Ghana, Sierra Leone and Tanganyika and the diamond fields in Yakutia in Russia, too, are now rich sources of diamonds. Mir, a hundred and sixty miles from a port on the river Lena was developed and yielded diamonds of more than four carats per tonne. The total production of gem quality diamonds inthe world is around thirty-one million carats, most of it being from Zaire.
When, in 1872, the great diamond rush had more than fifty-thousand miners looking for diamonds and chaotic conditions reigned, Cecil Rhodes bought them all out and formed the De Beers Consolidated Mines Company. With the help of the British government, this company began to take control of most of the diamond activity in South Africa and later formed the Diamond Trading Company (DTC). The DTC rigidly controled and still controls the sale of all diamonds. Even a part of the Russian diamonds has to be channelled through it. This cartelisation of the sale of diamonds has benefited the customer because the company stabilises the price by restricting the supply of rough diamonds. In principle, this control by a single company should make diamonds a good investment, but in practice other market forces prevail.
The profits of diamond mines depend mostly on gem quality stones. For example, twenty per cent of the diamonds mined in Congo is of gem quality. These gemstones are sent to London, where they are sorted according to their shape, quality, colour and size into about two thousand categories. The quality of the stones is judged according to the transparency and the flaws abserved. Colour makes a big difference to the value of the stone. The best are clear 'white' or colours stones, while pink, pastel green or blue stones have a special rarity value. The yellow or brown stones are very common and do not count for much. All diamonds are valued and collected into packets and sold in London to selected buyers. These 'sight holders' are offered the packets on a 'take it or leave it' basis. No selection is allowed. Sight holders then take the stones in their packets back to their own conutries for cutting and polishing.
A number of rough diamonds originate in the disturbed war zones of Angola or the Congo. Most of these 'conflict diamonds' from Congo and Sierra Leone appear to be smuggled into Zimbabwe. Liberia and other neighbouring countries. Diamond experts believe that only about a third of Congo's annual diamond production in being sold through the country's official market. Human rights groups have been concerned that the trade in these diamonds is being used ti finance rebel groups fighting in African countries. One such group based in London showed that in October 1998, Be Beers pumped large amounts of money into rebel coffers by purchasing diamonds from unrecognized sources in the Congo and Angola. Refuting these charges, the DTC now guarantees that one of its diamonds originate from African rebels, but come instead from its own mines is South Africa, Botswanna or Namibia, or are bought from mines in Russia or Australia. However, even a powerful organization like De Beers cannot totally stop diamonds from being smuggled from the war zones in exchange for arms or drugs. Thought perhaps only three percent come from these areas, in spite of strict vigilance, some conflict diamonds from the war zones of Africa will continue to leak into the market until the diamond industry finds a way to stop it.
The diamonds came from Indian mines. Among the merchants who sailed east seeking to profit from the sale of diamonds and spices was the great Portuguese navigator Vasco da Gama. He was one of the first to sail via the Cape of Good Hope, hoping to avoid the Arab pirates who roved the Arabian Sea. He landed near Goa and this port became the Portuguese trading centre in India, and a flourishing trade in diamonds developed from Goa to Lisbon and then on to Antwerp.
The discovery of diamonds in Brazil caused the collapse of the diamond market in 1725 although it was initially advertised that these diamonds came from India. India and Brazil were the main sources of diamond up until 1851. Fifteen years later, the children of an African farmer picked up a white pebble that turned out to be a 21-carat diamond. This was followed soon afterwards by the discovery of another stone of 83 carats. These finds triggered a major diamond rush in South Africa and Rhodesia that later expanded into mining for gold and copper. Deep volcanic pipes that were apparently an inexhaustible source of diamond were then located, mined and factories started production.
In 1908, diamonds were found near the sea shore in South West Africa and by 1925, the stones that were found below thirty feet of sand on the coast of Namaqualand as well as north of the Orange River, proved to be the richest source of high quality gems. An unbelievable twenty-five per cent of the gathered stones were of the finest quality. Prospecting then began in the Belgian Congo; now Congo provides sixty per cent of world diamond output. Ghana, Sierra Leone and Tanganyika and the diamond fields in Yakutia in Russia, too, are now rich sources of diamonds. Mir, a hundred and sixty miles from a port on the river Lena was developed and yielded diamonds of more than four carats per tonne. The total production of gem quality diamonds inthe world is around thirty-one million carats, most of it being from Zaire.
When, in 1872, the great diamond rush had more than fifty-thousand miners looking for diamonds and chaotic conditions reigned, Cecil Rhodes bought them all out and formed the De Beers Consolidated Mines Company. With the help of the British government, this company began to take control of most of the diamond activity in South Africa and later formed the Diamond Trading Company (DTC). The DTC rigidly controled and still controls the sale of all diamonds. Even a part of the Russian diamonds has to be channelled through it. This cartelisation of the sale of diamonds has benefited the customer because the company stabilises the price by restricting the supply of rough diamonds. In principle, this control by a single company should make diamonds a good investment, but in practice other market forces prevail.
The profits of diamond mines depend mostly on gem quality stones. For example, twenty per cent of the diamonds mined in Congo is of gem quality. These gemstones are sent to London, where they are sorted according to their shape, quality, colour and size into about two thousand categories. The quality of the stones is judged according to the transparency and the flaws abserved. Colour makes a big difference to the value of the stone. The best are clear 'white' or colours stones, while pink, pastel green or blue stones have a special rarity value. The yellow or brown stones are very common and do not count for much. All diamonds are valued and collected into packets and sold in London to selected buyers. These 'sight holders' are offered the packets on a 'take it or leave it' basis. No selection is allowed. Sight holders then take the stones in their packets back to their own conutries for cutting and polishing.
A number of rough diamonds originate in the disturbed war zones of Angola or the Congo. Most of these 'conflict diamonds' from Congo and Sierra Leone appear to be smuggled into Zimbabwe. Liberia and other neighbouring countries. Diamond experts believe that only about a third of Congo's annual diamond production in being sold through the country's official market. Human rights groups have been concerned that the trade in these diamonds is being used ti finance rebel groups fighting in African countries. One such group based in London showed that in October 1998, Be Beers pumped large amounts of money into rebel coffers by purchasing diamonds from unrecognized sources in the Congo and Angola. Refuting these charges, the DTC now guarantees that one of its diamonds originate from African rebels, but come instead from its own mines is South Africa, Botswanna or Namibia, or are bought from mines in Russia or Australia. However, even a powerful organization like De Beers cannot totally stop diamonds from being smuggled from the war zones in exchange for arms or drugs. Thought perhaps only three percent come from these areas, in spite of strict vigilance, some conflict diamonds from the war zones of Africa will continue to leak into the market until the diamond industry finds a way to stop it.
Gem Cutting
In laser sawing, the stone is positioned on the X-Y table and moved across the laser beam that is fixed in position. Stepping motors control the movement, while the operator watches the stone through a stereomicroscope and protective glass. Sophisticated installations use a closed circuit TV monitor and a programmed microprocessor controlled movement of the platform. The laser beam converges asymmetrically at an angle of six degrees. As the stone is cut, the computer focuses the laser beam at a lower point in place. In order to saw the diamond efficiently, the laser has to be pulsed at widths of around excessive re-condensation and cooling before the carbon escapes from the hole, while longer pulses heat the mentire stone by conduction or radiation. A ten carat octahedral diamond can be laser sawn in one hour, while mechanical saws would take ten to thirty hours for the sam job. Breakages with laser sawing are greatly reduced and the weight yield is better, particularly for knaats. The disadvantages are the high capital and maintenance costs and the safety precautions that are to be observed. Internal stresses in the stones can cause breakage of the stone but this can also happen during mechanical sawing.
Depending on the size of the stone, the platform is moved from one to a hundred millimetre, in steps of 0.02 mm. As the stone is observed on the TV monitor, it is possible to move it in different directions and so cut circles and other fancy shapes. As a working rule, the width of the cut is about 0.05 times the depth. The V-shape of the cut is inevitable to prevent shadowing of the laser beam. After cutting and de-graphitising of the stone, polishing is done by the usual mechanical methods.
The laser is also used to drill inclusions cut of a stone. The stone is then boiled in acid to dissolve the spot and then filled with clear material. Only careful inspection through a microscope can detect this repair of the stone. Another interesting application of the laser drilling apparatus is scribing, to identify selected stones. Commercial systems and sevices offer to scribe characters in sizes ranging from 0.1 mm to 2 mm in height. A laser -drilling machine operated at low power is employed to scribe coded numbers on diamonds. The power level for this purpose is around 40 watts at ten kilocyles and the scribing rate is ten characters per second. The entire process is done by suitably programming the microprocessor that controls the X-Y movement of the table carrying the stone. Another installation has a microprocessor character generating system where a reflecting mirror is moved rapidly and generates characters on the diamond, which are monitored on the TV screen.
Depending on the size of the stone, the platform is moved from one to a hundred millimetre, in steps of 0.02 mm. As the stone is observed on the TV monitor, it is possible to move it in different directions and so cut circles and other fancy shapes. As a working rule, the width of the cut is about 0.05 times the depth. The V-shape of the cut is inevitable to prevent shadowing of the laser beam. After cutting and de-graphitising of the stone, polishing is done by the usual mechanical methods.
The laser is also used to drill inclusions cut of a stone. The stone is then boiled in acid to dissolve the spot and then filled with clear material. Only careful inspection through a microscope can detect this repair of the stone. Another interesting application of the laser drilling apparatus is scribing, to identify selected stones. Commercial systems and sevices offer to scribe characters in sizes ranging from 0.1 mm to 2 mm in height. A laser -drilling machine operated at low power is employed to scribe coded numbers on diamonds. The power level for this purpose is around 40 watts at ten kilocyles and the scribing rate is ten characters per second. The entire process is done by suitably programming the microprocessor that controls the X-Y movement of the table carrying the stone. Another installation has a microprocessor character generating system where a reflecting mirror is moved rapidly and generates characters on the diamond, which are monitored on the TV screen.
Gem Faceting
With use, plastic flow closed up the pores of the cast iron and the cutting power of the Scarface was greatly reduced unless the surface was machined again. Diamond impregnated scaifes, though expensive, are much more productive. However, this investment is made up as the consumption of the diamond power is minimal and far less time is spent on maintenance. Resin bonded diamond impregnated scaifes and those made by electroplating an aluminum or steel wheel with nickel in a suspension of diamond powder are useless for cutting diamonds, though softer coloured stones are polished on them. Metal bonded scaifes are much harder and now used for diamond processing. They are made by splintering a mixture of diamond powder and cobalt, molybdenum, tungsten and tungsten carbide on to a steel base. This process is done by cold pressing followed by heat treatment. Cobalt is ideal as the bonding material in the metal matrix as it wets and sticks to diamond. Unfortunately, toxic cobalt dust is generated during grinding; newer models of scaifes replace cobalt by iron and tin as the matrix that bonds the diamond powder. The matrix is usually an alloy containing tungsten and other metals, the composition tailored by each manufacturer according to the requirment of the user. The diamond grit is uniformly distributed throughout the bond, so that the diamond and the matrix wear out together. Ideally the matrix should be hard enough to wear away just fast enough to expose new diamond points, Grit size, proportion of diamond and the grade of matrix should ensure a working balance; this is determined by practical experience.
Grinding a diamond with coarse powder leaves parallel scratch marks that are obvious to the eye. The final polish with fine mesh diamond powder gets rid of these lines so that examination through a lens of 10x magnification cannot see them. However, even the finest polish leaves lines whose sides slpe at about one degree or so, when the stone is observed through a microscope of very high magnification. Several new techniques to obtain an extra fine finish on the surface of a diamond have now been developed. The most straightforward way is to use finer an very uniform diamond powder. Such fine powders are made by putting the suspension of the diamond dust into an ultra-centrifuge to obtain the required uniformly. The scaife must also be ground very flat to great accuracy and must be mounted on high precision and large bearings to reduce vibrations. This ensures stability at high speeds, even when the downward pressure of the drop increases friction. Some installations are fixed on shock absorber mountings and are located far from machinery that might cause vibrations.
Softer powders give a good polish, but the polishing rate drops so fast with decreasing hardness that this method becomes expensive. Chemical etching can also reduce surface roughness; for example, an iron scaife charged with potassium nitrate or potassium chloride removes polish lines, but the scaife has to be cleaned continuously. If the diamond is allowed to char at low temperatures on the scaife and the graphiote removed, a smoother polish results.A simpler technique is to put the diamond into an acid etch solution that removes only the outstanding points.
When facets are cut on a scaife a part of the diamond is ground to powder. A narrow laser beam on the other hand, can slice facets rather like a knife on the rough stone. The application of high power lasers to the processing of diamonds has been termed as the greatest advance in diamond cutting and sawing since the high speed saw was invented in 1930. The use of a laser beam saves a great deal of time and material and so is more economical than conventional techniques. Consequently, lasers are now widely used for drilling, kerning, sawing and bruiting not only single stones, but a set of stones of similar size in one operation. Improvements in technology have made laser processing more cost effective than manual cutting and polishing, particularly for bruiting and when fancy cuts have to be shaped.
Grinding a diamond with coarse powder leaves parallel scratch marks that are obvious to the eye. The final polish with fine mesh diamond powder gets rid of these lines so that examination through a lens of 10x magnification cannot see them. However, even the finest polish leaves lines whose sides slpe at about one degree or so, when the stone is observed through a microscope of very high magnification. Several new techniques to obtain an extra fine finish on the surface of a diamond have now been developed. The most straightforward way is to use finer an very uniform diamond powder. Such fine powders are made by putting the suspension of the diamond dust into an ultra-centrifuge to obtain the required uniformly. The scaife must also be ground very flat to great accuracy and must be mounted on high precision and large bearings to reduce vibrations. This ensures stability at high speeds, even when the downward pressure of the drop increases friction. Some installations are fixed on shock absorber mountings and are located far from machinery that might cause vibrations.
Softer powders give a good polish, but the polishing rate drops so fast with decreasing hardness that this method becomes expensive. Chemical etching can also reduce surface roughness; for example, an iron scaife charged with potassium nitrate or potassium chloride removes polish lines, but the scaife has to be cleaned continuously. If the diamond is allowed to char at low temperatures on the scaife and the graphiote removed, a smoother polish results.A simpler technique is to put the diamond into an acid etch solution that removes only the outstanding points.
When facets are cut on a scaife a part of the diamond is ground to powder. A narrow laser beam on the other hand, can slice facets rather like a knife on the rough stone. The application of high power lasers to the processing of diamonds has been termed as the greatest advance in diamond cutting and sawing since the high speed saw was invented in 1930. The use of a laser beam saves a great deal of time and material and so is more economical than conventional techniques. Consequently, lasers are now widely used for drilling, kerning, sawing and bruiting not only single stones, but a set of stones of similar size in one operation. Improvements in technology have made laser processing more cost effective than manual cutting and polishing, particularly for bruiting and when fancy cuts have to be shaped.
Monday, April 4, 2011
Caring for Gems & Jewelry
Caring for Gemstones
Men and women buy gemstones to set in jewellery to be worn and flaunted on special occasions. The brighter and more pure these are, the more they will enchance the beauty of the whole piece and, naturally of the wearer, too. Great care should therefore be taken to store and clean precious jewellery after wearing them. Gems and gemstones set ornaments therefore need to be carefully chosen and carefully worn, cared for, properly stored, and cleaned with caution to keep them valuable and in good condition for as long as possible.
Choosing Jewellery
Rings and bangles are used constantly and do get knocked around even if worn only for festive occations. Gemstones for these pieces should not be brittle or soft. Such stones, as for example, pearls and opals are better set in earrings, pendants or brooches. They can be set for special rings, but even then the stone should be in a closed setting fpr protection.
Diamonds are often held by four prongs or claws but this is not as safe as a six-prong setting. If one of the claws of a four prong setting breaks, the stone will fall out. When the claws get weak after constant wear, the stone should be reset instead of repairing the claw. Even during setting, the goldsmith should be warned not to overheat the stone, especially where platinum jewellery is concerned. A strong tap with a hammer can break or ship a diamond.
In the case of pear shaped or marquise diamonds, the pointed ends should be covered by the setting, or else the stones may chip off during wear. Closed setting are always safer, but the stone could ship 01 crack when the jewel is brocken up for resetting or redesign. Soft gold such as 22-karat is better for losed settings or else the design should allow the stone to be removed without too much effort by the goldsmith.
Caring
Generally speaking, the best and simplest way to keep gem set jewellery clean is to wipe it with a soft damp cloth after it is taken off. Perfume, perpiration, nail polih, polish removers and other beauty products leave a deposit that is hard or remove after they dry out.
The harder a gemstone, the more brittle it is. Diamonds and sapphires therefore often chip or crack and should be carefully protected, cleaned and maintained. Coloured gemstones like tanzanite, kunzite, topaz, feldspar, moonstone and sunstone are fragile and can aplit or crack if hit. Amethyst, turquise, red tourmaline, opal, malachite, kunzite, chrysoprase, citrine, flurite, rose and smoky quartz and emerald fade and discolour in sunlight. Opal, turquoise and malachite may crack if exposed to heat. These stones close set in a ring can crack when the temperature drops abruptly as for instance,when going from 40C weather into an air-conditioned building of 20C temperature.
Pearls need special care. They should be wiped and dried before storage in a silk pouch, never in a plastic bag. They should be cleaned regularly, at least once a year and re-strung ith silk or polyester thread with knots between each pearl. Any necklace strung with silk thread should never be under tension to prevent the thread from stretching. Pearls are sometimes dyed to give various colours but these dyes fade in patches with use. Once this happen, the dyes cannot be rejuvenated. Pearls, coral, and porous stones such as opal, turquise, or malachite should be kept away from dirty water and oils to avoid discoloration.
Rings should be removed by pulling on the gold and not on the gemstones. As a general rule, all jewellery should be handled as little as possible, and should be picked up by its edges.
Storage of Jewellery
Jewellery should be stored individual soft cloth bags in a strong box with compartments. It pieces are thrown one on top of the other, they may be bent, and may be scratched or dented by other pieces. Jewellery that is worn regularly should be examined to see if the setting have become loose. Even if it appears to be tight, a loose setting causes the stones to rattle when the piece is taken.
Loose gems of any kind should be stored in tissue paper packets that are folded in such a way that the stones do not fall out when inspected. Jewellers store their loose gemstones in specially lined paper packets that can be bought from the jewellery market. Pearls should be treated with great care and kept in soft chamois pourches or tisssue papaer. They should be cleaned before storage. Pearls, opal and emerald jewellery should be stored in cotton or silk cloth and never with other jewels as they are easily cracked and scratched.
Diamonds may scratch rubies, sapphires, or emeraldss or even other diamonds. They get easily coated with oil and grease, so much so that this property is used to sort diamonds out of other stones in the mines. A diamond coated with oil collects dust and loses lustre. One should therefore never touch clean diamonds with fingers.
Gems and gem quality items, improperly stored, can damage each other. Gem set jewellery should be stored in soft lint free cloth or soft tissue paper to prevent any such harm. Elaborate pieces like necklaces and bracelets should not be tangled together in storage.
Wear
When rings are never removed, as with engagement or wedding rings, they accumulate dirt within the setting. The gemstones, be it diamond or any other stone, gets coated with a grease and dust film that obscures the beauty of the jewel. For this reason, periodic cleaning of jewellery is a must. It is wise to remove all hand jewellery, rings and bangles before starting on heavy household work like dusting and washing. Other jobs like gardening, playing sports and repairing cars or bicycles may also damage a gem, even diamonds, set in a ring or bangle.
Stones such as lapis, turquoise, coral, onyx and malachite are soaked in dye to increase their colour. Emeralds are treated with oil to fill cracks and so increase their glitter. These dyes and oils will dissolve in detergents and chemicals such as nail polish remover. One should therefore remove such jewellery whille going to bathe or swim, or when working with detergents and chemicals. Opals in particular are very sensetive to heart and cold. Chemicals presennt in hair sprays and perfumes may damage organic gemstones and in particular, cultured pearls. Each time any pearls are worn they should be wiped with a soft cloth to remove any oil film. Some gemstones, even treated sapphire and kunzite, may fade in sunlight.
Cleaning
Diamond studded jewellery should be cleaned using warm water in which a few drops of liquid detergent is dissolved, and then dried with a soft cloth or tissue. Pure alcohol or better, isopropanol removes all the grease that abheres to diamonds, Soaking the item in cold water and ammonia and brushing with a toothbrush cleans dirtier settings. The piece should then be washed thoroughly and dried. This method works for alexandrite,amethyst, andalusite, aquamarine, citrine, garnet, iolite, moonstone, ruby, sapphire, spinel, tanzanite, topaz, tourmaline, and zircon. However, this treatment is not suitable for emeralds as jewellers sometimes fill cracks and holes with oil and when this oil is removed the emerald becomes very dull and hazy. Do not scrub amber, coral, jade, kunzite, lapis, lazuli, or turquoise with soap and water.
Opals, emeralds and tanzanite require far more care than other gemstones and should never be put into very hot water. Pearls never take to washing thought they were born in water. The silk thread often comes apart when soaked in detergent and water. The pearls should be gently wiped and put away wrapped in soft tissue or silk. Opals contain some water and so they should not be dried in sunlight. They should be merely wiped dry and stored.
Ultrasonic cleaners are sometimes recommended for deep cleansing. While these are good for cleaning pure gold jewellery, they may damage amber, coral, emerald, kunzite, lapis lazuli, tanzanite, opal, pearl, ruby, or turquoise. Organic gems like pearls, coral, amber can get damaged by ultrasonic cleaners. Tanzanite has been known to shatter and opals to craze under ultrasound. Ultrasound also removes the oil or resin that may be in emeralds and expands existing fractures.
Gold Jewellery
Gold jewellery is easily scratched and distorted. The 24 karat pure gold jewellery that was once so common in south India was so soft that after a year or two of wear it had to be reworked. As the ratio of gold decreases, the metal becomes hairder. Bangles and rings made of 22 karat gold are still liable to be dented and scratched. Presently 18 karat gold is recommended for everyday wear, but even so these articles lose their shine in a year or two of normal use.
To preserve these pieces, remove all gold jewellery before bathing, swimming or cleaning the house. Soap leaves a dull film on gold jewellery, while chlorine attacks gold to a small extent. Once in six months gold bangles and rings and earrings should be cleaned with a soft toothbrush and detergent. Rubbing with silver polish followed by polishing with a soft cloth improves their appearance considerably. Finally, one could soak them in a solution of baking soda in boiling water and dry with face tissue or soft cloth.
Silver Jewellery
Siver tarnishes very rapidly in the polluted almosphere of cities. Traditional Indian silver is almost pure blackens very quickly while sterling silver is ninety-two percent pure and resists tarnishing somewhat better. Silversmiths recommend ordinary cleaning powder for restoring heavily tarnished pices, afterwhich polishing is done with a soft tissue and silver polish. Jewellers also dip silver in a zinc chloride solution before scrubbing the pieces. A soft toothbrush removes dirt and blackening from within embossed designs.
Men and women buy gemstones to set in jewellery to be worn and flaunted on special occasions. The brighter and more pure these are, the more they will enchance the beauty of the whole piece and, naturally of the wearer, too. Great care should therefore be taken to store and clean precious jewellery after wearing them. Gems and gemstones set ornaments therefore need to be carefully chosen and carefully worn, cared for, properly stored, and cleaned with caution to keep them valuable and in good condition for as long as possible.
Choosing Jewellery
Rings and bangles are used constantly and do get knocked around even if worn only for festive occations. Gemstones for these pieces should not be brittle or soft. Such stones, as for example, pearls and opals are better set in earrings, pendants or brooches. They can be set for special rings, but even then the stone should be in a closed setting fpr protection.
Diamonds are often held by four prongs or claws but this is not as safe as a six-prong setting. If one of the claws of a four prong setting breaks, the stone will fall out. When the claws get weak after constant wear, the stone should be reset instead of repairing the claw. Even during setting, the goldsmith should be warned not to overheat the stone, especially where platinum jewellery is concerned. A strong tap with a hammer can break or ship a diamond.
In the case of pear shaped or marquise diamonds, the pointed ends should be covered by the setting, or else the stones may chip off during wear. Closed setting are always safer, but the stone could ship 01 crack when the jewel is brocken up for resetting or redesign. Soft gold such as 22-karat is better for losed settings or else the design should allow the stone to be removed without too much effort by the goldsmith.
Caring
Generally speaking, the best and simplest way to keep gem set jewellery clean is to wipe it with a soft damp cloth after it is taken off. Perfume, perpiration, nail polih, polish removers and other beauty products leave a deposit that is hard or remove after they dry out.
The harder a gemstone, the more brittle it is. Diamonds and sapphires therefore often chip or crack and should be carefully protected, cleaned and maintained. Coloured gemstones like tanzanite, kunzite, topaz, feldspar, moonstone and sunstone are fragile and can aplit or crack if hit. Amethyst, turquise, red tourmaline, opal, malachite, kunzite, chrysoprase, citrine, flurite, rose and smoky quartz and emerald fade and discolour in sunlight. Opal, turquoise and malachite may crack if exposed to heat. These stones close set in a ring can crack when the temperature drops abruptly as for instance,when going from 40C weather into an air-conditioned building of 20C temperature.
Pearls need special care. They should be wiped and dried before storage in a silk pouch, never in a plastic bag. They should be cleaned regularly, at least once a year and re-strung ith silk or polyester thread with knots between each pearl. Any necklace strung with silk thread should never be under tension to prevent the thread from stretching. Pearls are sometimes dyed to give various colours but these dyes fade in patches with use. Once this happen, the dyes cannot be rejuvenated. Pearls, coral, and porous stones such as opal, turquise, or malachite should be kept away from dirty water and oils to avoid discoloration.
Rings should be removed by pulling on the gold and not on the gemstones. As a general rule, all jewellery should be handled as little as possible, and should be picked up by its edges.
Storage of Jewellery
Jewellery should be stored individual soft cloth bags in a strong box with compartments. It pieces are thrown one on top of the other, they may be bent, and may be scratched or dented by other pieces. Jewellery that is worn regularly should be examined to see if the setting have become loose. Even if it appears to be tight, a loose setting causes the stones to rattle when the piece is taken.
Loose gems of any kind should be stored in tissue paper packets that are folded in such a way that the stones do not fall out when inspected. Jewellers store their loose gemstones in specially lined paper packets that can be bought from the jewellery market. Pearls should be treated with great care and kept in soft chamois pourches or tisssue papaer. They should be cleaned before storage. Pearls, opal and emerald jewellery should be stored in cotton or silk cloth and never with other jewels as they are easily cracked and scratched.
Diamonds may scratch rubies, sapphires, or emeraldss or even other diamonds. They get easily coated with oil and grease, so much so that this property is used to sort diamonds out of other stones in the mines. A diamond coated with oil collects dust and loses lustre. One should therefore never touch clean diamonds with fingers.
Gems and gem quality items, improperly stored, can damage each other. Gem set jewellery should be stored in soft lint free cloth or soft tissue paper to prevent any such harm. Elaborate pieces like necklaces and bracelets should not be tangled together in storage.
Wear
When rings are never removed, as with engagement or wedding rings, they accumulate dirt within the setting. The gemstones, be it diamond or any other stone, gets coated with a grease and dust film that obscures the beauty of the jewel. For this reason, periodic cleaning of jewellery is a must. It is wise to remove all hand jewellery, rings and bangles before starting on heavy household work like dusting and washing. Other jobs like gardening, playing sports and repairing cars or bicycles may also damage a gem, even diamonds, set in a ring or bangle.
Stones such as lapis, turquoise, coral, onyx and malachite are soaked in dye to increase their colour. Emeralds are treated with oil to fill cracks and so increase their glitter. These dyes and oils will dissolve in detergents and chemicals such as nail polish remover. One should therefore remove such jewellery whille going to bathe or swim, or when working with detergents and chemicals. Opals in particular are very sensetive to heart and cold. Chemicals presennt in hair sprays and perfumes may damage organic gemstones and in particular, cultured pearls. Each time any pearls are worn they should be wiped with a soft cloth to remove any oil film. Some gemstones, even treated sapphire and kunzite, may fade in sunlight.
Cleaning
Diamond studded jewellery should be cleaned using warm water in which a few drops of liquid detergent is dissolved, and then dried with a soft cloth or tissue. Pure alcohol or better, isopropanol removes all the grease that abheres to diamonds, Soaking the item in cold water and ammonia and brushing with a toothbrush cleans dirtier settings. The piece should then be washed thoroughly and dried. This method works for alexandrite,amethyst, andalusite, aquamarine, citrine, garnet, iolite, moonstone, ruby, sapphire, spinel, tanzanite, topaz, tourmaline, and zircon. However, this treatment is not suitable for emeralds as jewellers sometimes fill cracks and holes with oil and when this oil is removed the emerald becomes very dull and hazy. Do not scrub amber, coral, jade, kunzite, lapis, lazuli, or turquoise with soap and water.
Opals, emeralds and tanzanite require far more care than other gemstones and should never be put into very hot water. Pearls never take to washing thought they were born in water. The silk thread often comes apart when soaked in detergent and water. The pearls should be gently wiped and put away wrapped in soft tissue or silk. Opals contain some water and so they should not be dried in sunlight. They should be merely wiped dry and stored.
Ultrasonic cleaners are sometimes recommended for deep cleansing. While these are good for cleaning pure gold jewellery, they may damage amber, coral, emerald, kunzite, lapis lazuli, tanzanite, opal, pearl, ruby, or turquoise. Organic gems like pearls, coral, amber can get damaged by ultrasonic cleaners. Tanzanite has been known to shatter and opals to craze under ultrasound. Ultrasound also removes the oil or resin that may be in emeralds and expands existing fractures.
Gold Jewellery
Gold jewellery is easily scratched and distorted. The 24 karat pure gold jewellery that was once so common in south India was so soft that after a year or two of wear it had to be reworked. As the ratio of gold decreases, the metal becomes hairder. Bangles and rings made of 22 karat gold are still liable to be dented and scratched. Presently 18 karat gold is recommended for everyday wear, but even so these articles lose their shine in a year or two of normal use.
To preserve these pieces, remove all gold jewellery before bathing, swimming or cleaning the house. Soap leaves a dull film on gold jewellery, while chlorine attacks gold to a small extent. Once in six months gold bangles and rings and earrings should be cleaned with a soft toothbrush and detergent. Rubbing with silver polish followed by polishing with a soft cloth improves their appearance considerably. Finally, one could soak them in a solution of baking soda in boiling water and dry with face tissue or soft cloth.
Silver Jewellery
Siver tarnishes very rapidly in the polluted almosphere of cities. Traditional Indian silver is almost pure blackens very quickly while sterling silver is ninety-two percent pure and resists tarnishing somewhat better. Silversmiths recommend ordinary cleaning powder for restoring heavily tarnished pices, afterwhich polishing is done with a soft tissue and silver polish. Jewellers also dip silver in a zinc chloride solution before scrubbing the pieces. A soft toothbrush removes dirt and blackening from within embossed designs.
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