Diamond crystal in matrix rock.  Image provided with permission of the National Museum of Natural History, Smithsonian Institution, Washington, DC.
http://goode.si.edu/web/objects/common/webmedia.php?irn=1000453

    When Emily Hahn interviewed Mr. Briefel in the early 1950s, the scientific community was not sure why diamonds had color.  Actually, we still do not know what causes some colors to occur, and sometimes there can be more than one cause for a color.  Our culture has placed a lot of emphasis on the 'perfect' colorless diamond, but fancy colored diamonds (have significant, noticable color) are much more rare.  Different estimates put the occurence of fancies at one in 1,000 diamonds² to 1 in 10,000³.  Even fewer of these will be above 1 carat in weight.

    While colored diamonds are significantly more rare than colorless, poor knowledge of these gems has depressed the price somewhat.  The prices of fancy diamonds are more subjective than colorless diamonds.  For example, since most gem-quality fancy diamonds tend to be very small, a diamond larger than one carat is incredibly rare and expensive.  Each can be priced separately.  Pink diamonds are now more common (relatively) because of production in the Argyle mine of Australia, but still a medium pink (not the most intense color of pink) runs from $25,000-$40,000 per carat for stones around half a carat.⁴  For green diamonds, one of the more rare colors, a price record was set in 2000 when a 0.90 carat vivid green brilliant cut was sold for $600,000.  At this pricing, a one carat diamond of the same quality works out to be $670,000.⁵

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Black

    Black diamonds are opaque and although they do not show the fire normally valued in diamonds, they are still desired.  The color is caused by inclusions of graphite within the crystal.  The graphite inclusions cause the diamond to be a conductor.³  Diamond and graphite are both made of carbon, the carbon atoms are just bonded differently.  Knowing this, it is not difficult to reason graphite being found in diamond.

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Gray

    Gray diamonds are colored by hydrogen, and more rarely boron (unknown how, since boron nearly always forms blue).  The defect causes the stone to absorb all wavelengths of light equally.  Gray color can tint nearly every other shade.  Gray-greens are called "olive."  The Argyle mine produces some gray-blues, which are sometimes tinged with purple.  The Argyle mine will be mentioned thoughout the document, as it is an important and relatively new (1985) diamond mine that produces a wide array of colors.³

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White

Photo courtesy Howard Stroupe, http://www.duke.edu/ ~hls1/diamant/b_w.html.

"White" diamond differ from colorless in that they are not clear.  These diamonds are colored by inclusions so tiny that it is unknown the exact cause, though it may be from nitrogen.  Some white diamonds are opalescent due to the scattering of light.3

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Brown

Browns are by far the most abundant color of diamond, and the least desired.  Gem quality browns are often given elaborate names, anything to avoid calling them brown.  Champagne is a code word for lightly tinted brown diamond.  Darker browns are often called "cognac" (does anyone else wonder about this trend in alcohol references?).  The color in most brown diamonds results from parallel lamellae (like very small stripes).  The origin of the lamellae is unknown.3 Return to Table of Contents

Photo courtesy Howard Stroupe, http://www.duke.edu/~hls1/diamant/common.html

Red/Pink

Photo courtesy Howard Stroupe, http://www.duke.edu/ ~hls1/diamant/blueredpink.html.

Pink and red diamonds are fairly rare colors, but have increased in numbers since the opening of the Argyle mine in Australia.  Pinks often have a purplish tint.  Like brown diamonds, these are colored by lamaelle of uncertain composition (the greater the number of lamaelle, the darker the color).   The composition of the coloring agent is probably very simular since diamonds have been found that have both pink and brown lamellae.3 The Argyle mine, famous for its pinks, also produces a large amount of "cognacs" and "champagnes."

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Orange

Overall, the most infrequently occuring color of fancy diamond is orange.  To be classified as orange, there must be a complete absence of brown to the stone.  This color of orange is called "apricot."  It is unknown what causes this coloration.  There are so few actual oranges, especially ones of known mine origin, that it is difficult to study.  The color was thought to be related to nitrogen inclusions, but this is unverified.3

Photo courtesy Howard Stroupe, http://www.duke.edu/ ~hls1/diamant/other.html.

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Yellow

Photo courtesy of Bijoux Extrodinaire

Sometimes the 'pure' diamond you have in your ring is not clear at all, but slightly yellow.  Slight yellow is almost considered a flaw, and often played down by yellow gold setting.  No setting could disguise the intense color of the above diamond, an intense yellow.  These deep yellows are much more rare than those masquerading as colorless.  Some shades of dark yellow are called "canary."  Most yellows are colored by molecules of nitrogen in the crystal lattice, though coloring through hydrogen is not uncommon. A fun fact about yellows: the largest cut diamond is the Golden Jubilee at 545.67 carats.3

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Green

Green was thought to be caused only by exposure to natural radiation in the diamond's host rock.  The radiation damages the crystal structure of the diamond, causing selective absorbtion.  The problem with green diamonds, and the reason that a good one is so expensive, is that the radiation usually does not effect the entire diamond.  It may be green only in patches or on the surface of the crystal.  Faceting a diamond that is only green on the surface just cuts off the green color.  That is why the Dresden Green is so special (see Famous Fancies) and the green diamond's exorbitant price mentioned above is justified.   However, recent research may yield other sources.  Very rarely, hydrogen may be the cause in some grayish-green stones.  There is also the special case of chameleon diamonds (see A Fancy Oddity). ³

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Blue

You may want to sit down.  There are not any 'don't knows' when it comes to blues.  Boron is often a coloring agent.  In the Argyle blues, which are usually gray-blue, the color is related to hydrogen.  More rarely nitrogen is involved.  When boron is the cause, the diamond is a semiconductor.  Other causes do not yield conductive diamonds.  Blues are also a very rare.  Don't miss the Hope Diamond, discussed below in Famous Fancies.3 Return to Table of Contents

Photo courtesy Howard Stroupe, http://www.duke.edu/ ~hls1/diamant/blueredpink.html.

Violet

There seem to be no actual purple stones.  No one has even discovered a way to make a purple diamond.  What is called violet and purple are extremely rare.  "Violets" from the Argyle mine actually look more grayish blue, and thought to be related to hydrogen.  The Argyle pinks usually have a purple flash that varies in intensity, but it is unknown what causes the purple.  The purple seems to be in no way related to the coloring lamaellae of the stone.  Sometimes synthetic pinks will be strongly tinged with purple, but I do not think they can be called actual purple.³

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Synthetic Coloring

Synthetic colored diamonds are made by introducing the same elements responsible for natural coloring.  This works well with some colors, like yellows, since yellows are colored by nitrogen and this gas is 80% composition of air.  Yellow synthetics could then be treated to make other colors.

Sometimes treatments induce the formation of the same defects that cause the color in natural gems.  The treatments are generally one or a mixture of surface coating (kind of like painting), irradiation, heat treatment (annealing), and pressure treatment.³  The diamond may have been a lighter shade of the desired, more intense color, or what is considered an undesirable color such as brown.  There is a high pressure and high heat (2000 deg. Celcius) method that turns brown diamond into a yellowish-green that looks very much like natural greens.⁶

Irradiation alone is also used to create greens and blues (usually a light blue) from browns.  Irradiation followed by annealing makes yellows, pinks, and oranges normally from pale yellow diamonds.³

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A Fancy Oddity: Chameleons

The top diamond, green, is this one under normal light.  The bottom, yellow, is the diamond after being stored in darkness for more than 24 hours.  The change back to green normally only takes a few minutes.  The strange property of these diamonds were discovered by accident, and originate from a small mine in China.  The price?  In 1999 when they were discovered, a 0.01 carat color-changer would cost $450 and up.  The largest stones (0.28-0.38 ct) would cost $1,850.⁷

Photo courtesy Howard Stroupe,
http://www.duke.edu/~hls1/diamant/yellowgreen.html
 
 

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Famous Fancies

Hope Diamond Information and image provided with the permission of the National Museum of Natural History, Smithsonian Institution, Washington DC, http://www.si.edu/resource/faq/nmnh/hope.htm

This is probably the most famous diamond in the world, and still very few people realize that it is blue.  The color is so deep on the Hope it is nearly opaque.  This results in a great dimishment of fire, the normal attractor of a diamond, but the Hope is valued because of its strong color, and its rich history. The Hope Diamond is thought to be what is left of the French Royal Blue, a massive gem that had belonged to several generations of French kings until its disappearance during the French revolution.  It was recut from an original triangular shape to disguise it, and eventually came to be called the Hope Diamond.  The Hope developed an association with bad luck when several of its owners came to bad ends (sudden death or bankruptcy).  It was purchased as a part of the estate of Evalyn Walsh McLean by Harry Winston after McLean's death, and donated to the Smitsonian in 1958.  Visit the Smithsonian for the whole story on the Hope Diamond and a picture of someone wearing the stone.  The Hope weighs 45.52 carats, think of that when you look at the picture.  It can help you estimate how big some of these other famous stones are.  The Hope is surrounded by sixteen small(er) colorless diamonds, and has 45 diamonds on its chain.

Dresden There are not many flattering pictures of the Dresden, but this is a good one.  You can actually tell that it is green!  Being photographed against a white background would wash out the colorless ones, but who cares?  We demand to see the green!  The Dresen is classified as an "apple-green" color and weighs in at 40.70 carats.  It was bought in 1741 by Frederick Augustus II, King of Saxony (Poland), and was probably from India.  It is set to be worn as a shoulder knot.  Originally, it was set in another shoulder knot, the Golden Fleece (see The Legendary Dresden Green Diamond for an artist's rendering of the previous setting).  After World War II, it was taken along with other items of historical significance by the Soviet Trophies Commission.  It was returned to Dresden in 1958, to be put back on display as it has been for nearly two hundred years.8

Photo courtesy Love Story Diamonds

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