PLOT OR NOT?
Hello Fellow Appraisers,
If you are a gemologist-appraiser, then you probably were taught how to plot or diagram a diamond. Red ink, green ink, black ink and perhaps some of that white-out stuff that becomes pasty soon after opening. You cleaned the diamond to be plotted and positioned it carefully in your grading binocular microscope. Then you carefully marked each inclusion or blemish to create a fingerprint of the diamond. It will help to identify the diamond for future needs, substantiate the clarity conclusion and document the condition of the diamond.
If a customer suspects that their diamond has been part of the old switcheroo - a detailed plot can be exactly what is needed to determine if that is the case.
Gemologist-appraisers often have thresholds for when they plot a diamond and when they don't. For example, some appraisers will only plot diamonds that exceed half carat in weight. Others plot diamonds only when requested by clients - often charging an extra fee to perform this service. Some gemologist-appraisers plot only if a laboratory report is not accompanying the stone. Then there are appraisers who plot most diamonds providing they are considered significant - and yes, a significant diamond will vary in definition from appraiser to appraiser.
I am not going to tell you what standards for plotting you should employ or when to draw the line at a specific weight when deciding whether to plot a diamond or not. Make that threshold flexible. A diamond that is a K color, I3 clarity that happens to weigh 0.51 ct. would be plotted and a D color, VVS1, 0.49 ct. diamond would not?
In fact, in some cases even a 0.20 ct. diamond may call for a plot. A young man and his bride-to-be come to you for an appraisal. He sold his car to buy her a small engagement ring. The reason that he came to you is because his rich aunt liked the appraisal you rendered for her 3-carat diamond ring. Can you tell him that his diamond is too small to warrant a plot like his aunt's stone? Remember, this is a future customer for earrings, watches, etc. to be appraised. Be flexible.
Customers usually do not ask for a plot. Although it may not be unethical to charge an extra fee for a plot - you may simply want to include it in the fee. Case in point - a customer calls you a year later for an appointment. When they arrive, they are accompanied by their attorney. She had taken the diamond ring to a set-while-you-wait mounting show and believed the goldsmith had chipped the stone. She now sees a small chip under a prong that was not there before. You examine the diamond and confirm that it is chipped. The goldsmith will, in his defense, claim it was always there. The plot is evidence that not only bolsters your customer's case but gains you additional money through expert witness fees. Or the plot will exonerate the goldsmith. Either way, case solved!
Some gemologists-appraisers use a digital camera to record the main inclusions and blemishes in a diamond. This is usually faster than plotting. And the plots can be added to the appraisal with a minimum of effort. However, unless the gemologist-appraiser understands how to take a series of photographs that are combined into one photograph, called stacking, the result cannot get every detail. Or a series of separate photographs are used and published as a series.
If the goal is to substantiate the diamond's clarity, lack or extent of damage as well as its unique features for future identification, then why not use a camera? However, one must ensure that the above criteria are met in each digital plot. Of course, the same standards are mandatory in hand-plotting.
If you use a camera, ensure that the digital photograph is not distorted or otherwise misleading. Does the photograph have to be in color? Since a hand-plot does not have the advantage of a color matching the diamond, neither does the photograph have this requirement. In essence, the photograph could very well be without color (in black and white with perhaps gray scaling).
Best but most time consuming is to hand plot, then add microphotographs to detail the main inclusions or blemishes. This link will tell you about the software and has a how-to video.
This is a link where you can download a set of sample diagrams to try and then order the full set.
Written by Bill Hoefer
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1. Illustrations - IStock.com.