Colour

Typically diamonds are transparent with barely perceptible hints of colour. With the exception of fancy-coloured diamonds — where colour is the prize — the rarest diamonds are the most colourless. Grades run from D to Z, D being the rarest of all.

In its purest state a diamond is carbon and nothing else. Such purity is rare: as the crystal grows, stray atoms of other elements become caught among the carbon, and it is their presence that gives a stone its tint. Nitrogen is the usual culprit, lending the faint yellow warmth the scale measures. The less of it a diamond carries, the more colourless — and the more prized — the stone.

Reading the scale

Grade	GIA category	Old-world name
D – F	Colourless	Exceptional white · Rare white
G – J	Near colourless	Fine white · Top crystal
K – M	Faint	Top cape · Crystal
N – R	Very light	Very light yellow
S – Z	Light	Light yellow

Colourless (D–F). The top of the scale. D–F stones show virtually no colour and are valued accordingly; the difference between them is visible only to a trained grader against a comparison set.

Near colourless (G–J). Excellent value. Faint warmth exists but is hard to detect once the stone is set, especially in white-gold or platinum mounts.

Faint to light (K–Z). A warmth becomes perceptible, most often from nitrogen scattered through the lattice. Many buyers find a warm K beautiful in yellow gold, where the metal flatters the tint.

Beyond the bottom of the scale, the rules invert: when colour deepens past Z into a true, saturated hue, a diamond is no longer “tinted” but fancy-coloured — and among the rarest, most valuable stones on earth.