Heat-treated brown diamonds

Heat-treated brown diamonds:
The observation that brown color might related to the lattice imperfections has led to a technique to convert brown diamonds into more valued light-yellow or even colorless ones: the diamond is subjected to high pressures of 6-10 GPa and temperatures above 1600 °C that heals (anneals) those defects.The technique has been demonstrated in several research laboratories in Russia and US. In March 1999, Pegasus Overseas Ltd (POL) from Antwerp, Belgium, a subsidiary of Lazare Kaplan International, has started marketing of such diamonds which were processed by the General Electric (GE). Those diamonds have therefore received a name GE POL (or GEPOL) and were marketed in the US as Bellataire diamonds. The fact and the identity of the treatment process was considered so important that micrometer-sized letters "GEPOL" were inscribed with a laser on the girdles of every treated diamond.In 2004, however, the GE diamond section has been purchased by Littlejohn & Co. and renamed into Diamond innovations. Since 1999, several companies around the world have adopted the technique and use various brand names for the processed diamonds.

Natural brown diamonds

Natural brown diamonds:
Whereas the brown color due to irradiation or nickel impurity can be easily recognized through spectroscopic (e.g. absorption) measurements, the majority of natural brown diamonds do not show any characteristic absorption peaks. Whereas the consensus has been reached that the color relates to the plastic deformation, the particular reason has not been reliably identified yet. Extended lattice defects such as dislocations and slip planes were the most popular candidate, however, recent results favor large clusters of vacancies (mini-voids) as a more likely cause.

Causes of color

Irradiation:
Irradiation of diamond by high-energy particles (electrons, ions, neutrons or gamma rays) knocks off carbon atoms and produces vacancies in the diamond lattice. Those vacancies produce green color centers in pure transparent diamond and yellow-green color in yellow diamonds. Yellow diamonds have it color mostly due to the nitrogen impurity and they constitute the majority of all natural diamonds. Heating those irradiated diamonds to temperatures above 600 °C results in brown color associated with aggregation of the vacancies, with or without nitrogen involved.

Such irradiation and annealing treatment can occur in nature because diamonds are often accompanied by uranium-containing ores which emit alpha particles. However, the thus produced color is restricted to a thin surface layer of few micrometers.Homogeneous color can be produced if the treatment was performed artificially, using electrons, neutrons or gamma-rays. Radiation treatment induces characteristic sharp optical absorption lines which can be easily detected by spectroscopic techniques

Famous brown diamonds

• Golden Jubilee Diamond is currently the largest cut diamond in the world. it was found in 1985 as a rough stone of 755.5 carats (151 g) in the Premier mine, South Africa - one of the most famous diamond mines in the world operated by De Beers. The stone was cut into a 545.67 carats (109.13 g) gem and has been purchased from De Beers by a group led by Henry Ho of Thailand in 1995. The Golden Jubilee Diamond was named by King Bhumibol Adulyadej and given to him on occasion of his 50th coronation anniversary.

• Earth Star Diamond was found at another South African mine of De Beers, the Jagersfontein Mine on May 16, 1967. The diamond came from the 2,500-foot (760 m) level of the volcanic diamond-bearing pipe. The rough gem weighed 248.9 carats (49.8 g) and was cut into a 111.59 carats (22.32 g) pear-shaped gem with a strong brown color and extraordinary brilliance. The diamond was bought in 1983 for $900,000.

• Star of the South (original name was Portuguese "Estrela do Sud") is one of the largest diamonds found in Brazil and the first Brazilian diamond to receive international acclaim.^[10] The original rough stone was found in 1853 by an African slave woman, for which she received her freedom and life pension. The diamond was cut into a cushion shaped gem weighing 128.48 carats (25.70 g). For long time, the Star of the South was considered as "by far the largest diamond discovered by any woman anywhere", until the Incomparable Diamond was discovered in the 1980s.

• Incomparable Diamond is another African diamond, one of the largest ever found in the world (890 carats or 178 g). A young girl encountered it in 1984 a pile of rubble collected from old mine dumps of the nearby MIBA Diamond Mine, Democratic Republic of the Congo. The rubble was sorted out during the recovery process because it was considered too bulky to contain diamonds. This massive diamond was considered to be cut into the world largest gem, but finally, the size was reduced to 407.5 carats for the sake of having less internal flaws; nevertheless, it was the 3rd largest cut diamond after the Cullinan I and Golden Jubilee Diamonds. Before cutting, the stone was the largest brown diamond and the fourth largest diamond of any color ever discovered after the Cullinan (3106.75 carats), Excelsior Diamond (995 carats) and Star of Sierra Leone (968.9 carats).The stone was cut by a team led by Marvin Samuels, who co-owned the stone along with Donald Zale of Zales Jewellers and Louis Glick. In November 1984 the finished stones were put on display: a single golden diamond of 407.48 carats (81.50 g) in a 'triolette' shape, and fourteen additional gems. Notably, the satellite stones cut from the Incomparable varied greatly in color, from near-colorless to rich yellow-brown. The largest of these stones still bears the name 'Incomparable Diamond', and was graded by the GIA as internally flawless in 1988.

• Lesotho Brown was unearthed at the Letseng diamond mine in Lesotho in 1967 at Letseng-la-Terai by Ernestine Ramaboa. The rough stone weighed 601 carats (120 g) and was cut in 1968 into 18 polished diamonds totaling 252.40 carats (50.48 g). The largest was a 71.73 carats (14.35 g) emerald cut known as the Lesotho I. The Lesotho III (the third largest stone cut from the crystal) is a 40.42 carats (8.08 g) marquise-shaped gem that was once owned by Jackie Kennedy, given to her by her husband Aristotle Onassis. The ring had an estimated value of $600,000 US, but at the Jackie Kennedy estate sale auction in April 1996 it reached a price of $2,587,500 US dollars. It was mounted in a platinum ring created by Harry Winston. The Lesotho I was offered at Sotheby's, Geneva on November 19, 2008 as part of a Magnificent Jewels sale, but it did not sell. It'd had a presale estimate of 3,360,000 to 5,600,000 Swiss francs, which equated to $2,783,894 to $4,639,824 US dollars. The lot's description mentioned it was being offered for sale by the same owner who had originally bought it from Harry Winston around 1969. It also listed the gem as having a clarity of VVS2, excellent polish and excellent symmetry, and although the stone (and the other Lesotho fragments) is a pale brown color, no color grade is mentioned in the auction text. This might have been deliberate on Sothebys part, so as not to detract potential buyers, since pale brown diamonds traditionally aren't as valuable as colorless and near-colorless diamonds.

Brown diamonds

The majority of natural diamonds are brown in color which makes them less attractive as gemstones. Australian diamonds, which constitute one third of the world production, are especially rich in brown stones. Large amount of scientific research was spent to understand the origin of the brown color. Several causes have been identified, including irradiation treatment, nickel impurities and lattice defects associated with plastic deformation, the latter are considered as the predominant cause, especially in pure diamonds. A high-pressure high-temperature treatment has been designed to heal those lattice defects and convert brown diamonds into yellow or even colorless stones.

Synthetic Diamond

Synthetic diamond is diamond produced in a technological process as opposed to natural diamond, which is created in geological processes. Synthetic diamond is also widely known as HPHT diamond or CVD diamond where HPHT and CVD refer to the production method, namely high-pressure high-temperature synthesis and chemical vapor deposition, respectively.

Numerous claims of diamond synthesis were documented between 1879 and 1928; every attempt has been carefully analyzed and none has been confirmed. In the 1940–1950s, systematic research began in the United States, Sweden and the Soviet Union to grow diamond using CVD and HPHT processes. The first reproducible synthesis was reported around 1953. Those two processes still dominate the production of synthetic diamond. A third method, known as detonation synthesis, has entered the diamond market in the late 1990s. In this process, nanometer-sized diamond grains are created in an explosion of carbon-containing explosives. A fourth method, treating graphite with high-power ultrasonic radiation, has been demonstrated in the laboratory, but has no commercial use yet.

The properties of synthetic diamond depend on the details of the manufacturing processes, and can be inferior or superior to those of natural diamond; the hardness, thermal conductivity and electron mobility are superior in some synthetic diamonds (either HPHT or CVD). Consequently, synthetic diamond is widely used in abrasives, 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 (UV) 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.

Both CVD and HPHT diamonds can be cut into gems of various colors: clear white, yellow, brown, blue, green and orange. The appearance 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.

Synthetic Diamond

Synthetic diamond is diamond produced in a technological process as opposed to natural diamond, which is created in geological processes. Synthetic diamond is also widely known as HPHT diamond or CVD diamond where HPHT and CVD refer to the production method, namely high-pressure high-temperature synthesis and chemical vapor deposition, respectively.

Numerous claims of diamond synthesis were documented between 1879 and 1928; every attempt has been carefully analyzed and none has been confirmed. In the 1940–1950s, systematic research began in the United States, Sweden and the Soviet Union to grow diamond using CVD and HPHT processes. The first reproducible synthesis was reported around 1953. Those two processes still dominate the production of synthetic diamond. A third method, known as detonation synthesis, has entered the diamond market in the late 1990s. In this process, nanometer-sized diamond grains are created in an explosion of carbon-containing explosives. A fourth method, treating graphite with high-power ultrasonic radiation, has been demonstrated in the laboratory, but has no commercial use yet.

The properties of synthetic diamond depend on the details of the manufacturing processes, and can be inferior or superior to those of natural diamond; the hardness, thermal conductivity and electron mobility are superior in some synthetic diamonds (either HPHT or CVD). Consequently, synthetic diamond is widely used in abrasives, 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 (UV) 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.

Both CVD and HPHT diamonds can be cut into gems of various colors: clear white, yellow, brown, blue, green and orange. The appearance 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.