Ruby — styles you will see at the showroom.

What to look at

The trade talks about "pigeon blood" — a red with a faint blue undertone that keeps its colour under any light. Under the halogen of a showroom every ruby looks good, so step to the daylight by the entrance and check whether the stone turns brown or stays clean. A warm, slightly pink red is worth more than a dark one, which is the opposite of what most visitors expect.

Fine ruby above two carats is genuinely rare, so treated and composite material is common everywhere in the world, Thailand included. Ask what was done to the stone: heating is standard and disclosed, glass-filled material is a different product at a different price, and the paperwork will name it.