Will a Lab-Grown Diamond Pass a Diamond Tester? Yes. Here Is Why

Common examples of Diamond Testers are: Presidium Gem Tester II, Presidium Multi Tester III, and other similar handheld pen testers.

The Short Answer

The short answer is yes. A lab-grown diamond will pass a standard diamond tester, and it will pass it with exactly the same confidence as a natural diamond mined from the ground. This is not a flaw in the tester. A lab-grown diamond is a diamond, chemically and physically identical to a natural one, and a diamond tester is built to answer one narrow question: is this stone made of diamond? For a lab-grown stone, the honest answer to that question is yes.

The problem is that most people who pick up a diamond tester are not asking "is this diamond material?" They are asking "is this a natural diamond?" Those are two different questions, and the second one is the one that carries the financial and legal risk in 2026. This guide explains what each kind of diamond tester actually measures, why lab-grown diamonds sail through, why a few of them confusingly fail, and what kind of instrument you need if the question you are really asking is natural or lab-grown.

What a Diamond Tester Actually Detects

A standard diamond tester is a handheld probe that measures a physical property of the stone, almost always thermal conductivity, electrical conductivity, or both.

A thermal diamond tester works because diamond moves heat away from a warm probe tip faster than almost any other gem material. Touch the tip to a stone, and if the heat drains quickly, the meter reads "diamond." Cubic zirconia, glass, white sapphire and most other simulants conduct heat poorly, so they read as "not diamond." That is the entire test.

An electrical diamond tester, or the electrical half of a combination tester, measures how readily a small current passes through the stone. This was added to the market for one reason: moissanite. Moissanite conducts heat as well as diamond, sometimes better, so a thermal-only tester reads moissanite as diamond nearly every time. Moissanite does, however, conduct electricity in a way most diamonds do not, so a combination thermal and electrical tester can separate the two in most cases.

Notice what is missing from both tests: origin. Neither thermal nor electrical conductivity carries any information about where a diamond formed or how. The tester is reading the material, not the history.

Why a Lab-Grown Diamond Passes a Diamond Tester

Lab-grown diamonds are produced by two methods. HPHT (high pressure, high temperature) replicates the conditions under which natural diamonds crystallize, and CVD (chemical vapor deposition) grows diamond layer by layer from a carbon-rich gas. Both produce real diamond: pure carbon in the same cubic crystal lattice, with the same hardness, the same refractive index, the same thermal conductivity and the same density as a natural diamond.

Because a diamond tester measures thermal conductivity, and lab-grown diamond has the thermal conductivity of diamond, the tester reads "diamond." A CVD stone grown last month and a natural stone that formed over a billion years ago produce the same reading on the same meter. There is no setting, no calibration trick and no premium model of thermal tester that changes this. The tester is working correctly. It was simply never built to detect lab-grown diamonds.

This is the single most important thing for a jeweler, a pawnbroker, an appraiser or a buyer to understand about diamond testing today: passing a diamond tester confirms that a stone is diamond. It does not confirm that the stone is natural.

Why Some Lab-Grown Diamonds Fail a Diamond Tester

Here the picture gets more confusing, and it is worth being precise, because the confusion causes real mistakes at the counter.

Occasionally a lab-grown diamond will fail a combination tester, reading as "moissanite" rather than "diamond." This happens most often with HPHT-grown stones. During HPHT growth, boron can be incorporated into the crystal, and boron makes diamond electrically conductive. Some HPHT stones also retain microscopic metallic flux inclusions from the growth process. Either can trip the electrical half of a combination tester, which was tuned to treat electrical conductivity as the signature of moissanite.

The same thing happens with natural boron-bearing diamonds, the rare type IIb stones that include most natural blue diamonds. They conduct electricity too, and they can also read as moissanite on a combination tester.

So a "fail" on a diamond tester does not mean lab-grown, and a "pass" does not mean natural. A tester cannot be read backwards to infer origin. A stone that reads "moissanite" could be moissanite, a boron-doped HPHT lab-grown diamond, or a natural blue diamond. A stone that reads "diamond" could be natural, CVD lab-grown, or HPHT lab-grown. The tester has done its job either way; it has told you about conductivity, and nothing else.

Diamond Tester Results at a Glance

What About UV Diamond Testers and "Diamond Tester Color Meaning"?

A newer generation of handheld diamond testers adds a long-wave ultraviolet lamp, usually around 365 nm, alongside the conductivity probe. The idea is that natural and lab-grown diamonds often respond differently to ultraviolet light, so the operator looks at the fluorescence color and draws a conclusion. Searches for "diamond tester color meaning" are usually people trying to interpret this.

Ultraviolet response is a real signal, and it is in fact the physical principle that proper diamond screening devices are built on. But a handheld UV lamp used by eye, in a lit room, with a single long-wave source, is a weak version of it. Many natural diamonds show no visible fluorescence under long-wave UV at all. Many lab-grown stones show none either. The distinguishing responses, especially under short-wave (deep) UV and in the phosphorescence that follows, are often faint, brief and impossible to judge reliably by eye in a jewelry store. A handheld UV tester can raise a suspicion. It cannot clear a stone, and it cannot be relied on to catch one.

For a full breakdown of the three tiers of diamond detecting equipment and where each one fails, read our guide, Diamond Tester vs Diamond Screening Device.

Why This Matters More in 2026 Than It Did Five Years Ago

Lab-grown diamonds now make up a large share of the stones moving through the trade, and the price gap between a lab-grown and a natural diamond of the same size and quality has widened to the point where a single misidentified stone can cost a business thousands of dollars, and its reputation. Lab-grown melee is routinely found mixed into parcels and set in finished jewelry, sometimes without the seller's knowledge. Estate pieces, trade-ins, memo goods and returns all arrive without a reliable paper trail.

A diamond tester remains a useful tool for what it does, separating diamond from CZ and, with the electrical check, from moissanite. But a business that relies on a diamond tester as its only line of defense is checking the one thing that is no longer the main risk, and leaving the main risk unchecked.

What Detects Lab-Grown Diamonds: The Diamond Screening Device

The instrument built to answer "natural or lab-grown" is a diamond screening device, also called a diamond screener or diamond verification device. Instead of touching the stone with a probe, it images the stone under controlled ultraviolet excitation inside a dark chamber and reads the response.

The physics is this: natural diamonds and lab-grown diamonds crystallize under different conditions, and those conditions leave different defects in the carbon lattice. The overwhelming majority of natural diamonds contain nitrogen arranged in a particular way, and that structure produces a characteristic blue fluorescence under deep ultraviolet light with little or no afterglow. Lab-grown diamonds, grown far faster and in far purer or differently doped environments, produce different responses: a different fluorescence color, a persistent phosphorescence after the UV source is switched off, or both. Simulants produce their own distinct patterns, and a cubic zirconia or moissanite stands out as clearly as a lab-grown stone does.

The REVEAL Diamond Detector 3S and REVEAL Diamond Detector 2S from JTR, Jewellery Technology Research, are diamond screening devices built on exactly this principle. Each stone is captured in several image modalities. The REVEAL Diamond Detector 2S captures images in Daylight, Deep UV (fluorescence) and Phosphorescence, with images under different exposures for each modality. The REVEAL Diamond Detector 3S captures those three and adds Long UV as a fourth standard modality, a second excitation wavelength that gives the operator more evidence per stone.

Three practical differences from a diamond tester follow from this.

The stones do not need to be touched one at a time. A tray of loose stones, a bag of melee, or a finished piece of jewelry with mounted stones is placed in the chamber and screened in a single cycle, with every stone in the image evaluated at once. The REVEAL Diamond Detector 3S screens up to 100 loose stones per batch with auto-detection, provided the stones do not touch.

The result is about origin, not material. On the REVEAL Diamond Detector 3S, auto-detection classifies every stone larger than 1 mm and returns one of four results: Natural, Potential Lab-Grown, Potential Simulant or Undetermined, the last meaning the instrument could not obtain a sufficient reading and the stone should be repositioned and run again. Lab-grown and simulant are separate verdict classes, so a flagged stone comes back with a reason, not an undifferentiated warning. The raw images stay on screen beside every verdict, so the operator always has the evidence and the final call. On the REVEAL Diamond Detector 2S, the operator reads the same images against reference patterns, and existing 2S owners can add auto-detection through JTR's upgrade program.

The performance is independently measured. Both instruments have been tested under ASSURE 2.0, the independent protocol for diamond verification instruments run on behalf of the Natural Diamond Council, with fact sheets published in the ASSURE Directory. The REVEAL Diamond Detector 3S, tested in September 2026, recorded a Diamond False Positive Rate of 0.0% on every sample set, loose, smalls and mounted: no lab-grown stone was ever passed as natural, which is to say a 100% lab-grown and simulant detection rate. Its Diamond Referral Rate on the Primary Loose set was 4.2%, meaning roughly one natural diamond in twenty-four was flagged for a second look rather than cleared immediately, and its test speed was 553 stones per hour. The REVEAL Diamond Detector 2S, tested in April 2025, recorded the same 0.0% false positive rate with a 5.6% referral rate at 421 stones per hour. A diamond tester has no equivalent figure for lab-grown detection, because a diamond tester does not detect lab-grown diamonds.

A Practical Workflow: Tester and Screener Together

The two instruments are not rivals; they answer different questions, and many businesses run both. A sensible counter workflow in 2026 looks like this. A diamond tester is a quick first check on an unknown stone: is this even diamond material, or is it CZ or glass? Anything that reads as diamond, or as moissanite, then goes through a diamond screening device, which separates natural from lab-grown and from simulants. Stones the screener clears as Natural are cleared. Stones it flags as Potential Lab-Grown or Potential Simulant go to a gemologist or a laboratory for confirmation.

This is, in outline, how large operations already work. In one well-known online retailer's quality control process, novice operators run the REVEAL as the first line of defense, stones that fluoresce blue under deep UV are passed, and anything questionable goes to in-house graduate gemologists for the final verdict. The screening device does the volume; the experts handle the exceptions.

Frequently Asked Questions

Will a lab-grown diamond pass a diamond tester? Yes. A lab-grown diamond is a real diamond with the same thermal conductivity as a natural diamond, so a thermal diamond tester reads it as "diamond." A diamond tester checks whether a stone is diamond material; it cannot tell natural from lab-grown.

Do diamond testers work? Yes, for the job they were built for. A diamond tester reliably separates diamond from cubic zirconia, glass and most other simulants, and a combination thermal and electrical tester separates diamond from moissanite in most cases. It does not detect lab-grown diamonds.

Can moissanite pass a diamond test? On a thermal-only tester, yes, nearly every time, because moissanite conducts heat as well as diamond. A combination tester with an electrical check will usually identify moissanite correctly.

Is there a lab-grown diamond tester? Not in the handheld probe sense. Detecting lab-grown diamonds requires a diamond screening device, which images the stone under ultraviolet light and reads its fluorescence and phosphorescence. The REVEAL Diamond Detector 3S & 2S are diamond screening devices built for this purpose and tested under the independent ASSURE 2.0 protocol.

Is there a CVD diamond tester or an HPHT diamond tester? A diamond screening device detects both. CVD and HPHT lab-grown diamonds leave different signatures under deep UV and in phosphorescence, and both are separated from natural diamonds by the same screening process. The REVEAL Diamond Detector 3S reports either as Potential Lab-Grown.

Why did my lab-grown diamond fail the diamond tester and read as moissanite? Some HPHT lab-grown diamonds contain boron or metallic inclusions that make them electrically conductive, which the electrical check on a combination tester interprets as moissanite. Natural blue diamonds can do the same. A moissanite reading on a conductive diamond is a limitation of the tester, not evidence of origin either way.

What does the diamond tester color mean on a UV tester? On handheld UV testers, blue fluorescence is often treated as a sign of natural origin and other colors or no response as a reason for suspicion. The signal is real but weak when judged by eye under long-wave UV alone; many natural diamonds show no fluorescence and some lab-grown stones mimic the response. Reliable interpretation requires deep UV, controlled imaging and phosphorescence capture, which is what a diamond screening device provides.

What is the best tool to test lab-grown versus natural diamonds? A diamond screening device with an independently published ASSURE 2.0 fact sheet, so that its lab-grown detection rate and referral rate are measured by a third party rather than claimed by the manufacturer. The REVEAL Diamond Detector 3S & 2S both hold a published 0.0% Diamond False Positive Rate across every ASSURE 2.0 sample set.

About JTR

JTR, Jewellery Technology Research, designs and manufactures the REVEAL Diamond Detector 3S & 2S diamond screening devices and the LOUPE S 10x triplet loupe, with offices in New York, Istanbul and Shenzhen. Every REVEAL screens, auto-detects and receives complimentary lifetime software updates with no subscription. Both instruments are solid state with no mechanical parts and require no calibration. Fact sheets for both are published in the ASSURE Directory.