Diamond (gemstone)

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

The process of diamonds being used for drilling ornamental beads dates back to 2nd millennium BC. Archaeologists working in Yemen have excavated beads with evidences of diamond drilling from 1200 BC to 1st century AD from the site of Hajar ar Rayhani, with double diamond drilling from 1000 to 600 BC.[2][3][4] The double diamond drill technique was present in Western India prior to 600 BC (7th century BC).[5] There is also evidence of technique of double diamond drilling from Southern Thailand dating back to 400 BC.[6]

Before diamonds were discovered in Brazil in the 1700s, India was the only place where diamonds were mined. Early references to diamonds in India come from Sanskrit texts.[7] The Arthashastra of Kautilya mentions diamond trade in India.[8] Buddhist works dating from the 4th century BC describe the diamond as a well-known and precious stone but do not mention the details of diamond cutting.[9] Another Indian description written in 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.[10] Kalkutta was an important trading center for diamonds in central India.[11]

Diamonds were traded to the east and west of India and were recognized by various cultures for their gemmological or industrial uses. In his work Naturalis Historia, the Roman writer Pliny the Elder referred to the adamas (invulnerable stone) that occurred alongside gold and was used for ornament and engraving. This was long believed to refer to diamond, but is now thought more likely to mean other hard minerals such as corundum or spinel.[lower-alpha 2]

Diamonds eventually spread throughout the world, even though India had remained the only major source of the gemstone until diamonds were discovered in Brazil in 1725.[8] A Chinese work from the 3rd century BC mentions: "Foreigners wear it [diamond] in the belief that it can ward off evil influences".[10] The Chinese, who did not find diamonds in their country, initially did not use diamond as a jewel but used it as a "jade cutting knife".[10] Diamonds reached ancient Rome from India.[7] Diamonds were also discovered in 700 in Borneo, and were used by the traders of southeast Asia.[7]

The modern era of diamond mining began in the 1860s in Kimberley, South Africa with the opening of the first large-scale diamond mine.[12][13] The first diamond there was found in 1866 on the banks of the Orange River[14] and became known as the Eureka Diamond.

Fleetwood Rawstone's "Red Cap Party" of prospectors on Colesberg Kopje

In 1869, an even larger 83.50-carat (16.700 g; 0.5891 oz) diamond was found on the slopes of Colesberg Kopje on the farm Vooruitzigt belonging to the De Beers brothers. This sparked off the famous "New Rush" and within a month, 800 claims were cut into the hillock which were worked frenetically by two to three thousand men. As the land was lowered so the hillock became a mine—in time, the world-renowned Kimberley Mine.[15] Following agreement by the British government on compensation to the Orange Free State for its competing land claims, Griqualand West was annexed to the Cape Colony in 1877.[16]

The Big Hole.

From 1871 to 1914, 50,000 miners dug the Big Hole with picks and shovels, yielding 2,722 kg (6,001 lb) of diamonds,[17] and by 1873 Kimberley was the second largest town in South Africa, having an approximate population of 40,000.[18]

The various smaller mining companies were amalgamated by the British businessmen Cecil Rhodes and Charles Rudd into the De Beers Mining Company, and the Barnato Diamond Mining Company by Barney Barnato. In 1888, the two companies merged to form De Beers Consolidated Mines, which proceeded to establish a monopoly over the world's diamond market.[19] That monopoly had ended by 2005, following an antitrust lawsuit in the US[20] (which De Beers settled without admitting wrongdoing, upon payment of a US$295 million settlement),[21] and a voluntary agreement between De Beers and the European Commission.[22] The latter agreement had been overturned upon appeal by the Russian mining company Alrosa, but the European Court of Justice then upheld the decision and the European Commission subsequently concluded its investigation with no more action being taken against De Beers.[23]

Today, annual global rough diamond production is estimated to be about 130 million carats (26 tonnes; 29 short tons),[1] of which 92% is cut and polished in India, mostly in the city of Surat.[24] 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.[25] The city of Antwerp also hosts the Antwerpsche Diamantkring, created in 1929 to become the first and biggest diamond bourse dedicated to rough diamonds.[26] 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 District, at 380 workshops, serving 1,500 firms and 3,500 brokers and merchants.

In the 21st century, the technology to produce perfect diamonds synthetically was developed. Diamonds produced by the latest technologies are visually identical to mined, naturally occurring diamonds. It is too early to assess the effect of future wide availability of gem-quality synthetic diamonds on the diamond market, although the traditional diamond industry has taken steps to try to create a distinction between diamonds dug from the ground and diamonds made in a factory, in part by downplaying the fact that diamonds from both sources are actually visually identical.[27] Synthetics currently represent 2% of gem-quality diamond supply used for jewelry, but 98% of industrial-quality supply used for abrasive applications.[28]

The carat weight measures the mass of a diamond. One carat is defined as 200 milligrams (about 0.007 ounces 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 linearly 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 0.99-carat diamond may have a significantly lower price per carat than a comparable 1.01-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.[31] 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 (20 g) of 0.5-carat (100 mg), D–F, VS2-SI1, excellent cut diamonds, indicating a wish to purchase 200 diamonds (100 carats (20 g) 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 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 10× magnification.

Diamonds become increasingly rare when considering higher clarity gradings. Only about 20% 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% are relegated to industrial use. Of that top 20%, 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. When set in jewelry, it may also be possible to hide certain inclusion behind mounting hardware such as prongs in a way that renders the defect invisible. However, large clouds can affect a diamond's ability to transmit and scatter light. Large cracks close to or breaking the surface may increase the likelihood of a fracture.

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

Jewelers sometimes set diamonds in groups of similar colors.

The Darya-I-Nur Diamond

The finest quality as per color grading is totally colorless, which is graded as D color diamond across the globe, meaning it is absolutely free from any color. The next grade has a very slight trace of color, which can be observed by any expert diamond valuer/grading laboratory. However, when studded in jewellery these 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 show 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 color in addition to colorless. Some of the colored diamonds, such as pink, are very rare.

A chemically pure and structurally perfect diamond is perfectly transparent with no hue, or color. However, in reality most gem-sized natural diamonds are imperfect. 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 a 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, which occur in every color of the rainbow.[32][33]

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.[34] 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. 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 appears 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. There is also a kind of pebble containing polycrystalline diamond that is black or gray, called carbonado, which may be of extraterrestrial origin. It is the toughest form of diamond and is used as an abrasive, though sometimes also as precious stone[35] (for example The Enigma). Diamonds with unusual or intense coloration are sometimes labeled "fancy" in 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 such diamonds.[36]

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 refract light into various colors and the pavilion's function to reflect light back through the top of the diamond.[37]

Tolkowsky's calculations included some approximations. He calculated the ideal dimensions as:

• Table percentage (corner-to-corner diameter of the table divided by overall diameter) = 53%
• Depth percentage (overall depth divided by overall diameter) = 59.3% (not including adjustments for the culet height and girdle thickness)
• Pavilion angle (angle between the girdle and the pavilion main facets) = 40.75°
• Crown angle (angle between the girdle and the crown's kite facets) = 34.5°
• Pavilion depth (depth of pavilion divided by overall diameter) = 43.1%
• Crown depth (depth of crown divided by overall 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 calculations included neither a culet nor a girdle. However, a girdle is required in reality in order to prevent the diamond from easily chipping in the setting. The thick part of the girdle is normally about 1.7% (of the overall diameter) thicker than the thin part of the girdle.[37]

The further the diamond's characteristics are from the Tolkowsky's ideal, the less light will be reflected. However, there is a small range in which the diamond can be considered "ideal". Tolkowsky's calculations can be repeated for a narrow range of pavilion angles. Such calculations show a slightly larger table percentage, and a trade-off between pavilion angle and crown angle.[37]

Today, because of the relative importance of carat weight among buyers, many diamonds are often intentionally cut poorly to increase carat weight. There is a financial premium for a diamond that weighs the desirable 1.0 carat (200 mg), so often the girdle is made thicker or the depth is increased. Neither of these changes makes the diamond appear any larger, and both greatly reduce the sparkle of the diamond. (A poorly cut 1.0-carat (200 mg) diamond may have the same diameter and appear as large as a 0.85-carat (170 mg) 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 (200 mg) diamond should have a diameter of about 6.5 mm (0.26 in). Mathematically, the diameter in millimeters of a round brilliant should approximately equal to 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.

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 into a round brilliant shape are known as "fancy cuts." Popular fancy cuts include the baguette (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 popular 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.[37]

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 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 extreme cases the setting may be seen 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.[38] Proponents of these machines argue they help sellers demonstrate the light performance of the diamond in addition to the traditional 4 Cs. Detractors, however, see these machines as marketing tools rather than scientific ones. 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.

The 253-carat (50.6 g) Oppenheimer Diamond, 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.[39] 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%.[40] 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 (200 mg)), many one-carat diamonds are the result of compromising cut for carat. Some jewelry experts advise consumers to buy a 0.99-carat (198 mg) diamond for its better price or buy a 1.10-carat (220 mg) diamond for its better cut, avoiding a 1.00-carat (200 mg) diamond which is more likely to be a poorly cut stone.

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 three 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.

A population of diamonds exhibiting an ultra rare purple fluorescence were discovered in 2020 at a new alluvial deposit within the Ellendale diamond field in Australia. Credit: IBDH

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 did not fluoresce. Of the 35% that did fluoresce, 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. In October 2020, a population of diamonds were discovered within an alluvial deposit at the Ellendale diamond field in Australia that exhibit an ultra rare purple fluorescence.

Some diamonds with "very strong" fluorescence can have a "milky" or "oily" look to them, but they are also very rare and are termed "over-blues." Their study concluded that with the exception of "over-blues" 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 so 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 or J color, but had little effect on the more colorless D, E, and F color grades.[41]

Before the diamond industry standardized to the GIA grading terminology the term "Blue White" (Blauweiss) was widely used to describe the most highly regarded white diamonds. The term described colorless diamonds with a tinge of blue fluorescence. These stones were actively sought by merchants thanks to their appealing ‘ice’ effect and consumers paid higher prices for diamonds with fluorescence. Quality retailers such as C. D. Peacock of Chicago Il.[42] made their name selling genuine Blue-White diamonds, but others in the industry saw the opportunity to use the term to sell lower quality diamonds.

By 1938, the term "Blue White" and the underlying concept that blue (i.e. fluorescence) added value to white (colorless) diamonds had become abused by too many unscrupulous dealers and the U.S. Federal Trade Commission outlawed the use of the term Blue White. The subsequent FTC restrictions undoubtedly encouraged the establishment of today's GIA color grading system. The new GIA grading system had no place for the effect of fluorescence on color and the desirability of fluorescence in a diamond began to wane in the years that followed. Diamonds with fluorescence were marked down in price.

Ironically, in 1997, a seminal study by the Gemological Institute of America (GIA) concluded that, "in general, the strength of fluorescence had no widely perceptible effect on the color appearance of diamonds viewed table-down (as is typical in laboratory and trade grading). In the table-up position (as is commonly encountered in jewellery stores), diamonds described as strongly or very strongly fluorescent were, on average, reported as having a better color appearance than less fluorescent stones".[43] The GIA study concluded that "the diamond industry would be better served by considering each individual diamond on its own visual merits."

Today, fluorescent natural diamonds are again becoming very desirable with major diamond miners such as the world's largest diamond producer, Alrosa, reminding the industry of the historic desirability and beauty of naturally fluorescent diamonds.[44]

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.