“G or H is not a color. Yellow, green, blue — [those] are colors,” a diamond industry professional once commented. And it’s true — these alphabetical or numerical allocations actually indicate the degree to which color is absent from diamonds.
When it comes to cutting colorless, near-colorless and slightly tinted diamonds, the focus is always on light performance — that is, reflecting as much light as possible back to the viewer. Our human eyes are attracted to symmetry, and that is why the symmetrical patterns of hearts and arrows in diamonds are so appealing. Precision cutting is therefore key to creating the best possible symmetry for so-called white diamonds.
For colored diamonds, however, the goal of the cut is to bring out the color as strongly as possible. Fancy shapes allow the cutter to do that geometrically: When the angles on the pavilion are lowered to around 35 degrees, the facets of the pavilion reflect the diamond’s girdle. Since the girdle in such a cut is wider than the depth of the diamond (culet to table), the volume of the stone is greater at the girdle, and the color therefore appears more intense. It’s like driving on a foggy day: If there are just some small fog patches, you can easily see through them, but if the fog is several kilometers thick, it appears more solid. The lower the volume, the more transparent it will look — and vice versa.
There is a strange phenomenon in fancy yellow diamonds. If the color is not intense, one runs the risk of “lightening” the diamond by sawing it. This actually used to be the custom back when cutters wanted to get rid of color in diamonds. With large yellow stones, they would saw off the six points of an octahedron or dodecahedron, then bisect the remaining center cube into two parts for a total of eight lighter-colored diamonds. Today we would never dream of taking a 100-carat yellow diamond and sawing it into smaller stones; we would avoid sawing it altogether, and cut just a single diamond from it. While doing so entails substantial weight loss, it offers better color optimization.
The best diamond shapes for optimizing color include cushion, oval, radiant, pear, heart, marquise and princess. A classic example is the 132.55-carat Golden Empress, a cushion-cut, fancy intense yellow diamond that Graff Diamonds unveiled in 2015. It came from a 299-carat rough diamond recovered at the Letšeng mine in Lesotho, and its girdle facets can be clearly seen in the pavilion.
Sometimes, a diamond turns out to have other colorful surprises. I once cut a block-shaped, 100-carat brown diamond from Mato Grosso province in Brazil. The diamond had black inclusions in several places, but it did show promise, as there were some clean zones. As I worked on the diamond after sawing, it seemed to lose some of its brown color along with most of the black inclusions, and a hint of pink became noticeable. The final results blew us away: It yielded two pear shapes, both natural fancy pink — one a 7.42-carat, internally flawless stone, and the other a 16.57-carat diamond with SI2 clarity.
Then there are the intense and vivid specimens for which there is no need to induce more color. Such was the case with the impressive Oppenheimer Blue, a 14.62-carat, fancy vivid blue diamond. These outstanding stones can be cut into any shape for maximum light return, so cutters can focus on optimizing weight and value without worrying about the color.
Which cut do I personally prefer for colored diamonds? I’m partial to square cushions, because the even distribution of girdle reflection in the pavilion means these cuts also boast an even distribution of color. That and their soft, flowing lines make cushions a favorite of mine.
Mike Botha is one of the foremost authorities on diamond design, cutting and polishing in North America.
Image: one of the largest and rarest fancy intense yellow diamonds in the world, the Golden EmpressArticle from the Rapaport Magazine - September 2017. To subscribe click here.