Gemstone Treatments Explained: From Legitimate to Trap
Almost every gem on the market is treated in one way or another — and that is not a scandal, provided it is disclosed. Here is the guide to treatments, from the most harmless to the one that should make you walk away.
Heating: the traditional treatment
Practised for centuries, heating reveals or intensifies a stone's natural colour (sapphire, ruby, tanzanite, aquamarine…). It is stable and permanent: the colour will never change. It is the most widely accepted treatment on the market — but an unheated stone, being rarer, will always be worth more. Remember: heated = natural and legitimate, but the seller must disclose it.
Oiling: the emerald tradition
Emeralds almost always show fine fissures, which are impregnated with colourless oil to improve transparency — a practice accepted for centuries. Certificates state the degree: “minor” (low oil, highly sought after), “moderate”, “significant”. The only rule: avoid coloured oils and undisclosed resins.
The treatments to know… and to watch out for
- Irradiation: used notably for commercial blue topaz — stable, but must be disclosed;
- Diffusion (beryllium, titanium): colouring elements are driven into the surface of a sapphire. The colour is not the stone's own: value is heavily reduced;
- Lead-glass filling (“fissure filled”): heavily fractured rubies filled with glass. Fragile, sensitive to household products: to be avoided at all costs in serious jewellery.
The stones that are never treated
Some gems hold a trump card: they undergo no treatment at all. That is the case of spinel and garnet (including tsavorite): their colour is always 100% natural. A peace of mind that explains their growing success.
The golden rule
Treatment is not a flaw — silence about treatment is. With us, every listing states “heated”, “unheated” or “untreated”. Browse our exceptional gems or book an appointment to discuss it with the stone in hand.
