We previously wrote an article entitled Was Your Diamond Mined? or Did it Come from a Lab?. The article focused on using FT-IR spectroscopy in order to identify synthetic and treated diamonds — one of the major challenges for the gem industry. That article spurred some discussion in a networking group. One member of the group explained that she had some stones that tested positive for diamond on some machines and tanzanite on the others, but those doing the testing did not think the stones were real. Although the mystery stones tested positive for diamond, the color was wrong for a diamond. Are the labs wrong? Antoinette Matlins, an internationally respected gem and jewelry expert, explained:
When it comes to the color of diamonds, about the ONLY thing the labs cannot always identify is the origin of the GREEN color in diamonds. This is because … natural green diamonds obtain their green body color as a result of exposure to irradiation in the earth, eons ago, while one can also irradiate an off-color diamond to “create” a green diamond today. As a result, in many cases the labs cannot identify the origin of color. In some stones, however, there are indicators of natural origin (rust stains, for example) which do not occur in diamonds that are irradiated today to create a green color. And there are also some characteristics that occur ONLY in green diamonds where the color is the result of man-induced irradiation. Thus, we have a situation where we can tell definitively that the color of a particular green IS natural; others where there is insufficient data provided by the diamond to be able to say whether natural color or the result of man-induced irradiation; and then those that we can definitively identify as green due to man-induced “irradiation.”
Other diamonds obtain their color either by the presence of “trace elements” (ie, boron = blue diamonds; nitrogen = yellow and so on) OR by defects in the crystal lattice, as is the case with “type II” diamonds — the more “perfect” the diamond structure of a type IIa, the more colorless the stone, or in very rare cases, the purer the PINK, while the more deformed the crystalline structure, the more brownish; in type IIb diamonds, the more perfect the structure, the purer the “BLUE” color, the more deformed, the more brownish the color. Whether type IIa or IIb, if the crystal structure is extremely deformed, the diamond will appear brown. The reason brown type II diamonds are now more and more rare is that these diamonds respond very well to high pressure/high temperature annealing techniques to “fix the deformity” and the more the treatment can correct the deformity, the whiter, pinker or bluer the diamond (depending on whether it’s a type IIa or IIb).
But green diamonds can definitely pose a problem…which is why it is so rare to get a lab-report on a green diamond that indicates natural color!
I want to thank Antoinette for giving us permission to publish her explanation and we have invited her to publish more information on this blog. In addition to being a gem expert, she is also an author and lecturer whose expertise is sought worldwide by clients who retain her to seek fine, rare, or unusual gems and jewels for acquisition. We welcome hearing more.