Gemstones & Pearls: Gemology
Judging the Amount of Emerald Filler
GIA lays out a plan to classify the extent of emerald enhancement and announces a new emerald report
The emerald industrys dire straits can be traced to buyers fears they simply dont know to what extent an emerald might have been enhanced. This lack of information makes it hard for a prospective buyer to determine an emeralds value. The Gemological Institute of America has unveiled a new study and proposed an enhancement classification system to shed some light in this obscure area.
The system, presented in the Winter 1999 edition of GIAs quarterly Gems & Gemology, seeks to classify the degree to which an emerald is enhanced. Titled Classifying Emerald Clarity Enhancement at the GIA Gem Trade Laboratory, the report by Shane F. McClure, Thomas P. Moses, Maha Tannous and John I. Koivula follows a report early last year about the identification of emerald fillers. The two reports (and a final pending report on the durability of fillers) form the basis of GIAs well-publicized emerald study.
The latest report also announces the development of a new emerald lab report to be issued starting later this year. It will incorporate a Gem Trade Lab assessment of the degree to which an emerald is enhanced: minor, moderate or significant.
Minor, Moderate and Significant
GIA says it studied some 500 emeralds representative of those regularly available in the trade. Half were studied before and after enhancement with various substances.
Researchers made unaided visual assessments and examined the emeralds under a range of magnification (between 10X and 25X) in dark-field, overhead and fiber-optic illumination. They first had to locate surface-reaching fissures and classify them according to their size, nature and position relative to the size of the emerald.
GIA used diamond clarity-grading criteria as a frame of reference. But researchers are quick to point out some obvious differences: While all clarity characteristics are noted when grading diamonds, for example, only surface-reaching fissures are noted when grading emerald enhancement. (Internal fissures that dont break the surface of the emerald are incapable of receiving enhancement).
For the purposes of this study, the researchers say they established the following correlations between diamond clarity grades and emerald enhancement grades:
- Emeralds with minor enhancements (with regard to the size, position and extent of the filled fissures and size of the emerald) correspond to VVS2-VS2 diamond grades.
- Emeralds with moderate enhancement correspond to diamonds of SI1-SI2 clarity.
- Emeralds with significant enhancement correspond to diamonds of I1 clarity and below.
Researchers are careful to note the clarity criterion for diamonds is only a framework for the emerald study and is not an attempt to establish a clarity grading system for emeralds.
Aiming for a Clean Bill of Health
Interestingly, the report notes emeralds with VVS1-type clarity, in which minute filled fissures do not noticeably affect the appearance of the emerald, would be labeled on the report as No evidence of clarity enhancement was detected. Say the authors: We based this on the premise that if the appearance of the emerald is not affected, then the presence of a minute amount of filler does not constitute an enhancement.
The authors also say that for the purposes of this study, the quality of the filler is not a crucial factor, while the quantity relative to the size of the stone is.
Authors express the hope that information of this kind, plus the more informative, secure and visually oriented lab reports (yet to be issued) will help reestablish flagging consumer confidence in emeralds.
For a copy of the Gems & Gemology article Classifying Emerald Enhancement at the GIA Gem Trade Laboratory call (800) 421-7250, ext. 7138.
by Robert Weldon, G.G.
Courtesy of GIA's Gems & Gemology, Winter 1999