Fluorescence Takes a Filtering

October 1998

Diamonds:Gemology

Fluorescence Takes a Filtering

The Gem Quality Institute and the AGS Lab filter out UV rays when color grading diamonds. GIA doesn't. Is there one right way?

The effect blue fluorescence has on yellowish diamonds has led to differences in the way gemological laboratories grade diamonds.

At the center of the difference is the Diamondlite, a color grading tool that creates uniform lighting conditions with Verilux bulbs. These bulbs are known to emit small amounts of ultraviolet waves, which excite blue fluorescence. In turn, the blue fluorescence can mask yellowish body color and make diamonds appear whiter than they really are.

For this reason, the Gem Quality Institute (doing business as European Gemological Laboratories) in Los Angeles, CA, and the American Gem Society Laboratory in Las Vegas, NV, now grade diamond color using filters that block UV wavelengths. Otherwise, they say, color grades could end up higher than they should be.

Meanwhile, the Gemological Institute of America does not use the filters at its Gem Trade Labs, located in Carlsbad, CA, and New York City. Tom Moses, vice president of identification services at GIA-GTL in New York City, says GIA's grading system combines a completely inert environment and Diamondlites with Verilux bulbs, which are designed to be as UV-free as possible. Still, GIA's own Diamond Lab Manualmakes the following suggestion for color-grading diamonds: "Use cool white, filtered, fluorescent light (UV-free) in a darkened room."

Why the difference between policy and practice? GIA experiments found UV filters may cause unwanted changes in non-fluorescent stones. "We saw several lower color grades, but we saw other changes as well," says Moses. "It's possible the filters themselves impart color."

Moses says GIA continues to study the issue and is mindful of the market. "We don't want to create too rarefied of an environment that other people would not be able to reproduce," he says. But it's also important, he says, to remember consumers view diamonds in natural light, which almost always has UV waves.

On that point, The Gem Quality Institute and the AGS Lab say consumers deserve consistent color grading under conditions best suited to fluorescence-free viewing. They also say even small amounts of UV waves emitted by Verilux bulbs can be eliminated with a simple, inexpensive filter.

To Filter or Not To Filter
In an informal experiment (attended by Professional Jeweler) conducted at the Gem Quality Institute's laboratory/booth at the JCK Show in Las Vegas in June, personnel color-graded a strongly fluorescent diamond twice – once with a UV-blocking filter, once without – using a Diamondlite with Verilux bulbs in a darkened room. The difference: two color grades.

Tom Tashey, owner of the Gem Quality Institute, says he has conducted many such experiments with moderately to strongly blue fluorescent diamonds and seen a difference of two to four grades in some cases.

Because of these results, the Gem Quality Institute now issues two grades for strongly fluorescent diamonds: one reflecting use of a filter, one without.

The AGS Lab uses a permanent filter to screen UV light when color-grading diamonds. Director Peter Yantzer says a diamond's true color should never be called into question.

Martin Haske, owner of Adamas Gemological Laboratory in Brookline, MA, agrees. "If UV in varying amounts is available under different lighting conditions, causing different grades, why not take it out completely?"

Perception
Some in the industry believe the Gem Quality Institute and the AGS Laboratory are using their UV filtering position to differentiate themselves as more precise in color grading than GIA.

Diamond market expert Martin Rapaport believes the debate over whether to use filters is a tempest in a teapot. He says the issue deserves further study, but that "GIA is still the standard. Attempts to change the standards will only confuse the issue and not be in the interests of the ultimate consumer."

Yantzer disagrees: "We have a working relationship with the industry, but one of the tenets [of AGS] is to protect consumers."

– by Robert Weldon, G.G.

 

 

 

 



Copyright © 1998 by Bond Communications.


 

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