On the D-Z color scale, what do the letters denote, and what does each masterstone indicate regarding color?

• A. The letters denote color range; each masterstone marks the least color in that range
• B. Letters denote clarity; each masterstone marks the most color in that range
• C. The letters denote fluorescence; each masterstone marks fluorescence
• D. Letters denote carat; each masterstone marks weight categories

Answer: (A)

In the D-Z color scale, the letters represent color ranges for the body color of a white diamond. They tell you which band of color a diamond’s body color falls into, from colorless (D) through increasingly colored (toward Z).

Masterstones are reference stones used to calibrate grading. Each masterstone shows the color at the lower end of its range—the least color that still belongs to that color band. Graders compare a diamond to these masterstones in a controlled viewing setup to decide which range its color fits into. If a diamond’s body color matches or resembles the masterstone at the lower edge of a given range, it’s placed within that range; if it appears more colorless than the lower edge, it would be graded in a more colorless (higher) range, and if it shows more color, it would sit in a more colored (lower) range.

So the letters denote color range, and each masterstone marks the least color that defines that range.