Diamond enhancement

Diamond enhancements are specific treatments, performed on natural and sometimes synthetic diamonds (usually those already cut and polished into gems), which are designed to improve the gemological characteristics — and therefore the value — of the stone in one or more ways. These include clarity treatments such as laser drilling to remove inclusions, application of sealants to fill cracks, color treatments to improve a white diamond's color grade, and treatments to give fancy color to a white or off-color diamond.

The CIBJO and government agencies such as the United States Federal Trade Commission explicitly require the disclosure of most diamond treatments at the time of sale. Some treatments, particularly those applied to clarity, remain highly controversial within the industry — this arises from the traditional notion that diamond holds a unique or "sacred" place among the gemstones, and should not be treated too radically, if for no other reason than a fear of damaging consumer confidence.

Treated diamonds usually trade at a significant discount to untreated diamonds. This is due to several factors, including relative scarcity — a much larger number of stones can be treated to reach gem quality than are found naturally occurring in a gem quality state — and the potential impermanence of various treatments. Therefore, it is unusual to see a diamond with good overall gemological characteristics undergo treatment. Diamonds which are chosen for treatment are usually those that would be otherwise difficult to sell as gem diamonds, where inclusions or fractures noticeably detract from the beauty of the diamond to even casual observers. In these cases, the loss in value due to treating the diamond is more than overcome by the value added by mitigating obvious flaws.

Clarity enhancements

The clarity or purity of a diamond — the relative or apparent severity of flaws within the stone — has, like the other "four Cs", a strong bearing on the evaluation of a diamond's worth. The most common flaws or inclusions seen in diamond are fractures (commonly called feathers due to their feathery whitish appearance), and solid foreign crystals within the diamond; such as garnet, diopside, or even other diamonds. The size, color, and position of inclusions can reduce the value of a diamond, especially when other gemological characteristics are good. Those who prepare diamonds for sale sometimes choose to reduce the visual impact of inclusions through one or more of a variety of treatments.

Laser drilling

The combustibility of diamond has allowed the development of laser drilling techniques which, on a microscopic scale, are able to selectively target and either remove or significantly reduce the visibility of crystal or iron oxide-stained fracture inclusions. Diamonds have been laser-drilled since at latest the mid-1980s. Laser drilling is often followed by glass infilling.

The drilling process involves the use of an infrared laser (wavelength about 1060 nm) to bore very fine holes (less than 0.2 millimeters or 0.005 inches in diameter) into a diamond to create a route of access to an inclusion. Because diamond is transparent to the wavelength of the laser beam, a coating of amorphous carbon or other energy-absorbent substance is applied to the surface of the diamond to initiate the drilling process. The laser then burns a narrow tube to the inclusion. Once the included crystal has been reached by the drill, the diamond is immersed in sulfuric acid to dissolve the crystal or iron oxide staining. This process is not effective for inclusions which are diamonds themselves, as diamond is not soluble in sulfuric acid.

Several inclusions can be thus removed from the same diamond, and under microscopic inspection the fine bore holes are readily detectable. They are whitish and more or less straight, but may change direction slightly, and are often described as having a "wrinkled" appearance. In reflected light, the surface-reaching holes can be seen as dark circles breaching the diamond's facets. The diamond material removed during the drilling process is destroyed, and is often replaced with glass infilling, using the fracture filling techniques described below.

Fracture filling

Around the same time as the laser drilling technique was developed, research began on the fracture filling of diamonds to better conceal their flaws. The glass filling of diamond often follows the laser drilling and acid-etching of inclusions, though if the fractures are surface-reaching, no drilling may be required. This process, which involves the use of specially-formulated glasses with a refractive index approximating that of diamond, was pioneered by Zvi Yehuda of Ramat Gan, Israel. Yehuda is now a brand name applied to diamonds treated in this manner, and the process has apparently changed little since its inception. Koss & Schechter, another Israel-based firm, attempted to modify Yehuda's process in the 1990s by using halogen-based glasses, but this was unsuccessful. The details behind the Yehuda process have been kept secret, but the filler used is reported to be lead oxychloride glass, which has a fairly low melting point. The New York-based Dialase also treats diamonds via a Yehuda-based process, which is believed to use lead-bismuth oxychloride glass.

The glass present in fracture-filled diamonds can usually be detected by a trained gemologist under the microscope: the most obvious signs — apart from the surface-reaching bore holes and fractures associated with drilled diamonds — are air bubbles and flow lines within the glass, which are features never seen in untreated diamond. More dramatic is the so-called "flash effect", which refers to the bright flashes of color seen when a fracture-filled diamond is rotated; the color of these flashes ranges from an electric blue or purple to an orange or yellow, depending on lighting conditions (light field and dark field, respectively). The flashes are best seen with the field of view nearly parallel to the filled fracture's plane. In strongly colored diamonds the flash effect may be missed if examination is less than thorough, as the stone's body color will conceal one or more of the flash colors. For example, in brown-tinted "champagne" diamonds, the orange-yellow flashes are concealed, leaving only the blue-purple flashes to be seen. One last but important feature of fracture-filled diamonds is the color of the glass itself: it is often a yellowish to brownish, and along with being highly visible in transmitted light, it can significantly impact the overall color of the diamond. Indeed, it is not unusual for a diamond to fall an entire color grade after fracture-filling. For this reason fracture-filling is normally only applied to stones whose size is large enough to justify the treatment: however, stones as small as 0.02 carats (4 mg) have been fracture-filled.

The fracture-filling of diamond is a controversial treatment within the industry — and increasingly among the public as well — due to its radical and impermanent nature. The filling glass melts at such a low temperature (1673 Kelvin) that it easily "sweats" out of a diamond under the heat of a jeweler's torch; thus routine jewelry repair can lead to a complete degradation of clarity or in some cases shattering, especially if the jeweler is not aware of the treatment. Similarly, a fracture-filled diamond placed in an ultrasonic cleaner may not survive intact. Yehuda diamonds are however given a warranty, which allows owners of their diamonds to return them for retreatment following any degradation of the glass filling.

It is notable that most major gemological laboratories, including that of the influential Gemological Institute of America, refuse to issue certificates for fracture-filled diamonds. Labs that do certify these diamonds may render any treatment benefit moot by disregarding apparent clarity and instead assigning the diamond a grade reflecting its original, pre-treatment clarity.

Color enhancements

Generally there are three major methods to artificially alter the color of a diamond: irradiation with high-energy subatomic particles; the application of thin films or coatings; and the combined application of high temperature and high pressure (HTHP). However, there is recent evidence that fracture filling is not only used to improve clarity, but that it can be used for the sole purpose to change the color into a more desirable color as well.

The first two methods can only modify color, usually to turn an off-color Cape series stone (see Material properties of diamond: Composition and color) into a more desirable fancy-colored stone. Because some irradiation methods produce only a thin "skin" of color, they are applied to diamonds that are already cut and polished. Conversely, HTHP is used to modify and remove color from either rough or cut diamonds—but only certain diamonds are treatable in this manner. Irradiation and HTHP treatments are usually permanent insofar as they will not be reversed under normal conditions of jewelry use, whereas thin films are impermanent.

Irradiation

Irradiated natural diamonds

Sir William Crookes, a gem connoisseur as well as a chemist and physicist, was the first to discover radiation's effects on diamond color when in 1904 he conducted a series of experiments using radium salts. Diamonds enveloped in radium salt slowly turned a dark green; this color was found to be localized in blotchy patches, and it did not penetrate past the surface of the stone. The emission of alpha particles by the radium was responsible. Unfortunately radium treatment also left the diamond strongly radioactive, to the point of being unwearable. A diamond octahedron so treated was donated by Crookes to the British Museum in 1914, where it remains today: it has not lost its color nor its radioactivity.

Nowadays diamond is safely irradiated in four ways: proton and deuteron bombardment via cyclotrons; gamma ray bombardment via exposure to cobalt-60; neutron bombardment via the piles of nuclear reactors; and electron bombardment via Van de Graaff generators. These high-energy particles physically alter the diamond's crystal lattice, knocking carbon atoms out of place and producing color centers. Irradiated diamonds are all some shade of green, black, or blue after treatment, but most are annealed to further modify their color into bright shades of yellow, orange, brown, or pink. The annealing process increases the mobility of individual carbon atoms, allowing some of the lattice defects created during irradiation to be corrected. The final color is dependent on the diamond's composition and the temperature and length of annealing.

Cyclotroned diamonds have a green to blue-green color confined to the surface layer: they are later annealed to 800°C to produce a yellow or orange color. They remain radioactive for only a few hours after treatment, and due to the directional nature of the treatment and the cut of the stones, the color is imparted in discrete zones. If the stone was cyclotroned through the pavilion (back), a characteristic "umbrella" of darker color will be seen through the crown (top) of the stone. If the stone was cyclotroned through the crown, a dark ring is seen around the girdle (rim). Stones treated from the side will have one half colored deeper than the other. Cyclotron treatment is now uncommon.

Gamma ray treatment is also uncommon, because although it is the safest and cheapest irradiation method, successful treatment can take several months. The color produced is a blue to blue-green which penetrates the whole stone. Such diamonds are not annealed. The blue color can sometimes approach that of natural Type IIb diamonds, but the two are distinguished by the latter's semiconductive properties. As with most irradiated diamonds, most gamma ray-treated diamonds were originally tinted yellow; the blue is usually modified by this tint, resulting in a perceptible greenish cast.

The two most common irradiation methods are neutron and electron bombardment. The former treatment produces a green to black color that penetrates the whole stone, while the latter treatment produces a blue, blue-green, or green color that only penetrates about 1 millimeter deep. Annealing of these stones (from 500–900°C for neutron-bombarded stones and from 500–1200°C for electron-bombarded stones) produces orange, yellow, brown, or pink. Blue to blue-green stones that are not annealed are separated from natural stones in the same manner as gamma ray-treated stones.

Prior to annealing, nearly all irradiated diamonds possess a characteristic absorption spectrum consisting of a fine line in the far red, at 741 nm — this is known as the GR1 line and is usually considered a strong indication of treatment. Subsequent annealing usually destroys this line, but creates several new ones; the most persistent of these is at 595 nm. If however an irradiated diamond is annealed above 1000°C, the 595 line too is destroyed, but leaves two new lines at 1936 and 2024 nm in the infrared. These lines are detected in gemological laboratories using spectrophotometers: the lines are best detected when the stone is cooled to very low temperatures (below -150°C).

It should be noted that some irradiated diamonds are completely natural. One famous example is the Dresden Green Diamond. In these natural stones the color is imparted by "radiation burns" in the form of small patches, usually only skin deep, as is the case in radium-treated diamonds. Naturally irradiated diamonds also possess the GR1 line.

The largest known irradiated diamond is the Deepdene.

Coatings

The application of colored tinfoil to the pavilion (back) surfaces of gemstones was common practice during the Georgian and Victorian era; this was the first treatment — aside from cutting and polishing — applied to diamond. Foiled diamonds are mounted in closed-back jewelry settings, which may make their detection problematic. Under magnification, areas where the foil has flaked or lifted away are often seen; moisture that has entered between the stone and foil will also cause degradation and uneven color. Because of its antique status, the presence of foiled diamonds in older jewelry will not detract from its value.

In modern times, more sophisticated surface coatings have been developed: these include violet-blue dyes and vacuum-sputtered films resembling the magnesium fluoride coating on camera lenses. These coatings effectively whiten the apparent color of a yellow-tinted diamond, because the two colors are complementary and act to cancel each other out. Usually only applied to the pavilion or girdle region of a diamond, these coatings are among the hardest treatments to detect — while the dyes may be removed in hot water or alcohol with ease, the vacuum-sputtered films require a dip in sulfuric acid to remove. The films can be detected under high magnification by the presence of raised areas where air bubbles are trapped, and by worn areas where the coating has been scratched off. These treatments are considered fraudulent unless disclosed.

Another coating treatment applies a thin film of synthetic diamond to the surface of a diamond simulant. This gives the simulated diamond certain characteristics of real diamond, including higher resistance to wear and scratching, higher thermal conductivity, and lower electrical conductivity. While resistance to wear is a legitimate goal of this technique, some employ it in order to make diamond simulants more difficult to detect through conventional means, which may be fraudulent if they are attempting to represent a simulated diamond as real. The firm Better Than Diamond, for example, uses this method applied to cubic zirconia. The result is a finished stone, as claimed on the company website, with a Mohs hardness of 9.7 to 9.8. They offer colorless, pink and yellow stones, but have not disclosed whether the pink and yellow stones receive their color from their coatings, or if the base cubic zirconias are pink and yellow.

High-temperature, high-pressure

A small number of otherwise gem-quality stones that possess a brown body color can have their color significantly lightened or altogether removed by HTHP treatment, or, depending on the type of diamond, improve existing color to a more desirable saturation. The process was introduced by General Electric in 1999. Diamonds treated to become colorless are all Type IIa and owe their marring color to structural defects that arose during crystal growth, known as plastic deformations, rather than to interstitial nitrogen impurities as is the case in most diamonds with brown color. HTHP treatment is believed to repair these deformations, and thus whiten the stone. (This is probably an incorrect conclusion, the whitening due to destruction of stable vacancy clusters according to one of the researchers). Type Ia diamonds, which have nitrogen impurities present in clusters that do not normally affect body color, can also have their color altered by HTHP. Some synthetic diamonds have also been given HTHP treatment to alter their optical properties and thus make them harder to differentiate from natural diamonds. Pressures of up to 70,000 atmospheres and temperatures of up to 2,000°C (3,632°F) are used in HTHP.

Also in 1999, Novatek, a Provo, UT manufacturer of industrial diamonds known for its advancements in diamond synthesis, accidentally discovered that the color of diamonds could be changed by the HTHP process. The company formed NovaDiamond, Inc. to market the process. By applying heat and pressure to natural stones, NovaDiamond could turn brown Type I diamonds light yellow, greenish yellow, or yellowish green; improve yellowish Type IIa diamonds by several color grades, even to white; intensify the color of yellow Type I diamonds; and make some bluish gray Type I and Type IIb colorless (although in some cases natural bluish gray diamonds are more valuable left alone, as blue is a highly desired hue). In 2001, however, NovaDiamond quit the HTHP gem business because of what the company's leader, David Hall, characterized as the underhanded practices of dealers. Apparently, dealers were passing off NovaDiamond enhanced gems as naturally colored, and the company refused to be party to this deception.

Definitive identification of HTHP stones is left to well-equipped gemological laboratories, where Fourier transform spectroscopy (FTIR) and Raman spectroscopy are used to analyze the visible and infrared absorption of suspect diamonds to detect characteristic absorption lines, such as those indicative of exposure to high temperatures. Indicative features seen under the microscope include: internal graining (Type IIa); partially healed feathers; a hazy appearance; black cracks surrounding inclusions; and a beaded or frosted girdle. Diamonds treated to remove their color by General Electric are given laser inscriptions on their girdles: these inscriptions read "GE POL", with "POL" standing for Pegasus Overseas Ltd, a partnered firm. It is possible to polish this inscription away, so its absence cannot be a trusted sign of natural color. Although it is permanent, HTHP treatment should be disclosed to the buyer at the time of sale.

Synthetic diamond

A collection of colorless cultured diamonds grown by Apollo Diamond, Inc. via chemical vapour deposition

Synthetic diamond (also known variously as lab-created, manufactured, lab-grown or cultured diamond) is a term used to describe diamond crystals produced by a technological process, as opposed to natural diamond, which is produced by geological processes.

Synthetic diamond is not the same as diamond-like carbon, DLC, which is amorphous hard carbon, or diamond simulants, which are made of other materials such as cubic zirconia or silicon carbide. The properties of synthetic diamond depend on the manufacturing process used to produce it, and can be inferior, similar or superior to those of natural diamond.

History

Experimental set-up of Williard Hershey

The idea of making less expensive, gem-quality diamonds synthetically is not a new one. H. G. Wells described the concept in his short story "The Diamond Maker," published in 1911 . In Capital Karl Marx commented, "If we could succeed, at a small expenditure of labour, in converting carbon into diamonds, their value might fall below that of bricks".

After the 1797 discovery that diamond was pure carbon, many attempts were made to alter the cheaper forms of carbon — generally with little success. One of the early successes reported in the field was by Ferdinand Frédéric Henri Moissan in 1893. His method involved heating charcoal at up to 4000 °C with iron in a carbon crucible in an electric furnace, in which an electric arc was struck between carbon rods inside blocks of lime. The molten iron was then rapidly cooled by immersion in water. The contraction generated by the cooling supposedly produced the high pressure required to transform graphite into diamond. Moissan published his work in a series of articles in the 1890s.

Many other scientists tried to replicate his experiments. Sir William Crookes claimed success in 1909. Ruff claimed in 1917 to have reproduced diamonds up to 7 mm in diameter, but later retracted his claims. In 1926, Dr. Willard Hershey of McPherson College read journal articles about Moissan's and Ruff's experiments and replicated their work, producing a synthetic diamond. That diamond is on display today in Kansas at the McPherson Museum. Despite the claims of Moissan, Ruff, and Hershey, many other experimenters had enormous difficulty in creating the required temperatures and pressure with similar equipment, leading some to contend that the early successes were the result of seeding by good-willed co-workers.

The most definitive duplication attempts were performed by Sir Charles Algernon Parsons. He devoted 30 years and a considerable part of his fortune to reproduce many of the experiments of Moissan as well as those of Hannay but also adapted processes of his own. He wrote a number of articles — one of the earliest on high-pressure/high-temperature (HPHT) diamonds — in which he claimed to have produced small diamonds. However in 1928 he authorized C.H Desch to publish an article in which he stated his belief that no synthetic diamonds (including those of Moisan and others) had been produced up to that date. In fact he found that most diamonds produced so far were more likely than not synthetic Spinel.

The GE diamond project

In 1941 an agreement was made between General Electric, Norton and Carborundum to further develop diamond synthesis. They were able to heat carbon to about 3000 °C (5432 °F) under a pressure of half a million psi, for a few seconds. The Second World War ended this project soon thereafter. It was resumed in 1951 at the Schenectady Laboratories of GE and a high pressure diamond group was formed with F.P. Bundy and H.M. Strong. Shortly afterwards Tracy Hall and others joined it.

The group improved on the anvils designed by Percy Bridgman, who received a Nobel prize for his work in 1946. Bundy and Strong made the first improvements and more were made later by Hall. The GE team used a tungsten carbide anvil within a hydraulic press to squeeze the carbonaceous sample held in a catlinite container, the finished grit being squeezed out of the container through a gasket. It was believed that on occasion a diamond was produced, but since experiments could not be reproduced, such claims could not be maintained.

Hall achieved the first commercially successful synthesis of diamond on December 16, 1954 (announced on February 15, 1955). His breakthrough was using an elegant "belt" press apparatus which raised the achievable pressure from 6 to 18 GPa and the temperature to 5000 °C, using a pyrophyllite container, and having the graphite dissolved within molten nickel, cobalt or iron, a "solvent-catalyst". The largest diamond he produced was 150 micrometres across, clearly unsuitable for jewelry but very useful in industrial abrasives. Hall was able to have co-workers replicate his work and the discovery was published in Nature. He was the first person to grow a synthetic diamond according to a reproducible, verifiable and witnessed process and received a gold medal of the American Chemical Society in 1972 for his work. Hall left GE in 1955, and three years later developed a completely independent apparatus for the synthesis of diamond, the tetrahedral press with four anvils, thus avoiding infringement of his previous patent, which was still assigned to GE.

Later developments

Another successful diamond synthesis was produced on February 16, 1953 in Stockholm, Sweden by the QUINTUS project of ASEA (Allemanna Svenska Elektriska Aktiebolaget), Sweden's major electrical manufacturing company using a bulky split sphere apparatus designed by Baltzar von Platen and the young engineer Anders Kämpe (1928–1984). Pressure was maintained within the device at an estimated 83,000 atmospheres (8.4 GPa) for an hour. A few small crystals were produced, but not of gem quality or size. The work was not reported until the 1980s.

During the 1980s a new competitor emerged in Korea named Iljin Diamond, followed later by hundreds of Chinese entrants. Iljin Diamond allegedly accomplished this by misappropriating trade secrets from GE via a Korean former GE employee in 1988.

Synthetic gem-quality diamond crystals were first produced in 1970 (reported in 1971) again by GE. Large crystals need to grow very slowly under extremely tightly controlled conditions. The first successes used a pyrophyllite tube seeded at each end with thin pieces of diamond and with the graphite feed material placed in the centre, the metal solvent, nickel, was placed between the graphite and the seeds. The container was heated and the pressure raised to around 55,000 atmospheres. The crystals grow as they flow from the centre to the ends of the tube, the longer the process is extended the larger the crystals - initially a week-long growth process produced gem-quality stones of around 5 mm and one carat. The graphite feed was soon replaced by diamond grit, as there was almost no change in material volume so the process was easier to control.

The first gem-quality stones were predominantly cubic and octahedral in form and, due to contamination with nitrogen, always yellow to brown in color. Inclusions were common, especially "plate-like" ones from the nickel. Removing all nitrogen from the process by adding aluminium or titantium produced a colourless 'white' stone, while removing the nitrogen and adding boron produced a blue. However removing nitrogen slows the growth process and reduces the quality of the crystals, so the process is normally run with nitrogen present. In terms of physical properties the GE stones were not quite identical to natural stones. The colourless stones were semi-conductors and fluoresced and phosphoresced strongly under short-wave ultraviolet radiation but were inert under long-wave UV - in nature only blue stones should do this. All the GE stones also showed a strong yellow fluorescence under X-rays. De Beers Diamond Research Laboratory has since grown stones of up to 11 carats, but most stones are around 1 to 1.5 carats for economic reasons, especially with the spread of the Russian BARS apparatus since the 1980s.

Following on from work by John Angus and Boris Spitsyn researchers at the National Institute for Research in Inorganic Materials in Tsukuba produced diamonds at less than one atmosphere of pressure and only 800 °C through chemical vapor deposition (CVD). The Japanese had begun their research in 1974 and reported their success in 1981.

Properties

The gem diamond is just one of many different forms that diamond can take. Natural gem diamond is a single crystal diamond with low levels of impurities. This homogeneity is what allows it to be clear, while its material properties and hardness are what make it a popular gemstone. Most natural diamond removed from the earth's crust does not have the high purity or high crystallinity necessary to be a quality gemstone. Following are some important properties by which various types of diamond are described.

Crystallinity

A mass of diamond may be one single, continuous crystal or it may be made up of many smaller crystals ("polycrystalline"). Single crystal diamond is typically used in gemstones, while polycrystalline diamond is commonly used in industrial applications such as mining and cutting tools. Within polycrystalline diamond the diamond is often described by the average size of the crystals that make it up, called the "grain size." Grain sizes range from nanometers to hundreds of micrometers, usually referred to as "nanocrystalline" and "microcrystalline" diamond, respectively.

Hardness

A diamond's hardness can vary depending on its impurities and crystallinity. Nanocrystalline diamond produced through CVD diamond growth, for instance, can have a wide range of hardness from 30% to 75% of single crystal diamond, and the hardness can be controlled to be used in specific applications. Some single crystal diamonds grown through chemical vapor deposition have been shown to be harder than any known natural diamond.

Impurities and inclusions

No crystal is absolutely pure. Any substance other than carbon found in a diamond is an impurity, and may also be called an inclusion, due to the way these impurities fall in the crystal lattice. While inclusions can be unwanted, they can also be introduced on purpose to control the properties of the diamond. For instance, while pure diamond is an electrical insulator, diamond with small amounts of boron added is an electrical conductor, possibly allowing it to be used in new technological applications.

Gem-quality diamonds grown in a lab can be chemically, physically and optically identical to naturally occurring ones although they can be distinguished by spectroscopy in infrared, ultraviolet, or X-ray wavelengths. The DiamondView tester from De Beers uses UV fluorescence to detect trace impurities of nickel or other metals in HPHT diamonds, or hydrogen in some LP CVD diamonds.

Manufacturing technologies

There are several methods used to produce synthetic diamonds. The original method is High Pressure High Temperature (HPHT) and is still the most widely used method because of its relative low cost. It uses large presses that can weigh a couple of hundred tons to produce a pressure of 5 GPa at 1,500 degrees Celsius to reproduce the conditions that create natural diamond inside the Earth. A second method, using chemical vapor deposition or CVD, was invented in the 1980s, and is basically a method creating a carbon plasma on top of a substrate onto which the carbon atoms deposit to form diamond. A recent method uses thermal decomposition of the preceramic polymer poly(hydridocarbyne) to produce Diamond-like carbon and hexagonal diamond (Lonsdaleite). Other methods are explosive formation (detonation nanodiamond) and ultrasound sonication of solutions of graphite.

High pressure, high temperature

The GE method is called HPHT (High Pressure, High Temperature). There are two main press designs used to supply the pressure and temperature necessary to produce synthetic diamond. These basic designs are the belt press and the cubic press. There are a number of other designs, but only belt press and cubic press are used for industrial scale manufacturing.

The original GE invention by Tracy Hall, uses the belt press, wherein upper and lower anvils supply the pressure load and heating current to a cylindrical volume. This internal pressure is confined radially by a belt of pre-stressed steel bands. A variation of the belt press uses hydraulic pressure to confine the internal pressure, rather than steel belts. Belt presses are still used today by the major manufacturers at a much larger scale than the original designs.

The second type of press design is the cubic press. A cubic press has six anvils which provide pressure simultaneously onto all faces of a cube-shaped volume. The first multi-anvil press design was actually a tetrahedral press, using only four anvils to converge upon a tetrahedron-shaped volume. The cubic press was created shortly thereafter to increase the pressurized volume. A cubic press is typically smaller than a belt press and can achieve the pressure and temperature necessary to create synthetic diamond faster. However, cubic presses cannot be easily scaled up to larger volumes. To illustrate, one could increase the pressurized volume by either increasing the size of the anvils, thereby increasing by a great factor the amount of force needed on the anvils to achieve a similar pressurization, or by decreasing the surface area to volume ratio of the pressurized volume by using more anvils to converge upon a different platonic solid (such as a dodecahedron), but such a press would be unnecessarily complex and not easily manufacturable.

Chemical vapor deposition

Chemical vapor deposition of diamond is a method of growing diamond by creating the environment and circumstances necessary for carbon atoms in a gas to settle on a diamond substrate in diamond crystalline form. This method of diamond growth has been the subject of a great deal of research since the early 1980s, especially due to its potential applications in the cutting tool, semiconductor and diamond gem industries.

In their pioneering work in the area, the Japanese passed a mixture of carbon-containing gas (methane in their case) and hydrogen into a quartz tube at a pressure of 0.05 atmospheres. Using microwaves the mixture was heated to 800 °C, disassociating both the methane and hydrogen into elemental forms. The carbon is deposited on a substrate, the majority as graphite but a very small proportion as diamond crystal. The graphite is 'removed' by the hydrogen leaving a thin layer of diamond; initially the layer was around 25μm in thickness.

Explosive detonation

Diamond nanocrystals can be formed from the detonation of certain explosives, resulting in the formation of detonation nanodiamond. These nanodiamonds are only now beginning to reach the market in bulk quantities, principally from Russia and China.

Ultrasound cavitation

Diamond nanocrystals can be synthesized from a suspension of graphite in organic liquid at atmospheric pressure and room temperature using ultrasonic cavitation. The yield is approximately 10%. Cost of nanodiamonds produced by this method are estimated to be competitive with the HPHT process.

Applications

Given the extraordinary set of physical properties diamond exhibits, diamond has and could have a wide-ranging impact in many fields.

Machining and cutting tools

Diamonds have long been used in machine tools, especially when machining non-ferrous alloys. While natural diamond is certainly still used for this, the amount of synthetic diamond is far greater. The most common usage of diamond in cutting tools is done by distributing micrometer-sized diamond grains in a metal matrix (usually cobalt), hardening it and then sintering it onto the tool. This is typically referred to in industry as poly-crystalline diamond (PCD). PCD tipped tools are often used in mining and in the automotive aluminium cutting industry.

Diamond tools have been developed for stone, construction, etc for easy cutting, demolition of structures

For the past fifteen years work has also been done in the hope of using CVD diamond growth to coat tools with diamond, and though the work still shows promise it has not significantly displaced traditional PCD tools.

Electronics

CVD diamond also has applications in electronics. Conductive diamond is a useful electrode under many circumstances. University of Wisconsin-Madison chemistry professor Robert Hamers developed photochemical methods for covalently linking DNA to the surface of polycrystalline diamond films produced through CVD. In addition, the diamonds can detect redox reactions that cannot ordinarily be studied and in some cases degrade redox-reactive organic contaminants in water supplies. Because diamond is almost completely chemically inert it can be used as an electrode under conditions that would destroy traditional materials. For such reasons waste water treatment of organic effluents, as well as production of strong oxidants, have been published. A number of companies produce diamond electrodes.

Diamond shows great promise as a potential radiation detection device. Diamond has a similar density to that of soft tissue, is radiation hard and has a wide bandgap. It is employed in applications such as the BABAR detector at Stanford.

Diamond also has potential uses as a semiconductor. This is because the diamonds can be "doped" with impurities like boron and phosphorus. Since these elements contain one more or one less valence electron than carbon, they turn the diamonds into p-type or n-type semiconductors. Diamond transistors are functional to temperatures many times that of silicon and are resistant to chemical and radioactive damage. While no diamond transistors have yet been successfully integrated into commercial electronics, they show promise for use in exceptionally high power situations and hostile environments.

CVD diamond growth has also been used in conjunction with lithographic techniques to encase microcircuits inside diamond. Researchers at Lawrence Livermore National Laboratory and the University of Alabama at Birmingham use this process to create designer diamond anvils as a novel probe for measuring electric and magnetic properties of materials at ultra high pressures using a Diamond Anvil Cell.

HPHT "type IIa" diamonds are, as of 2007, approaching the very high purity and crystallographic structure perfection required to replace silicon in applications like X-ray tomographic imaging at synchrotrons; they will be able to sustain the increased intensities of next generation light sources.

Gemstones

Several companies currently produce gems made through HPHT technology. They are grown in split sphere high-pressure, high-temperature (HPHT) crystal growth chambers that resemble washing machines. The device bathes a tiny sliver of natural diamond in molten carbon at 1500 °C and 58,000 atm (5.9 GPa). This produces a rough diamond which can be cut down to a polished size close to half its original carat weight. D.NEA, formerly Adia Diamonds, produces diamonds in various shades of yellow and orange as well as blue and white (colorless). The blue color comes from doping the diamond with boron, rather than nitrogen, during the growth process. White diamonds must be grown in an environment free of nitrogen and boron, which makes them very difficult to produce. Yellow diamonds are more profitable because they can be made more quickly and cost less to manufacture than blue or colorless diamonds. The largest synthetic diamond crystal grown to date via this method was a 34-carat yellow stone. Apollo Diamond is a company that currently produces gem diamond through chemical vapor deposition and sells clear diamond gemstones.

The mined diamond industry is evaluating marketing and distribution countermeasures to these less expensive alternatives. The three largest distributors have made public statements about selling their diamonds with full disclosure and have implemented measures to laser-inscribe serial numbers on their gemstones.

There are also several companies which offer synthetic memorial diamonds. They include:

• Algordanza, a company based in Switzerland
• Anniversary Diamonds, a company based in United Kingdom
• GemSmart, a company based in San Diego, California
• Heart-In Diamond, a company based in Russia
• LifeGem, a company based in the US

Diamonds as an investment

An uncut diamond does not show its prized optical properties.

History

Diamonds have been treasured as gemstones since the ancient times. Popularity of diamonds has risen since the 19th century because of successful advertising in spite of an outrageously increased supply. Diamonds are not normally used as a mainline store of value during times of crisis, due to their lack of fungibility and low liquidity. However, they may still be useful during times of hyperinflation.

Approximately 20% of mined diamonds are used in jewelry and 80% for industrial uses (such as lasers, drill parts and surgical equipment).

Chemical vapor deposition is now used to produce cultured diamonds which, unlike diamond simulants, require very close inspection to distinguish them from natural diamonds.

Diamond price

Historically, the wholesale diamond price has been controlled by De Beers Group, which has an estimated 40% to 50% of the market. Botswana is currently the largest producer of diamonds with mines operated by Debswana, a joint venture between De Beers and the Botswana government. However, since the 1980s, other producers have developed new mines in Russia, Canada and Australia for example, challenging De Beers' dominance (historically De Beers market share was considerably higher, e.g. 80%). De Beers through its trading company known as the DTC raised wholesale diamond prices three times in 2004 by a total of 14%.

The United States is the biggest consumer of diamonds in the world. The U.S. accounts for 35% of diamond sales, Hong Kong 26%, Belgium 15% (Antwerp is the world's diamond-trading centre), Japan 6%, and Israel 4% ,Israel and Belgium are important Hubs for trading diamonds thus consumption numbers are a bit misleading. The price of diamonds fluctuates with global demand and the world economy.

Diamond prices vary widely depending on a diamond's carat, color, clarity and cut (The 4 C's). In contrast to precious metals, there is no universal world price per gram for diamonds. However the industry does use tools such as the Rapaport Diamond Report and The Gem Guide which are published weekly or quarterly, as a price references.

In addition to print and online references, numerous institutions have varying standards which can be used to aid in diamond identification and pricing. Gemological Institute of America, American Gemological Society and International Gemological Institute are three such institutions. Often these organizations focus on new research and education which they pass on to their members and the public.

Feasibility of using diamonds as an investment

There is no natural shortage of diamonds. Diamonds can be synthesized at much lower cost than the equivalent natural diamond price, and the chemical and structural purity of a synthetic diamond can exceed a natural one. However, the chemical composition is not the only factor that determines their value - the quality of the cut is of as much, if not greater, importance.

Diamonds are a problematic investment. While it is easy to buy a diamond, it is not easy to sell one unless one is already an established diamond merchant. Another problem for investors is that purchasers other than established jewelers will be paying retail for a stone but can get only wholesale at most if they sell it back to a jeweler. If buying from non-industry sources, fraud is a major risk and even retail jewelers are skittish about it following Jewelers Vigilance Committee warnings in the 1990s about numerous fraud schemes by customers selling jewelry to jewelers or bringing it in for repair.

Some firms offer "investment-grade" diamonds for sale to the public. A prudent investor should ask for a written promise to rebuy the diamonds at or near the purchase price within a specified period.

Today there are a few funds that are investing in diamonds. These funds purchase unique diamonds (very large in size or color); each stone is checked by a few professionals and negotiated until the fund decides to purchase it. Then a marketing team goes into action and through an extensive work the fund yield is gained. Between 2007 and 2008 the price of a diamond from the top range of color, clarity, cut and carat went up by over 50%.

Methods of investing in diamonds

Polished diamonds

Cut and polished diamonds.

Polished and rough diamonds lack some of the desirable attributes of investment vehicles, including liquidity, homogeneity and fungibility. Grading and certification by recognised laboratories goes some way to redressing this. Weight and cutting proportions are parameters which can be precisely measured. Colour and clarity grades are parameters which need to be determined by gemologists.

The increasing quality and size, and decreasing price, of synthetic diamonds also presents a threat to the value of polished diamonds as a long-term investment. The possibility of low-cost ultra-high-quality diamonds becoming available in industrial quantities at some time in the future is not an encouraging prospect for long-term investors in diamonds. However, synthetic diamonds have been manufactured since the 1950s and have yet to make a major impact on the market.

A cautionary example of such a price fall caused by introduction of a new simulant strongly undermining the prices of a natural gem was the permanent fall in natural pearl prices with the introduction of cultured pearls. The mechanism by which prices were affected is complex. In part because of the social acceptability of wearing cultured pearls to much of the market, customers migrated from the natural to the lower priced cultured product. This altered the supply and demand situation for natural pearls and perhaps the overall prestige of pearls in general was lowered. Where synthetic stones are less socially acceptable to the market for the natural version, arguably as with synthetic corundums where the two markets, natural and synthetic, are mostly separate, the prestige of the natural stones has been, with effort, retained. Thus increased availability and lowered prices of synthetics may or may not have major implications for the future price of natural diamonds. The fall in natural pearl prices was also affected by the onset of the Great Depression and the development of the oil industry in the Persian Gulf (which not only provided pearl divers with better-paid, safer jobs, thereby increasing production costs and lowering production capacity, but also increased pollution in the gulf, thereby reducing supply) - neither of these factors apply to diamonds. In addition, the introduction of synthetic rubies in the late 19th Century did not appear to have a permanent effect on the price of natural rubies.

There are several factors contributing to low liquidity of diamonds. One of the main is the lack of terminal market. Most commodities have terminal markets, and some form of commodities exchange, clearing house, and central storage facilities. This does not exist for diamonds. Diamonds are also subject to value added tax in the UK, EU, and sales tax in most developed countries, therefore reducing their effectiveness as an investment medium. Most diamonds are sold through retail stores at very high profit margins.

As diamonds in larger sizes become increasingly rare and valuable, any easily visible and readily understood pricing system has been difficult to establish. Martin Rapaport produces the Rapaport Diamond Report, which lists prices for polished diamonds. The Rapaport Diamond Report is relatively expensive to subscribe to, and as such is not readily available to consumers and investors. Each week, there are matrices of diamond prices for round brilliant cut diamonds, by colour and clarity within size bands, and also other shapes. The price matrix for brilliant cuts alone exceed 1,400 entries, and even this is achieved only by grouping some grades together. There are considerable price shifts near the edges of the size bands, so a 0.49 ct stone may list at $5,500 per carat = $2,695, while a 0.50 ct stone of similar quality lists at $7,500 per carat = $3,750. This may appear such a large difference as to defy logic, but in reality stones near the top of a size band tend to be uprated slightly. Some of the price jumps are related to marketing and consumer expectations. A buyer expecting a 1 carat (200 mg) diamond solitaire engagement ring may be unprepared to accept a 0.99 carat (198 mg) diamond.

There are numerous diamond grading laboratories, and there is no easy way for investors, consumers, or even dealers to know the relative competence and integrity of each. Even the market-leading Gemological Institute of America (GIA) suffered embarrassment recently when a small number of large, important and valuable diamonds were overgraded, resulting in legal action by one dealer against the dealer who had submitted them to the GIA for grading. A number of GIA employees left after the scandal emerged, and the GIA has changed a number of its procedures. There are also a number of laboratories affiliated to CIBJO (Confédération Internationale de la Bijouterie, Joaillerie et Orfèvrerie, also known as the World Jewellery Confederation). There must be commercial pressure on all labs to upgrade marginal stones or lose business to other labs who are prepared to reduce standards.

Leaving the concept of fungibility to those expert economists who understand it, the non-linear pricing of different sizes (weights), means that it is not realistic to exchange, for example, 2 quarter carats (50 mg) for 1 half carat (100 mg), even if their relative values can be calculated. With commodities such as gold, it is clear that 1 twenty gram bar is worth the same as 2 ten gram bars, assuming the same quality. In most terminal markets, there needs to be a readily available standard quality, or limited number of qualities, available in sufficient quantity to be tradable. It is this factor which affect liquidity. There are far too many variables in diamond quality, and an almost infinite graduation of each quality parameter.

There are fashion and marketing elements to take into consideration. De Beers expends marketing efforts to encourage sales of diamond sizes and qualities which are being produced in relatively large quantities. They have also been known to take steps to discourage investment, primarily because they perceive, probably correctly, that bubble prices which are followed by sharp falls are bad for long term consumer confidence in diamonds as a long-term store of value. Diamonds are primarily a consumer item.

The main positive investment parameter of diamonds is their high value per unit weight, which makes them easy to store and transport. A high quality diamond weighing as little as 2 or 3 grams could be worth as much as 100 kilos of gold. This extremely condensed value and portability does bestow diamonds as a form of emergency disaster fund. People and populations displaced by war or extreme upheaval have utilised this property successfully, and presumably will do so again in the future.

The arguments given mean that it is almost certain that diamonds can never be commoditized sufficiently to allow efficient and sufficiently liquid markets. This does not mean, however, that diamonds can never be used or considered as investments. The very lack of liquidity itself could be used by a speculator who was prepared to make a market in diamonds. Any such investor would need to ensure that he maintained sufficient personal liquidity to avoid distress selling, except by others. Such an investor would need to expend effort to market his stock, and to advertise his readiness to buy and would effectively become a trader rather than investor.

Funds

In 2008 Diapason Commodities Management listed an investment company called Diamond Circle Capital, which aims to invest in rare colored and colorless diamonds worth more than $1m each. As of July 2008 the IPO for the closed-end fund was postponed until further notice.

Mining companies

These do not represent diamonds at all, but rather are shares in companies that mine diamonds. The largest diamond company in the world is De Beers, which is jointly owned by Anglo American (45%), the Oppenheimer family (40%) and the Botswana government (15%).

The Argyle mine in Australia (owned by the Rio Tinto Group) is the largest single producer of diamonds in the world.

Taxation

Diamonds are subject to value added tax in the EU, and sales tax in most developed countries. Other taxes such as capital gains tax may apply for individuals depending on citizenship and if the asset is sold at increased value. Rough diamonds are also subject to taxation and in the near future all rough diamond mined in South Africa will be subject to a 7% royalty.

Diamond (gemstone)

The diamond ( from the ancient Greek ἀδάμας (adamas) meaning invincible ) is one of the best-known and most sought-after gemstones. Diamonds have been known to mankind and used as decorative items since ancient times; some of the earliest references can be traced to the Indians. Diamond's hardness and high dispersion of light make it useful for industrial applications and jewelry. One of the characteristics of diamonds that make them so desirable as jewelry is their tendency to disperse white light into its component colors, giving the diamond its characteristic "fire." Diamonds are such a highly traded commodity that multiple organizations have been created for grading and certifying diamonds based on the four Cs which are carat, cut, color, and clarity. Other characteristics, such as shape and presence or lack of fluorescence also affect the desirability and thus the value of a diamond used for jewelry. Perhaps the most famous use of a diamond in jewelry is its use in engagement rings. This use became popular in the early to mid 1900's due to an advertisement campaign by the De Beers company, though diamond rings were used to symbolize engagements since at least the 15th century. The diamond's high value has also been the driving force behind dictators and revolutionary entities, especially in Africa, using slave labor to mine blood diamonds to fund conflicts.

History

The Hope Diamond. Its deep blue coloration is caused by trace amounts of boron in the diamond

Early references to diamonds in India come from Sanskrit texts. The Arthashastra of Kautilya mentions diamond trade in India. Buddhist works dating from the 4th century BC describe the diamond as a well-known and precious stone but don't mention the details of diamond cutting. Another Indian description written at the beginning of the 3rd century describes strength, regularity, brilliance, ability to scratch metals, and good refractive properties as the desirable qualities of a diamond. Golconda served as an important center for diamonds in central India.

Diamonds eventually spread throughout the world, even though India had remained the only major source of the gemstone in the world until the discovery of diamonds in Brazil. A Chinese work from the 3rd century BC mentions: "Foreigners wear it [diamond] in the belief that it can ward off evil influences". The Chinese, who did not find diamonds in their country, initially did not use diamond as a jewel but used as a "jade cutting knife". The diamonds reached ancient Rome from India. Diamonds were also discovered in 700 AD in Borneo, and were used by the traders of southeast Asia. With the depletion of India's diamond resources the exploration for seeking out and finding diamonds from other parts of the world began, which led to discoveries in Brazil (1725) and South Africa (Kimberley, 1867). South Africa became the favored center for diamond resources, and quickly rose as the world's biggest diamond producer.

Diamonds were traded to both the east and west of India and were recognized by various cultures for their gemological or industrial uses. In his work Naturalis Historia, the Roman writer Pliny the Elder noted diamond's ornamental uses, as well as its usefulness to engravers because of its hardness. It is however highly doubtful that Pliny actually meant diamonds and it is assumed that in fact several different minerals such as Corundum, Spinel, or even a mixture with Magnetite were all referred to by the word "adamas".

Today, some 85% of the world's rough diamonds, 50% of cut diamonds, and 40% of industrial diamonds are traded in Antwerp, Belgium - the diamond center of the world. Antwerp's association with diamonds began in the late 15th century when a new technique to polish and shape the gems evolved in this city. The diamond cutters of Antwerp are world renowned for their skill. More than 12,000 expert cutters and polishers are at work in the Diamond Quarter, at 380 workshops, serving 1,500 firms and 3,500 brokers and merchants.

Gemological characteristics

The most familiar usage of diamonds today is as gemstones used for adornment a usage which dates back into antiquity. The dispersion of white light into spectral colors, is the primary gemological characteristic of gem diamonds. In the twentieth century, experts in the field of gemology have developed methods of grading diamonds and other gemstones based on the characteristics most important to their value as a gem. Four characteristics, known informally as the four Cs, are now commonly used as the basic descriptors of diamonds: these are carat, cut, color, and clarity.

Most gem diamonds are traded on the wholesale market based on single values for each of the four Cs; for example knowing that a diamond is rated as 1.5 carats (300 mg), VS2 clarity, F color, excellent cut round brilliant, is enough to reasonably establish an expected price range. More detailed information from within each characteristic is used to determine actual market value for individual stones. Consumers who purchase individual diamonds are often advised to use the four Cs to pick the diamond that is "right" for them.

Other characteristics not described by the four Cs influence the value or appearance of a gem diamond. These characteristics include physical characteristics such as the presence of fluorescence, as well as data on a diamond's history including its source and which gemological institute performed evaluation services on the diamond. Cleanliness also dramatically affects a diamond's beauty.

There are three major non-profit gemological associations which grade and provide reports or certificates ("certs") on diamonds; while carat weight and cut angles are mathematically defined, the clarity and color are judged by the trained human eye and are therefore open to slight variance in interpretation. The associations are listed below.

• Gemological Institute of America (GIA) was the first laboratory in America to issue modern diamond reports, and is held in high regard amongst gemologists for its consistent, conservative grading.
• American Gem Society (AGS) is not as widely recognized nor as old as the GIA but garners a high reputation. The AGS employs a number system for grading cut quality, color grade, and clarity. The highest grade being '0', and the lowest being '10'.
• Diamond High Council (HRD) Official certification laboratory of the Belgian diamond industry, located in Antwerp. Antwerp World Diamond Center

Within the last two decades, a number of for-profit gemological grading laboratories have also been established, many of them also based in Antwerp or New York. These entities serve to provide similar services as the non-profit associations above, but in a less expensive and more timely fashion. They produce certificates that are similar in detail to the GIA's.

Carat

The carat weight measures the mass of a diamond. One carat is defined as 200 milligrams (about 0.007 ounce avoirdupois). The point unit—equal to one one-hundredth of a carat (0.01 carat, or 2 mg)—is commonly used for diamonds of less than one carat. All else being equal, the price per carat increases with carat weight, since larger diamonds are both rarer and more desirable for use as gemstones.

The price per carat does not increase smoothly with increasing size. Instead, there are sharp jumps around milestone carat weights, as demand is much higher for diamonds weighing just more than a milestone than for those weighing just less. As an example, a 0.95 carat diamond may have a significantly lower price per carat than a comparable 1.05 carat diamond, because of differences in demand.

A weekly diamond price list, the Rapaport Diamond Report is published by Martin Rapaport, CEO of Rapaport Group of New York, for different diamond cuts, clarity and weights. It is currently considered the de-facto retail price baseline. Jewelers often trade diamonds at negotiated discounts off the Rapaport price (e.g., "R -3%").

In the wholesale trade of gem diamonds, carat is often used in denominating lots of diamonds for sale. For example, a buyer may place an order for 100 carats of 0.5 carat, D–F, VS2-SI1, excellent cut diamonds, indicating he wishes to purchase 200 diamonds (100 carats total mass) of those approximate characteristics. Because of this, diamond prices (particularly among wholesalers and other industry professionals) are often quoted per carat, rather than per stone.

Total carat weight (t.c.w.) is a phrase used to describe the total mass of diamonds or other gemstone in a piece of jewelry, when more than one gemstone is used. Diamond solitaire earrings, for example, are usually quoted in t.c.w. when placed for sale, indicating the mass of the diamonds in both earrings and not each individual diamond. T.c.w. is also widely used for diamond necklaces, bracelets and other similar jewelry pieces.

Clarity

Clarity is a measure of internal defects of a diamond called inclusions. Inclusions may be crystals of a foreign material or another diamond crystal, or structural imperfections such as tiny cracks that can appear whitish or cloudy. The number, size, color, relative location, orientation, and visibility of inclusions can all affect the relative clarity of a diamond. The Gemological Institute of America (GIA) and other organizations have developed systems to grade clarity, which are based on those inclusions which are visible to a trained professional when a diamond is viewed under 10x magnification.

Diamonds become increasingly rare when considering higher clarity gradings. Only about 20 percent of all diamonds mined have a clarity rating high enough for the diamond to be considered appropriate for use as a gemstone; the other 80 percent are relegated to industrial use. Of that top 20 percent, a significant portion contains one or more visible inclusions. Those that do not have a visible inclusion are known as "eye-clean" and are preferred by most buyers, although visible inclusions can sometimes be hidden under the setting in a piece of jewelry.

Most inclusions present in gem-quality diamonds do not affect the diamonds' performance or structural integrity. However, large clouds can affect a diamond's ability to transmit and scatter light. Large cracks close to or breaking the surface may reduce a diamond's resistance to fracture.

Diamonds are graded by the major societies on a scale ranging from flawless to imperfect.

Color

Jewelers sometimes set diamonds in groups of similar colors

The Darya-I-Nur Diamond

The most fine quality as per color grading is totally colorless which is Graded as "D" color diamond across the globe which means it is absolutely free from any color. The next is very very slight traces of color which can be obseversed by any expert Diamond valuer/grading laboratory.However when studded in the jewellery these very very light colored diamonds do not show any color or it is not possible to make out color shades.These are graded as E color or F color Diamonds. Diamonds which shows very little traces of color are graded as G or H color diamonds.Slightly colored diamonds are graded as I or J or K color. A diamond can be found in any other color also other than colorless. Some of the color diamonds such as pink are very very rare diamonds and are priceless.

A chemically pure and structurally perfect diamond is perfectly transparent with no hue, or color. However, in reality almost no gem-sized natural diamonds are absolutely perfect. The color of a diamond may be affected by chemical impurities and/or structural defects in the crystal lattice. Depending on the hue and intensity of a diamond's coloration, a diamond's color can either detract from or enhance its value. For example, most white diamonds are discounted in price as more yellow hue is detectable, while intense pink or blue diamonds (such as the Hope Diamond) can be dramatically more valuable. The Aurora Diamond Collection displays a spectacular array of naturally colored diamonds.

Most diamonds used as gemstones are basically transparent with little tint, or white diamonds. The most common impurity, nitrogen, replaces a small proportion of carbon atoms in a diamond's structure and causes a yellowish to brownish tint. This effect is present in almost all white diamonds; in only the rarest diamonds is the coloration from this effect undetectable. The GIA has developed a rating system for color in white diamonds, from "D" to "Z" (with D being "colorless" and Z having a bright yellow coloration), which has been widely adopted in the industry and is universally recognized, superseding several older systems once used in different countries. The GIA system uses a benchmark set of natural diamonds of known color grade, along with standardized and carefully controlled lighting conditions. Diamonds with higher color grades are rarer, in higher demand, and therefore more expensive, than lower color grades. Oddly enough, diamonds graded Z are also rare, and the bright yellow color is also highly valued. Diamonds graded D-F are considered "colorless", G-J are considered "near-colorless", K-M are "slightly colored". N-Y usually appear light yellow or brown.

In contrast to yellow or brown hues, diamonds of other colors are more rare and valuable. While even a pale pink or blue hue may increase the value of a diamond, more intense coloration is usually considered more desirable and commands the highest prices. A variety of impurities and structural imperfections cause different colors in diamonds, including yellow, pink, blue, red, green, brown, and other hues. Diamonds with unusual or intense coloration are sometimes labeled "fancy" by the diamond industry. Intense yellow coloration is considered one of the fancy colors, and is separate from the color grades of white diamonds. Gemologists have developed rating systems for fancy colored diamonds, but they are not in common use because of the relative rarity of colored diamonds.

Cut

An AGS ideally cut round diamond from Russia.

Diamond cutting is the art and science of creating a gem-quality diamond out of mined rough. The cut of a diamond describes the manner in which a diamond has been shaped and polished from its beginning form as a rough stone to its final gem proportions. The cut of a diamond describes the quality of workmanship and the angles to which a diamond is cut. Often diamond cut is confused with "shape".

There are mathematical guidelines for the angles and length ratios at which the diamond is supposed to be cut in order to reflect the maximum amount of light. Round brilliant diamonds, the most common, are guided by these specific guidelines, though fancy cut stones are not able to be as accurately guided by mathematical specifics.

The techniques for cutting diamonds have been developed over hundreds of years, with perhaps the greatest achievements made in 1919 by mathematician and gem enthusiast Marcel Tolkowsky. He developed the round brilliant cut by calculating the ideal shape to return and scatter light when a diamond is viewed from above. The modern round brilliant has 57 facets (polished faces), counting 33 on the crown (the top half), and 24 on the pavilion (the lower half). The girdle is the thin middle part. The function of the crown is to diffuse light into various colors and the pavilion's function to reflect light back through the top of the diamond.

Tolkowsky defines the ideal dimensions to have:

• Table percentage (table diameter divided by overall diameter) = 53%
• Depth percentage (Overall depth divided by the overall diameter) = 59.3%
• Pavilion Angle (Angle between the girdle and the pavilion) = 40.75°
• Crown Angle (Angle between the girdle and the crown) = 34.5°
• Pavilion Depth (Depth of pavilion divided by overall diameter) = 43.1%
• Crown Depth (Depth of crown divided by crown diameter) = 16.2%

The culet is the tiny point or facet at the bottom of the diamond. This should be a negligible diameter, otherwise light leaks out of the bottom. Tolkowsky's ideal dimensions did not include a culet. However, a thin culet is required in reality in order to prevent the diamond from easily chipping in the setting. A normal culet should be about 1%–2% of the overall diameter.

The further the diamond's characteristics are from Tolkowsky's ideal, the less light will be reflected. However, there is a small range in which the diamond can be considered "ideal." Today, because of the relative importance of carat weight in society, many diamonds are often intentionally cut poorly to increase carat weight. There is a financial premium for a diamond that weighs the magical 1.0 carat, so often the girdle is made thicker or the depth is increased. Neither of these tactics make the diamond appear any bigger, and they greatly reduce the sparkle of the diamond. So a poorly cut 1.0 carat diamond may have the same diameter and appear as large as a 0.85 carat diamond. The depth percentage is the overall quickest indication of the quality of the cut of a round brilliant. "Ideal" round brilliant diamonds should not have a depth percentage greater than 62.5%. Another quick indication is the overall diameter. Typically a round brilliant 1.0 carat diamond should have a diameter of about 6.5 mm. Mathematically, the diameter in millimeters of a round brilliant should approximately equal 6.5 times the cube root of carat weight, or 11.1 times the cube root of gram weight, or 1.4 times the cube root of point weight.

Ideal cuts can be controversial as the definitions of brilliance and beauty are very subjective.

Tolkowsky's mathematical model is now superseded by the GIA Facetware software that is the culmination of 20 years of studies on diamond cuts.

New diamond cuts are now all the rage in the diamond industry as for example a design invented in 2003 and called the Genesis cut. This cut differs in shape from the more traditional cuts in its concave surfaces and angles and resembles a 4-pointed star.

Shape

Diamonds do not show all of their beauty as rough stones; instead, they must be cut and polished to exhibit the characteristic fire and brilliance that diamond gemstones are known for. Diamonds are cut into a variety of shapes that are generally designed to accentuate these features.

Diamonds which are not cut to the specifications of Tolkowsky's round brilliant shape (or subsequent variations) are known as "fancy cuts." Popular fancy cuts include the baguette (from the French, meaning rod or loaf of bread), marquise, princess cut (square outline), heart, briolette (a form of the rose cut), and pear cuts. Newer cuts that have been introduced into the jewelry industry are the "cushion" "radiant" (similar to princess cuts, but with rounded edges instead of square edges) and Asscher cuts. Many fancy colored diamonds are now being cut according to these new styles. Generally speaking, these "fancy cuts" are not held to the same strict standards as Tolkowsky-derived round brilliants and there are less specific mathematical guidelines of angles which determine a well-cut stone. Cuts are influenced heavily by fashion: the baguette cut—which accentuates a diamond's luster and downplays its fire—was all the rage during the Art Deco period, whereas the princess cut —which accentuates a diamond's fire rather than its luster—is currently gaining popularity. The princess cut is also popular amongst diamond cutters: of all the cuts, it wastes the least of the original crystal. The past decades have seen the development of new diamond cuts, often based on a modification of an existing cut. Some of these include extra facets. These newly developed cuts are viewed by many as more of an attempt at brand differentiation by diamond sellers, than actual improvements to the state of the art.

Quality

The quality of a diamond's cut is widely considered the most important of the four Cs in determining the beauty of a diamond; indeed, it is commonly acknowledged that a well-cut diamond can appear to be of greater carat weight, and have clarity and color appear to be of better grade than they actually are. The skill with which a diamond is cut determines its ability to reflect and refract light.

In addition to carrying the most importance to a diamond's quality as a gemstone, the cut is also the most difficult to quantitatively judge. A number of factors, including proportion, polish, symmetry, and the relative angles of various facets, are determined by the quality of the cut and can affect the performance of a diamond. A poorly cut diamond with facets cut only a few degrees out of alignment can result in a poorly performing stone. For a round brilliant cut, there is a balance between "brilliance" and "fire." When a diamond is cut for too much "fire," it looks like a cubic zirconia, which gives off much more "fire" than real diamond. A well-executed round brilliant cut should reflect light upwards and make the diamond appear white when viewed from the top. An inferior cut will produce a stone that appears dark at the center and in some extreme cases the ring settings may show through the top of the diamond as shadows.

Several different theories on the "ideal" proportions of a diamond have been and continue to be advocated by various owners of patents on machines to view how well a diamond is cut. These advocate a shift away from grading cut by the use of various angles and proportions toward measuring the performance of a cut stone. A number of specially modified viewers and machines have been developed toward this end. Hearts and Arrows viewers test for the "hearts and arrows" characteristic pattern observable in stones exhibiting high symmetry and particular cut angles. Closely related to Hearts and Arrows viewers is the ASET which tests for light leakage, light return, and proportions. The ASET (and computer simulations of the ASET) are used to test for AGS cut grade. These viewers and machines often help sellers demonstrate the light performance results of the diamond in addition to the traditional 4 Cs. Detractors see these machines as marketing tools rather than as scientific tools.

The GIA has developed a set of criteria for grading the cut of round brilliant stones that is now the standard in the diamond industry and is called Facetware.

Process

The famous 253-carat Oppenheimer Diamond Crystal, at a 2001 diamond exhibition in Paris. An uncut diamond does not show its prized optical properties

The process of shaping a rough diamond into a polished gemstone is both an art and a science. The choice of cut is often decided by the original shape of the rough stone, location of the inclusions and flaws to be eliminated, the preservation of the weight, popularity of certain shapes amongst consumers and many other considerations. The round brilliant cut is preferred when the crystal is an octahedron, as often two stones may be cut from one such crystal. Oddly shaped crystals such as macles are more likely to be cut in a fancy cut—that is, a cut other than the round brilliant—which the particular crystal shape lends itself to.

Even with modern techniques, the cutting and polishing of a diamond crystal always results in a dramatic loss of weight; rarely is it less than 50%. Sometimes the cutters compromise and accept lesser proportions and symmetry in order to avoid inclusions or to preserve the carat rating. Since the per carat price of diamond shifts around key milestones (such as 1.00 carat), many one-carat diamonds are the result of compromising "Cut" for "Carat." Some jewelry experts advise consumers to buy a 0.99 carat diamond for its better price or buy a 1.10 carat diamond for its better cut, avoiding a 1.00 carat diamond which is more likely to be a poorly cut stone.

Light performance

In the gem trade the term light performance is used to describe how well a polished diamond will return light to the viewer. There are three light properties which are described in relation to light performance; brilliance, fire, and scintillation. Brilliance refers to the white light reflections from the external and internal facet surfaces. Fire refers to the spectral colors which are produced as a result of the diamond dispersing the white light. Scintillation refers to the small flashes of light that are seen when the diamond, light source or the viewer is moved. A diamond that is cut and polished to produce a high level of these qualities is said to be high in light performance.

The setting diamonds are placed in also affect the performance of light through a diamond. The 3 most commonly used settings are: Prong, Bezel, and Channel. Prong settings are the most popular setting for diamond jewelry. The prong setting consists of four or six 'claws' that cradle the diamond, allowing the maximum amount of light to enter from all angles, allowing the diamonds to appear larger and more brilliant. In bezel settings the diamond or gemstone is completely surrounded by a rim of metal, which can be molded into any shape to accommodate the stone. Used to set earrings, necklaces, bracelets, and rings, bezel settings can have open or closed backs, and generally can be molded to allow a lot of light to pass through. Channel settings set the stones right next to each other with no metal separating them. This setting is mostly used in wedding and anniversary bands. The outer ridge is then worked over the edges of the stones to create a smooth exterior surface. This also protects the girdle area of the stone.

Fluorescence

About a third of all diamonds will glow under ultraviolet light, usually a blue color which may be noticeable under a black light or strong sunlight. According to the GIA, who reviewed a random sample of 26,010 natural diamonds, 65% of the diamonds in the sample had no fluorescence. Of the 35% that did have fluorescence, 97% had blue fluorescence of which 38% had faint blue fluorescence and 62% had fluorescence that ranged from medium to very strong blue. Other colors diamonds can fluoresce are green, yellow, and red but are very rare and are sometimes a combination of the colors such as blue-green or orange. Some diamonds with "very strong" fluorescence can have a "milky" or "oily" look to them, but they are also very rare and are termed "overblues." Their study concluded that with the exception of "overblues" and yellow fluorescent diamonds, fluorescence had little effect on transparency and that the strong and very strong blue fluorescent diamonds on average had better color appearance than non-fluorescent stones. Since blue is a complementary color to yellow and can appear to cancel it out, strong blue fluorescence had especially better color appearance with lower color graded diamonds that have a slight yellowish tint such as "I" color or "J" color but had little effect on the more colorless "D" through "F" color grades.

Cleaning

Cleanliness significantly affects a diamond's beauty. A clean diamond is more brilliant and fiery than the same diamond when it is "dirty". Dirt or grease on the top of a diamond reduces its luster. Water, dirt, or grease on the bottom of a diamond interferes with the diamond's brilliance and fire. Even a thin film absorbs some light that could have been reflected to the viewer. Colored dye or smudges can affect the perceived color of a diamond. Historically, some jewelers' stones were misgraded because of smudges on the girdle, or dye on the culet. Current practice is to clean a diamond thoroughly before grading its color.

Maintaining a clean diamond can sometimes be difficult as jewelry settings can obstruct cleaning, and oils, grease, and other hydrophobic materials adhere well to a diamond. Many jewelers use steam cleaners. Some jewelers provide their customers with ammonia-based cleaning kits; ultrasonic cleaners are also popular.

Symbolism and lore

Mary of Burgundy is the first known recipient of a diamond engagement ring, in 1477.

Historically, it has been claimed that diamonds possess several supernatural powers:

• A diamond gives victory to he or she who carries it bound on his left arm, no matter the number of enemies.
• Panics, pestilences, enchantments, all fly before it; hence, it is good for sleepwalkers and the insane.
• It deprives lodestone and magnets of their virtue (i.e., ability to attract iron).
• Arabic diamonds are said to attract iron greater than a magnet.
• A diamond's hardiness can only be broken by smearing it with fresh goat's blood.
• In traditional Hinduism one should avoid contact with a diamond which surface area is damaged by a crack, a crowfoot, round, dull, speckled area or which is black-blue, flat, and if uncut, other than the (ideal) hexagonal shape.

Because of their extraordinary physical properties, diamonds have been used symbolically since near the time of their first discovery. Perhaps the earliest symbolic use of diamonds was as the eyes of Hindu devotional statues. In Hinduism Indra uses Vajrayudham or the thunderbolt as his primary weapon. Vajra is the word for diamond and ayudham means weapon in Sanskrit. Another name for it was Agira which means fire or the sun. In fact there are 14 names counted to be given to a diamond in traditional Hinduism.

The oldest dated printed book in the world is called the Diamond Sutra, a Chinese text dates from AD 868 and was found in the Mogao Caves. Sutras are most used to describe the teachings of Buddha. In this case the title of the Sutra refers not to the diamond itself but to a 'diamond blade that will cut through worldly illusion to illuminate what is real and everlasting'. Jewel imagery forms a central part of Buddhism: the triple-jewel represents 'Buddha', his teachings 'Dharma' and the spiritual community 'Shangha'. The book presently resides in the British Library.

Many cultures use divine intervention to explain the origin and creation of gemstones, and diamonds were no exception to this. In Greek mythology for example it was the youth on the island of Crete that disturbed Zeus and who were then (as a form of punishment) transformed into the adamas.

Philosophers however had a more naturalistic approach to explain the origin of gems: Plato for example believed gemstones were a consequence of fermentation in the stars, where a diamond actually formed the kernel of gold-bearing mass. In fact often diamonds were linked to gold, which may have found its origin in the joint occurrence of diamonds with quartzite, quartz veins and an occasional occurrence of gold in them.

In later times, Robert Boyle actually believed that gems (including a diamond) were formed of clear, transparent water, and that their colors and characteristics were derived from their metallic spirit.

The diamond is the birthstone for people born in the month of April, and is also used as the symbol of a sixty-year anniversary, such as a Diamond Jubilee. In a system of heraldry by gemstone occasionally used in the past for the arms of nobles, diamond was used to represent the color sable, or black.

The ring

1.13 carat round diamond engagement ring.

The origin of the custom to use diamonds in rings, and more recently, in engagement rings, can be traced back to the Middle Ages and even the Romans. The Romans valued the diamond entirely on account of the supernatural powers they ascribed to it. Pliny wrote that a diamond baffles poison, keeps off insanity, and dispels vain fears. The medieval Italians copied these beliefs and added some to it: they called it the "Pietra della Reconciliazone" because it maintained concord between husband and wife. On this account it was recommended as the stone to be set in wedding (or espousal) rings—not on account of its beauty therefore, which was described by Isidore of Seville as a small stone devoid of beauty.

In more recent times a Parisian Oracle of mystic subjects, the Baron d'Orchamps, announced the diamond, if worn on the left (hand) warded off evil influences and attracted good fortune and since he had fashionable clients the word spread and the wearing of the diamond on the left hand became in itself a fashion.

One of the first occurrences of the diamond engagement (or wedding) ring can be traced back to the marriage of Maximilian I (then Archduke of Austria) to Mary of Burgundy in 1477. Other early examples of betrothal jewels incorporating diamonds include the Bridal Crown of Blanche (ca. 1370–80) and the Heftlein brooch of Vienna (ca. 1430–40), a pictorial piece depicting a wedding couple.

The popularity of the diamond ring as an engagement ring for a much wider audience can be traced directly to the marketing campaigns of De Beers, starting in 1938. Such a campaign had become necessary to sell the large quantity of diamonds suddenly available because of the large diamond finds particularly in South Africa.

"Blood" diamonds

In some of the more politically unstable central African and west African countries, revolutionary groups have taken control of diamond mines, using proceeds from diamond sales to finance their operations. Diamonds sold through this process are known as conflict diamonds or blood diamonds. Major diamond trading corporations continue to fund and fuel these conflicts by doing business with armed groups. In response to public concerns that their diamond purchases were contributing to war and human rights abuses in central Africa and West Africa, the United Nations, the diamond industry and diamond-trading nations introduced the Kimberley Process in 2002, which is aimed at ensuring that conflict diamonds do not become intermixed with the diamonds not controlled by such rebel groups, by providing documentation and certification of diamond exports from producing countries to ensure that the proceeds of sale are not being used to fund criminal or revolutionary activities. Although the Kimberley Process has been moderately successful in limiting the number of conflict diamonds entering the market, conflict diamonds smuggled to market continue to persist to some degree (approx. 2–3% of diamonds traded today are possible conflict diamonds). According to the 2006 book The Heartless Stone, two major flaws still hinder the effectiveness of the Kimberley Process: the relative ease of smuggling diamonds across African borders and giving phony histories, and the violent nature of diamond mining in nations that are not in a technical state of war and whose diamonds are therefore considered "clean."

The Canadian Government has setup a body known as Canadian Diamond Code of Conduct to help authenticate Canadian diamonds. This is a very stringent tracking system of diamonds and helps protect the 'conflict free' label of Canadian diamonds.

Currently, gem production totals nearly 30 million carats (6,000 kg) of cut and polished stones annually, and over 100 million carats (20,000 kg) of mined diamonds are sold for industrial use each year, as are about 100,000 kg of synthesized diamond.

Other facts

Diamonds are a common focus of fiction. Notable pieces of fiction include Ian Fleming's Diamonds Are Forever (1956), Arthur C. Clarke's 2061: Odyssey Three (1988), F. Scott Fitzgerald's "The Diamond as Big As the Ritz" (1922), and Neal Stephenson's The Diamond Age (1995). In addition, diamonds are the subject of various myths and legends.