Cut is how well a diamond’s facets are angled, proportioned and polished, and it decides how much light the stone returns to your eye. A well-cut diamond looks brighter and livelier than a poorly cut one of higher color or clarity. For round brilliants, laboratories issue a cut grade from Excellent to Poor; for other shapes, look at polish, symmetry and proportions. Shape, round, oval or emerald, is a separate choice from cut quality; see Diamond Shapes.

White diamonds are graded on a scale from D, colorless, to Z, with a light yellow or brown tint. D to F are colorless, G to J near-colorless. In a ring or earring, most people cannot tell neighboring grades apart without comparing stones side by side, and yellow gold settings make a slight warmth less noticeable.

Clarity describes inclusions inside the stone and blemishes on its surface, judged under 10x magnification. The scale runs from Flawless (FL) through Internally Flawless (IF), VVS, VS and SI to Included (I). What matters in wear is whether a stone is eye-clean, meaning nothing is visible face-up with the naked eye. Read Diamond Clarity.

Carat is weight: one carat equals 200 milligrams. Size on the hand depends on the cut too; a well-cut stone can face up larger than a heavier, deeper one. Jewelry with several stones is described in total carat weight (ctw), the combined weight of all the diamonds in the piece.