Gem treatments
A gem treatment is a process that changes a gem's colour, clarity, appearance or durability, such as heating, dyeing or filling. GB/T 16552 sorts each method into optimization or treatment. Under CIBJO, disclosure means giving the buyer all material information, including care needs, before or during the sale.
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Disclosure requirement by treatment
Disclosure differs by treatment: for heating and for routine pearl bleaching it depends on which code is followed, and the other treatments here must be disclosed.
This table scrolls sideways on narrow screens.
| Treatment | GIA code | Naming rule | Disclosure requirement |
|---|---|---|---|
| Heated / Heat-treated | H | Heated [material name] | Heating is a common treatment, and acceptance varies by material. Whether heated ruby or sapphire must be declared separately depends on which code is followed (see the comparison on this page); unstable colour or foreign residues must be disclosed. |
| Filled / Fracture-filled | F; Resin-filled; Glass-filled; Oil-filled | [Filler]-filled [material name] | Name the filler (resin, oil, polymer, glass or lead glass) and bear in mind that fillings can be unstable and may deteriorate or change colour over time. LMHC Information Sheet #3 treats corundum with glass in two ways: glass in fissures or cavities is still reported on natural corundum as a filling, and only a badly fractured single piece infused throughout, or small fragments bound together with glass, is reported as a manufactured product. |
| Diffusion-treated | U; Surface diffusion; Lattice/Bulk diffusion | Diffusion-treated [material name] | Must be disclosed. Surface diffusion produces colour only in a thin layer that repolishing can remove; bulk diffusion is permanent but still requires disclosure. |
| Irradiated | IR | Irradiated [material name] | Must be disclosed. Stability under irradiation varies by material: irradiated blue topaz keeps a stable colour and irradiated smoky quartz or coloured diamond can, but in some materials the irradiated colour fades in light or heat; colour stability must be pointed out. |
| Dyed | D | Dyed [material name] | Must be disclosed. Dye may fade, bleed or dissolve in solvents (alcohol, acetone), and dyed material must not be labelled "natural colour"; dyed jadeite counts as B/C jade and must be conspicuously labelled; dyed agate and chalcedony are extremely common. |
| Bleached | B | Bleached [material name] | Bleaching may affect the durability of the material. Codes differ on whether routine pearl bleaching needs its own declaration (compare the rows on this page); chemical bleaching that changes the structure, or bleaching followed by impregnation, must be disclosed. |
| Coated | C | Coated [material name] ([coating material]) | Must be disclosed. Coatings may be abraded, flake off or discolour, and coating is not a permanent enhancement; the coating material must be disclosed (e.g. Mystic Topaz is coated topaz), and the treated effect must not be implied to be natural. |
| HPHT treated | HPHT | HPHT-treated [material name] | Must be disclosed. Mainly applied to diamond (to improve brown to colourless or near-colourless) and may also apply to coloured stones; HPHT treatment is not HPHT synthesis: the former alters an existing natural diamond, the latter produces a new one, and both must be disclosed. |
| Laser-drilled | L | Laser-drilled [material name] | Must be disclosed. Used mainly on diamond; after treatment the remaining channel may be filled with glass or resin, and if it is filled, the filling must be disclosed as well; the laser channel is irreversible. |
| Waxed | Waxed [material name] | Must be disclosed. CIBJO's care annex counts wax among the treatments that are not permanent, so the matching care must also be passed on to the buyer: keep it away from solvents, household chemicals and heat. | |
| Impregnated | Impregnated [material name] | Must be disclosed. Where the impregnation also brings colour, as in jadeite that has been acid-treated and then impregnated with polymer and colour, or Zachery-treated turquoise, the colouring is part of what has to be declared. |
What to ask for on a report, by treatment
Each treatment page says what a laboratory report should state; the text of each is below, and laboratory testing and report wording explains how reports word their findings.
This table scrolls sideways on narrow screens.
| Treatment | What to ask for |
|---|---|
| Heated / Heat-treated | LMHC Information Sheet 1 and Information Sheet 7 set the corundum wording: indications of heating, heating residues. A ruby or sapphire report should be read against it. Those sheets do not apply to other materials, so for quartz, beryl, zircon, tanzanite or topaz the paperwork follows the naming pattern Heated [material name], GB/T 16552 Table 1 classifying heating as optimization. |
| Filled / Fracture-filled | Filler and extent both belong on the paperwork: CIBJO requires the substance to be named, and glass-filled corundum is graded minor, moderate or significant on a corundum report (LMHC Information Sheet 3 covers corundum glass-filled fissures). A significant extent stays in the treated-corundum branch rather than becoming a manufactured product. |
| Diffusion-treated | A corundum report following LMHC Information Sheet 2 says (lattice) diffusion and may name the element; it adds “shallow” when the created colour sits near the surface, and that word is the signal that repolishing could take the colour away. |
| Irradiated | Who holds the licence for this batch? Neutron-irradiated topaz requires a US NRC licence for initial distribution in the United States, and before sale the goods must also meet the applicable residual-radioactivity limits. |
| Dyed | Dyeing sits on the treatment side of GB/T 16552 Table 1, with a remark that for chalcedony the method counts as optimization instead. Treatment goods are represented under §5.4.2.2 b), the clause recorded here, where the name must carry the treatment method or the word treated; here that gives Dyed [material name]. For jadeite the question is treatment status, dyed goods being B/C jade. |
| Bleached | Under FTC rules the pearl provision sits at §23.23. GB/T 16552 Table 1 treats bleaching as optimization but classifies bleaching and filling combined as treatment. For jadeite, then, the question to ask is whether polymer impregnation followed: if it did, the goods are B jade. |
| Coated | An invoice that says Mystic or Azotic has named a brand, not a substance. The naming pattern reserves a slot for the substance, so ask which material the film is made of. |
| HPHT treated | US paperwork is judged under FTC §23.14, which sends diamond treatments to the §23.24 test; Part 23 prescribes no particular wording for HPHT. Ask that the report on a treated natural diamond name the process, not just the grade. |
| Laser-drilled | Where the drill channels were filled, AGTA's rule that every treatment be listed applies; its own example is a diamond coded LF, lasered and filled. A listing that stops at laser-drilled while the channels carry glass has declared half of the work. |
| Waxed | Ask whether the report or invoice says the piece is waxed: CIBJO's buyer-facing word is simply “Waxed”. Wax found in fissures or cavities is a different finding, reported under LMHC Information Sheet 12 on organic fillers. |
| Impregnated | Ask the report to name the impregnation and anything done before it. AGTA requires all treatments to be listed, so jadeite bleached and then impregnated should read as two treatments, not one. |
Care after treatment
Some treatments are not permanent, and the CIBJO Gemstone Book names them in its special-care codes; General gem care gives the full wording of every code.
CIBJO definitions
CIBJO definitions of disclosure, trade documents and advertising, which apply to every treatment, are on: CIBJO term definitions
GB/T 16552-2017, Annex B, Table B.1
How GB/T 16552 classifies each method as optimization or treatment, with all rows of Table B.1, is on: GB/T 16552: optimization vs treatment
JJA/AGL table: treatments with no page on this site
The definitions and nomenclature of the Japan Jewellery Association (JJA) and the Association of Gemological Laboratories, Japan (AGL), revised November 2025, list in their table of principal gem names (pp.9–16) the treatments that may be applied, by species, gem name and colour range. The table says only which treatments may be applied; it is not a frequency and not a test result for any stone. Its “—” line is the untreated tier for that colour range, and “no indication of …” is listed as a tier of its own. This site restates each cell on the entry and treatment pages; the two treatments below have no treatment page here:
- soaking in sugar solution: Black Opal (p.9) Black Opal
- chemical treatment: Turquoise (p.14) Turquoise
Clause 2-1-1 of the source twice refers to the table as “→p.7”, but the table is on pp.9–16 (p.7 holds clause 2-2). Locators here use the actual pages.
By the numbers
- Common treatments
- 11
- Materials that need a note to buyers
- 422