Wednesday, May 25, 2011

Ruby and Sapphire - Identification and differences

In nature, impurities of all kinds are simultaneously present. For instance, iron adds a yellow tinge that turns a pure red ruby into an orange (padparacha) specimen that is cheaper. Similarly, when iron enters a blue sapphire, the yellow admixture produces green or blue green overtones that are not very desirable. Most sapphires are of this colour and attempts are made to change it to pure blue. Iron may give a ruby a brown tinge and the presence of titanium and vanadium in ruby turns it purple reducing the value of the stone.

Corundum is doubly refracting and a ray of white light passing through it breaks up into rays, each polarised in a different plane and travelling in slightly different directions, depending also on the colour of the ray. An object viewed through the stone therefore appears as a double image. As the stone is rotated, the colour of ruby and sapphire may also vary somewhat because of an effect called dichroism or pleochroism. Ruby and sapphire are therefore cut to exhibit the best colour a deep red or a royal blue when viewed from the top or table facet.

Seen through a magnifying lens, natural corundum exhibits inclusions that resulted from slow crystallisation in nature. The inclusions are generally like 'feathers' or fingerprints. Liquid inclusions looking like lace are also sometimes visible. A specimen without these inclusions would almost certainly be a synthetic stone or even a piece of glass. Sapphires also have a silky sheen caused by needles of titanium oxide (rutile). The rutile needles from Sri Lankan sapphires are longer and wider spaced than the stones from Burma. Montana sapphires show long rods or tubes ending in projections, while Australian sapphires have liquid filled cavities and dark flat cavities with strong zonal colouring.

The appearance of both sapphire and ruby can be altered by heat treatment in a proper environment. It is estimated that virtually all blue, yellow and golden sapphires are heated to intensify their colour permanently (see chapter on 'Gemstone Enhancement'). Except for white sapphire, all sapphires turn rich yellow to orange yellow when irradiated with gamma rays but the colour fades on exposure to light. Irradiation intensifies the colour of pale yellow sapphires, but the sapphires are unchanged or become a blue-tinged amber colour.

Synthesis of ruby and sapphire is done on a large scale, as large ruby rods are required to generate laser beams. Synthetic rubies and sapphires are very common in the market and many traders sell them as naturals in order to earn fast money. The synthetics show bubble-like inclusions under magnification and so can be distinguished from the natural gems. The better synthetics sometimes have feather-like inclusions, but shine abnormally under light as compared to natural stones.

A recent technical development gives ruby a rich red colour that penetrates into the stone and is not totally removed by polishing. Heavy elements like chromium can be diffused into sapphire and ruby, given enough temperatures and long enough time. The process apparently takes several days at a temperature of 1,600C, but the time reduces rapidly if the temperature is increased somewhat less high 2,070C, the melting point of corundum. Even at this high temperature, iron, titanium or chromium diffuses only to a few tenths of a millimetre in a reasonable time. Diffusion treatment is done on a cut stone and only light polishinng folllows diffusion and nickel diffusionn gives a yellow colour, while chromium and nickel together give a padparacha effect. These colours are all stable, even if the stone is heated. Apparently the diffusion can be detected by examining the stone in methyl iodide solution.

Titanium oxide and iron oxide mixtures are also deposited on a sapphire to crete a blue stone. The heating is done in a reducing atmosphere; sometimes after diffusion in air, the stone is heated in a reducing atmosphere to bring out the colour. This process was patented by Linde and is widely prevalent in Bangkok and Hong Kong.

The value of star rubies and sapphires in influenced by the intensity and attractiveness of the body colour and the strength, sharpness and uniformity of the star. Diffusion can be used to make a star gem out of a sapphire or ruby. Aluminium titanate is mixed with borax and silica as a flux and filler and painted on to the stone. The stone is then heated to 1,750 C for several days for the titanium to enter the stone is again heated to 1,300C to develop a good star. Fractured stones unsuitable for cutting are chosen for this treatment. The stars so produced are very sharp and of uneven colour.

Gemstone Trading in India

Another trading centre for gemstones was in Goa. Many merchants and miners went there to sell the best they had, for they were given full liberty to sell whereas in their own countries, they were compelled to show their output to the kings and princes and sell gems at whatever price the rulers ordered.

During the nineteenth century, Crawfurd (1827), G,d'Amato (1833), Oldham (1855) and Bredermeyer (1868), among others, have reported in detail on the Burmese mines. The rubies produced were generally very small, less than 0.25 rati because Chinese and Tartar merchants had smuggled out the larger pieces. The few big stones they left behind were flawed and valuable stones were rare. A full account of the ruby mines in Burma is also given by Scott and Hardiman in the Gazetteer of Upper Burma and the Shan States, Rangoon of 1901 and the Imperial Gazetteer of the same year. Dr Ball locates the principle mines in three valleys, Mogok (Mogout), Kathe and Kyatpyen. The elevated tract including these valleys was situated at a distance of about one hundred and forty kilometres from Mandalay at an elevation of about eighteen hundred metres above sea level. The ruby tract covered a very beautiful but malarial area of twenty-six sq kilometres with the mining in around two thirds of this area. Sagyin, only twenty five kilometres from Mandalay, had also some ruby mines, but the stones obtained there were of inferior quality.

Several other gemstones were found in this mining area, sapphires, emeralds, amethyst, topaz, white sapphires, spinel, zircon (hyacinth), iolite and rubellite (a variety of tourmaline). Only about one per cent of the corundum was ruby. Caves in the marble hills of the area contained ruby clay from which the finest stones were extracted.

Located in thick jungle, pure red rubies from the Mogok Stone Tract in Burma, one of the richest gem bearing areas of the world, are now in constant demand. Ruby and sapphire deposits lie within thirty metres below ground and Burmese ruby miners sift out gravel obtained by digging short tunnels into the hillside where deposits have been located. When deposits are found in old river beds, small tunnels of about ten metres are dug and the watery sludge is panned to retrieve the heavier gem concentrates. Final sorting is by hand. Large mining enterprises carry out open cat mining by eroding the rock and earth with strong water jets. The wet slurry is then washed and sieved to separate the gemstones. Such mining leaves the dug out area in the form of terraces.

Corundum has a specific gravity of 4.0, a refractive index of around 1.765 and a hardness of 9 on the Moh's scale (on this scale, diamond is the hardest substance with a value of 10). The elementary crystal is barrel shaped, with six oxygen atoms surrounding each aluminium atom. Because of this complex crystal structure, ruby and sapphire cannot be cleaved or split like a rough diamond and cutting or sawing may often cause the stone to crack during grinding. While it is being polished overheating often leaves parallel cracks that run from facet edges.

The impurity elements that colour corundum are usually iron, chromium, titanium and vanadium in concentrations of a few parts per million. When they occupy interstitial sites displacing the aluminium atoms, these impurities cause defects in the crystal lattice-this can produce extra energy levels in the crystal which the takes on a colour that ranges through pink, blue, yellow and orange, the varied hues of sapphire and ruby.

The purity of the colour of a sapphire depends greatly on the concentration of iron as an impurity. If only iron is present, the stone assumes a yellow tinge that is in great demand in India and is known as 'Pushkraj'. The presence of vanadium and titanium atoms in close proximity within the aluminium oxide crystal causes a deep blue colour in the stone- termed 'Neelam' in India. When only Chromium is present as an impurity, corundum becomes a pure red ruby through pink and violet sapphires indicate the presence of chromium in the stone. The Chromium content in ruby usually varies from 0.05 per cent in the palest pink stones to about 0.5 per cent in the deepest red, at which point the colour saturates. Black sapphire is coloured by an admixture of magnetite, hematite or spinel. The value of corundum depends mostly on its colour and clarity. The best corundum does not have much 'fire' or lustre, but blue pure yellow sapphire and the red ruby are the most valuable in this category.

Friday, May 20, 2011

Rubies and Sapphires

Ruby and sapphire belong to the mineral family called corundum. Chemically they are both aluminium oxide in a crystalline formthat was made deep underground into clear and beautiful gemstones under high pressure and heat. Impurities within the crystals give it the attractive, glowing colours. Good specimens of these gems are perhaps almost as valuable as diamonds. All colours of corundum except red are known as sapphires. The colourless variety is called white sapphire and was once a cheap substitute for diamond. Yellow, purple, pink, green or white sapphires are called 'fancy' by the trade. Red corundum is now termed as ruby but there was a controversy some years ago on the difference between ruby and red or pink sapphire. In 1991, the International Coloured Gemstone Association ruled that even the lighter shades of red corundum should be termed ruby.

Sapphire and rubies are found all over the world and are mined in Australia, Brazil, Cambodia, China, Kenya, Nigeria, Russia, Sri Lanka, Tanzania, U.S.A. and Zambia, but the gemstones from India, Myanmar, Thailand and other countries in the Far East were and still are renowned for their pure, rich colour and quality. Good quality stones have been found all over India, from Tamil Nadu in the south to Kashmir in the North. The blue sapphires from the very inaccessible mines of the Zanskar valley in Kashmir are the finest in the world. Discovered in 1880 after a huge rock slide, they have a pure intense blue colour, with a slight measure of silk or milkiness. The oldest sapphire mines were in Sri Lanka and gems found there are light to medium blue in colour. Sapphires from Madagascar are of high quality with some exceptional yellow and pink stones. Brazil has unearthed some good blue to purple and pink stones recently.

Corundum was mined in the East for centuries and there are fascinating reports on the ruby mines by European travellers at the end of the fifteenth century and by Portuguese traders in the sixteenth century. The red coloured corundum got its name from the Latin word, 'rubrum' or 'ruber' meaning red. The great French traveller of the seventeenth century, Tavernier found that the coloured stones of Eastern Asia were only mined in the kingdom of Pegu (now Myanmar) and in the island of Ceylon. The first Pegu mine was on mountain called Capelan, twelve days journey from Ava, the capital of Pegu. It was a long and tiresome journey after landing at the port of Siren, or Syriam or Siriam, some ten kilometres east of the present day Rangoon. The trip from Ava to Siriam had to be made at the time by boat because the jungles teemed with wild animals. Wonderful rubies, sapphires and spinels came out of the Pegu mine, but Tavenier never saw any that were of good quality and size, and 'not one heavier than three or four carats'. This was because the Burmese King there kept all the largest and best stones. In those days, all the coloured stones from Pegu were called rubies, irrespective of their colour. The sapphire was a blue ruby, the amethyst a violet ruby and the topaz a yellow ruby.

Ruby, spinel, yellow topaz, blue and white sapphire, amethyst and other stones were also found in Capelan, or Kyatpyen, about one hundred ten kilometres north-east of Siriam. Sapphires also came from a river that flowed down from high mountains in the middle of the island of Ceylon. About three months after the spring floods, the local people searched the river banks, and found these precious stones in the sand. The stones from the river were generally cleaner and more beautiful than those from Pegu. Inferior stones were found in the beds of streams around Kandy, Nuwara Eliya, Badulla and some of the small rivers in the south. But the more precious gems such as ruby, sapphire, topaz, alexandrite and catseye had to be sought within a rubies of fifty kilometers of Ratnapura, thought rubies are occasionally found in Uva.

Tavernier also mentions that rubies were found in Camboya (Cambodia) and from this kingdom came 'balas' rubies, spinels, sapphires and topazes, apart from gold. By balas rubies, Tavernier meant not the spinels that are characteristic of Baluchistan, but any rubies of light colour resembling them. Other travellers found rubies mined in Chantabun (Chantanburi) and Krat and at Mounth Klung.

The stones were then exported to Masulipatam and Golconda in India, where they were sold by the weight called rati (0.875 carat). The coinage in these places was the pagoda. A ruby of 1 rati was sold for 20 pagodas; that of 2.5 rati cost 85 pagodas; for 3.25 rati the price was 185 pagodas, while a 5 rati stone was worth 525 pagodas; and 920 pagodas would buy a 6.5 rati stone. The price pf a heavier stone was negotiable. The dealers were so particular about their profit in trade that they would not open a parcel of fine rubies unless they were promised beforehand that in case the sale was not made, they would get a present such turban or a waistband. A liberal buyer would then be able to see all their stock and could then transact some business.

Monday, May 9, 2011

Other Large and Famous Diamonds

The Braganza from a Brazilian mine is reported to be the largest diamond ever found and weighs 1680 carats. It is part of the Portuguese crown jewels, but is not available for testing. Some sau it is not a diamond, but a colourless topaz.
The Presidente Vargas of 726.6 carat is the largest Brazilian diamond ever found in that country.
The Jonker diamond was discovered in 1934. The 726-carat stone, said to be flawless purity, was cut into twelve smaller stones.
The Star of Africa, is the largest polished diamond in the world. It weighs 530.2 carats and has been cut with 74 facets.
The Victoria, Imperial, or Great White weighing 457.5 carats came from a South African mine and reached Europe in 1884. It was cut to a beautiful 180 carats and valued in 1900 at 6,200,000.
The Pitt, supposedly the most perfect and beautiful diamond ever known, was found in Patiala in the Punjab in 1701. William Pitt, then Governor of Madras, had the rough stone of 410 carats cut to a perfect brilliant of 163.9 carats. Duc d'Orleans, Regent of France, bought it and Napolean Bonaparte wore it on the pommel of his sword. The gem was said to be the key to his success.
The danau Rajah, a stone from Borneo found in 1787 and now in the treasury of the Rajah of Mattan in Borneo, is reported to weigh 367 carats. In 1868 gem experts found it to be only a rock crystal, but the story was spread that an imitation was submitted for the examination.

The Nizam, a diamond of 440 carats, was said to have been picked up in Golconda by a child in 1835. Cut to 227 carats from the rough, it is part of the Nizam's collection, now with the Government of India.It was brocken up during the Indian Mutiny of 1857. It may soon be exhibited in the museum at Hyderabad.

The Star of the South, found in 1853, is the largest rough diamond from Brazil. Weighing 254.5 carats, it was part of a cluster of crystals. The Gaekwad of Baroda bought it after it was cut to a pure brilliant of 125 carats.

The Great Table of Tavernier weighed 242.2 carats and was found in 1642 near Golconda.

The Darya-i-noor or Sea of Light of 186 carats and the Taj-e-mah or Crown of the Moon, weighing 146 carats, were both cut as rosettes and were part of the collection of the Shah Pahlevi of Iran.

The Florentine of 137 carats, yellow but clear and lustrous, also known as The Great of Tuscany or the Austrian, is in the Imperial Palace treasury at Vienna. Charles the Bold lost it on the battlefield of Granson, where a Swiss soldier found it. Ultimately the Grand Duke Francis Stephen of Tuscany took it to Vienna.

The Stewart, a large diamond of 288.4 carats was found in 1872 in the river diggings on the Vaal. It was later cut to a slightly yellowish brilliant of 120 carats.

The DeBeers diamond of 228.5 carat was cut from a rough of 428.5 carats soon after the company was formed. Itw as first shown at the Paris Exhibition of 1889 and is recognised as the fourth largest cut diamond in the world.

The Millennium Star was discovered in the Congo in the early 1990s by De Beers. It took three years to cut the stone with lasers, but it is the only completely flawless, 203-carat, pear-shaped diamond known.

The Porter Rhodes, a perfectly colourless blue-white stone, was found at Kimberely on February 12, 1880. It weighed around 150 to 160 carats.

The Tiffany Brilliant, is also from South Africa. Flawless and with a beautiful orange-yellow colour, it weighs 125.5 carats.
The Nasik diamond is a triangular brilliant of 89.5 carats. The last Prince of Peshawar took it from the Shiva temple at Nasik and finally sold it to the East India Company. It is said to be in the possession of the Duke of Westminster.

The Shah of weight 88 carats, was in the collection of the Shah of Iran. It has a peculiar shape and the names of tree Persian kings are engraved on it. The Persian prince, Chosroes, the younger son of Abbas Mirza, presented it to the Tsar Nicolas in 1829.

The Idol's Eye diamond is pear-shaped and weighs 70 carats. It is said that it was used to pay ransom to the Sultan of Turkey for a princess he abducted.
The Empress Eugenic diamond of 51 carats is a beautiful brilliant that Catharine 2 of Russia gave her favourite, Potemkin. Napoleon bought it as a wedding-gift to his bride, Eugenie but it was later sold to the Gaekwad of Baroda.

The Piggott is a brilliant cut diamond of 49 carats brought by Lord Piggott to England around 1775 from India. It was later given to A1 Pasha, the Viceroy of Egypt. This stone has since been lost, and, according to rumour, has been destroyed.

The white Saxon is a beautiful square diamond, and weighs 48.75 carats. August the Strong, Duke of Saxony is said to have paid 1,000,000 thalers for it in 1707 and kept it in the Zwinger Castle in Dresden.

The Pasha of Egypt is a fine eight-sided brilliant of 40 carats, purchased by the Viceroy Ibrahim of Egypt for 28,000.

The Dresden Green, an almond-shaped diamond owned by the Saxon crown since 1743 weighs 40 carats. It is a very clear green, perfectly transparent and flawless.

The Polar Star is a beautiful brilliant cut diamond of 40 carats set in the Russian crown.

The Star of Este of 25.4 carats is absolutely flawless. The cut as a brilliant is so perfect that it appear bigger than the Empress Eugenie ot the Sancy diamond. The Archduke Franz Ferdinand of Austrian-Este, eldest son of the Archduke Karl Ludwig bought it for 64,000 Austrian florins in 1876.

The Hortensia diamond of 20 carats has a peach colour. Named after the Queen of Holland, Napoleon Bonaparte's stepdaughter, it is set in one of the French crown jewels.

The Burton Taylor diamond weighed 244 carats when unearthed from the Premier mine of South Africa in 1966. Harry Winston cut it to a pear shaped beauty of weight 69 carats. The jeweller Cartier bought it in an auction in 1969 and sold it to Richard Burton, the actor. It was sold for around $ 3,000,000 recently to fund a hospital in Botswana.

Amazing Gemstones

There is a tradition that this lustrous blue diamond was cursed and brought bad luck to its owner. Tavernier died penniless as an obscure exile. After he acquired the diamond, Louis 14 died of gangrene after suffering unbearable pain for three weeks. It is said that the jeweller who cut the stone died of grief after learning that his son had stolen the valuable diamond; the son, upon hearing of his father's death, committed suicide. The man who found the diamond among the son's possessions, apparently died the very next day. Soon after King George 4 of England bought the stone, he was so much in debt that it was sold through private channels. Mrs. Walsh lost her brother, son, and daughter after she bought the Hope diamond.

The star South Africa was the first large diamond from South Africa and weighed 83.5 carats. The African shepherd boy who discovered it on the banks of the Orange River in 1869 bartered it to a settler for 500 sheep, 10 oxen, and a horse. After it was cut to an oval three-sided brilliant of about 48 carats, it was sold to the Countess of Dudley for nearly 25,000 and for a time it was called the Dudley diamond. It is presently among the British Crown Jewels.

The Sancy, a stone of 53.75 carats, was taken from an Indian quarry near Golconda and finally came into the possession of Charles the Bold. Charles lost his life and the diamond at the battle of Nancy in AD 1477, after which a soldier took it to Portugal and sold it to de Sancy, a French nobleman. Queen Elizaneth 1 of England acquired it around 1600. Hanrietta Maria, the Queen of Charles 1, took it back of France and pledged it with Cardinal Mazarin. In 1791, it was part of the crown jewels of Louis 14 of France. Itw as stolen in the French Revolution, and reappeared as the property of the Spanish Crown some years later. Prince Demidoff sold it to the Maharaja of Patiala in 1865 and it is presumed to be with the Patiala family today.

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