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GIA Finds Imitation Emerald Made of Layered Glass
The 3.35-carat stone had a natural beryl core; glass layers were attached to it with a “colorless cement.”
A face-up view of the imitation emerald under cross-polarized light showing the inert reaction of the outer material and interference planes that outline the beryl core (Photomicrograph by Tyler Smith, GIA)
New York—Another gem has surfaced at a lab that was not entirely what it seemed.
A 3.35-carat “emerald” submitted to the Gemological Institute of America’s New York lab turned out to be an assembled imitation gemstone composed of five layers of glass cemented to a beryl core, according to an article by Tyler Smith and Augusto Castillo in the Summer 2018 issue of Gems & Gemology.
The rectangular core was a natural beryl, the mineral species to which emerald belongs, but the crown was a single piece of glass attached to the pavilion, while the pavilion was composed of four asymmetrical glass segments glued to the core using a “colorless cement.”
The imitation stone probably took a while to create using a “laborious multistep cut-and-glue process,” GIA authors said, as indicated by the way the four glass segments in the pavilion are interlocked. 
The manufacturing of the piece started by attaching a glass segment to the beryl core. Both were then cut to create a flat surface for a second piece of glass. The second was then added, cut to allow for the third, and so forth.
After all four had been added, the assembled pavilion likely would have been polished flat to allow for the crown, which then would have been attached.
(Check out the original lab note from GIA for a diagram showing the process.)
The article also noted that while assemblages of various materials have long been used to imitate precious stones—with the most common kind using two or more pieces joined together in parallel, layered fashions—GIA researchers weren’t able to find record of another stone assembled using the process applied to this “emerald.”
RELATED CONTENT: Glued-Together Diamond Turns Up at GIAGIA said it was the first time one such assembled stone has been submitted to its New York or Carlsbad laboratories.
Researchers surmise that the imitation emerald was created relatively recently, given the fact that all its exposed surfaces are made of glass and, yet, the facet junctions are still sharp and the stone lacks wear.
“It is intriguing that an antiquated technique is updated in modern times, serving as a cautionary tale of the ingenuity counterfeiters employ,” the authors said.
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