Why Do Diamonds Come in Different Colors?

Posted on June 04, 2015 by Mary Hood | 0 Comments

Colored diamonds may occur naturally or through controlled irradiation treatment. 

While a pure, colorless diamond will always be classic, diamonds of various colors have certainly made their mark on jewelry trends and gem lore. The deep blue Hope Diamond is one of the most famous—and infamous—gems out there! And who could forget Jennifer Lopez’s stunning pink engagement ring?

J. Lo's gorgeous pink diamond engagement ring. Naturally occurring pink diamonds are rare and highly valuable.

Colored diamonds can occur naturally, but they can also be the result of lab irradiation (i.e. cooking the stones). If you’re in the market for a colored diamond, it’s important to know the difference between the two since the source of the stone’s color may affect its value.

Naturally Occurring Colored Diamonds

A pure, colorless diamond is crystal clear. When diamonds have a natural color, it means that the stone has lattice defects and impurities (this doesn’t mean that the stone can’t be beautiful, however). During a diamond’s growth, it may pick up concentrations of nitrogen, boron, and hydrogen. Each of these elements affect the resulting color of the diamond in different ways.

Nitrogen is the most common diamond impurity and is responsible for yellow and brown diamonds while traces of boron result in blue diamonds. Blue diamonds, along with pink and red diamonds are rare and therefore, more valuable. Additionally, the degree of color intensity also determines a stone’s value with more intensely colored stones commanding the highest prices. Be aware of brown diamonds being marketed as “chocolate diamonds.” These diamonds may be of very low quality.

The Gemological Institute of America (GIA) describes light yellow and brown diamonds as of “normal color range” while blue diamonds, or diamonds of another color, are “fancy colored” diamonds.

Black diamonds get their color from multiple inclusions (mostly from graphite and amorphous carbon) while their polycrystalline structure renders them opaque.

Custom Turquoise and Black Diamond Ring

Irradiated Colored Diamonds

When a stone is irradiated, it’s bombarded with neutrons and electrons that alter the stone’s crystal lattice, thereby modifying its as-grown color. Heating a stone (also known as annealing) results in further alterations to its color. Normally, this process is applied to diamonds with pre-existing impurities—usually yellow stones. Through irradiation, yellow stones may be used to create pink, purple, red, and green diamonds.

Smaller diamonds (or those under ½ carat) are typically easier to treat completely. In thicker stones, the center may not be completely reached. The preexisting saturation of the stone also affects the resulting color. Darker diamonds will result in a more intense color post-irradiation.

While treated colored diamonds can be worn daily, care should be taken when the stones are being serviced by a jeweler. High temperatures can make their color unstable. These stones should be set using safe “cold setting” methods.

It should be disclosed if a diamond has been color-treated. Often diamonds are color-treated to disguise impurities and make them more sellable.

Photos: Fancy Diamonds via Flickr, Breslauer & Warren

Posted in black diamonds, colored diamonds, diamonds, gemological institute of america, gems, gemstones, gia, informative

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