Treatments
HPHT colour enhancement, laser drilling, fracture filling, irradiation, and coating — what each technique does, how to detect it, and why undisclosed treatments are the trade's largest unforced loss.
A treatment is any artificial process applied to a natural diamond after it has been mined and cut, with the goal of improving its visible characteristics. Unlike laboratory-grown diamonds — which are real diamonds produced from scratch in a reactor — treated stones start as ordinary natural diamonds. The treatment changes their colour, hides their inclusions, or otherwise upgrades their apparent grade so they can be sold for more.
This is one of the few topics in the trade where the consequences of ignorance are direct and immediate. A buyer who doesn't recognise treatments will pay untreated prices for treated goods, and the gap can easily be 50% or more on a single stone. Treatments are also the most common vector for fraud in the diamond market — not because the treatments themselves are illegal, but because failing to disclose them is.
Why treatments exist
Diamond rough sells at wildly different prices depending on its quality. A piece of rough that yields a clean, well-coloured 1 ct round may cost a cutter $5,000–10,000. A similar-sized piece with brown tint and visible inclusions may cost $500–1,000. The finished stone from the cheap rough faces a market that doesn't want it: at K colour with a centre feather, it sells for 30% of an equivalent G/VS1.
Treatment changes the math. Apply HPHT to the brown rough and the cut stone reads as G colour. Apply laser drilling and the centre crystal vanishes from the loupe view. The same physical stone now sells at perhaps 60% of the natural G/VS1 price. The treatment cost is small; the markup is large.
This economic logic drives the entire treatment industry. Every treatment in this article exists because someone discovered they could buy cheap rough, apply a process, and sell the result for meaningfully more — provided the buyer either doesn't know, doesn't notice, or doesn't price the difference correctly.
The five major treatments
High-pressure high-temperature treatment of an existing natural diamond. Brown and greenish stones (commonly Type IIa) are placed in the same kind of press used to grow lab-grown diamonds and held at 1500–2000°C for several hours. The carbon lattice rearranges, removing the structural defects that cause the colour, and the stone emerges as a near-colourless D–G grade.
Detectable only by specialised spectroscopic equipment looking for atypical photoluminescence patterns and absence of natural growth strain. GIA and other major labs detect HPHT-treated stones routinely; small jewellers cannot.
Permanent — the lattice change cannot be reversed
Sells at 30–50% of equivalent untreated colour
Mandatory; all major labs note it explicitly on the report
The dangerous treatment for buyers without major-lab certification. An HPHT-treated D-colour stone looks identical to a natural D — only spectroscopy tells them apart, and the price gap can be 50% or more. Always require a GIA, HRD, or IGI report on near-colourless stones above 0.50 ct.
Click through the five treatments to see what each does, how detectable it is, what it costs in resale, and what the trade should know. The summary:
HPHT enhancement is the most economically significant treatment for the trade because it targets colour — the highest-value characteristic — and produces the most convincing result. A well-treated HPHT stone reads as a top colour grade and is detectable only by spectroscopy. This is why every commercial buyer must require certification from a major lab on near-colourless stones above commercial sizes. Without that certification, you cannot tell HPHT-treated apart from natural by sight or by loupe.
Laser drilling is the most common clarity treatment in commercial trade. It's easy to detect under a 10× loupe — the drill channel is a straight line from the surface to the inclusion site, completely unlike anything that occurs naturally — but only if you actually look. The treatment is honest in the sense that it doesn't try to hide; it's just used in channels where buyers don't loupe-inspect.
Fracture filling is the dangerous treatment for the jeweller, not just the buyer. The filler boils out at temperatures reached during normal jewellery operations — ultrasonic cleaning, ring resizing, prong tipping — and the customer's stone "develops" a previously invisible crack right after a routine repair. GIA refuses to grade fracture-filled stones at all, which is the strongest market signal any treatment carries. Fracture-filled stones should not enter commercial inventory unless you run a dedicated channel that discloses upfront and accepts the legal risk.
Irradiation creates fancy colours from off-colour rough. The economic incentive is enormous because natural fancy colours — true natural blue, pink, green diamonds — are among the rarest and most expensive goods on the market, easily $100,000+/ct for top grades. Treated equivalents sell at 5–15% of those prices. The detection is straightforward at major labs but impossible without spectroscopy. Never source fancy colours without a current major-lab report.
Coating is mostly a consumer-fraud treatment. The film wears off, the disguise fails, and the underlying low-grade stone becomes visible. It rarely appears in legitimate trade channels because the value proposition is dishonest by construction — but you'll see coated stones in informal sales, estate liquidations, and retail markdowns where chain of custody is unclear.
Detection landscape
The five treatments differ enormously in how easy they are to catch:
| Detection requirement | Who can catch it | |
|---|---|---|
| Coating | Loupe at the girdle / pavilion edge | Any trained eye with a 10× loupe |
| Laser drilling | Loupe — look for straight line to inclusion | Any trained eye with a 10× loupe |
| Fracture filling | Loupe / microscopy — flash effect under angled light | Any trained eye with a loupe; certain at microscopy |
| Irradiation | Spectroscopy — UV-Vis-NIR absorption signatures | Major laboratory only |
| HPHT enhancement | Spectroscopy — photoluminescence and FTIR | Major laboratory only |
The takeaway: for HPHT and irradiation, certification is non-negotiable. There is no cheap substitute for spectroscopic analysis, and these treatments are exactly the ones with the largest pricing impact. For laser drilling, fracture filling, and coating, careful loupe inspection is sufficient — but you have to actually loupe-inspect every stone, every time.
Disclosure and the legal landscape
Treatment disclosure is mandated in every major diamond market:
- United States: The FTC Jewelry Guides require disclosure of any treatment "at the time of sale or transfer of the diamond" through every level of the supply chain. Penalties range from civil enforcement actions to criminal fraud charges for repeated or large-scale violations
- European Union: CIBJO Blue Book standards and national consumer-protection laws require disclosure. EU members enforce through national-level fraud and consumer protection regimes
- India: Bureau of Indian Standards mandates disclosure. The Indian wholesale market has had multiple high-profile crackdowns on undisclosed laser drilling
- CIBJO (the international jewellery confederation): publishes mandatory disclosure standards adopted by member countries and used as the trade benchmark globally
Disclosure must be specific, in writing, and at every transfer. A wholesaler who discloses to a retailer, who then fails to disclose to the consumer, has both committed a violation; the retailer carries primary liability for the final consumer transaction. The wholesaler does not get to assume the retailer will pass on the disclosure — the obligation runs at every step.
In practice, the major laboratories enforce disclosure through their grading reports. A stone certified by GIA, HRD, IGI, or any other major lab will have any detectable treatment noted explicitly on the report. The trade therefore solves most of the disclosure problem by insisting on certification for stones above commercial mêlée sizes. Uncertified stones in informal channels are where the disclosure failures cluster.
Why treated goods price the way they do
The market discounts treated stones for three independent reasons, and the size of the discount reflects all three:
- Reversibility risk — treatments that can be undone (coating, fracture filling) carry the largest discount because the treatment may stop working after sale. The buyer is purchasing a stone that may revert to its lower grade
- Detection risk — easily-detected treatments (laser drilling) carry smaller discounts because the buyer can verify what they're getting. Hard-to-detect treatments (HPHT) carry larger discounts because the buyer has to trust the certification chain
- Liquidity risk — treated stones have a smaller addressable resale market. Many buyers will not touch treated goods at any price, which compresses demand and widens the discount versus untreated equivalents
The combined effect:
| Typical price as % of untreated equivalent | Commercial role | |
|---|---|---|
| HPHT-treated | 30–50% | Mainstream commercial; sold to budget-segment buyers who accept the treatment in exchange for the colour upgrade |
| Laser-drilled | 40–60% | Commercial grade clarity-enhanced goods; common in mass-market jewellery |
| Fracture-filled | 30–50% | Specialist channels only; declined by major labs and most retailers |
| Irradiated fancy colour | 5–15% (vs natural fancy colour) | Fashion and budget fancy-colour goods; never confuse with natural fancy |
| Coated | ~0% premium over underlying grade | Effectively no commercial value — coating is a consumer-fraud treatment that retail buyers will discover within months |
Practical sourcing notes
- Require major-lab certification on every stone you buy above 0.50 ct. This catches HPHT and irradiation, the two treatments you cannot detect yourself
- Loupe-inspect every uncertified stone — laser drill paths, fracture-filling flash effect, and coating edges are all visible at 10× to a trained eye
- Refuse fracture-filled stones for general inventory. The repair-shop liability and the GIA refusal-to-grade signal are both clear. If you handle them at all, run a separate channel with explicit disclosure documentation
- Treat fancy-colour buying as a specialist domain. Without major-lab confirmation that a fancy colour is natural, assume it is irradiated and price accordingly — which means assume 5–15% of the natural fancy colour price
- Read the report comments line on every certificate. Treatments are noted there, not in the headline grade fields. A stone with an HPHT note in the comments is HPHT-treated regardless of how good its colour grade looks
- Disclose at every transfer. Even when a treatment is obvious from the certificate, the legal obligation runs from each link of the supply chain to the next. Pass through the disclosure in writing on the invoice or transfer document
Related
- Certification & Lab Grading — how labs detect and report treatments
- Color — what HPHT enhancement targets
- Clarity — what laser drilling and fracture filling target
- Natural vs Lab-Grown — the other category of "not exactly natural" stones