Treated stones: how to read a label (heated, dyed, stabilised)
What the words on a stone label mean: natural, treated, heated, dyed, stabilised, reconstituted, synthetic, imitation, and what French law says.
Key points
| Legal framework | Decree no. 2002-65 of 14 January 2002: names of gemstones, synthetic stones, imitations and pearls |
|---|---|
| To be disclosed | Irradiation, laser, dyeing, surface diffusion, filling visible under a 10x loupe, other laboratory methods |
| Exempt from disclosure | Colourless oil, heating with no visible residue, bleaching without added substances |
| Mandatory qualifier | “Synthetic” for a manufactured stone that reproduces the composition and structure of a natural stone |
| Common trap | “Natural stone” does not mean “untreated” |
| Recourse for valuable pieces | Certificate from a recognised gemmological laboratory |
Why the label matters
A large share of the stones sold are altered before they reach you: heated, dyed, irradiated, impregnated, coated or reconstituted. These practices are often long-established and do not make the stone a bad purchase; they do, however, change its price, its care and its lifespan. A clear label is therefore information, not a formality. This guide explains the most common terms, what they imply, and how to ask the right questions.
In France, decree no. 2002-65 of 14 January 2002 governs the names of gemstones, synthetic and artificial stones, imitations, organic materials of animal or plant origin, and pearls. According to the available summaries (including one by a specialist in gemmological law):
- Article 2 requires the name to be supplemented by a disclosure of treatment in several cases: irradiation, laser, dyeing, surface diffusion, filling of cavities with a foreign material visible under a 10x loupe, and any other laboratory method that changes appearance, colour or purity;
- Article 3 exempts certain traditional treatments: impregnation with a colourless fluid (oil), heating with no residue visible under a 10x loupe, bleaching without added product or varnish;
- Article 4 requires the qualifier “synthetic” for a manufactured stone that reproduces the properties and structure of a natural stone.
DGCCRF investigations find that these disclosures are rarely displayed in full. Consultations since 2022 have also addressed a possible revision of the decree: for the text in force, consult Légifrance. The general information duty of the Consumer Code also applies to every seller. What follows is general information, not legal advice.
The label glossary
| Term | What it means | Keep in mind |
|---|---|---|
| Natural | The material formed in the earth, without being manufactured | Says nothing about any possible treatment |
| Untreated | No change to its appearance (other than cutting and polishing) | A rare and valuable claim; request it in writing |
| Heated | Heat used to change or fix the colour (amethyst into citrine, tiger's eye into bull's eye (red tiger's eye)) | Old and common; often exempt from disclosure |
| Irradiated | Radiation used to change the colour (blue topaz, some quartz) | Must be disclosed; see also associated heating |
| Dyed | Added colourant (agate, howlite, jade, coral, quartz) | Must be disclosed; may fade |
| Stabilised, impregnated | Resin, wax or oil used to harden a porous stone (turquoise, malachite, type B jade) | Oil is exempt; resin may be visible and must be disclosed |
| Bleached | Lightened by a chemical bath (pearl, jade) | Exempt if there is no addition or varnish; type B jade is also impregnated with resin |
| Reconstituted, pressed | Fragments or powder bound together with a resin (turquoise, malachite, amber) | Not a single-piece stone |
| Synthetic, lab-grown | Manufactured, with the same composition as a natural stone | Mandatory qualifier in France |
| Imitation | Another material that resembles the stone (glass, plastic, other dyed mineral) | Must not carry the name of the stone |
| Doublet, triplet | Stone assembled from several glued layers (opal) | Only part of it is the stone |
| Coated, aura | Quartz with a metallic deposit on the surface | The coating wears away |
| Crystal | Often a leaded glass; sometimes quartz | Ask for clarification |
| Fine stone, precious, semi-precious | Former trade terms, removed from official denominations according to a commentary on the decree | Guarantee neither the nature nor the quality |
Common treatments, stone by stone
| Stone | Common treatment | What you can ask |
|---|---|---|
| Citrine | Heated amethyst | Natural or heated? |
| Agate, black onyx, carnelian | Dyed or heated | Natural colour or dyed? |
| Turquoise | Stabilised, Zachery, reconstituted, or imitation (dyed howlite) | Stabilised? Reconstituted? |
| Jade (jadeite) | Types B and C (bleached, impregnated, dyed) | Type A? Certificate? |
| Opal | Smoked, sugared, impregnated, assembled | Solid? Treated? |
| Amber | Heated, pressed, dyed | Natural or pressed? |
| Pearls | Bleached, dyed, irradiated | Natural colour? |
| Blue topaz | Irradiated and heated (very common) | Treated? |
| Emerald | Oiled or resin-filled to hide fractures | Type and level of treatment |
| Bull's eye (red tiger's eye) | Heated tiger's eye | Heated? |
| Lapis lazuli, malachite | Wax, resin; reconstitution | Waxed? Reconstituted? |
These examples appear on the pages of this guide devoted to each stone, such as citrine, turquoise, jade, opal, amber and pearl.
Reassuring phrases that promise too much
- “Natural stone”: the material is natural, but a treatment is not ruled out.
- “Authentic”, “genuine”, “100% pure”: advertising terms, with no legal definition.
- “AAA quality” or “grade A”: commercial rankings specific to each seller, with no common standard.
- “Certified” without the name of a laboratory: a certificate issued by the seller itself is not an independent appraisal.
- “Energised”, “charged”, “purified”: belongs to the seller's symbolic practice and says nothing about the nature of the material.
- A place name or an exotic name: “Malaysian jade”, “golden topaz”, “Chinese turquoise” sometimes refer to other materials.
Questions to ask, and the role of the laboratory
A few questions are enough, in writing, before buying:
- What is the exact nature of the material (name of the mineral or material)?
- Has the piece undergone any treatment: heating, irradiation, dyeing, impregnation (oil, wax, resin), bleaching, coating?
- Is it a single-piece stone, assembled (doublet, triplet) or reconstituted?
- Is the material natural or synthetic?
- What care precautions follow from this (water, sun, perfume)?
For valuable pieces, a recognised gemmological laboratory (for example GIA, SSEF, Gübelin Gem Lab, IGI or the Laboratoire français de gemmologie in Paris) issues an independent report. It identifies the nature, the origin for some stones and detectable treatments, but its conclusions only apply to the piece examined. See labels and certificates: what are they worth?.
And with us?
Our commitments are public: we state the material of each product, we do not sell glass, resin or reconstituted stone under the name of a natural stone, we disclose treatments as soon as our supplier tells us about them, and we make clear that photos of a unique natural stone are indicative. See our commitments. If information is missing, write to us before you buy. For other reference points: real or fake stone and choosing and caring for your stones.
Frequently asked questions
Does “natural stone” mean “untreated”?
No. The material is natural, but it may have been heated, dyed, irradiated or impregnated. Ask about the treatment.
Must a seller disclose heating?
In France, decree no. 2002-65 exempts heating from disclosure when it leaves no residue visible under a 10x loupe. An honest shop discloses it anyway.
What is the difference between a synthetic stone and an imitation?
A synthetic stone is made with the same composition and structure as a natural stone; in France it must carry the qualifier “synthetic”. An imitation is a different material, such as glass.
Is a seller's certificate enough?
It does not replace an independent laboratory opinion. For a valuable piece, look for a report from a recognised gemmological laboratory.
Should I avoid treated stones?
Not necessarily. Many are beautiful and honest. What matters is knowing what you are buying and adapting the care accordingly.
Also read
The meanings mentioned belong to tradition and symbolism. They are neither promises of results nor medical advice. Back to Recognizing real stones.