Short answer: “treated” means something was done to a natural gemstone beyond cutting and polishing to change its color, its apparent clarity or its durability. Heating, common in ruby and sapphire, is durable and permanent under normal handling, according to GIA. Most emeralds are filled with oil or resin, and blue topaz gets its color from irradiation and heat. Filled, coated and dyed stones need more care. A glass-filled ruby needs more care than a heated one and, by GIA’s account, is worth less. In the US, the FTC’s Guides say a treatment should be disclosed when it is not permanent, creates special care requirements or significantly affects value. A missing word on a listing doesn’t tell you a stone is untreated, so ask.
What “treated” means
GIA’s guide to gem treatments notes that “treatments can be permanent, long lasting, or short-lived under normal jewelry use”. The American Gem Trade Association’s Gemstone Information Manual (17th edition) says that because many enhancements are hard to prove, its approach is “to assume that such traditional enhancement has been done”. The trade uses letter codes (H for heating, F for filling, O for oiling), but AGTA says that for retail customers “all required disclosure must be made in plain language. Codes and/or abbreviations are not sufficient.”
“Not heated” is also not the same as “untreated”. One forum member wrote: “I have a GIA report that says my Burma ruby is not heated, but that it has treatment.” (IGS forum, 2023). A GIA report “names any detectable treatments”, so read the whole line.
Common treatments, gem by gem
| Gem | Common treatments (GIA) | Care note (GIA) |
|---|---|---|
| Ruby | Heating; some surface diffusion; some lead glass filling | Heated or lattice-diffused: ultrasonic and steam “usually safe”. Filled: damp cloth only |
| Sapphire | Heating; lattice (beryllium) diffusion; lead glass filling, much less often than in ruby | As ruby; shallow diffused color can be lost in recutting |
| Emerald | Fractures filled with oils, waxes or resins | No ultrasonic or steam; warm, soapy water |
| Blue topaz | Irradiation followed by heating; some topaz is coated | No steam or ultrasonic; coatings scratch |
| Amethyst and quartz | GIA’s buying guide says “rarely treated”, but its treatment guide lists amethyst among heat-treated gems (heat can lighten very dark stones); some quartz dyed or irradiated | No steam or heat |
GIA’s ruby buying guide says: “You should assume your ruby is heated.” Its sapphire buying guide says “Sapphire treated by lattice diffusion often has vivid color but is less valuable than heated sapphire.”
Which treatments last, and which need special care
- Heating. According to GIA, heat treatments are “considered durable and permanent under normal handling conditions”, though heating “may render them slightly more brittle than usual”, so corners and edges deserve care.
- Diffusion. “The treatment is considered permanent”, but when the added color is shallow, GIA warns that “Surface damage or re-cutting can remove the color” (GIA sapphire care).
- Irradiation. “Blue topaz, diamond and quartz tend to have very stable colors as long as they are not exposed to high temperatures.” Some other irradiated colors fade in strong light. GIA’s topaz guide says the US standard for release and import of topaz “is a small fraction of the background radiation that everyone is exposed to every day.”
- Filling. “Glasses tend to be harder and therefore more durable than resins, oils or waxes.” GIA advises avoiding heat, chemicals and changes in air pressure.
- Coating. Thin films “are susceptible to scratching, particularly along facet edges and junctions.” GIA’s topaz care guide adds: “The coating is not very durable.”
- Dyeing. “Many dyes can be removed if the gem comes into contact with a solvent such as alcohol or acetone.”
- Impregnation. Keep these stones away from heat “such as that encountered by a jeweler’s torch”.
Heated ruby or glass-filled ruby?
Both may contain glass. AGTA codes heated corundum with residues visible under 10x magnification as HR (heating with residue), separate from F for filling. A lead glass-filled ruby is a different product: GIA’s treatment guide says “In some cases, the amount of filler glass can be significant in a treated ruby.” GIA’s ruby guide adds: “Rubies that have been diffused or are glass filled are worth less than heated rubies.”
GIA’s ruby care guide says “Ultrasonic and steam cleaners are usually safe for untreated, heat-treated, and lattice diffusion treated stones”, but “Fracture-filled, cavity-filled, or dyed material should only be cleaned with a damp cloth.” It also warns: “Even relatively mild substances like lemon juice can cause changes in the high-lead content glass.”
A 2006 GIA study reported that “Durability testing of a few samples by highly skilled jewelers indicated that the filler was fairly resistant to heat exposure during jewelry repair procedures, but it reacted readily with solvents.” A jeweler’s pickling solution etched the filler. Careful cleaning, setting and re-tipping did not damage the few stones tested, though GIA’s care guide is more cautious. The authors noted that “jewelers’ guidelines typically advise against exposing any ruby or sapphire to the direct heat of a torch during the retipping of prongs”.
A 2016 report in GIA’s journal Gems & Gemology describes a ruby filled with silica-rich glass that, according to the client, was “broken into two pieces by a goldsmith who only applied standard pressure on the claws when setting the stone”. The author’s advice: “Careful inspection of any stone prior to setting is recommended.”
A Ganoksin member writing “As a repair cutter I have had to repolish many of them” said lead glass-filled rubies “can also be damaged by lemon juice, vinegar and some household cleaners” (Ganoksin, 2010).
Oiled and resin-filled emeralds
GIA’s emerald care guide says: “Some estimates state that 90 percent or more of emeralds are fracture-filled.” GIA explains that “Ultrasonic vibrations can weaken already-fractured stones, and hot steam can cause oil or unhardened resin to sweat out of fractures.” A GIA emerald report rates the clarity enhancement as “minor, moderate, or significant” (GIA).
One forum poster wrote that a jeweler doing work on a ring “put my emerald into an acidic bath, and then also put it in an ultrasonic bath” (IGS forum, 2018).
What the FTC Jewelry Guides say
This section is general information, not legal advice. In the FTC’s Guides for the Jewelry, Precious Metals, and Pewter Industries (16 CFR Part 23), gemstone treatments are covered by §23.24, which was numbered §23.22 before the 2018 revision:
“It is unfair or deceptive to fail to disclose that a gemstone has been treated if: (a) The treatment is not permanent. The seller should disclose that the gemstone has been treated and that the treatment is or may not be permanent; (b) The treatment creates special care requirements for the gemstone. The seller should disclose that the gemstone has been treated and has special care requirements. It is also recommended that the seller disclose the special care requirements to the purchaser; or (c) The treatment has a significant effect on the stone’s value. The seller should disclose that the gemstone has been treated.”
For products bought without seeing them in person, such as online, the note to §23.24 says “disclosure should be made in the solicitation for, or description of, the product.” Section 23.25(d) covers products “made with gemstone material and any amount of filler or binder, such as lead glass”. It lists as unfair or deceptive calling them by the unqualified gem name, a “treated ruby” or other “treated” gem name, or a lab-grown, lab-created or synthetic gem name. Composite, hybrid or manufactured gem names are listed too, unless the term is qualified to disclose clearly that the product does not have “the same characteristics as the named stone” and “requires special care.” The Guides say they “do not confer any rights on any person and do not operate to bind the FTC or the public.”
Lab-created, synthetic and simulated
A treated stone is natural material that was altered. A lab-created (or lab-grown, or synthetic) ruby was made in a laboratory, and under §23.25(c) those words belong only on a product with “essentially the same optical, physical, and chemical properties as the stone named.” A simulated or imitation stone only looks like the gem it names. Our guide to lab-grown, simulant and natural labels explains how these words work.
What to ask before you buy, and before a repair
- Is this stone natural, lab-grown or simulated?
- Has it been treated, how, and is the treatment permanent or in need of special care? Ask for plain words, in writing.
- Is there a lab report, does it match this stone, and what does its treatment line say?
- Before sizing, re-tipping, resetting or professional cleaning, tell the jeweler what you know about the stone, or ask them to check it before any heat, pickle or ultrasonic work.
For diamonds, see our guide to filled, drilled and coated diamonds. If a listing doesn’t say whether a stone is natural, lab-grown or treated, ask our Concierge (Concierge@impervora.com) before you order.
