How to Grade Set Gemstones

Set Gemstones and the Four Cs

Assessing each of the Four Cs (Carat, Cut, Clarity, and Color) for a set stone presents challenges. We’ll go through each of these categories and also consider the differences between grading mounted colored gems and diamonds.

Carat Grading Set Gemstones

Removing a gem from its setting for weighing is possible but rarely done. The primary exception is when there’s a serious discrepancy between your weight estimate and what the customer or supplier says a stone should weigh. Removing a stone requires a competent bench jeweler and, thus, additional time and expense. You’ll also face the risk of damage to the stone or setting.

If necessary, for high-value stones, jewelers will usually cut the prongs rather than pry out the gem. Of course, they must then re-prong the setting.

Weight

You can calculate a gem’s weight by its proportions. You can usually measure the dimensions of a set stone directly. Where this isn’t possible, you can estimate a measurement. Take as many measurements as you can and estimate the rest.

The accuracy of your estimate is determined by the quality of your instruments and how…

Donald Clark, CSM IMG

Donald Clark, CSM founded the International Gem Society in 1998. Donald started in the gem and jewelry industry in 1976. He received his formal gemology training from the Gemological Institute of America (GIA) and the American Society of Gemcutters (ASG). The letters “CSM” after his name stood for Certified Supreme Master Gemcutter, a designation of Wykoff’s ASG which has often been referred to as the doctorate of gem cutting. The American Society of Gemcutters only had 54 people reach this level. Along with dozens of articles for leading trade magazines, Donald authored the book Modern Faceting, the Easy Way.

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