Treated gemstones: what to ask before buying or cleaning

Understand heat treatment, fracture filling and why cleaning methods must suit the actual stone.

3 minUpdated 18 September 2026Money OK

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Example items; some may have been sold. Check with the branch before visiting.

“Natural gemstone” does not necessarily mean untreated. Knowing what a stone has undergone helps you compare its price and look after it. Ask which treatment was used and what care the stone needs.

Ask which treatment

Heating, oiling, resin or glass filling, dyeing, diffusion and coating are different processes. Ask for the method identified, rather than using “heated” as a blanket description. Care requirements can differ substantially.

Treatment is not the same as laboratory growth

Origin tells you whether a stone formed naturally or in a laboratory. Treatment tells you what processing it has undergone. Ask about both. If a seller describes a stone as “unheated”, ask what evidence supports that description.

Be cautious with cleaning

If material and treatment are unknown, avoid ultrasonic machines, steam, harsh chemicals or prolonged soaking until advised. Emeralds with fracture-filling substances and vulnerable stones may need particular care. Protect jewellery from knocks and check the setting periodically.

Questions for a pre-owned piece

Ask about stone identity, known treatments, fractures, documented repairs and care. If the report leaves a question unanswered, ask the seller to explain what it covers. Gemstone introduction · Find a branch.