Emerald Detectives

May 1999

Gemstones & Pearls:Gemology

Emerald Detectives

The Gemological Institute of America prepares to shine the light on the elusive world of fillers

Research scientists at the Gemological Institute of America are putting the finishing touches on a study into one of the biggest challenges in modern gemology: understanding and classifying the vast array of substances used to fill fissures in emeralds.

The study, details of which will be published later this year in GIA's quarterly Gems & Gemology, comes at a critical time. Emerald sales have plummeted in the past two years following numerous exposés of unreported and sometimes unstable treatments.

The new study should help the emerald universe – miners, dealers, retailers and consumers – understand differences in the durability, stability, removability and "re-treatability" of emerald fillers. For those involved in the sale of emeralds, it should serve as a reference in setting policies on guarantees and disclosure. And for consumers, it should help to restore confidence in the embattled gemstone.

But the research scientists at GIA's Gem Trade Lab in Carlsbad, CA, emphasize they are only studying and classifying the fillers. The market must decide which ones it prefers.

Durability of Fillers
The study is no small task, says Dr. Mary Johnson, GIA-GTL's top research scientist conducting the study. Thousands of materials could be used to fill emerald fissures, she explains.

For this reason, GIA confined the durability portion of the study to a handful of the most commonly used fillers: cedarwood oil, natural resin, paraffin oil, unhardened synthetic resin, surface-hardened Opticon, hard synthetic resin and UV-setting adhesives.

Researchers examined 230 filled and unfilled emeralds from different localities to learn the effects of cleaning, wear, display and recutting.

Substance Differentiation
The reseachers grouped the many fillers into two main categories:

  • Oils – cedarwood oil and mineral oils.
  • Resins – epoxy-based synthetic resins and UV-setting adhesives or hardeners.

One consideration in doing the study, says Johnson, is that some standard trade definitions for emerald treatments are confusing. For example, palm oil (also known as palma oil) sounds like a natural substance from a palm tree. In fact, it's a synthetic material. What's more, it has virtually the same properties as two epoxy resins: Araldite 6010 and Epon 828. No wonder use of the term palm oil can be confusing.

Challenges of Identification
To lessen the confusion, GIA's study will explain how to detect fillers gemologically. Factors to consider in examining filled emeralds include:

  • Fluorescence. Certain fillers fluoresce different colors and intensities.
  • Relief and "flash effect" characteristics. The contrast visible under magnification between the filler and the emerald can create interference colors.
  • Near-surface material movement. Gentle heating softens the filler, which then moves when probed, as seen under magnification.

The study also will describe such filler characteristics as flow structure, gas bubbles, cloudy inclusions and incomplete filling.

The study has shown it will be difficult to identify the filler positively in some cases, Johnson cautions. Even with diagnostic tools such as refractive index readings and sophisticated Raman and infrared spectroscopy, she says, you may be unable to identify all components that make up the filler. Furthermore, some fillers mask the identifying features of others.

"Despite the limitations, it is possible to detect and identify – at least at a broad level – some of the emerald fillers some of the time," she says.

GIA To Offer New Service
In related news, Johnson says GIA-GTL will respond to industry requests for reporting clarity enhancement in emeralds. "We are looking into offering a service that will state the degree to which an emerald has been clarity-enhanced: not at all, a slight amount, a moderate degree or a large degree," she says. "We hope to offer this service within a few months."

– by Robert Weldon, G.G.



Copyright © 1999 by Bond Communications.


 

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