Step 4: Gem Grading

Lesson 4

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.


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…