The 4Cs of a Diamond

Cut is the one the eye actually sees. It isn't the diamond's shape — it's how well it's proportioned and faceted, which decides how it returns light as brilliance, fire, and sparkle. A poorly cut stone looks dull even if it's flawless and colourless. GIA grades a standard round brilliant on five levels.

For a white diamond, less colour is rarer. GIA grades it from D (completely colourless) through to Z (a light yellow or brown), in 23 steps. The differences are subtle — often invisible to the naked eye, but they move the price. Below Z, strong colour becomes a "fancy" diamond, graded on its own scale.

Diamonds form under heat and pressure, so most carry tiny internal features (inclusions) or surface ones (blemishes). Clarity grades how few and how faint they are, on eleven grades from Flawless to Included. Many SI-grade stones are "eye-clean" — the inclusions need a loupe to see — which is where value often hides.

Carat is weight, not size. One carat is 0.20 grams, divided into 100 "points" — so a half-carat stone is 50 points. Two diamonds of equal carat can look different sizes depending on their cut. Because large rough is rare, price climbs sharply at the round-number weights (1.00 ct, 2.00 ct).