A cutter decides how bright a stone will be when choosing its angles. Pick a gem, move the pavilion and crown angles, and follow the light through a slice of the stone: where it comes back to the eye and where it leaks out.
Hue, tone and saturation
How the trade describes a coloured stone's colour: hue, tone and saturation
Birthstones around the world
Every month on the American, British, Japanese and nine-gem lists
Where gems come from
A world map of where each gem is mined, today and historically
The 7 pearl value factors
GIA's seven pearl value factors, changed one at a time on one pearl
Gem treatments explained
Usual treatments gem by gem, the trade codes, care and disclosure rules