Let there be light(s)

To be most effective at our jobs, having access to a variety of types of lighting environments is vital. We’re all familiar with dark-field illumination and its ‘opposite,’ light-field illumination. While important and useful, they are just the tip of the iceberg, so to speak. In my practice, I tend to use pinpoint fibre-optic light, polarized, and diffused lighting resources at least as much as dark-field. I recently acquired a small, but powerful 405nm laser pointer that I’m discovering has many important uses.

The limits to our ability to examine mounted stones can have a significant impact on the accuracy of our grading. For example, closed-back settings can make dark-field illumination virtually impossible. Fibre-optic lighting with a pinpoint adapter can allow us to direct an intense beam horizontally between the prongs. One can simulate the ‘shadowing’ technique by drawing the light beam across a prong. Direct horizontal illumination can make small pinpoints, clouds, and other inclusions appear in high relief. Combined with shadowing, pinpoint fibre-optic examination can make glass filling, oiling, growth lines, polish lines, colour zoning, and other subtle attributes of coloured gemstones more visible. If one doesn’t have access to a fibre-optic light and pinpoint adapter, a small, single LED penlight also works well when it is narrow enough to be placed precisely.

My preference to see growth and zoning in coloured gemstones is a special tool I make with a white diffusion filter on one side of a glass slide and a polarizing filter on the other. The tool’s diffuser side is invaluable for detecting colour zoning and growth characteristics in coloured gems and coloured diamonds. When used as a polarizing filter, dichroic colours can be detected, along with features visible with the diffuser. A polariscope can be created with a second, transparent polarizing plate to produce a polarizing microscope. Polarizing microscopy allows one to ‘type’ diamonds based on their internal strain, detect growth patterns in diamonds and gemstones, find and analyze the optic axis of gems, and see otherwise invisible attributes that can be crucial for gem identification.

My newest ‘toy’ is a powerful near-ultraviolet laser pointer. It is extremely important to wear protective eyewear when using this or any other laser, due to the very real danger of damage to one’s eyesight. A laser operates at essentially a single wavelength of light and with an intensity not possible with any other form of illumination. Ultraviolet wavelengths are defined as beginning below 400nm, however, this laser operates at near 405nm in the deep violet. It is capable of causing a fluorescent reaction that is, for our purposes, equivalent to UV excitation.

Among the uses for this pointer are the preliminary separation of synthetic or high temperature, high pressure- (HPHT-) treated diamonds, cobalt treatment of corundum, and seeing the extent of filler in emeralds and other gems. Natural diamonds generally react with a blue-white fluorescence, while chemical vapour deposition (CVD) synthetic diamonds typically exhibit pink/pinkish-orange fluorescence. HPHT-grown and -treated diamonds usually display a yellowish-green fluorescence. While not conclusive, these fluorescent reactions to the laser can serve to separate stones that need to be tested more extensively. The ‘filler’ used in emeralds and ‘B’ jadeite often react differently from the background when excited by the laser. This can show the extent of ‘oiling’ in emeralds and can pinpoint jadeite that may need additional testing. I am enjoying my new high-tech toy and discovering more ways it can help me to better do my job.

Keeping up

Technology can be a wonderful thing, but sharing our knowledge with colleagues is the most important way we can raise the collective competency. The tiny selection of tips and tricks I’ve shared is likely ‘old news’ to many readers; however, if someone becomes a better gemmologist or appraiser as a result, then this article will have fulfilled my hopes. Often it seems that fear of losing a competitive advantage keeps us from disclosing our discoveries or teaching a ‘newbie’ the techniques that will speed their progress toward greater ability. Sometimes belonging to an organization with geographically dispersed membership can make the process less scary. Ultimately, however, we all benefit individually when the profession as a whole moves forward—an unskilled gemmologist/appraiser reflects poorly on us all. Please take the opportunity to share what you know with someone who may need assistance; you could also consider becoming a mentor or willing advisor to someone starting out. If we truly want to excel at our craft, learning and sharing knowledge must become a lifelong endeavour.

Mark T. Cartwright, ASA, ICGA, CSM-NAJA, GG (GIA), is president of The Gem Lab, I.C.G.A., an independent American Gem Society (AGS)-accredited gem laboratory. He has been a jewellery designer, goldsmith, gemmologist, and appraiser for more than a quarter century. Cartwright can be contacted via e-mail at gemlab@cox-internet.com.