Orange Diamond Buying Guide – Orange Diamond or White Whale?
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Though orange diamonds and yellow diamonds can claim similar causes of color, orange diamonds are rarer than yellows. Since orange is between the colors red and yellow on the color wheel, natural orange diamonds range from orangey-red diamonds to yellowish-orange diamonds. Modifying hues for orange diamonds include red, pink, purple, and yellow in natural stones, and although orange is not one of the rarest colors to be found it is amazingly rare to find a natural orange diamond that lacks a modifying color. A pure orange diamond is among the rarest stones in existence and highly sought after by investors and collectors.
What is an Orange Diamond?
Treated orange diamonds are colorless diamonds that have been sent to a lab to be subjected to a chemical process (HPHT) so that the color of the surface of the diamond artificially changes to orange while its interior remains colorless. If you insist on purchasing a rare and natural orange diamond it is paramount to buy one which has been graded by a reputable gemological laboratory that can determine the origin of color.
Pure orange natural diamonds are so rare that supply cannot reach the demand for them throughout the world. Synthetic gem-quality diamonds have been commercially available in the market since the mid-1990s. General Electric developed the first high-pressure, high-temperature (HPHT) chamber in 1955, but it was not until the 1990s that these stones were being created at a rate and a quality that would go on to greatly affect the jewelry industry.
Today it is possible to create a gem-quality diamond that displays the same color as a natural orange diamond material. The HPHT process may result in an orangy-yellow, yellow-orange, or unmodified orange, while the CVD (Chemical Vapor Deposition) process may result in a pinkish-orange stone or orangey-brown.
With the rapid growth of the synthetic diamond industry over the past few years, experimentation in that sector has yielded the creation of vivid pinkish-orange color by using post-growth irradiation and annealing in a CVD created diamond. Annealing is the process of heating and cooling a diamond. When annealing is used in addition to irradiation the result can be an orange diamond.
Cause of Color
Orange diamonds owe their color to nitrogen impurities that are incorporated in the diamond lattice during growth deep in the earth. Nitrogen is the most common impurity seen in diamonds due to its abundance in the growth environment deep underground. Ninety-eight percent of natural gem-quality diamonds are type 1a, meaning that they contain concentrations of nitrogen impurities. Diamond types act to scientifically classify them by the type of chemical impurities found within them at an atomic level. Unlike inclusions, diamond types can only be determined by the use of highly advanced testing equipment such as an infrared spectrometer.
Yellow diamonds also owe their color to nitrogen impurities and the line which divides an orange bodycolor from a yellow one is extremely thin. Body colors in diamonds are produced by an arrangement of transmitted visible light over a certain wavelength. Yellow body color is observed when the nitrogen absorptions are found at wavelengths less than ~510 nm, and orange body color is seen when those absorptions extend to ~600 nm. However, it is important to note that when defects reach certain concentrations the absorption band can shift in wavelength location, meaning it is possible to view a yellow body color that displays an absorption band at ~600 nm.
One of the most interesting causes of color in orange diamonds that lack a modifying color and is responsible for the majority of these amazingly rare natural orange diamonds is the 480 nm visible absorption band. Aside from being present in 86% of natural pure orange diamonds, the presence of this band also contributes to thermochromic properties. The color is affected by temperature changes. When a diamond with this feature is heated to 400° – 500° C, the absorption band expands and creates a temporary color shift to more orangey hues. This effect can also be seen in chameleon diamonds which always exhibit the same 480 nm absorption band.
High concentrations of c-centers within the molecular structure can result in orangey elements to the diamond hue. The only other cause of orange color in natural diamonds is the H3 defect when combined with plastic deformation-related defects such as the 550 nm absorption band. The H3 is an uncharged defect made up of two nitrogen atoms adjacent to a vacancy in the diamond lattice with a ZPL at 503.2 nm. This combination produces orangey-yellow to orange colors.
The Gemological Institute of America (GIA) classifies natural orange diamonds in the following grades: faint orange, very light orange, light orange, fancy light orange, fancy orange, fancy intense orange, fancy vivid orange, and fancy deep orange. Fancy vivid & fancy deep are the most desirable grades attracting the highest price points. The GIA estimates that the presence of pure, unmodified orange diamonds in existence makes up 0.05% of all-natural fancy color diamonds.
The largest orange sold at auction was named “The Orange,” a fancy vivid orange diamond weighing 14.82 carats. “The Orange” sold in 2013 for $35.5 million, which is just under $2.4 million per carat, a record-breaker at the time. Another important mention is the “Pumpkin,” a 5.54-carat fancy vivid orange diamond that came from South Africa and was sold the day before Halloween in 1997 for $1.3 million.
Orange diamonds, whether pure or modified, are found in the mines of South Africa and Australia. The “Pumpkin” diamond was sold by a farmer which led many to believe that it was found from an alluvial deposit. The famous Argyle mine in Australia will have one more collection produced from its final year of operation in 2021. The Argyle consistently provided rich pinks with orange modifiers to the market for years.