Field report · 361
Untreated vs treated stones: what disclosure means
Heat, irradiation, oiling, fracture-filling, dye — what each does, when it's standard practice, and why we disclose all of it.
The gemstone trade has a treatment problem. Or rather, the trade has solved most of its appearance problems through treatments, and has a disclosure problem about it.
The most common treatments
- Heat — heating to 200-1,800°C to deepen or change color. Universal for blue topaz, tanzanite, aquamarine, citrine (most), and ruby/sapphire (most commercial material). Permanent and stable.
- Irradiation — exposing stone to controlled radiation to change color centers. Standard for blue topaz, most smoky quartz, some diamonds. Permanent and stable.
- Oiling / fracture-filling — filling surface-reaching cracks with cedar oil or polymer resin. Standard for emerald, occasional for ruby and others. Stable for years but can deteriorate; needs re-oiling.
- Lattice diffusion — heating with beryllium or other elements to change color from the inside. Some sapphires.
- Dye — coloring porous stones. Common in agate, jasper, sometimes lapis. Not always stable.
- Coating — applied surface treatment for color or shine. Less stable.
- Impregnation — filling porous stones with wax or polymer for stability. Standard for turquoise, some opals.
The trade's disclosure convention
The gem trade follows an informal rule: if a treatment is so universal that essentially every stone in a category has it, disclosure becomes redundant and stops happening. By this convention, you don't need to disclose that:
- Blue topaz is irradiated (because it all is)
- Tanzanite is heated (because it all is)
- Citrine sold commercially is heat-treated amethyst (because most is)
The convention assumes a buyer who already knows the convention. For everyone else, it's an information gap.
What we do
We disclose every treatment on every listing. If we don't know the treatment status (because the supplier didn't disclose), we say "treatment status unconfirmed." If a stone is untreated, we say so explicitly. This costs us some sales — a buyer who didn't know that their last citrine was treated may feel disappointed seeing it on the label here.
We think the cost is worth it. Treatments aren't bad — they make stones beautiful and accessible. Hidden treatments are bad. The choice belongs to the buyer.
What you should ask
Before any significant purchase, ask the seller:
- Has this stone been treated? Be specific: heat, irradiation, oil, dye, coating.
- If yes, is the treatment stable / permanent?
- Can you provide documentation?
- Does this affect the price compared to untreated material?
A seller who answers these clearly is a seller worth buying from.