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November 1999

Gemstones & Pearls: Gemology

On the Trail of Emerald Fillers

The first part of the Gemological Institute of America's study of emerald fillers focuses on identification

The Gemological Institute of America released the first part of its long-awaited study of emerald fillers in the Summer 1999 issue of Gems & Gemology, its quarterly journal. The study, "On the Identification of Various Emerald Filling Substances," evaluates gemological methods used to identify the many substances used to fill fissures in emeralds. The authors –  Mary L. Johnson, Shane Elen and Sam Muhlmeister – then propose a broad scientific classification system.

The vast majority of emeralds have fissures that extend from the interior to the surface. The fissures are filled with various substances to make them less visible, improving the appearance of the emerald and making it more salable. But there's considerable debate on the virtues of various fillers.
GIA examined substance identification first; later studies will focus on the effect different fillers have on the appearance of emeralds. They also will look at how fillers may change over time. Anecdotal

Evidence suggests fillers age differently, further altering the emerald's appearance.
The ultimate benefit for jewelers? If emerald fillers can be identified accurately and their durability known, jewelers can better disclose specific emerald enhancements to their customers, restoring confidence in this popular gemstone.

It's Classified

The article first sets ground rules by scrutinizing the definitions of many terms commonly used to describe emerald fillers. The authors propose a classification system that broadly defines the correct gemological use of the words:

  • Oil.
  • Essential oils.
  • Resins (natural vs. synthetic).
  • Polymers and prepolymers.

Terms commonly used, often incorrectly, such as cedarwood oil, Opticon and palm oil are carefully defined and listed in the proper categories defined by the study's more scientific classification system.

How to ID

The Gems & Gemology article then focuses on methods of identification of these fillers, including the use of traditional gemological tools such as refractive index and flash effect, fluorescence, viscosity, specific gravity, clarity and internal appearance.

The study also focuses on the capabilities – and limitations – of more complex and expensive gemological tools such as infrared spectroscopy and Raman microspectrometry.

The authors believe a separation of the categories of fillers is possible – as long as they are pure substances. (Emeralds often contain mixed substances; these are more difficult to identify because the characteristics of one substance may conceal those of another.)

The authors conclude the study by suggesting the trade follow these guidelines in disclosing emerald fillers:

  • Avoid using the word "natural" because science often can't distinguish between natural and synthesized fillers.
  • Understand the distinction between essential oils (aromatics) and other oils.
  • Avoid the term "synthetic resin" in favor of "artificial resin."
  • Artificial resins should not be called epoxies unless they contain epoxide groups.
  • Artificial resins should not be called Opticon or Opticon-type unless they contain Opticon 224 made by Hughes Corp.
  • Because one filler can obscure another one, the authors recommend restricting comments to the filler identified.

by Robert Weldon, G.G.

Copyright © 1999 by Bond Communications.


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