When most people think of diamond color, white is the first thing to come to mind. Others might consider the various shades of yellow or brown, so subtle they must be detected by trained eyes. Still more may imagine famous colored jewels like the Hope Diamond.
Color or the lack thereof occurs when light touches a gemstone. White light is the combination of many hues and their wavelengths. When white light interacts with the elements inside the diamond and the jewel’s crystal structure, certain wavelengths may be absorbed while others are reflected. The latter is what creates color. Depending on certain qualities of the diamond, different hues may appear.
There are many ways to catalogue diamonds, whether it’s by country of origin, clarity, fluorescence and so on. One classification organizes diamonds by their chemical purity, also known as diamond types. There are two major designations, known as Type I and Type II. These are further subdivided by the exact nature of a diamond’s trace elements, which in turn impacts the jewel’s color.
Type I is the most common of all diamonds. These stones contain nitrogen elements mixed into their crystal structure. Type Ia diamonds make up the vast majority of natural diamonds, or 95%. These diamonds are the most likely to have a yellowish tint to them, from barely perceptible to a canary like hue.
Depending on how the nitrogen manifests in a Type Ia diamond, it may fall into one of two specific categories. If nitrogen atoms appear as pairs inside the diamond’s crystal structure, the stone is a Type IaA diamond and less likely to have a noticeable color. Type IaB has an even number of nitrogen atoms surrounding a gap in the diamond’s lattice.
Type Ib diamonds have lone nitrogen atoms scattered within the stone. They make up 0.1% of all natural diamonds and have an array of unusual colors. There are intense yellows and browns well out of the color range of most diamonds. Some Type Ib specimens even have blue-grey hues, though this is from a variety of factors, like crystal defects, not just the arrangement of nitrogen.
The other major diamond classification, Type II, has no detectable traces of nitrogen. Type IIa stones make up 2% of natural diamonds and are the most chemically pure of all diamond types. While they are most often colorless, the heat and pressure that brings diamonds to the earth’s crust may alter portions of the diamond lattice. This in turn may create colors such as pink, purple, yellow or grey.
Type IIb diamonds contain traces of boron. They make up the majority of blue diamonds, though Type IIb stones are 0.1% of all natural diamonds. Boron is what makes these stones the only diamonds capable of conducting electricity. Just one boron atom per million atoms of carbon is enough to make this phenomenon happen.
The most common diamond color is white, also known as colorless. Diamonds are allochromatic, meaning that on their own, they exhibit no color. The chemical formula of diamonds is pure carbon, its crystal structure resembling two pyramids joined on a four sided base. When light passes through a diamond, no particular wavelengths are absorbed. White light is reflected, making the jewel appear white.
The vast majority of diamonds have traces of nitrogen mixed into their crystal structure. While nitrogen influences diamond’s color, the results are often so minute that it takes skilled professionals and specialized equipment to determine the degree of color. The Gemological Institute of America (GIA) rates the color of diamonds on a scale of D-Z, with D purely colorless and Z with the most notable tinge.
Grades D, E and F diamonds have little to no traces of nitrogen or other elements in their crystals. Such jewels are very rare, making up less than two percent of all natural diamonds. The further down the scale the more visible the tint, though they are still described in terms like “faint” and “very light.”
The hues of stones with grades like N may be downplayed or highlighted through choices in precious metal. A grade R diamond may look lighter when mounted onto yellow gold or look more prominent when mounted onto platinum. Diamonds with grades like Y or Z may appear yellow to the naked eye, though cut may influence its color.
For about every ten thousand colorless diamonds, one may have a tinge stronger than a Z grade. Such gemstones are categorized as Fancy Color diamonds, and are subject to different evaluations than their white counterparts. Instead of the D-Z scale, they’re rated from Fancy Light, Fancy, Fancy Intense, Fancy Dark, Fancy Deep and Fancy Vivid.
The six grades are meant to reflect that while some Fancy diamonds may share the same hue, the color intensity and how light or dark the color is can vary. Of the color ratings, Fancy Vivid has medium to medium dark tone and vivid saturation, showing off hue to its best advantage. This category of Fancy diamond is the rarest and most sought after. However, even Fancy Light jewels are unusual and in demand.
The two most common Fancy diamond colors are brown and yellow. As with the tints in colorless diamonds, brown and yellow diamonds occur through trace elements of nitrogen which take the place of carbon in the crystal structure. Brown diamonds are the more plentiful of the two, though for many years brown diamonds were only used for industry.
In the 1980s, Australia’s Argyle diamond mine unearthed an abundance of brown diamonds. Many of these stones were faceted, mounted into jewelry and given names like “cognac” or “chocolate” diamonds. The campaign to popularize brown diamonds was a success, the stones are found on today’s jewelry.
Yellow diamonds were very rare until the 1860s, yet not completely unheard of. Jewel merchant Jean-Baptiste Tavernier noted one large yellow diamond on a trip to India, and one family of Maharajas had a yellow diamond in their family for centuries. Deposits in South Africa in the 1860s helped lead to the discovery of many named yellow diamonds such as the Golden Eye as well as less famous but still intriguing jewels. Yellow diamonds may be marketed as “canary” to highlight their hues.
With the right cut, diamonds that are rated a Z on the colorless scale may become fancy yellow diamonds. To concentrate the color in a diamond, the jewel is faceted into a radiant cut or other fancy cuts known for their intensity. If the diamond is being cut from an already faceted shape, this will lead to a loss in carat size, but value will be increased by the unusual color. Yellow gold settings can also help highlight the Fancy color.
Diamonds don’t turn pink or red through trace minerals. They achieve these hues through plastic deformation, or quirks in their crystal structure which causes color centers. These in turn make the jewel absorb most spectral hues and reflect red light. The intensity of the color and whether the diamond is pink or red depends on the number of color centers in the stone.
Pink diamonds are more common than red, but still difficult to find. Southern India was a source of these jewels in the 1600s, and others have been found in Africa, Brazil and Russia. Today, the Argyle mine in Australia is one of the world’s greatest sources of pink diamonds. However, less than 1% of Argyle’s total yield is pink diamond rough.
Adding to the complications of finding pink diamonds is the demand of pure pink diamonds and the greater availability of pink tinted stones. A jewel that is pinkish brown, orangey pink or purplish pink are easier to find than one that is just pink. The latter type, due to how scarce and desirable they are, are known to reach record breaking prices at auctions. Once such jewel, the Graff Pink, was sold through Sotheby’s for $46 million in 2010.
Red diamonds are the rarest of all diamond colors. Of all the diamonds GIA evaluated between 1957 and 1987, none were red. Even jewels with reddish hues, such as red-brown or purplish red are sought after, though not as much as pure reds. One such jewel, the Moussaieff Red, measures 5.11 carats and is unusual enough to have been displayed with much larger diamonds in a 2003 Smithsonian exhibit.
The majority of blue diamonds are Type IIb stones, which have no trace of nitrogen, but hints of boron in the jewel. This causes the diamond to absorb orange, yellow and red lights while reflecting blue. Diamonds with traces of boron make up 0.1% of all diamonds, placing them in short supply.
Even rarer are Type Ib and IIa diamonds who achieve their blues through lattice deformation. For this to happen, the pressure that formed the original stone must have also changed part of the crystal structure, creating color centers. Type Ib diamonds may have their color further influenced by the presence of hydrogen in addition to lattice deformations. Still more diamonds may turn a bluish color with the help of naturally occurring radiation.
Blue diamonds are often greyish, and those colored through irradiation will have a greenish cast. It’s uncommon for their blues to achieve the saturation of other gemstones like tourmalines or sapphires. In their rough state, blue diamonds may have color zoning, or uneven coloration. Diamond cutters must be careful to cut the jewel so that the most desirable blues appears face up, while keeping as much carat weight of the rare diamond as possible.
Many factors help make blue diamonds intriguing. On top of their beauty and rarity, some of them are the stuff of legend. One of the most famous diamonds in the world is the blue Hope Diamond. Though it’s said to bring misfortune to its owners, when the Hope Diamond was donated to the Smithsonian Institute, visitors arrived in droves, and others were compelled to donate gemstones to the museum. More recent blue diamond tales include the 14.62 carat Oppenheimer Blue. In May 2016, it sold for $50.6 million, breaking the Blue Moon of Josephine diamond’s 2015 record of most expensive jewel sold at auction.
Unlike brown, blue or yellow diamonds, green diamonds don’t gain color from trace minerals. When a diamond is exposed to radiation, such as from naturally occurring uranium sources, bits of carbon are displaced from their lattice. This in turn forms color centers which causes the diamond to reflect green light.
Naturally green diamonds are often yellow green with low tone and saturation. The coloring is likely to be uneven, confined to the surface with patches of green or brown known as radiation stains. While diamond cutters may remove these stains, in some cases they are left on the girdle to help preserve the diamond’s hue.
While green diamonds are extremely rare in nature, they’re easier to create in a laboratory setting. The Dresden Green, a forty-one carat natural green diamond, has been carefully studied to find ways to help gemologists determine if other diamond’s green hues are natural. Green diamonds are also tested before they’re placed on the market, to determine if they are safe enough to wear.
In 1866, a diamond merchant named Georges Halphen wrote of a strange diamond that changed color. By 1943, such stones were known as chameleon diamonds. These normally greenish or yellowish diamonds, when exposed to heat up to 150 degrees Celsius, temporarily become brown, orange or yellow. When these jewels are exposed to ultraviolet light, they will glow yellow for up to an hour. What causes this color change is still a mystery.
Fancy diamonds can be any color, such as boron and plastic deformations combining to create purple, or hematite crystals within the diamond turning the jewel black. While some hues are rarer than others, Fancy diamonds make up 2% of all gem quality diamonds, making them even more precious. Colored diamond jewelry can be found at select jewelry establishments. Some of the most notable colored diamonds are available for viewing at institutions like the Smithsonian and GIA.
From AAA to D
Over ninety percent of diamonds mined contain traces of nitrogen which replace carbon atoms in the diamond’s lattice structure. Depending on how the nitrogen is arranged within the diamond, the jewel may take on a brown or yellow tint. This coloring can be so subtle only a trained professional can find it, or apparent to the naked eye. Many connoisseurs gravitate towards lighter or colorless diamonds. Certified diamonds help attest to a gemstone’s color.
When it comes to grading, tradition dictates that A denotes the best quality. Depending on the system, the top grade may go a step further, stating AA or even AAA as the pinnacle rating. Diamond color grades were no different. Prior to the 1950s, different organizations would mark their lightest diamonds as A, AAAA and other designations. For a person looking for loose diamonds, the contradicting grade scales lead to confusion.
When the Gemological Institute of America (GIA) developed its color grading system, it chose D as its top color grade. This designation helped GIA’s ratings stand out from others, making it unlikely a GIA grade would be mistaken for one from another system. It also furthered GIA’s goal of certified diamonds with a standard easily understood by both professionals and lay people.
GIA certified diamonds are color graded under strict circumstances. For optimal accuracy, jewels are graded under standardized lighting conditions. Laboratories have sets of master stones representing all the colors in the grading system from D to Z.