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Making the grade: Tips to ensure your lab is up to snuff

Master diamond grading set

How often do you clean your master diamond grading set? If you have an older set, inspect it to see whether the girdles are bruted. The rough surface can trap dirt, grime, and metal fragments from your tweezers, causing the stone colour to appear darker. Regular cleaning in sulphuric acid resolves this.

GIA recommends cleaning a master set every two to four weeks. Since I use my master set less frequently than a lab like GIA, I clean it every few months. Your local bench jeweller or diamond cutter should be able to help.

Calibrate your instruments

No matter how precise, digital gauges can change over time due to wear; they can also become misaligned after being dropped. To check that your gauge is accurate, consider picking up a calibration block at your local jewellery supply house. Made from steel, calibration blocks offer precise measurement. (I own a 5-mm and a 10-mm block.) You can determine the accuracy of your digital gauge by simply measuring the block. I recommend doing this monthly and keeping a log of the date and measurements.

Colour vision

Proper equipment and a consistent grading environment are of little use without the regular screening of your own colour vision. American Society of Appraisers (ASA), American Gem Society (AGS), and National Association of Jewelry Appraisers (NAJA) require members regularly take (and pass) the Farnsworth-Munsell 100 hue test to ensure they have normal colour vision.

Take-in procedure

Regular cleaning of your diamond colour master set removes dirt and debris that may affect grading.
Regular cleaning of your diamond colour master set removes dirt and debris that may affect grading.

Your take-in procedure is critical to the appraisal process. First off, ask your client to bring all relevant paperwork that came with their diamond, including the purchase receipt, prior appraisals, and of course, the lab report. These papers reveal what the client paid, along with what they understand to be the quality and value of their stone. They also alert you to potential areas that need to be discussed or clarified.

A great deal of my time is spent educating my clients. Given the subject matter, the substantial cost of the item being appraised, and the emotional or sentimental circumstances surrounding it, what I say during the evaluation is critical. As appraisers, we are required to be impartial third parties. If you arrive at a grade that is several off from what the report states, it’s time to have a very delicate conversation with your client. After explaining you’ve verified the diamond is in fact the one described in the report, your next course of action is to describe how you arrived at your opinion, the typical tolerances for grading a mounted or loose diamond, and how and why labs differ in their grades. You may also want to give the client the backstory to the standards you follow (e.g. GIA, AGS, etc.) and what the industry finds to be an acceptable variance (i.e. one colour and one clarity grade). If the stone is mounted, you should also indicate how colour grade can be affected by the metal around it, and that to remove the stone from the setting may affect your opinion of the grade. Finally, explain how you will be approaching your research and replacement value. As always, include limiting conditions in your report. Remember that appraisers don’t mediate disputes between client and vendor—we merely offer our opinion and disclose any limiting conditions in our valuation.

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