Jewel of the Month

Diamonds may be called “ice,” but the vast majority look more like pieces of a rainbow than chips of frozen rain. Although most contain only slight traces of color—usually yellows, browns, or grays—diamonds span a wide range of hues, varying in intensity from faintly tinted to extremely saturated and from very light to deep dark—even black.

Generally, the more saturated the color, the more valuable the stone. Yellow is the most prevalent diamond hue, and stones with enough yellow body color to be considered pretty by consumers are called “fancies” by diamond merchants and graded “fancy” by the leading gem labs.

History and romance. The most famous colored diamonds are the blue Hope, the Dresden Green, the black Orloff, and the yellow Tiffany, but colored diamonds lack the rich history and lore associated with colorless diamonds. Colored diamonds often were thought to be other gems, such as sapphire or citrine.

The largest of all the fancy yellows is the Tiffany diamond, discovered in the late 1800s as a 287-ct. rough yellow crystal. George Kunz, Tiffany & Co.’s young gemologist, fashioned it into a 128-ct. cushion brilliant. It’s on display at Tiffany’s flagship store in New York.

Color variations. The many variations of yellow have given rise to descriptive terminology that would do the Lands’ End catalog proud. Terms include buttercup, daffodil, dandelion, goldenrod, sunflower, banana, lemon, straw, butter, wine, and, most notably, canary. (The yellow Harz Roller breed of canaries is what most people would consider to be the classic color model for a true canary diamond.) Use of such easily recognized descriptive names has been traced back hundreds of years in the diamond literature. They make wonderful communication tools to characterize the unique beauty of these gems.

Qualities. Purity of color is the most critical quality to consider. The more pure yellow a diamond’s hue—without modifiers of brown, green, or orange—the more value increases. Intensity of color is also important.

The grade “fancy” begins after grade Z on the Gemological Institute of America’s alphabetical color-grading scale. As saturation of hue increases beyond fancy, the grades “intense” and “vivid” are used. Vivid, the highest grade, indicates that the color is highly saturated and extremely bright. Color that’s saturated but lower in tone receives a call of “fancy deep.” Some very intensely saturated yellow diamonds have earned the name “canary,” and now, after years of study, we have a specific gemological definition: A true canary yellow diamond is one whose yellow body color can be described as intense to vivid and can be modified with green or orange in bright or deep tones. This characteristic color results from isolated nitrogen atoms. Therefore, a standard hand-held spectroscope does not reveal the absorption lines you would expect to see in a typical “cape” yellow diamond.

Fluorescence under longwave ultraviolet can be negligible, but some canaries show strong yellow or orange fluorescence, which helps create the illusion of a glow when the stone is viewed in daylight.

Value. Color is the most important value factor of a colored diamond. Clarity has less effect on value, since inclusions in colored gems can be hidden more easily than those in colorless gems.

Cut can affect the face-up appearance of color. If a gem has been cut for greater brilliance, the color may appear washed out. When a diamond is cut to decrease brilliance, color (i.e., saturation) may be enhanced. Henry Grossbard of the Radiant Cut Diamond Corp., the designer of the Radiant cut, enhanced the color of some diamonds by recutting. Grossbard took cape yellow emerald-cut and old mine-cut diamonds and recut them into Radiants, which improved the intensity of color in the face-up position. He was able to transform many S, T, U, and other “lower cape” colors into fancy yellow Radiant cuts.

Pricing. According to The Guide, November/December 1999, for “fancy yellows” of VS to SI clarity, melee prices range from $400-$1,000 per carat to $350-$900 per carat. Quarter-carats in the VS to SI range are priced between $900-$2,500 per carat and $800-$1,800 per carat. Half-caraters range in price from $1,900-$3,300 per carat to $1,600-$2,500 per carat.

“Fancy intense yellows” are priced higher: In melee, they range from $500-$1,400 per carat to $450-$1,100 per carat; in quarter-carat sizes, from $1,500-$3,500 per carat to $1,200-$2,300 per carat; and in half-carat sizes, from $3,000-$5,000 per carat to $2,500-$3,500 per carat. Prices quoted are for square and rectangular Radiant cuts. For emerald cuts, add 35% to 50%. For marquises, pears, and ovals, add 50%. For rounds multiply by 2.0 to 2.5. The price of vivid yellows is calculated by adding 50% to 100% to the per-carat price.

Enhancement disclosure. The color of yellow diamonds can be enhanced through electron bombardment (a safe and easy process) and subsequent heat treatment. The electrons push nitrogen atoms and radiation defects together, creating stronger color centers and producing a greenish colored diamond that is then heated to create a stable and pleasing yellow color. It would be prudent to have all fancy yellow diamonds examined by a qualified gem lab to determine the origin of color.

Care and cleaning. Fancy yellow diamonds require the same care as other diamonds. The stones can withstand high temperatures during repair, but because of their rarity and the difficulty in replacing them, reasonable caution is advised.

Bench settings and precautions. Yellow diamonds usually are no more strained than colorless diamonds, so any number of settings can be designed. Closed-back styles are most likely to enhance the richness of the gem’s color.

Recommended reading. For more information, see the following:

Stephen C. Hofer, Collecting and Classifying Coloured Diamonds (Ashland Press, New York, 1998).

John King, Thomas Moses, James Shigley, and Yan Liu, “Color Grading Colored Diamonds,” Gems & Gemology, Winter 1994, pp. 220-242.