Cut is the most important factor in a diamond's beauty. It governs how light enters, reflects and returns to the eye as brilliance and fire. A well-cut diamond sparkles even in low light; a poorly cut one looks dull regardless of its other qualities.

Diamonds are graded from D (completely colorless) through Z (light yellow or brown). The less colour a diamond has, the rarer and more valuable it is. D–F are colourless; G–J are near-colourless and offer exceptional value.

Clarity measures the tiny natural inclusions and surface blemishes present in nearly every diamond. The scale runs from Flawless (FL) to Included (I). Most inclusions are invisible to the naked eye, especially from VS2 and above.

Carat is the weight of a diamond, not its size. One carat equals 0.20 grams. Because larger diamonds are rarer, price rises sharply with weight — two half-carat stones cost far less than a single one-carat stone of equal quality.