Last Updated: April 2026
TL;DR:
- Lab-grown diamonds pass every standard thermal-conductivity diamond tester because they’re chemically identical carbon crystals — the tester can’t tell lab from mined.
- 61% of U.S. engagement rings now feature a lab-grown center stone, up from just 6.3% in 2019, according to JCK.
- The only reliable way to identify a lab diamond is the laser-inscribed report number on the girdle — not a handheld tester.
Lab-grown diamonds have taken over engagement ring counters, and the reason is simple: brilliant shine at a fraction of the price. Since they’re grown from the same carbon atoms as mined stones, a natural question comes up constantly in my shop — will lab made diamonds pass a diamond tester? I’ll walk you through exactly why the answer is yes, what actually tells them apart, and how the two lab-growing methods, HPHT and CVD, differ. If you’re also weighing a mined stone as an investment purchase, keep that context in mind as you read.
Will Lab-Grown Diamonds Pass a Diamond Tester?
Yes. Lab-grown diamonds pass thermal-conductivity diamond testers every time. The probe measures how fast heat moves through the stone, and lab diamonds conduct heat at the exact same rate as mined diamonds — around 2,200 watts per meter-kelvin — because both are pure carbon crystallized in the same cubic structure.
A tester lights up green or beeps “diamond” for both types. It was never built to spot the difference — it was built to catch cubic zirconia and glass, which conduct heat far slower. According to Brilliant Earth, a $30 pen tester from a jewelry supply catalog simply cannot distinguish origin, only mineral identity.
Why Does the Tester Fail to Tell Them Apart?
Diamond testers use one of two methods: thermal conductivity or a combination thermal-and-electrical-conductivity probe. Either way, they’re checking atomic structure, not birthplace. A lab-grown diamond formed in a Chicago factory chamber has the same lattice as one pulled from a South African kimberlite pipe 3 billion years ago. Same hardness (10 on the Mohs scale), same refractive index (2.42), same thermal signature.
Only advanced gemological equipment — spectroscopy that reads trace nitrogen patterns or growth-line fluorescence under UV — can separate the two. That equipment costs upwards of $15,000 and sits in labs like GIA’s, not on a jeweler’s countertop. If you want to see how the basic tools actually work, our diamond tester breakdown covers the mechanics step by step.
What Are HPTP Diamonds?
HPHT stands for High Pressure/High Temperature — a process invented in the 1950s that squeezes carbon at roughly 2,600°C under crushing pressure to force it into a diamond lattice in under two weeks. Manufacturers also use HPHT to clean up cheap, flawed diamonds into higher color grades.
The process mimics what happens naturally inside the earth’s mantle, just compressed into a machine instead of a few billion years. Cheaper, included rough is fed into the press to remove brown or gray tints and push the stone toward a colorless D-E-F grade.
Pros of HPHT Diamonds
- Reprocessing minimizes internal strain, so the finished crystal is often structurally stronger than an untreated stone.
- The atomic rearrangement can push a stone into D or E color grade — the top of the scale.
- Even after grading up, HPHT stones typically sell for roughly half the price of a naturally colorless diamond of the same grade.
Cons of HPHT Diamonds
- Colorless HPHT stones can betray faint blue, brown, or yellow flashes when viewed at an angle.
- Internal flux (a byproduct of the growth process) can dent clarity.
- The stones lose a small amount of weight during processing.
- Magnetic fields used in the HPHT chamber leave many stones weakly magnetic — a trait real mined diamonds never have.
- Only rough between VVS1 and flawless clarity survives the process intact; anything lower-grade risks fracturing under the pressure.
What Are CVD Diamonds?
CVD means Chemical Vapor Deposition, a method used since the 1980s that grows diamonds inside a vacuum chamber filled with methane and hydrogen gas. A laser ionizes the gas, releasing carbon atoms that bond layer by layer onto a diamond seed until it crystallizes into a full-size gem.
A technician locks a diamond seed into a chamber heated to about 800°C, then pumps in the gas mixture. As carbon builds up on the seed, it forms a black-coated crystal that gets cut and polished to reveal the clear stone underneath. Unlike HPHT’s two-week turnaround, CVD is slow — a 1-carat stone typically takes about a month to grow, and smaller target sizes can take even longer.
Pros of CVD Diamonds
- Lower production overhead than mining means CVD stones typically cost 20-30% less than a comparable mined diamond, sometimes more.
- No mining means no land disruption. According to JCK, that environmental argument is a major driver of the category’s growth.
- Traditional mining disturbs roughly 100 square feet of land and displaces about 6,000 pounds of mineral debris per carat recovered — CVD sidesteps that entirely.
- CVD diamonds still qualify for full GIA grading reports, so you get the same 4Cs documentation as a mined stone.
Cons of CVD Diamonds
- The growth process isn’t perfectly controlled, so faint color tints can still show up.
- Growth striations — thin graining lines — are sometimes visible to the naked eye on larger stones.
How Can a Jeweler Tell If a Tester Can’t?
Jewelers identify lab-grown diamonds through the laser inscription etched into the girdle, not through a tester. Every diamond graded by GIA or IGI gets a report number inscribed at microscopic scale, and lab-grown stones are explicitly labeled “Laboratory-Grown” right on the stone itself.
You’ll need a jeweler’s loupe (10x magnification minimum) to read it, but it’s there on every certified stone. If your ring doesn’t have a visible inscription or accompanying report, that’s a red flag worth asking about before you buy — not a reason to assume it’s fake. Our guide on whether a jeweler can spot a lab diamond covers the full verification process, including spectroscopy and fluorescence testing that advanced labs use.
Once you have the report number, you can look it up directly on the grading lab’s website to confirm origin, carat, color, and clarity match what you were told at purchase.
Do Moissanite or Cubic Zirconia Also Pass a Diamond Tester?
Moissanite frequently passes basic thermal testers too, which is why jewelers now use combined thermal-and-electrical testers to catch it — moissanite conducts electricity, real diamond doesn’t. Cubic zirconia, on the other hand, almost always fails a standard tester because its thermal conductivity is far lower than diamond’s.
This is exactly why a single $30 pen tester isn’t enough proof either way. For the full mechanics on each simulant, see our breakdowns on whether moissanite passes a diamond tester and whether cubic zirconia passes a diamond tester.
Lab Diamonds vs. Natural Diamonds: Price and Market Share in 2026
The price gap has widened fast. A well-cut, certified 1-carat lab-grown diamond now runs roughly $700-$1,500 depending on color and clarity, down more than 70% from 2020 prices. A comparable mined stone of the same grade often costs 4-6 times more. That gap is the single biggest reason lab-grown center stones jumped from 6.3% of engagement rings in 2019 to 61% today.
Both HPHT and CVD stones are also considered slightly more structurally sound than untreated mined diamonds, since the controlled growth process reduces internal strain. If you’re curious whether that durability edge holds up under daily wear, our post on whether synthetic diamonds are as hard as real diamonds breaks down the hardness data. And if resale value matters to your decision, read whether lab-created diamonds hold any resale value before you buy.
The Bottom Line
Lab-grown diamonds will pass any thermal or thermal-electrical diamond tester you put them through, full stop — the tester checks atomic structure, and a lab diamond’s atomic structure is identical to a mined one’s. The only trustworthy way to confirm origin is the laser-inscribed report number on the girdle, checked against the grading lab’s database. Whether you go HPHT or CVD, insist on a GIA or IGI report before you buy, and check that inscription with a loupe. If you’re still weighing whether any diamond purchase makes financial sense, read whether diamonds are a good investment before you commit to a stone.
Frequently Asked Questions
Can a regular diamond tester tell lab-grown from natural?
No. Standard thermal and thermal-electrical testers only confirm a stone is diamond material — they cannot detect origin. Lab-grown and mined diamonds share identical thermal conductivity, so both trigger the same “diamond” reading every time.
Do lab-grown diamonds have the same hardness as natural diamonds?
Yes. Both rate a 10 on the Mohs hardness scale because they’re made of the same carbon lattice. HPHT reprocessing can even reduce internal strain, making some lab stones marginally more resistant to chipping than untreated mined rough.
How long does it take to grow a lab diamond?
HPHT diamonds can be finished in under two weeks. CVD diamonds take longer — roughly a month to grow a 1-carat stone, with smaller target sizes sometimes taking even more time due to the slower atom-by-atom bonding process.
Are lab-grown diamonds cheaper than mined diamonds?
Yes, significantly. A certified 1-carat lab-grown diamond typically costs $700-$1,500 in 2026, compared to several times that for a mined stone of equal color and clarity, largely because lab diamonds skip mining, exploration, and distribution overhead.
Do lab-grown diamonds come with GIA certification?
Yes. GIA issues a dedicated Laboratory-Grown Diamond Report covering the same 4Cs as a natural diamond report, and the stone’s girdle is laser inscribed with both the report number and the words “Laboratory-Grown.”
Can moissanite or cubic zirconia fool a diamond tester?
Moissanite often passes basic thermal testers, which is why combined thermal-electrical testers exist — moissanite conducts electricity and diamond doesn’t. Cubic zirconia almost always fails a standard tester since its thermal conductivity is much lower than diamond’s.
Why do lab diamonds look identical to natural diamonds?
Because they are chemically, physically, and optically the same material — pure crystallized carbon. Lab diamonds share the same refractive index, hardness, and brilliance as mined stones; the only difference is where and how the crystal formed, first demonstrated by General Electric back in 1955, according to Science Friday.
Stephanie is a jewelry lover when she was a teenager. Her major was fashion design when she was in college. She is a jewelry designer at SOQ Jewelry and other design companies. Now she is also a writer for our website. She writes a lot of designs&brands posts with very actionable tips.