Welcome to AGTA GTC's Laboratory Update for July 19, 2005

In this message

  1. Living in the Dark Ages: The fiber-optic light
  2. Meet our Staff: Richard Hughes
  3. AGTA GTC staff win Liddicoat Journalism Award

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).

Current turnaround time at the AGTA GTC
5–7 Business Days

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.

     Certainly darkfield illumination still has its place in diamond clarity grading since a uniform standard for lighting is most useful in diamond grading production work. However, even in diamond grading darkfield can prove to be inadequate and through its exclusive use interesting and major features can be overlooked or underestimated. One previously published example is the four point stellate cloud described in Gems & Gemology (Spring 2001, pages 58–59). Another is provided by comparing the low-power darkfield photomicrograph of a light green diamond shown here in Figure 5 with the fiber-optic illuminated image shown in Figure 6 in one and the same diamond. The darkfield image is the one that a diamond grader would see, while the one illuminated by a fiber-optic light wand is what the gem identification specialist would observe. There is obviously a big difference in the amount of detail lost through darkfield and revealed with fiber-optic illumination.

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.

     Given the complexity of today’s gemological problems it doesn’t seem possible for anyone on the technical side of the gem industry to get along without fiber-optic illumination. As shown in this article, at the microscopic level there are internal characteristics in gems that you just cannot see without fiber-optic lighting. If you are still using darkfield almost exclusively with your microscope, then you are living in the dark ages of gemological microscopy.
      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.


Meet our Staff:
Richard W. Hughes – Gemological Administrator

Richard W. Hughes is one of the world's foremost authorities on ruby and sapphire. A Fellow of the Gemmological Association of Great Britain, his first book, the highly regarded Corundum, was published in 1990. Richard's latest book Ruby & Sapphire is the standard work on the subject and is considered among the finest monographs ever written on a single gem species. He also contributed several chapters to Robert Webster's Gems.
    While a native of the United States, Richard has spent close to half his life in Asia, where his interest in gemstones was first kindled. Richard graduated from Bangkok's Asian Institute of Gemological Sciences in 1979; shortly thereafter he was invited to join their staff. He was later appointed executive vice-president, a position he held for close to a decade. Under his directorship, the institute blossomed into one of the world's leading facilities in gemological education.
    Richard has traveled to scores of countries in search of gemstones and authored over a hundred articles on all aspects of the gem and jewelry trades. His writings have appeared throughout Europe, Asia, North America, and Australia and are notable for their distinctive style.
    In addition to his writings, Richard is much in demand as a speaker and has delivered lectures across the globe. He is also an excellent webmaster, and was responsible for the creation of Pala International’s award-winning Palagems.com site, as well as this site. He maintains his own personal site, Ruby-Sapphire.com, where many of his unique writings can be found.
    Richard currently works alongside John Koivula at the West Coast branch of the AGTA GTC , where he is involved with gem testing, along with the creation of a new AGTA GTC website.

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:




The AGTA Gemological Testing Center provides the industry and the public with a complete range of lab services, including gemstone identification, origin determination and pearl identification. Located in New York City, the laboratory is equipped with the latest, technologically advanced, investigative equipment.The AGTA GTC is committed to providing excellent service, superior value and outstanding quality. A complete list of services and detailed pricing information is available on our website, www.agta-gtc.org. Please contact us with any questions.

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