Independent Verification & Second Opinion · Bedfordview, Johannesburg
How do you verify a diamond is real, natural and exactly as certified?
You verify a diamond with gemmological equipment and its independent laboratory report, not with kitchen tests. Instrument screening confirms the stone is a real diamond rather than a simulant, separates a natural diamond from a lab-grown one, and detects treatments such as HPHT colour or fracture-filling. The GIA report, matched to the stone by its laser inscription and measurements, confirms it is the exact diamond described. The safest moment to do all of this is before you pay anyone.
Arrange an independent verification How to read a GIA report →
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Natural diamonds only
Mined-Earth, never lab-grown, by conviction, not price. Kimberley-Process documented from the mine of origin. Why we don’t sell lab-grown →
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GIA & EGL certified
Every loose stone certified by the GIA or EGL. Cert PDF supplied per stone.
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Insured delivery, SA & worldwide
Overnight across South Africa via Brink’s, G4S or our nominated jewellery courier. Insured worldwide dispatch via Ferrari Group and FedEx Custom Critical.
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14-day in-person exchange
In-person sales at the viewing room come with a 14-day exchange courtesy on stock pieces. Distance-sale CPA cooling-off applies.
Why home tests will not tell you if a diamond is real
The internet is full of kitchen tests, and almost none of them work. The fog test asks you to breathe on the stone and watch how quickly the mist clears, on the theory that diamond disperses heat fast. In practice room humidity, surface oils and the simulant you are testing against all change the result, so a pass proves nothing. The scratch test is worse: it assumes only a diamond scratches glass, but moissanite, sapphire and cubic zirconia are all hard enough to mark glass, and a careless test can chip a genuine stone. Reflection and “sparkle” tests fail for the same reason a good simulant exists at all, it is built to imitate exactly those traits.
The honest position is that the eye cannot authenticate a diamond and neither can a loupe on its own. What separates real from imitation, and natural from grown, is calibrated equipment in trained hands, read alongside an independent report. That is the whole reason the report and the verification exist.
How the trade separates diamond, simulant, lab-grown and natural
There are three different questions hiding inside “is it real?”, and the trade answers them with different tools. First, is it a diamond at all, or a simulant such as cubic zirconia or moissanite? Second, if it is a diamond, is it natural or laboratory-grown? Third, whichever it is, has it been treated? The table below is the working order a cutting house moves through.
| The question | How it is answered |
|---|---|
| Diamond or simulant? | A thermal and electrical conductivity probe separates diamond from glass and cubic zirconia in seconds. Moissanite, which fools simple heat testers, is caught by a moissanite tester or by spotting its double-refraction (doubled facet edges seen through the table). |
| Natural or lab-grown? | Not visible to the eye. Stones are first screened by type: rare type IIa diamonds are routed for closer testing, because most CVD lab-grown material is type IIa while most naturals are not. Spectroscopy and fluorescence-imaging units (such as DiamondView) then read the growth signatures that confirm origin. |
| Treated or untreated? | Spectral and magnified screening flags HPHT colour, irradiation, fracture-filling and laser drilling. Anything found is disclosed on the laboratory report’s comments line. |
| The clean confirmation | A full GIA report. A natural diamond carries a natural-diamond report; a lab-grown stone carries a report that states lab-grown on its face. The report is the document that ends the argument. |
A diamond tester from a pharmacy will tell you a stone is probably a diamond. It will not tell you whether it is natural, and it will not see a treatment. That gap, between “it is a diamond” and “it is the natural, untreated diamond you are being charged for”, is exactly where value is lost, and exactly what a proper verification closes. The longer view on the three product categories is in our neutral comparison of natural, lab-grown and moissanite.
The treatments that change a diamond’s value, and how they show
A treated diamond is still a diamond, but it is worth materially less than an equivalent untreated natural stone, and some treatments are not permanent. This is why disclosure matters and why a quiet treatment is the costliest thing to miss. The four you are most likely to meet:
- 01
HPHT colour treatment
High pressure and high temperature lighten a brownish stone toward colourless, or push it into a fancy colour. It is identified from spectral signatures and disclosed by the laboratory; an unusually cheap “D-to-F” stone with no treatment note deserves a careful look.
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Fracture-filling
A glass-like filler is injected into surface-reaching cracks to make them disappear. Rock the stone under magnification and a filled fracture flashes an unnatural colour. The filling can be damaged by heat during later repairs, so it is never permanent.
- 03
Irradiation
Controlled radiation, sometimes with heat, produces strong fancy colours such as blue, green or yellow. The colour is real but treatment-derived, identified spectroscopically and always disclosed on the report. Its value sits well below a natural-colour stone.
- 04
Laser drilling
A fine laser channel is drilled to reach a dark inclusion and bleach it lighter. The channels are visible under the loupe as hair-thin lines running into the stone. It improves apparent clarity but is a permanent intervention that must be disclosed.
None of these is detectable by eye, and none changes how a basic diamond tester behaves. They are caught by the same independent screening that separates natural from lab-grown, and named on the report’s comments line. If a stone has obviously been worked and the report says nothing, treat the silence as information.
How to confirm a stone matches its GIA report
Authenticating the diamond is only half the job. The other half is confirming that the report in the folder actually belongs to the stone in the ring, because a real report for a different stone is a real problem. There are three independent checks, and a stone should pass all three.
- Verify the report number online. Enter it into GIA’s free Report Check on gia.edu. The carat, colour, clarity, cut and measurements that come back must match the printed report exactly. A mismatch means the report is out of date, swapped or fake.
- Read the laser inscription. On stones above 0.30ct, GIA inscribes the report number on the girdle. Under magnification, girdle-up, it must read as the same number on the report and the online record. This is the single most powerful check a buyer can make.
- Match the stone to the plot and the millimetres. The measurements on the report should match the physical stone, and the inclusions drawn on the clarity plot should sit where the plot says. If the plot shows one feather under the bezel and you find three crystals under the table, the report does not describe this stone.
The line-by-line walk-through, including the proportions and the comments line, is in how to read a GIA report, and the documents themselves are explained on our GIA certified diamonds page. When all three checks agree, you can be confident the stone in front of you is the exact diamond the report describes, untreated unless the report says otherwise.
Why a cutting house is the natural place for a second opinion
A verification is most useful when it comes from somewhere with no stake in the sale you are checking. Prodiam is a natural-diamond cutting house: we buy rough, cut and polish it on our own bench at Procut DCW, and sell direct. That means we read stones and reports every working day, and it means we can look at a diamond you are considering elsewhere, or one you already own, and tell you plainly what it is. We will say if it is a simulant, if it is lab-grown, if it has been treated, and whether it matches its certificate, with no pressure to buy anything from us.
There is a practical reason this is convenient here specifically. GIA South Africa shares our building in Bedfordview, so a stone that needs truly independent grading can go for re-grading on the same address. For buyers outside Johannesburg, the same check runs through our national remote pathway: a video viewing first, then insured overnight courier with Brink’s or G4S so the physical stone and report can be examined and verified. If the purpose of the visit is reassurance rather than a transaction, the unhurried version of it is the Diamond Confidence Session, a low-pressure appointment built around questions, not closing.
Verification and valuation are related but separate. Verification answers “is this what it claims to be?”; a written valuation answers “what is it worth, for insurance or sale?”. If you need the second, see how a diamond valuation from a desk that actually buys is put together. To start either, simply tell us about the stone and what you want confirmed.
Diamond verification: common questions
How can I tell if my diamond is real?
You cannot reliably tell at home. The only dependable way is gemmological testing: a thermal or electrical conductivity probe separates diamond from glass and cubic zirconia, a refractometer or a doubling check separates it from moissanite, and instrument screening separates natural from lab-grown. The fastest path to certainty is an independent check by someone with the equipment, ideally cross-referenced against a GIA report. Prodiam will look at a stone you already own and tell you plainly what it is, with no obligation to sell you anything.
Do the home tests, the fog test and the scratch test, actually work?
No, and the scratch test can damage the stone. The fog test (breathing on the stone to see how fast the mist clears) and the “does it scratch glass” test are folklore. Plenty of simulants pass them, and a hard simulant like moissanite or even sapphire will scratch glass too, so a pass tells you almost nothing. The scratch test risks chipping a real diamond or the stone you are testing it against. Skip the kitchen tests and have the stone screened on proper equipment instead.
How do you tell a natural diamond from a lab-grown one?
Not by eye, and not with a loupe. A laboratory-grown diamond is the same carbon crystal as a mined diamond, so it looks identical and passes a basic diamond tester. The trade separates them with instrument screening that reads growth signatures: a stone is first sorted by whether it is rare type IIa (most lab-grown CVD material and only a small fraction of naturals fall here), then confirmed on spectroscopy or a fluorescence-imaging unit such as DiamondView. The clean answer is the laboratory report: a natural stone carries a natural-diamond report, a lab-grown stone carries a report that says lab-grown on its face.
How are diamond treatments detected, and why do they matter?
Treatments are detected by trained screening and disclosed on the report’s comments line. HPHT colour treatment is inferred from spectral signatures, fracture-filling shows a tell-tale flash of colour as you rock the stone under magnification, irradiated colour is identified spectroscopically, and laser drill holes are visible as fine channels under the loupe. They matter because a treated stone is worth materially less than an equivalent untreated natural, and some treatments are not permanent. A genuine GIA report states the treatment status; silence about treatment on a stone that has clearly been worked is itself a warning.
How do I confirm a diamond matches its GIA certificate?
Three checks. First, enter the report number into GIA’s free Report Check on gia.edu and confirm the online grading matches the printed report exactly. Second, on stones above 0.30ct, read the laser inscription on the girdle under magnification and confirm it is the same report number. Third, compare the physical stone against the report: the measurements in millimetres, and the inclusions on the clarity plot, should all line up. If the inscription, the lookup and the stone do not all agree, stop, because the report no longer describes the stone in your hand.
Can I get an independent second opinion on a diamond before I pay?
Yes, and you should. An independent check before money changes hands is the single best protection a buyer has, whether the stone comes from a jeweller, a private seller or an online listing. Prodiam offers a no-pressure verification and second opinion from a working cutting house: we confirm what the stone is, screen for treatment, and check it against its report. Because GIA South Africa shares our building in Bedfordview, a stone can also be sent for independent re-grading on the same address. We do this whether or not you ever buy from us.
Last reviewed 2026-06-19 by the Prodiam bench, Bedfordview.