Do Lab-Grown Diamonds Pass Diamond Testers?
- nishalgems
- 6 days ago
- 6 min read
You're at a jewellery counter. The jeweller pulls out a small pen-like device, touches it to the stone, and it beeps. "Diamond," they say.
But what exactly just happened? And if you had handed over a lab-grown diamond instead — would it have beeped the same way?
The short answer is: yes. Lab-grown diamonds pass standard diamond testers — because they are real diamonds, made of the same pure carbon crystal structure as any stone formed deep in the earth. But the full story is more nuanced, and understanding it will make you a much more confident buyer.
How Does a Diamond Tester Actually Work?
Most diamond testers you'll encounter in jewellery stores are thermal conductivity testers. They work by passing a small amount of heat through the surface of the stone and measuring how quickly that heat is conducted away.
Diamond is the best thermal conductor of any natural material — significantly better than glass, cubic zirconia, or most other gemstones. When the tester's tip touches a diamond, heat dissipates almost instantly. The device detects this rapid conduction and signals "diamond".
1.Heat is applied to stone surface
The tester's metal tip conducts a tiny pulse of warmth onto the gemstone surface.
2.Conductivity is measured
The device measures how quickly heat moves away from the tip — diamond conducts heat extremely fast.
3.Result is compared to database
If conductivity matches diamond's profile, the tester signals positive — regardless of the stone's origin.
4.Lab-grown reads identical
Because CVD lab-grown diamonds are chemically pure carbon, their thermal conductivity is the same as mined diamonds.
Nishal Gems Expert Note
The thermal conductivity of a CVD lab-grown diamond is identical to that of a natural diamond — both are pure carbon in a crystalline structure. A thermal tester measures physical properties, not geological origin. The tester has no way of knowing where the stone was formed.
Which Types of Testers Do Lab-Grown Diamonds Pass?
There are several types of gemstone testing equipment used in the industry. Here is how lab-grown diamonds perform on each:
Tester Type | Lab-Grown Result | What It Measures | Available Where |
Thermal conductivity tester | ✅ Passes as Diamond | Heat conduction speed | Most jewellery stores |
Electrical conductivity tester | ✅ Passes as Diamond | Electrical resistance | Some jewellers |
Multi-tester (thermal + electrical) | ✅ Passes as Diamond | Both heat and electrical | Professional jewellers |
UV fluorescence lamp | ℹ️ May show differently | Fluorescence response | Gemological labs |
Specialist LGD detector (Diamond View, etc.) | ℹ️ Identifies as lab-grown | Growth pattern & UV luminescence | IGI / GIA labs only |
Important Transparency Note
Specialist equipment at certified gemological laboratories — such as the GIA's DiamondView — can identify lab-grown diamonds by analysing their unique growth patterns under deep UV light. This is not deception; it is the technology used to certify and disclose the stone's lab-grown origin on your grading certificate. At Nishal Gems, every stone comes with full disclosure and IGI certification.
Why Do Lab-Grown Diamonds Pass — What Does That Tell Us?
The fact that lab-grown diamonds pass thermal testers is not a technicality or a loophole. It is direct physical evidence of what lab-grown diamonds fundamentally are real diamonds.
A thermal tester does not ask "where did this stone come from?" It asks: "does this stone conduct heat at the rate of pure carbon crystal?" And the answer, for a lab-grown diamond, is always yes — because the carbon crystal structure is identical.
◆ The Science Behind It
Diamond's extraordinary thermal conductivity — around 5 times higher than copper — comes from its crystal lattice structure: carbon atoms arranged in a rigid tetrahedral pattern that allows phonons (heat carriers) to travel exceptionally fast. CVD lab-grown diamonds share this exact same crystal lattice. There is no physical difference that a thermal instrument can detect.
What About Moissanite — Why Is It Different?
You may have heard that moissanite — a popular diamond simulant — can fool older thermal testers. This is because moissanite has unusually high thermal conductivity for a non-diamond stone, causing some basic testers to register a false positive.
This is why modern jewellers use multi-testers that combine thermal and electrical conductivity. Moissanite is electrically conductive; natural and lab-grown diamonds are not. The combination test instantly separates them.
Natural diamond: Passes thermal ✅ · Fails electrical ✅ → Confirmed diamond
Lab-grown CVD diamond: Passes thermal ✅ · Fails electrical ✅ → Confirmed diamond
Moissanite: Passes thermal ✅ · Passes electrical ❌ → Identified as moissanite
Cubic zirconia: Fails thermal ❌ → Immediately ruled out
Does This Mean Lab-Grown Diamonds Are "Fake Diamonds"?
Absolutely not — and the diamond tester result is one of the clearest proofs of this.
A "fake diamond" — cubic zirconia, glass, or white sapphire — would not pass a thermal diamond tester. It fails immediately, because its molecular structure is completely different from diamond. The tester's response is based on physics, not marketing.
Lab-grown diamonds pass because they are diamonds. The US Federal Trade Commission, the GIA, and the IGI all recognise lab-grown diamonds as genuine diamonds. They are chemically, physically, and optically identical to mined stones — grown from the same element (carbon) in the same crystal structure (cubic), just in a different location.
Nishal Gems Perspective
At Nishal Gems, we have been in the diamond industry since 1992. When customers ask whether our CVD lab-grown diamonds are "real," we sometimes hand them a thermal tester. The beep answers the question more convincingly than any explanation. Physics does not lie.
What Does the Certificate Tell You?
Every lab-grown diamond from Nishal Gems comes with an IGI grading certificate. This certificate does two things that no thermal tester can:
It confirms the stone's 4Cs — cut, colour, clarity, and carat — graded to the same standard as mined diamonds
It clearly states the stone is "laboratory-grown" — full transparency about origin
The combination of passing a diamond tester and carrying an IGI certificate gives you complete confidence: the stone is a genuine diamond, and you know exactly what you have purchased.
New BIS Standard — January 2026
The Bureau of Indian Standards issued IS 19469:2025 in January 2026, mandating that lab-grown diamonds be clearly labelled as "laboratory-grown diamond" or "laboratory-created diamond." This is a consumer protection measure that Nishal Gems fully supports — transparency about origin is a standard we have always upheld.
Frequently Asked Questions
Will a lab-grown diamond pass a basic pen tester at a jewellery shop?
Yes. Standard thermal pen testers used in most jewellery stores will register a lab-grown diamond as a genuine diamond. The test measures thermal conductivity — a physical property that is identical in lab-grown and mined diamonds.
Can any equipment tell the difference between lab-grown and mined?
Specialist equipment used at gemological laboratories — such as the GIA DiamondView or HPHT detection tools — can identify a diamond's origin by analysing growth patterns under specialised UV light. This equipment is not available in standard jewellery stores and is used primarily by grading labs for certification purposes. The result is disclosed on your certificate.
Does a lab-grown diamond look different from a mined diamond?
No. Even experienced gemologists cannot visually distinguish a lab-grown diamond from a mined diamond. The sparkle, brilliance, and fire are identical because the optical properties — refractive index, dispersion, and hardness — are the same.
Is it deceptive to sell a lab-grown diamond that passes diamond testers?
Not when the diamond is properly certified and disclosed. All Nishal Gems lab-grown diamonds come with IGI certificates that clearly state their laboratory origin. The BIS standard (IS 19469:2025) also requires retailers to label lab-grown diamonds explicitly. Passing a thermal tester is simply a reflection of the stone being a real diamond — which it is.
How do I know the lab-grown diamond I buy from Nishal Gems is genuine?
Every diamond we supply comes with an IGI grading certificate documenting its 4Cs and confirming its lab-grown origin. You can also test it with any standard thermal diamond tester — it will confirm you have a real diamond.
Interested in sourcing CVD lab-grown diamonds? contact our team to discuss your requirements.
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