Gemstone treatments explained: heat, filling, diffusion, irradiation and oiling
· GemColony
Why treatments matter
A treatment is any process, other than cutting and polishing, that improves a stone's appearance or durability. Treatments change price, so they must be recorded and disclosed to the buyer. Selling a treated stone as untreated is a serious problem for any dealer.
Heat treatment
Heating is the most common treatment for sapphire and ruby, and is also used on tanzanite, aquamarine, citrine and others. It can improve colour and clarity. Heated stones are widely accepted in the trade when disclosed. Geuda, a milky corundum found in Sri Lanka, is often heated to bring out blue colour.
Filling, oiling and coating
Emeralds are commonly oiled or resin-filled to hide fractures. Glass-filling is used on lower-grade rubies to improve apparent clarity and is priced very differently from untreated stones. Some topaz is surface-coated. The level of enhancement affects both value and durability.
Diffusion and irradiation
Diffusion treatment introduces colour-causing elements into the surface layer of a stone, and irradiation changes colour with radiation, as in much blue topaz. Both need clear disclosure, and a re-cut can remove diffusion colour.
Recording treatments
Store treatment status on each stone record along with the lab report that supports it, and make sure it prints on the invoice and any certificate. In GemColony, treatment is a field on the stone, so it follows the stone through parcels, memos and sales.