Understanding Blue Diamonds

One of the rarest colors of diamond, blue also ranks among the most desired. Like the famous Hope Diamond, these blue gems will make stunning showcase stones in any jewelry piece. However, most blue diamonds exhibit grey hues and can never reach the saturation of top-grade blue sapphires. While the high price of naturally beautiful blue diamonds continues to rise, treated and created gems give buyers an affordable alternative to these collector's pieces. Most gem enthusiasts understand the four Cs of colorless diamonds, but the quality factors for fancy colored blue diamonds remain less familiar. Our blue diamond buying guide will help consumers understand them.

Fancy Colored Blue Diamond Buying and the Four Cs

The IGS colored diamond value listing has price guidelines for irradiated blue diamonds.

Color

Unlike colorless diamonds, where cut ranks above color, clarity, and carat, a fancy colored blue diamond's value comes primarily from its color. Hue, tone, and saturation are the three constituent components of gemstone color.

For a fancy colored blue diamond, the primary hue is blue. Green or, more rarely, purple secondary hues may be present. While neither is desirable, gems with greenish hues hold more value than those with a slight purple color. Still, greenish blue diamonds make lovely jewelry stones at a discount from pure blue prices.

When assessing the value of a fancy colored blue diamond, tone has somewhat less importance than hue and saturation. Neither very light nor very dark gems command high prices, since they render the blue hue difficult to discern. However, a wide range of tones in between can make excellent gemstones.

Very rare, highly saturated untreated fancy colored blue diamonds will fetch a good price. Most blue diamonds exhibit low saturation and appear greyish blue.

What Makes Color "Fancy?"

The Gemological Institute of America (GIA) grades fancy diamonds as Faint, Very Light, Light, Fancy Light, Fancy, Fancy Dark, Fancy Deep, Fancy Intense, or Fancy Vivid. These designations result from assessing the gem's tone and saturation. The GIA's colored diamond color reference chart shows examples of these designations.

Due to the extreme rarity of blue diamonds, gem graders rate nearly any diamond with a blue hue as Fancy Light or better. Most blue diamonds are very grey with a tint of blue, or "steely." Then, as tone darkens, greyish gems go from Fancy Light to Fancy or Fancy Dark.

As saturation increases, blue diamond ratings go from Fancy to Fancy Intense and Fancy Vivid. Gems with medium to high saturation and darker tones are Fancy Deep. Blue hues reach the highest saturation at medium to dark tones. As a result, on the GIA grading scale, the darkest fancy vivid diamonds and the most highly saturated fancy deep ones have the optimal tone and saturation for blue stones.

Clarity

Given the extreme rarity of natural blue diamonds, even high-quality specimens often contain inclusions. Although inclusions that detract from a gem's beauty or transparency will lower its value, small inclusions won't greatly affect clarity grading.

Cut

While cut ranks as the most important value factor for colorless diamonds, even blue diamonds with a poor cut hold significant value. In rare and natural gems, cuts may be somewhat asymmetrical or have large windows. Most importantly, blue diamonds should receive cuts that bring out their color. While brilliant cuts are standard for colorless diamonds because they enhance brilliance, they can detract from color.

Carat

Again, natural blue diamonds are extremely rare. Thus, their price per carat rises rapidly for stones of larger sizes. A one carat natural gem with good color will sell for six figures.

Treated Blue Diamonds

Some diamonds undergo irradiation or both irradiation and heat treatment to obtain a blue color. These are much less expensive than their untreated counterparts and usually exhibit high saturation. Because these radiation and heat treatments are permanent, no additional care is necessary.

Some diamonds may be coated with a blue substance to enhance their color. This coating can wear off with time and, as a result, will require extra care.

To improve clarity, some diamonds receive laser treatments to remove unattractive inclusions. In addition, diamonds with fractures may have fillings to obscure the cracks.

Gemological laboratory reports will always note these as well as other gem enhancements.

Synthetic Blue Diamonds

Laboratories can create blue diamonds. This is a great option for buyers on a budget or for those who prefer synthetic gems for ethical reasons.

Addison Rice

A geologist, environmental engineer and Caltech graduate, Addison's interest in the mesmerizing and beautiful results of earth's geological processes began in her elementary school's environmental club. When she isn't writing about gems and minerals, Addison spends winters studying ancient climates in Iceland and summers hiking the Colorado Rockies.

View All Articles

Previous Lesson

Understanding Yellow Diamonds

Go to PREVIOUS Lesson

Next Lesson

Understanding Black Diamonds

Go to NEXT Lesson