Ring Around the Girdle

June 1999

Diamonds:Gemology

Ring Around the Girdle

When it comes to your diamonds, don't be shy. Clean them!

Costly little sins embedded in the bruted girdle of a diamond can detract from its appearance. The good news is it's an easy problem to correct. To understand the problem, first imagine the difference between a bruted girdle and a faceted girdle. In fashioning a diamond, bruting is the last step before faceting the girdle. Some manufacturers don't facet girdles to save time and money (faceting a girdle can add $20-$50 to the cutting cost, and bruted girdles are considered acceptable in the trade) or to save weight (less than 1% of the total weight).

The bruted surface is frosted, almost sugary, and can pick up all sorts of debris, including grease, for which diamonds have a natural affinity. In extreme cases, this "ring around the girdle" – to loosely paraphrase an old detergent slogan – can make a diamond look darker and less valuable than it really is, say some experts.

For loose diamonds, the solution is simple: deep-clean them by boiling them in acid. For mounted diamonds, acid would attack the metal so a long, hot, sudsy bath in an ultrasonic cleaner is a better option.

The Case for Cleaning Girdles
Most gem labs view dirty girdles as an annoyance, but they have varying opinions about the extent to which dirty girdles actually change the perceived color or clarity of the diamond. Professional Jewelerchecked with four labs for their views:

  • Martin Haske at Adamas Gemological Laboratories in Brookline, MA, says his SAS 2000 Spectrophotometer system consistently registers "the distinctive spectra of dirty girdles." Visual observation backs up those findings with detrimental color shifts of up to two grades, he says.
  • Peter Yantzer, director of the American Gem Society Laboratories, says he's seen changes as dramatic as one color grade because of dirty girdles. But Yantzer is more concerned about diamonds that never go to a lab. "Some jewelers with master diamond sets [used to color grade diamonds] don't clean them regularly," he says. "They get incorrect color observations because dirty girdles seem to drain the subtle color in a diamond." This leads to incorrect color grading.
  • John King, laboratory projects officer at the Gemological Institute of America's Gem Trade Lab, takes a moderating position. "It would take handling far beyond the normal course of action to get girdles dirty enough to have a discernible face-up appearance change," he says. Still, he feels dirty girdles could affect diamonds with borderline color calls, so he encourages rigorous cleaning of all diamonds before grading.
  • Craig Slavens, diamond department manager at GQI Laboratory in Los Angeles, CA, says the biggest effect he has seen involves diamonds with very large bruted girdles; the effect was less obvious in smaller stones.

All of the labs take the precaution of boiling their master diamonds in sulfuric, muriatic or chromic acid routinely, some daily, others weekly or monthly. They also deep-clean customers' loose diamonds, especially before color grading.

Acid cleaning removes girdle debris ranging from pencil marks (pencils are often used to turn a diamond in tweezers) to metallic fragments (tweezers often leave behind metallic scrapings), not to mention human oils and skin particles. [Caution: If you use acid to clean diamonds, work in a well-ventilated area.]

Even if the labs don't agree on the extent of color shifts caused by dirty girdles, they agree it's best to err on the side of prudence and purity. Offer your diamonds up in their natural, unsoiled splendor. And for heaven's sake, clean your master set.

This diamond with a bruted girdle clearly shows the "dirty girdle" syndrome. Courtesy of Ernest Slotar, Chicago, IL.

This diamond shows that a faceted girdle leaves nowhere for debris to collect. Courtesy of Ernest Slotar, Chicago, IL.

– by Robert Weldon, G.G.



Copyright © 1999 by Bond Communications.


 

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