Seeing things clearly

Many of us are trained, credentialed gemmologists, and for most of us that means a ‘GG.’ Speaking for myself, I had always assumed that as long as I followed my training, I was grading diamonds like GIA Gem Trade Laboratory (GIA-GTL). Among the many, many things I learned during the course of the 16-hour class was that until very recently, the grading process used by GIA-GTL was considered proprietary and a ‘trade secret’ (and some things still are). In other words, what gemmology students were taught and what GIA lab employees were taught were very similar, but not the same. So let’s embark on an absurdly abbreviated attempt to see if there’s something about diamond clarity grading we’ve forgotten or perhaps were never taught.

The process of clarity grading is far more complex than many of us may believe or remember; let’s briefly review what we should already know. The five components of every clarity grade are: size, location, relief, nature, and number. Each is taken into account in determining the grade and none is more important than any other. After initially being considered as independent coequal parts of a whole, they are ultimately combined to create an impression that will be our initial grade.

The actual methodology begins with the binocular microscope using whatever magnification level is necessary to locate and identify the clarity characteristics. In general, this is best accomplished by dividing the stone into sections using the facets’ geometry as a guide. We might examine the gem ‘face-up,’ ‘table-down,’ through its side or, more likely, all of the above if we’re dealing with a loose stone. Keep in mind the best ‘dark-field’ effect is seen with the stone at or slightly below the level of the light well diaphragm, and it is rocked and rotated throughout the process.

For VS-1 and higher-clarity diamonds, dividing the stone into sections is a necessary and integral part of grading, as we focus from one surface through the stone to the opposite surface to verify that we’ve missed nothing. For VS-2 and lower-clarity diamonds, sometimes it’s just as easy to use a prominent inclusion as a guidepost to recognize when we’ve examined the entire stone. Remember, we’re trying to get an initial impression of the clarity range while identifying the ‘nature’ of the inclusions. Feathers, dark inclusions, or those that are visible (or their reflections) through the table will influence the final grade the most, while twinning wisps, clouds, non-reflecting colourless or white inclusions, or graining tend to have less impact.

The next step is to reduce the microscope’s magnification to 10X and to relocate the inclusions you’ve found to assess their visibility and overall impact on the stone’s beauty and durability. There’s no way to ‘tally’ the clarity characteristics’ individual impact on the grade; as we examine the stone, however, our internal dialogue will undoubtedly be pushing us toward a conclusion. The important thing to remember is that each of the grade’s five components has an equal role to play in the final decision and all the inclusions need to be considered as a whole assemblage. We were probably taught the buzz words: minute (VVS), minor (VS), noticeable (SI), and obvious (I) to establish the clarity grade range based on our initial impression; however, precisely repeating the process is necessary to be consistent from stone to stone.

The last step in the grading process is to finalize the grade or the level within the grade range. Generally speaking, except possibly in the flawless grades, this is done with a fully corrected 10X loupe. There is a specific technique and lighting environment required to accurately perform this step. In our class, the fluorescent overhead light that was attached to the microscope was fully rotated so it was pointing downward and extended off the front of the microscope’s stage with the diffuser plate installed. In real life, it should be possible to adapt the technique to other light sources. (Just remember the instructor’s opening remark about the importance of replicating the methodology to achieve the result.) The diamond is held in tweezers in preparation for being examined ‘face-up’ and positioned approximately half an inch below the front edge in the centre of the light. Having a black background behind the stone is important and can be accomplished using a cloth, paper, or whatever one can devise that will be consistent. The loupe is brought into focus and as the stone is gently rocked and focus extended from table to culet, it is simultaneously moved approximately one-half to three-quarters of an inch farther under the light and back to the starting point. The stone is then repositioned in the tweezers and the process repeated.

At least for me, learning the fine details of this technique opened a door to a whole new understanding of loupe grading. I discovered I had often been ‘generous’ when grading diamonds that were near a grade boundary because my loupe grading technique was lacking. Many times during the two-day class, we were encouraged to practice the various techniques that were being taught as often as possible using diamonds that had grading reports. How could I not offer the same advice?

Making the grade

My experiences over the two days provided me with many ‘Aha!’ moments, as we delved into topics like cut grading, colour grading, detecting treated and synthetic diamonds, and much more. Although I attend at least 20 hours of continuing education classes each year, I left Carlsbad, Calif., with the distinct feeling that a gemmological diploma should be like most advanced appraisal designations and require renewal/recertification after a specified time interval.

There are too many of us who received our diplomas decades ago who are still convinced that we’re right and the labs are wrong. As I explained at the beginning of this column, my goal isn’t to try to teach anyone how to grade diamonds—that would be virtually impossible to do in this medium. I do hope this brief foray into my understanding of some of the nuances of clarity grading ‘the GIA way’ will provide a spark that may incentivize a reader or two to seek out opportunities to improve their skills and competency, and perhaps experience their own ‘Aha!’ moments.

Mark T. Cartwright, ISA CAPP, 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.