A color grade is determined by gemologists using comparison stones from a master color set under special lighting conditions. Each of the master stones represents the color at the upper borderline between two color grades.
A quality master set is one of a lab’s most treasured items, and it’s not just because of the value of the diamonds. It is the difficulty in finding the perfect diamonds for a master set. The diamonds must be between 0.50 to 0.75 carats, well-proportioned, higher than SI1 clarity, have polished girdles, have no fluorescence and most importantly be the right color with even distribution.
Here’s how the color grader compares the sample being graded to the master set. The diamonds are compared table down against white, non-fluorescent cardstock, so that the diamond’s brilliance doesn’t influence the color grading.
If you’re buying a diamond, it can be helpful to compare two diamonds side-by side against a piece of white paper.
A Senior Gemologist with more experience rechecks the item and gives the final grade.
Mounted diamonds are graded by the same process, but because the metal can influence the color, a split color grade is given (for example G-H.)