August 2004 Diamonds/Gemology Getting to the Green This diamond's true color hides inside rough that offers no clues If diamond connoisseurs judged all diamonds by their rough surface, a green diamond’s beauty would rarely see the light of day. Its verdant glory is often concealed beneath a rugged and dreary exterior. In addition, polishing often rids a green diamond of its body color, says Alan Bronstein of Aurora Gems, New York City, a renowned collector of colored diamonds. Recently, however, Bronstein hit the jackpot when he acquired a superb green diamond from Guyana that’s destined for his noted Aurora Collection of fancy vivid colored diamonds. Passengers on a Bus While all diamond crystals are formed about 124 miles below the earth’s surface under intense heat and pressure, it’s what happens to the crystals as they subsequently are transported up a geological structure called a kimberlite pipe that matters most. Some of these diamond “passengers” get off at different depths, where they are exposed to other elements in the earth. Natural-color green diamonds owe their color to basking in the presence of radioactive elements. “Not too close, though, or they get burned throughout,” says Bronstein. But if it’s close enough, the diamond’s color turns intense green, like Bronstein’s new one. Even when a rough diamond crystal can be discerned as green, there’s a question of whether the color is more than skin-deep. “It’s like a scratch lottery because so many diamonds that look like this turn out to be worthless,” he says. “The cutter has to take great care to reveal – one step at a time – the colors that lie beneath.” Peeling Back Layers To determine whether a crystal is potentially a rare green, a tiny window is polished into the diamond’s skin. “This offers a clue, but you still can’t predict the outcome,” he says. For example, when a miner brought this diamond to his office for examination as a 0.97-ct. rough, Bronstein thought he saw a bluish color when he looked at a window polished in its skin. The green was revealed as material was slowly peeled away in the cutting process. “We had to nurture it through each cutting stage (a year-long process), obtaining laboratory certificates each step of the way,” says Bronstein. “It was necessary to do this to ensure the color was determinable as natural.” To the expert’s relief, this green stayed green. – by Robert Weldon, G.G. A saturated green diamond (right) new to the Aurora Collection weighs 0.62 carat. It was cut from a rough crystal similar to the one shown at left. The finished diamond includes a natural (a small part of the original crystal skin) at top right, hence the irregular outline. Naturals serve as further testament to a diamond’s natural origin, as a signature of the cutter and as a way to preserve weight. With extremely rare colors, such as this one, every point could be worth tens of thousands of dollars. Photo by Robert Weldon.