Filling a Need

June 1998

Gemstones & Pearls:Gemology

Filling a Need

One gemstone laboratory has taken some pioneering steps in detecting different emerald fillers

A few short years ago, you were ahead of the game if you could determine that someone had filled surface-reaching fractures in an emerald with a foreign substance to improve its appearance.

Today, a rapid increase in the number and types of fillers has left many emerald dealers, jewelry manufacturers and retailers confused and afraid. They can't identify which type of filler is present, so they can't even guess about its long-term effect on the emerald's clarity or durability.

In today's society, this could easily translate into lawsuits and lost business.

Scientists from gemological laboratories around the world agree that positively identifying fillers is crucial to a healthy emerald business. But at the recent World Emerald Congress in Colombia, some said they aren't comfortable making such distinctions yet.

Identifying Fillers
The basic challenge is that characteristics of some emerald fillers cross over in gemological testing but differ considerably in durability and ability to withstand pressure and heat.

One laboratory has made significant strides in understanding what fills the world's emeralds. SSEF (the acronym for the German name of the Swiss Gemmological Institute in Basel, Switzerland) uses traditional and Raman microscopic examination and infrared spectroscopy to detect traditional and epoxy resin emerald fillers.

Dr. Henry Hänni, who directs the lab; Dr. Lore Kiefert, the lab's research mineralogist; and their staff began to research emerald fillers in 1992. The three basic types of fillers:

  • Traditional fillers such as cedarwood, Canada balsam and whale oils.
  • Newer synthetic resin fillers.
  • Unacceptable fillers such as green Joban oil and dyed epoxy resins.

Each type has problems. Traditional fillers suffer from poor durability, synthetic resins are hard to remove and the unacceptable fillers change the color of an emerald with dyes, which is considered deceptive. But to transform the large volume of fractured emeralds into salable gemstones, says Hänni, treatments are here to stay despite the problems they present. The challenge for jewelers then is twofold: determine whether the emerald is treated and determine what treatment was used so you can buy and sell knowledgeably.

Final Analysis
The key to finding and determining emerald fillers involves magnification, careful observation and knowledge of the characteristics of different fillers.

Organic fillers tend to fluoresce under ultraviolet light, a characteristic that also helps to determine the quantity of filler present in an emerald.

To detect organic substances, SSEF uses an FTIR Phillips infrared spectrophotometer. This instrument features a broad infrared beam that collects spectral information throughout an emerald. The resulting spectrum shows all materials encountered in the path of the beam. Fillers and other materials are detected through a recognizable pattern of peaks and valleys.

The lab also uses a Raman microscope system, which includes a laser light source, a spectrophotometer box and a microscope to target microscopic areas in the emerald. This system helps to identify mixed substances, including synthetic resins. "When we lower the focus into the stone, we can follow the plane of an emerald fissure and find a promising spot for analysis," says Hänni. "Observations are usually made at 50X, and the area for analysis is centered in the viewing mode with a cross-hair ocular. The instrument is switched from viewing mode to analyzing mode, and the laser beam is directed onto the sample at the center of the cross-hairs." In other words, you find an area of interest in the viewing mode then switch to analyzing mode to obtain a Raman spectrophotometer reading. That, combined with gemological expertise, is used to identify fillers.

Hänni claims an 80%-90% success rate in identifying fillers with these methods. The fillings that can't be identified are too far decomposed, he says.

by Robert Weldon, G.G.

The graph shows a reference for epoxy resins (top) and cedarwood oil (bottom). The center reading shows that a tested emerald has been treated with both fillers. Courtesy of Dr. Henry Hänni and SSEF.

The graph illustrates typical readings observed for emerald spectra, as well as readings for epoxy resin. An understanding of the different readings, with characteristic peaks and valleys, helps an observer to identify the exact filler used. Courtesy of Dr. Henry Hänni and SSEF.

Copyright © 1998 by Bond Communications.


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