This page gathers the stones in our collection that display colour change — a phenomenon in which a gem presents one hue under daylight or daylight-equivalent lighting and a distinctly different hue under warm incandescent light. The effect is not a trick of setting or backing; it arises from the way trace elements such as chromium and vanadium allow a crystal to transmit light in two separate regions of the spectrum, so that the balance tips as the light source changes.
The varieties represented here are Alexandrite, Chrysoberyl, Blue Sapphire, Demantoid Garnet and Cats Eye. Alexandrite is the chromium-bearing variety of chrysoberyl and the classical reference point for the effect; sapphire achieves its shift through its own trace chemistry; and where a cat's eye stone also changes colour, chatoyancy and colour change appear together in a single gem.
When choosing, weigh three things: the completeness of the change — how fully one hue gives way to the other — the attractiveness of both colours in their own right, and clarity and cut, which govern how much light the stone returns and therefore how legible the change is to the eye.
