Diamond colors

High Pressure/High Temperature (HPHT) equipment 
from  Sundance to change diamond colors.

A Diamond colors Phenomenon

By Diana Jarrett Posted: 4/7/2006 2:29 PM found at http://www.diamonds.net/

A phenomenal gemstone exhibits unusual optical characteristics naturally, without laboratory enhancement. The mineral world is full of such examples, and not all of them are rare. In the case of phenomenal diamonds — known in the trade as “chameleons” — certain natural green diamonds react to heat or dark storage by temporarily changing color, often becoming bright yellow. This color change is short-lived as the diamond soon reverts to its stable color. Most specimens observed in gem laboratories show even color distribution, aiding in the dramatic transformation, and both color changes are documented on laboratory reports. Faceted chameleon diamonds of 2 carats or more occasionally appear on the market; the more sizable stones offer the maximum opportunity to see color change.

A phenomenal color-change diamond is such a rare and curious gem that very little has been written on the subject. The first documented report on chameleons appeared in 1943, according to the GIA Diamond Dictionary. It’s no wonder then that, some 35 years ago, while working at Lazare Kaplan, Peter Kaplan, Peter K. Kaplan Inc., was astonished to witness a diamond change color on the very hot polishing wheel. The peculiar diamond was later graded light yellow green. It sold, but the baffled customer promptly returned it for a refund when the yellow-green diamond changed to dark green after storage in a jewel box.

HOW IT OCCURS
An article in Gems & Gemology, Spring 2005, acknowledged that “...the mechanism behind chameleon coloration is not yet well understood. Nevertheless, chameleons are among the few green diamonds that can be conclusively identified as natural color, since their behavior cannot be created or enhanced in a laboratory.”

Fine-quality phenomenal diamonds often carry certificates verifying their natural characteristics. One such report by Gübelin Gem Lab, Lucerne, Switzerland, added, “Chameleon diamonds are one of the great mysteries of the diamond world. It is still not known why these diamonds change from deep green to yellow when heated or left in darkness . . . these qualities make ‘chameleons’ among the most fascinating of colored diamonds.”

Online jeweler Ariel Friedman of IceStore Inc., Beverly Hills, California, www.icestore.com, speculates that a combination of their phosphorescence and fluorescent properties contribute to the chameleon effect in these special diamonds. Friedman estimates that he sells between five and ten chameleons a year, attributing that success to his customers, who only buy high-end goods. Recently, one of his best phenomenal diamonds went to a well-known actor who desired a one-of-a-kind gem. Friedman’s clientele understands fancy color diamonds and that “with chameleons, they own something clearly unique among the fancy colors.” A 2.95-carat, round brilliant chameleon is offered on his website for $63,720.

A rare subset of natural fancy color diamonds, chameleons are so named for their repeatable color-change property. Prolonged dark storage, or photochroism, changes a “Classic” chameleon from its typically stable color of grayish-yellow-green to a temporary or unstable color of greenish-orangish-yellow. A few hours of dark storage might be all that is needed to bring on a color change. Also, heating a Classic chameleon, termed thermochromism, likewise results in a prominent temporary color change. At about 150º C, the induced color should be evident within a few seconds. The term “Reverse” chameleon refers to phenomenal diamonds that change from yellow in stable conditions to green after subjection to dark storage. Heating does not produce a color change in Reverse chameleons. With both groups, the change is infinitely repeatable.

Rarer still are some “maverick” color-change diamonds that have been found in Australia that exhibit this phenomenon with their own unique pair of colors. Australia’s Argyle diamond mine, famous for its fancy color diamonds, occasionally produces hydrogen-rich diamonds that also exhibit a “chameleonlike” color-change behavior. The stones are distinguished by either a blue-violet-gray color or a gray-olive color. They are thought to owe their phenomenon to high hydrogen content, but this has yet to be proven.

PHYSICAL ATTRIBUTES
The quickest way to identify a suspected green diamond of being a chameleon would be by heating and observation. Heating an enhanced diamond, however, might lead to an unwanted permanent modification of color. If one is leery that the green diamond might just be an enhanced stone, the recommended course of action would be to send it to a laboratory for testing. In a laboratory, the spectroscope reading, coupled with an ultraviolet (UV) radiation reaction, will positively separate a chameleon from another type of green diamond.

In an era fascinated with color diamonds, the chameleon holds unparalleled attributes. It is, in fact, the rarest of the color diamonds, with a characteristic that jewelry lovers never dreamed of. One has to wonder how many chameleon diamonds have, in the past, slipped thorough a merchant’s hand, dismissed as merely an odd-color diamond. David Berck of Lussori Jewelers, Carmel, California, offers chameleon diamond jewelry to his clientele, and affirms their rarity. “Many jewelers will go through their entire lifetime without ever seeing a chameleon diamond.”

Until recently, the appeal of the elusive chameleon diamond was for the most part limited to the connoisseur. For that reason, Christie’s New York finds it best to auction color-change diamonds in Hong Kong, because, according to Daphne Lingon, senior vice president, jewelry department, the Asian market is well-informed about phenomenal gems,which are avidly collected. During Christie’s Magnificent Jewellery & Jadeite Jewellery Hong Kong auction in May 2001, a platinum ring featuring a 4.41-carat “superb fancy dark-gray-yellowish-green chameleon diamond” went on the block. When the hammer came down for the last time, the chameleon ring fetched a stellar 1,915,000 Hong Kong dollars, roughly $240,000.

MARKETABILITY
Years ago, phenomenal diamonds were hidden and kept unmounted so collectors could enjoy conducting their own experiments. That, of course, contributed to the lack of familiarity within the A diamond world about this oddity. Understanding this situation gives rise to the quandary of how to properly value these gems, and that, in turn, stymies an appraiser who takes on the arduous task of researching phenomenal diamonds. Nevertheless, collectors appreciate the difficulty involved in establishing a value on a gem without peer.

Over the years, celebrities seen on the red carpet wearing naturally colored diamonds have fueled interest in color diamonds in general. Few diamond admirers, however, can afford these gems in large carats; add the phenomenon of color change to the equation and the list dwindles to a handful. Still, imaginative designers recognize the potential of featuring chameleon diamonds in luxury goods. It’s not uncommon for a designer to place great emphasis on creating the ideal presentation for a color-change diamond.

Originally setting a chameleon in an intricate mounting called “Guyana,” designer Hanan Savransky of Savransky Jewelry Designs, Ramat Gan, Israel, rethought the presentation of the stunning stone. He remounted the 1.51-carat oval, light green to light yellow diamond into his classically tailored “Isabella” setting, for $45,500, where the stone now takes center stage.

Should color-change diamonds become more readily understood and available, they’re destined to earn the following they deserve here and abroad. Knowing that rare naturally colored diamonds can manifest two prominent colors in a repeatable state is certain to beguile the most jaded jewelry collector.