A perfect diamond lattice is colourless. Every colour is something that went wrong: the wrong atom, a missing one, a shear through the crystal, a stray neutron. Set what the mantle did and read the grade.
The commonest impurity. Colour depends on how it is arranged, which the mantle decides below.
Each single nitrogen atom cancels one boron atom, so blue needs boron in excess of single nitrogen. A few ppm of Ib nitrogen kills any natural boron content.
Relative scale. Violet, grey and the chameleon effect all involve it.
Relative scale. Green-yellow; routine in HPHT synthetics, rare in nature.
A broad absorption nobody has pinned to a defect; orange and chameleon stones carry it.
Hotter and longer moves single nitrogen into pairs (A), then into fours (B); the N3 centres that make Cape yellow appear alongside B.
Most gem diamonds sat for one to three billion years. Type Ib survives only short or cool residence. Press play to watch the nitrogen aggregate.
Share of the crystal that grew late and kept its nitrogen single. Real Ia/Ib stones are zoned by sector, so this renders as a second tone.
Shear in the mantle drags glide planes through the crystal. Also lowers clarity: graining.
Why some deformed stones go pink and others brown is still contested. Slide it and see.
From uranium or thorium in the host rock, over millions of years. Creates GR1 vacancies: green.
Alpha particles stop within about 20 microns. They leave green spots on the surface and never reach the body colour.
Nothing to heat: there is no radiation damage yet.
Graphite and sulphide clouds. Grey through to black.
These scatter light. Milky, opalescent white.
Longer light path, more absorption. A faint tint at half a carat can grade a full step deeper at five.
Nothing to anneal: no brown and no radiation damage.
The colour comes from a spectral model. Each centre contributes an absorption band; the bands sum; the transmitted light is converted to a colour the way a spectrophotometer would do it. The band shapes are illustrative, chosen so that each centre alone reproduces its documented hue, and the nitrogen aggregation kinetics are qualitative. Grade thresholds approximate GIA practice. The pink-versus-brown partition is a slider because the literature has not settled it.