What are Masterstones?

• A. A set of color-comparison diamonds that defines GIA diamond color grades in the normal (D-to-Z) range.
• B. The method used to polish diamonds to achieve a consistent luster.
• C. A group of stones used to determine diamond clarity.
• D. A standard for assessing fluorescence in rough stones.

Answer: (A)

Masterstones are a set of color-reference diamonds used to calibrate and standardize color grading in the D-to-Z range. Graders compare a diamond to these known-color stones under standardized lighting to assign its color grade, helping ensure consistency across graders and labs. This tool is specific to color evaluation, not to polishing, clarity assessment, or fluorescence testing, which is why the other descriptions don’t fit.