The internet is full of diamond identification tests that range from mildly useful to completely useless.
The "fog test," the "water test," the "newspaper test," the "scratch test" — these approaches are either unreliable, incomplete, or outright myths that have survived because they feel intuitive.
Meanwhile, the real diamond fraud in India — involving glass, cubic zirconia, and increasingly sophisticated synthetic stones — requires equally sophisticated countermeasures.
This guide cuts through the noise: here is what genuinely works, what does not, and what every Indian jewellery buyer should demand before completing a significant diamond purchase.
Myths: Tests That Do Not Reliably Work
The Fog / Breath Test
The claim: breathe on a diamond — if the fog clears instantly, it's real; if it lingers, it's fake.
The reality: while diamond does conduct heat quickly (which dissipates fog faster), many simulants — particularly moissanite — also conduct heat well and may pass this test.
A well-cut CZ ring that is already at body temperature may also clear fog quickly.
This test is not reliable for distinguishing diamond from moissanite, and inconsistently reliable even for CZ. Useful only as a very rough first-pass filter.
The Water Immersion Test
The claim: a real diamond sinks in water because of its density; fakes float.
The reality: almost all diamond simulants also sink in water — CZ (density 5.5–6.0 g/cm³), moissanite (3.22 g/cm³), and glass (2.5–4.8 g/cm³ depending on type) all sink.
Diamond itself has a density of 3.52 g/cm³. Nothing commonly used as a diamond simulant floats in water.
This test identifies only plastic or foam masquerading as stones — not any of the actual simulants used in jewellery fraud. Useless.
The Newspaper Test
The claim: a real diamond is so refractive that you cannot read text through it; fakes let you read print clearly.
The reality: this works for round brilliant diamonds (true — their faceting scatters light too thoroughly to see through the stone) but fails for many fancy cuts (especially emerald and asscher cuts, which have fewer facets and a transparent windowing effect).
Not reliable across cut styles. An emerald-cut CZ may also scatter light sufficiently to fail this test.
Not a useful standalone test.
The Scratch Test
The claim: scratch the diamond across glass — if it scratches the glass, it's real.
The reality: diamond (hardness 10) scratches glass (hardness 5–6), but so does moissanite (9.25), sapphire (9), quartz (7), and many other minerals.
You will scratch your diamond or potentially your setting while proving only that the stone is harder than glass — which tells you almost nothing.
Destructive, inconclusive, and damaging. Never do this.
Tests That Actually Work
Thermal Conductivity Tester (Diamond Probe)
The most common legitimate tool in jewellery stores. A thermal probe measures the rate at which heat conducts through the stone.
Diamond conducts heat exceptionally well — when the probe tip touches a diamond, it reads the rapid heat transfer and signals "diamond." Glass and CZ conduct heat much more slowly and the probe signals "simulant."
Critical limitation: Moissanite also conducts heat well — close to diamond's rate. Standard thermal probes often indicate "diamond" when tested on moissanite.
If you suspect moissanite specifically, a thermal probe is insufficient. You need the combined electrical-thermal tester described next.
Electrical Conductivity Tester (Moissanite Tester)
Moissanite is a semiconductor — it conducts electricity to a small degree. Diamond does not conduct electricity at all.
A specialised moissanite tester (such as the Presidium Duo Tester or similar combined units) tests both thermal and electrical conductivity simultaneously, reliably distinguishing between diamond and moissanite.
Ask your jeweller if they have a combined tester if you have any reason to suspect a moissanite substitution.
UV Fluorescence Examination
Approximately 25–35% of natural diamonds exhibit blue fluorescence under longwave UV light (the black light commonly used in clubs and jewellery counters).
CZ also fluoresces, but with a distinctive yellow-orange colour. Most moissanite fluoresces differently (yellow or green depending on the specific material).
UV examination is a useful supplementary tool — not definitive on its own, but able to provide quick supporting evidence in ambiguous cases.
A standard UV flashlight (365nm longwave UV) costs ₹500–₹1,500 and is a reasonable addition to any serious buyer's toolkit.
10x Magnification (Loupe Examination)
Under a 10x magnification loupe:
- Moissanite vs Diamond: Moissanite has a double-refracting crystal structure. When viewed through the stone at approximately 45 degrees toward the back facets, the rear facet edges appear doubled — you see two lines where a diamond shows one. This is one of the most reliable loupe-visible tests. Diamond does not double-refract.
- CZ vs Diamond: CZ is visually very clean (usually no inclusions) and may show rounded facet edges under magnification (diamonds have sharp, crisp facet edges). CZ also has a slightly different surface lustre — "adamantine" for diamond, slightly different for CZ.
- Glass vs Diamond: Glass may show tiny bubbles (spherical inclusions) under magnification; diamonds never contain bubbles. Glass facet edges are often chipped or rougher; diamond facet edges are razor-sharp.
- GIA laser inscription: On GIA-certified diamonds, the certificate number is laser-inscribed on the girdle. This is visible under a loupe and is the most important thing to verify on any certified purchase.
Spectroscopic Testing (Only at a Lab)
Spectroscopy — particularly FTIR (Fourier Transform Infrared Spectroscopy) and Raman Spectroscopy — provides a definitive, unambiguous identification of the stone's material composition.
These instruments identify the specific spectral "fingerprint" of diamond, moissanite, CZ, glass, or any other material with certainty.
This technology is only available at gemological laboratories (GIA, IGI, SSEF, etc.) — not in retail stores.
For high-value purchases where any doubt exists after all other tests, laboratory submission is the definitive answer.
What Consumers Should Do: A Practical Protocol
Step 1: Buy Certified
The single most effective protection against diamond fraud is buying only certified stones — GIA for natural diamonds above 0.5ct, IGI for lab-grown diamonds.
A legitimate GIA certificate with a verifiable online report and a matching laser inscription on the stone eliminates almost all fraud risk without requiring any testing at all.
Step 2: Verify the Certificate Online
Visit gia.edu/report-check (for GIA certificates) and enter the report number. Verify all details match what is on the paper certificate.
Do this before leaving the store — not after you are home. For IGI, use igi.org/reports to verify.
Step 3: Confirm the Laser Inscription
Ask the jeweller for a 10x loupe and look at the stone's girdle. The GIA or IGI report number should be laser-inscribed and visible.
Confirm it matches the certificate. If the jeweller does not have a loupe, that itself is a red flag at any store selling diamond jewellery.
Step 4: Insist on a Thermal Test for Uncertified Stones
If you are buying an uncertified stone (which you should generally avoid for significant purchases), ask for a combined thermal-electrical test.
If the jeweller does not have the equipment or refuses to demonstrate it, that is a serious red flag.
Red Flags: Seller Behaviour That Warrants Caution
| Seller Behaviour | What It May Indicate |
|---|---|
| Refuses online certificate verification in-store | Certificate may be fake or unregistered |
| Cannot show laser inscription with a loupe | Stone may not match certificate |
| Price dramatically below market for stated grade | Grade inflation on certificate; stone may be lower quality |
| Provides only domestic lab (SGL/IGL) certificate for significant stone | Grade may not be reliable; resale will reflect this |
| Rushes you away from examining the stone | Examination would reveal something unfavourable |
| "I'll give you a certificate later" / certificate not present at point of sale | Certificate may not exist or may be fabricated after sale |
| No fixed address or online presence; market stall or door-to-door | No recourse if stone is fraudulent |
| Offers significant discount only if you "decide today" | High-pressure tactics to prevent verification |
No post-purchase test is as effective as buying correctly in the first place. A GIA-certified diamond from a BIS-registered, established jeweller with a physical address, a clear return policy, and a verified online presence is essentially fraud-proof. All the testing protocols above are for when you are unsure — the goal is never to be in that situation. Spend your energy choosing the right seller rather than planning how to detect fraud after the fact.
Diamond buying in India is overwhelmingly honest — the vast majority of established jewellers in India's towns and cities sell exactly what they say they are selling.
The fraud risk is concentrated in informal markets, online peer-to-peer transactions, "too good to be true" deals, and sellers without established reputations.
Stay within the established, verified network — BIS-registered jewellers, banks, and certified bullion dealers — and your diamond purchase will be as safe as any significant financial transaction can be.
Use JewellersinCity to find verified jewellers in your city with transparent diamond certification practices and authentic GIA/IGI stones.
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Our editorial team comprises jewellery industry veterans, certified gemmologists, and passionate writers with decades of combined experience across India's gold, diamond, and gemstone markets. Every article is researched, fact-checked, and written to help Indian buyers make smarter, safer jewellery decisions.
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