Hue: Pure, spectral (prismatic) colour. Hues include gradations and mixtures of red, orange, yellow, green, blue, violet, and purple.
Tone: A colour's position on a colourless-to-black scale.
Saturation: A colour's position on a neutral-to-vivid scale.
Fancy diamond: A diamond with an attractive natural body colour other than light yellow, light brown, or light gray.
Treated diamond: A diamond with body colour bodycolour induced by some form of artificial irradiation, often in conjunction with controlled heating (known as annealing).
Coated diamond: A diamond coloured by a surface coating which masks the body colour bodycolour; the coating may be extensive (entire pavilion, for example), but is more often limited to one or two pavilion facets or a spot on the girdle.
Treatment Clues: Even, medium to dark, vivid green, blue-green, or blue body colour.
Treatment Proofs: Umbrella effect, coloured pattern following facet junctions, coloured ring around the girdle (green, yellow, brown, pink); radioactivity (radium green); brown, disc-like inclusions (radium green); fogs photographic film (radium green); electrically non-conductive (blue); 592 nm absorption line (green, yellow, most brown, pink).
Natural Clues: Darker green or brown naturals or surface spots (light green, brown).
Natural Proofs: Electrically conductive (blue).
When in doubt, always submit coloured diamonds to GTL for an origin of colour report.
Examine the surface under high magnification (45x or more) in diffused or reflected light. Pay particular attention to areas near the girdle. The coating may have tiny pits or bubbles, and may be scratched with a probe; an orange filter may help. Other clues include subnormal brilliance and dispersion, an iridescent sheen or a lack of transparency when viewed table-down in the DiamondLite, or an odd look when compared to masterstones.
Use the colour Master to: