Thanks for the info Gav. Whilst it can be proven that a green diamond has been treated, it is by no means foolproof as the indicator lines suggesting irradiation may not be present. I'll detail below extracts from documents confirming that to be the case. However, more importantly, please can you answer the item in bold below:
You haven't confirmed your earlier statement where you said "When enhanced gems are undetectable, some companies will market them as natural" - that is a pretty bold statement to make .......... as I asked earlier, please can you quantify exactly who you are referring to please? This is extremely important to gem buyers and would be of great interest to the posters on this forum I'd think.
Green diamond certification:
"Gem diamonds have been irradiated on a commercial basis (sometimes followed by moderate-temperature heating), to produce a range of colors (green, blue, yellow, pink, red) since the 1950s. These treated-color diamonds can often be detected by induced color concentrations that lie just beneath the facet surfaces, unusual ultraviolet fluorescence reactions and by diagnostic features seen in their absorption spectra. However, it is sometimes impossible to distinguish green and blue diamonds subjected to laboratory irradiation from those subjected to natural radiation exposure."
Identifying synthetic and treated gem diamonds
James E. Shigley, GIA Research, Gemological Institute of America
Irradiated Diamonds:
Prior to annealing, nearly all irradiated diamonds possess a characteristic absorption spectrum consisting of a fine line known as the GR1 line and an associated broad band. This is usually considered a strong indication of treatment. Subsequent annealing usually destroys this line, but may create several new ones; the most persistent of these is at 594 nm. If, however, an irradiated diamond is annealed above 1000°C, the 594 nm line is also destroyed, but leaves two new lines at 1936 and 2024 nm in the infrared. These lines are detected using spectrophotometers: the lines are best detected when the stone is cooled to very low temperatures (below -180°C).
It should be noted that some irradiated diamonds are natural. One famous example is the Dresden Green Diamond. Naturally irradiated diamonds also possess the GR1 line.
International Diamond Laboratories
No fancy color diamond collection is complete without a green stone. But since, next to red, green is probably the rarest of all natural diamond hues, most collections lack representation from the green portion of the diamond rainbow. Even when they do contain greens, the stones’ color is usually not a bona fide natural one—or at least not classified as such by a gem lab of stature.
Needless to say, this is a rather frustrating situation for connoisseurs. And it arises out of the highly ironic fact that green, while among the rarest of natural diamond colors, is the commonest of artificial ones—easily induced by alpha, electron, gamma and neutron irradiation. Yet connoisseurs spurn stones with lab-contrived color, instead dreaming of some day owning a green diamond with incontestably natural color.
As things stand, that’s dreaming a nearly impossible dream. Since 1985, only a very few diamonds with color certified as being of natural origin have been sold at auction.
In the past, labs were loath to validate green in diamonds as natural unless stones showed what was once thought to be a telltale indicator of natural color origin: tiny circular green and/or brown stains seen with magnification on the unpolished surfaces, called naturals, of finished stones. For instance, the 3.02-carat stone just referred to had such stains (in a girdle fracture) and was accompanied by an April 1985 GIA report with the following comment: “Color and characteristics of this stone suggest natural color.”
Today, however, the same evidence of natural color origin would probably not be enough to merit a green diamond a comment this affirmative from GIA. Diamond graders there say that about the best such a stone can hope for at present from the school’s trade labs is to have its color origin classified as “undetermined.” While such wording may smack of fence-sitting, it is understandable since GIA feels that definitive proof—not merely educated opinion—is expected of it when making complicated color origin calls. Definite proof may be years away. In its absence, colored diamond experts think that both the gemological and connoisseur worlds must learn to live with educated opinion.
Unlike other natural colored diamonds, the cause of color in green stones is thought to result from natural irradiation in the earth—most likely after the stones’ formation. According to current diamond color theory, some time in a diamond’s history it comes into contact with a mineral (e.g., pitchblende) containing radioactive elements such as uranium whose high-energy particles create defects in the stone’s atomic structure.
These radiation-induced defects are, in turn, responsible for the absorption of wavelengths of red light by the diamond that result in the transmission of a complementary green color to the eye. During an examination of Germany’s famous 41-carat-plus Dresden diamond—to natural green diamonds what the Hope diamond is to natural blues—a team of three gemologists found that spectroscopic analysis of the diamond confirmed this explanation of green diamond color chemistry.
Irradiation (coupled with heating) can produce colors such as yellow and brown that often look identical to hues produced by nature. Fortunately, these treated colors betray their lab origin by showing absorption lines that are uncharacteristic of stones with natural colors. The reason for the different spectroscope readings between other-than-green natural and treated diamonds is their different color genesis. Excepting green, natural color stems from entrapment of impurity atoms (usually nitrogen) or crystal lattice damage during the creation process while treated color results from irradiation and subsequent heating after a diamond is formed.
On the other hand, nearly all green diamonds—natural or treated—own their color to irradiation (and, to a lesser extent, fluorescence). So whether stones are colored in the earth or in, say, a gamma cell, they will often show the same wavelength absorption lines. This doesn’t mean that experts can’t ever tell apart lab- from ground-greened diamonds. But even when they can, the job is never easy.
Article in Modern Jeweler
