AGTA GTC's Laboratory Update for July 19, 2005
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AGTA GTC at the JA Show
During the upcoming JA New York Summer Show (July 31st to August 3rd), members of the AGTA GTC will be present at the AGTA booth (#1182). The AGTA GTC staff will visit clients at their booths to discuss their needs and expectations. From July 31st to August 3rd, the AGTA GTC will have extended office hours for intake and pick-up of gemstones in our laboratory, so you can submit and receive your gemstones within 24 hours.
But even better than submitting gemstones during the JA New York Summer Show, is to submit them to the AGTA GTC in advance. By doing so, you'll have the gemstones in your showcase, ready for sale with reports. Gemstones submitted by Tuesday, July 26th, will be returned to you prior to opening day (July 31st).
Living in the Dark Ages – The fiber-optic light
What I give form to in daylight is only one per cent of what I have seen in darkness.
M.C. Escher (1898–1972)
A gemologist’s life would be far easier if gems were cut as parallel-sided plates. But they’re not. Facets are designed to reflect light back to the viewer, not transmit it. This means light entering the gemstone from behind (transmitted light) will typically not pass straight through. If we want to see inclusions, we must constantly change the light paths through the gemstone. This is done by changing the position of the gemstone relative to the light and changing the light relative to the gem. The most versatile and controllable method of doing this is with the fiber-optic light, an illumination technique “darker” than even darkfield.During a recent routine identification of a natural chrysoberyl a startling difference in two distinctly different types of illumination commonly used in the examination of gemstones was clearly revealed. These two methods are darkfield and fiber-optic illumination.
When this chrysoberyl was studied in darkfield (Figure 1), only a fine linear growth band was seen. However, when fiber-optic lighting was directed in along the girdle plane, bundles of fine light-scattering silky needles extending at 90˚ from the linear growth band became abundantly clear. At the same time the linear growth band itself was also more clearly detailed (Figure 2). The difference in the amount of visual information provided by these two different lighting techniques was startling. In this instance darkfield was clearly inferior to fiber-optic illumination.
Figure 1. The darkfield view of the interior of this natural chrysoberyl provides very little detail to the gemologist. Only a fine linear growth band is revealed. Magnified 10×. Photomicrograph © John I. Koivula, microWorld of Gems. |
Figure 2. When fiber-optic illumination is used on the same chrysoberyl, bundles of fine light-scattering silky needles are seen extending at 90˚ from the linear growth band which is also more clearly detailed now. With fiber optics a tremendous amount of detail is gained. Magnified 10×. Photomicrograph © John I. Koivula, microWorld of Gems. |
For decades, darkfield illumination has been considered the most useful illumination technique in gemological microscopy. Darkfield gained widespread acceptance in gemology primarily because it is the method used internationally in diamond grading, and as such virtually all gemological microscopes manufactured today come with a built in darkfield system. Simply flip the switch or turn the knob and the darkfield system is ready to use…simple and convenient.
As a result of this, darkfield illumination is the lighting technique most gemologists use for colored stones and diamonds. Most jewelers and appraisers rely almost entirely on darkfield illumination in their gemological work with a microscope. Darkfield illumination as married to the gemological microscope is what is taught, and darkfield illumination is what is sold as the “built-in” illumination system on today’s advanced gemological microscopes.
For skilled laboratory gemologists however, fiber-optic illumination is now considered to be the single most useful form of lighting in gemology for gem identification. What is missed in darkfield (Figure 3) is often visible in fiber-optic lighting (Figure 4), as is the case with the ultra-fine directionally visible particles of flux known descriptively as “rain” that are found in Kashan flux-grown synthetic rubies.
Figure 3. Using darkfield illumination this Kashan flux-grown synthetic ruby looks virtually flawless. Magnified 15×. Photomicrograph © John I. Koivula, microWorld of Gems. |
Figure 4. Fiber-optic illumination reveals the rain-like stringers of flux particles in the Kashan ruby that are so typical of this type of synthetic. Magnified 15×. Photomicrograph © John I. Koivula, microWorld of Gems. |
Figure 5. In darkfield illumination only a vague image of a cloud of pinpoint inclusions is visible in this pale green diamond. Magnified 10×. Photomicrograph © John I. Koivula, microWorld of Gems. |
Figure 6. When fiber-optic illumination is used on this same green diamond, the details of an amazing phantom cloud become visible. How many significant features in diamonds have been overlooked because of inadequate darkfield lighting? Magnified 10×. Photomicrograph © John I. Koivula, microWorld of Gems. |
While you might be content to live in the dark ages, this is one instance where you’d be better off going into the light. Step into the light and get yourself a fiber-optic illuminator. You might be surprised what you’ve been missing. Remember, just because you don’t see it, doesn’t mean it isn’t there.
Figure 7. A fiber-optic system such as that shown above offers unparalleled illumination. Shown are both a stiff “goose-neck” light guide, which is good for photography and a flexible rubber-sheathed light guide, which is best for everyday use. The flexible light guide has a pinpoint illuminator extension, which is also quite useful. Photo: Richard Hughes. |
The AGTA GTC’s Richard Hughes and AGTA GTC advisor John Emmett win second straight Richard T. Liddicoat journalism award
The American Gem Society (AGS) recently selected the winners of the Richard T. Liddicoat Journalism Awards and once again the AGTA GTC came out on top. This year’s top award went to the AGTA GTC’s Richard Hughes and John Emmett for their article “Fluxed up: The fracture healing of ruby.”
The Richard T. Liddicoat Journalism Awards were developed in his remembrance to honor journalists that have made exceptional contributions to the understanding of gemology, as well as AGS ideals. Since their inception three years ago, the current AGTA GTC staff have picked up three first-place awards, as well as numerous honorable mentions, as follows:
2003
- First place to John Koivula for “Photomicrography for Gemologists.” Gems & Gemology, Spring 2003, pp. 4–23.
- Honorable mention to Richard Hughes for “Walking the line in ruby & sapphire.” <www.ruby-sapphire.com> This article also appeared in The Guide.
2004
- First place to John Emmett, Kenneth Scarratt, Shane McClure, Thomas Moses, Troy Douthit, Richard Hughes, Steven Novak, James Shigley, Wuyi Wang, Owen Bordelon & Robert Kane for “Beryllium diffusion of ruby and sapphire.” Gems & Gemology, Summer 2003, pp. 84–135.
- Honorable mention to Richard Hughes & Charles Elias for “The Kimberley Process: Appeasement comes to the diamond trade.” <www.ruby-sapphire.com> This article also appeared in The Guide.
- Honorable mention to Richard Hughes & Brian Leber for “Banned! Burmese gems in the crossfire.” <www.ruby-sapphire.com> This article also appeared in The Guide.
2005
- First place to Richard Hughes and John Emmett for “Fluxed up: The fracture healing of ruby.” <www.ruby-sapphire.com> This article also appeared in The Guide.
