Professional Jeweler Archive: True Green

June 2001

Gemstones & Pearls/Gemology

True Green

Some gemstones are almost impossible to reproduce accurately on film. Digital photography provides a virtual rescue

Looking through a camera, you might think you’ve captured the precise color of a green gem. But when the film is developed, it’s another story.

Professional Jeweler photographed vibrant blue green demantoid garnets from a new source in Namibia for our report on the Tucson gem shows. But when the film was processed, the gems reproduced chartreuse instead of the blue green we saw with our eyes. So we set out to determine why the demantoids’ colors changed so dramatically while other gems photograph true to color.

Photographic Elements

John Koivula, chief gemologist at the Gemological Institute of America and a renowned microinclusion photographer, posed the same question to Kodak’s top film experts some years ago. “No one was able to give me a satisfactory answer,” he says. “What I’ve found is that green gems containing vanadium and/or chromium as coloring agents are the most difficult to reproduce accurate color on.” (Green gems containing chromium and/or vanadium include emerald, alexandrite, chrome tourmaline, tsavorite and demantoid garnet.)

The amount of coloring agent appears to play a role as well. A suite of green emeralds or garnets with similar hue and saturation often look different from each other on film. (As a side note, when chromium causes red, such as in rubies, the color appears far richer on film. “That may be due to fluorescence causing rubies to glow in various kinds of lighting,” says Ken Scarratt, director of the American Gem Trade Association Lab).

Other green gems photograph far more accurately. Those owing their color to iron – such as peridot and some green tourmaline – reproduce accurately on film.

Lighting is another factor in how a color reproduces on film. Gem photographers often shoot in incandescent light using matched tungsten film. Even then some color shifting can occur.
And subtle differences can be seen among brands and batches of film. “Fuji film tends to have much richer green colors,” says Koivula. Kodak, particularly Kodachrome, produces richer reds; Ektachrome has stronger blues.

For tricky gems, photographers sometimes use filters or subsequent color retouching to correct color shifts.

No More Film?

Recent advances in digital technology have come to the rescue of the gemstone photographer and retailers who document gems for their customers. Filmless images appear to capture color far more accurately than film, even green gems owing their color to chromium or vanadium.
Recently introduced digital cameras include appropriate white balance adjustments that can be registered for use in incandescent light, daylight and a variety of fluorescent lights.
So while most serious gem photographers say they’ll stick with film, the green light to convert to digital photography is shining a little stronger.

– by Robert Weldon, G.G.

This superb 7.24-ct. tsavorite garnet from Kenya toured several museums, including the American Museum of Natural History and the Smithsonian Gem Hall. It was photographed using tungsten film and green filters precisely matched to the color of the gem so it would appear acceptable on film. Gem courtesy of TsaVorite USA Inc., Carmel, IN; (317) 574-9761. Photo by Robert Weldon.
A suite of demantoid garnets from Namibia photographed with Fuji tungsten film and quartz halogen incandescent lighting. The chartreuse tones don’t represent the true colors of the gems. Gems courtesy of Gem Demantoid Inc., New York City; (212) 421-4574. Photo by Robert Weldon.
The same gems photographed with a digital camera on the same background and in the same light are rendered with much more accurate color. Photo by Robert Weldon.

Copyright © 2001 by Bond Communications