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GIA Spots Lab-Grown Ruby Layer on Natural Stones

Mar 19, 2018 7:42 AM   By Rapaport News
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Attempts to upgrade the size and color of gemstones using a layer of synthetic material have been around for decades, but signs indicate the techniques are changing.

The Gemological Institute of America (GIA) recently received two loose, oval-shaped, mixed-cut, red stones at its New York laboratory. On further inspection, they turned out to be natural sapphires with a synthetic ruby “overgrowth” — a cover of lab-grown stone that tinted the entire gems red, GIA staff gemologists Tyler Smith and Hollie McBride wrote in the Winter 2017 edition of the institute’s journal, Gems & Gemology.

The stones had a strong concentration of reddishness at the junctions of their facets. To the naked eye, this appeared to come from a treatment called chromium diffusion, in which someone adds extra chromium — the chemical element that gives ruby its distinctive color — to make the gem redder.

However, examinations under a microscope revealed the presence of the overgrowth, and showed that the main part of the stones was, in fact, natural, almost-colorless sapphire. In addition, the presence of platinum was consistent with previous cases of synthetic ruby overgrowths.

The stones had certain visual features that resembled those with coatings created using a technique known as “Lechleitner” — named for its pioneer, Johann Lechleitner — in which a synthetic emerald overgrowth gives greenness to a near-colorless beryl. (By chance, the GIA’s Carlsbad lab received one of those stones for identification at around the same time the red stones arrived at the New York branch.)

Lechleitner, who was active in Austria in the 1960s, also experimented with ruby overgrowths. However, the GIA had reason to believe the producers had employed different growth conditions to coat the New York stone: Lechleitner’s overgrowth rubies contained molybdenum, but that element was absent in this case.

“Although this is not the first report of synthetic ruby overgrowth on natural sapphire seeds, it marks the first time the New York [or] Carlsbad laboratories have had them submitted for identification,” according to Smith and McBride. “The resurfacing of these vintage overgrowth synthetics shows that once a material is in the trade, it is here to stay.”

Image: Hollie McBride
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Tags: carlsbad, Gemological Institute of America, gemology, gems & gemology, GIA, Hollie McBride, Johann Lechleitner, Lechleitner, overgrowth, Rapaport News, ruby, Synthetics, Tyler Smith
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