Short answer: some natural diamonds are treated, either to look clearer or to change their color. Laser drilling and fracture filling target clarity; coating, irradiation, annealing and HPHT (high pressure, high temperature) processing target color. The treatments differ in how long they last. GIA, the Gemological Institute of America, grades diamonds with stable treatments such as drilling, irradiation, annealing and HPHT, but it does not issue reports for filled or coated ones. Heat, steam, acids and ultrasonic cleaning can damage a filling. In the US, the FTC’s Jewelry Guides say a seller should disclose a treatment that isn’t permanent, needs special care or significantly affects value, and for online sales the disclosure belongs in the product description. Before you buy, ask in writing whether the diamond has been treated and how. Before any repair, tell the jeweler.
If you’ve seen “enhanced”, “CE” or “treated” on a diamond listing, receipt or appraisal and weren’t sure what it meant, here is what each treatment involves. A treated diamond is a legitimate choice when the treatment is disclosed. The problems described below start when nobody knows what was done to the stone.
What counts as a diamond treatment
A treatment changes how a diamond looks after it formed, and a treated natural diamond is still a diamond; our guide to diamond, lab-grown and simulant labels covers how those names work. Lab-grown diamonds can also be treated after growth, which our natural vs lab-grown guide explains, so this article sticks to natural diamonds.
Clarity treatments: drilling and filling
On laser drilling, GIA’s guide to diamond treatments says: “A laser bores tiny holes into a diamond’s interior.” A bleaching agent is then introduced through those channels to lighten small, dark inclusions. GIA adds: “Since this is a permanent treatment, GIA diamond grading reports will always mark laser drill holes in the inclusions plot.”
GIA notes that “internal laser drilling can also be used to alter inclusions.” Instead of a drilled channel, “This method opens a ‘feather’ or cleavage to the surface of the diamond”, which “can resemble natural feathers within a diamond and can be harder to detect”.
For fracture filling, GIA defines the filler as “A molten lead glass-like substance used to fill feathers or white fractures in a diamond.” A Winter 2025 lab note in GIA’s journal Gems & Gemology explains that the filler “has a refractive index close to that of diamond, reducing the visibility of the fractures and thus giving an appearance of improved clarity”. The cracks remain: a 1989 GIA study of filled diamonds said the fractures “still exist; they are just more difficult to see”. GIA’s treatments guide says “With proper care, these treatments can repair cracked diamonds and last for years”, but “it is not considered a permanent or stable treatment”.
Color treatments: coating, irradiation, annealing and HPHT
- Coating is a very thin layer of foreign material that masks a diamond’s color or adds one. GIA says “Coatings will scratch and wear off over time and can be damaged by heat and/or chemicals.”
- Irradiation, “most commonly by high-energy electrons, is used to produce different colors in diamonds”, and may be followed by annealing.
- Annealing is “A controlled heating and cooling process used to adjust a diamond’s color.”
- HPHT is “A method of annealing to alter color at high pressures and temperatures using a press.” GIA says it is often used to turn brownish diamonds yellow or green, and “this form of diamond treatment is stable. GIA will grade HPHT-treated diamonds.”
HPHT isn’t only used on lab-grown stones: a Spring 2018 GIA lab note describes a natural, HPHT-treated diamond presented with another stone’s untreated-diamond report, a fraud GIA calls “rarely encountered in larger stones”.
Which treatments last, and which a lab will grade
GIA: “We do not issue grading reports for diamonds that have received nonpermanent or unstable treatments.” For stable treatments, “Every GIA diamond grading report lists the presence of any known diamond treatments”.
| Treatment | Changes | How GIA describes it | GIA grading report? | Care note (GIA) |
|---|---|---|---|---|
| Laser drilling | Clarity | Permanent | Yes, with holes marked on the plot; no if the holes are filled | None given |
| Fracture filling | Clarity | Not permanent or stable | No | Steam, acid, ultrasonic and repairs can damage the filling |
| Coating | Color | Not permanent | No | Scratches and wears off; heat and chemicals can damage it |
| Irradiation | Color | Stable to regular wear | Yes | May be more sensitive to repair heat |
| Annealing | Color | Stable | Yes | None given |
| HPHT | Color | Stable | Yes | None given |
GIA also says “sometimes drill holes are fracture-filled, and GIA will not grade diamonds containing a foreign substance.” If a diamond has a report, our guide to reading a diamond grading report shows where to find its treatment line.
Cleaning and repairs
Filled stones need the most care. GIA: “Common repairs and cleaning with steam, acid or ultrasonic solutions can damage the filling.” And: “If the filler turns dark, it cannot be made colorless again.” The 2025 lab note adds that the filler “may degrade or become discolored over time, particularly when exposed to ultraviolet light, heat, ultrasonic cleaning, or certain chemicals.”
GIA’s 1989 study tested torch heat: the prongs holding a filled diamond were re-tipped with a jeweler’s torch, and afterwards “beads of the filling agent had sweated out of the separation”. The GIA jewelry-making staff who did the test concluded that such stones “should NEVER be subjected to the heat of a jeweler’s torch.”
In jewelers’ accounts, the owner often doesn’t know. On the Ganoksin jewelers’ forum, one repair jeweler described torch-tipping a filled diamond that nobody had told him was treated: “It is an interesting feeling watching a diamond go from a VS to an I2 before your eyes…” The customer had got the stone online and “stated he wasn’t aware of any enhancement after the fact” (Ganoksin, 2006). In another thread, a member who re-tips prongs wrote: “I’ve seen a few since that other people have burned, and customers have been unaware of. Most of the time it happens in retipping” (Ganoksin, 2008).
A damaged filling can’t always be put right. A member whose shop had handled “many dozens” of clarity-enhanced diamonds wrote that “once damaged they can not always be successfully retreated” (Ganoksin, 2017). For everyday cleaning, our care guide by metal and stone lists the methods to avoid for fracture-filled stones.
What the FTC Jewelry Guides say
This article is general information, not legal advice. The FTC’s Guides for the Jewelry, Precious Metals, and Pewter Industries (16 CFR Part 23) cover diamond treatments in §23.14:
“A diamond is a gemstone product. Treatments to diamonds should be disclosed in the manner prescribed in § 23.24 of these guides (Disclosure of treatments to gemstones).”
§23.24 reads:
“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.”
Its note adds that when a product can be bought without seeing it in person, such as online, “disclosure should be made in the solicitation for, or description of, the product.” The Guides also say disclosures “should be sufficiently clear and prominent” (§23.1). They set out the FTC’s current thinking and “do not confer any rights on any person” (§23.0(d)).
In a 2013 TV investigation reported by the trade magazine JCK, the show charged that two New York jewelers did not properly disclose that the diamonds they sold were fracture-filled. When the stone’s paper said “clarity enhancement”, the reporter was told: “That’s the polish they do for the stone.” Asked about special care: “Don’t be worried about anything.”
Questions to ask before you buy, and before a repair
- Has this diamond been treated, and how? “Enhanced” or “CE” alone doesn’t say.
- Is the treatment permanent, and does it need special care? Can you put that in writing?
- Is there a lab report, does it match this stone, and what does its treatment line say?
- If the treatment is ever damaged, what happens?
- Before a repair, sizing or re-tipping, tell the jeweler about any treatment you know of. For an inherited or gifted diamond with no paperwork, ask them to check it under magnification before any heat work.
Treated diamonds have a place. GIA says “There are many advantages to purchasing a treated diamond”, for example that treatment can create rare fancy colors that “may cost substantially less than their untreated counterparts”. The 1989 study concluded: “There is nothing inherently wrong with this or any other enhancement process provided it is always disclosed at every level of sale.”
Next step
Keep the seller’s written answers with your receipt. Our guide to choosing a diamond covers the other questions worth asking. If a listing doesn’t answer your question about treatment, email Concierge@impervora.com before you order.
