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Pink Scare

The company name is Serenity Technologies, but its new thin-film diamond coatings have hardly brought peace of mind to the jewelry industry.

To the contrary, the gemological grapevine is all aquiver with rumors about undetected pink diamonds that owe their color to a new coating process, similar to that which tints lenses. This new coating turns pale pink diamonds into blushing beauties. Consequently, "fancy light" pink diamonds were elevated to "fancy" and even "fancy vivid." Or so the rumors go. Of course, these are unconfirmed rumors.

But, and this is a big but, such tales could be true if some gemologist didn't do what is now called "due diligence." If you don't know to look for coating, you might not see it.

"Should a gemologist rely on spectroscopy when testing a stone's color origins, and forget microscopy [examination under a microscope], he could miss the coating," says Branko Deljanin, head of research at European Gemological Laboratory in Vancouver, Canada, a member of EGL USA Group, which joined forces with EGL's lab in New York to study coated diamonds. That's because the absorption lines (visible spectra) for the new pink color coating and natural pink diamonds are so close, they could be seen as one and the same. Under a microscope, however, tell-tale clues abound. Among them: uneven color, lack of color on some spots under methylene iodide, and an absence of the graining associated with pink diamonds.

Both EGL and GIA have published in-depth papers on the new coating process, which their tests show is more durable than past coatings—but still no match for boiling in sulfuric and other acids, temperatures between 800 and 1000ºC, or rub-a-dub-dubs with sandpaper.

The trouble is, those durability tests are rather extreme and considerably beyond the gamut of normal threats. Under the more routine rigors of ultrasonic, steam cleaning, nearness to a torch, and rhodium plating, EGL found the coating proved stable.

You heard right: Treatment stability tests that simulate conditions in a jewelry repair shop showed the new coating pretty abuse-resistant, except when exposed to high temperatures.

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purple-pink coated diamond
Face up: A 4.02 carat purple-pink coated diamond.
diamond under microscopic testing
EGL USA reports that in some coated cases, under standard microscopic tests, the body color was found to be uneven on both the crown and pavilion, and a few diamonds exhibited a lack of color in nicks on facet junctions.
diamond lost color from coating substance
EGL USA found that at higher temperatures of 900 to 1200ºC, the color was lost from the coating substance.
pink diamond
Surface treated: A 0.52 carat coated pink diamond.
two coated diamonds before boiling in sulfuric acid
Two coated diamonds before (ABOVE) and after (BELOW) boiling in sulfuric acid. All the coated diamonds reverted to their presumed original light brown color after being boiled for a few minutes, reports EGL USA.
two diamonds after boiling in sulfuric acid