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
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.
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:
- 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
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
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
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
- 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.