Following measurement, a diamond is sent to a clarity grader, who objectively evaluates its purity, which means a lack of blemishes (external marks) and inclusions (internal features). Colored gemstones are not evaluated for clarity. They are sent immediately to Color Grading.

GSI gemologists use binocular microscopes with high magnification to scan the diamond for any imperfections, treatments, and to check its "make" (proportion and finish).

Next, using a 10 power loupe, they give the diamond a clarity grade. The highest clarity grades are Flawless (FL) and Internally Flawless (IF) given to very rare diamonds. More common are gems with slight inclusions, which receive clarity grades from VVS to I. V stands for "Very," the S for "Slightly," and I for "Included."

Most inclusions don't compromise the beauty or structural integrity of a diamond, which is the hardest natural substance known to man.

A Final Grader, with more experience, rechecks the stone and gives the final Clarity Grade.