If you are trying to work out how to tell if a diamond is lab grown, start with the fact that settles most of the question: you cannot do it by looking, and the handheld diamond tester at a pawn counter cannot do it either. A lab-grown diamond is a real diamond, and it passes the same checks a mined one does.
GIA states that laboratory-grown diamonds are essentially chemically and optically the same as natural diamonds, so traditional gemological observations and instruments cannot tell them apart. To know for certain, the stone has to go to a gemological laboratory for advanced testing. What you can check at home is the paperwork, the girdle inscription, and the age of the setting.
That shifts the question from “what does the stone look like” to “what evidence came with it,” which is a question you can actually answer.
Lab grown is not fake: what the label means
Start with the definitions, because they decide what you are testing for. Under the FTC Jewelry Guides, a diamond is a mineral of essentially pure carbon crystallized in the isometric system. Lab-grown stones meet that definition. What the guides require is disclosure: laboratory-created diamonds with essentially the same optical, physical, and chemical properties as mined diamonds must be qualified with a clear term such as “laboratory-grown,” “laboratory-created,” or “[manufacturer name]-created” so no one mistakes them for a mined stone.
So there are three different things people lump together:
- A natural diamond: mined, formed in the earth.
- A lab-grown diamond: real diamond, grown by a manufacturer, legally required to be disclosed as such.
- A simulant: something that only imitates diamond, such as cubic zirconia, moissanite, or glass.
A simulant is the “is it real” question, and it can often be answered with a tester and a loupe, as covered in how to tell if a diamond is real and moissanite vs diamond. Lab grown vs natural is a different question with a different toolkit.
Why a diamond tester won’t tell you if a diamond is lab grown
The common handheld diamond tester reads how fast the stone carries heat away. Diamond conducts heat exceptionally well, which is what separates it from cubic zirconia and glass. A lab-grown diamond is diamond, so it passes that test in exactly the same way.
Loupe inspection has the same limit. Inclusions, color, and cut quality vary across both natural and lab-grown stones, and GIA’s position is that traditional observation is not enough to separate them. Any website that promises a home trick (breath fog, a water glass, a newspaper under the stone) is testing for simulants at best, and none of those tricks can tell a grown diamond from a mined one.
The instruments that can screen are spectroscopy devices used by labs and larger jewelers. GIA’s iD100, for example, is a desktop screening device that separates natural diamonds from stones that need further testing, such as laboratory-grown diamonds and simulants. If you want an answer without sending the stone away, ask a jeweler whether they have a screening device of that type, and ask what they do with a result that gets referred for further testing.
The checks you can do at home
These do not prove anything on their own, but together they usually tell you where you stand.
1. Look for a girdle inscription
Many graded diamonds carry a tiny laser inscription on the girdle, the thin outer edge of the stone. GIA says laboratory-grown diamonds it grades are laser-inscribed with the report number and the words “LABORATORY-GROWN.” You need at least 10x magnification to read it, and good light angled across the girdle. Our guide to how to use a jeweler’s loupe covers the holding technique that makes these inscriptions readable.
What the inscription tells you:
- A report number lets you look the stone up on the issuing lab’s website. The report states whether the stone is natural or laboratory-grown.
- “LAB GROWN,” “LABORATORY-GROWN,” or a similar word is a direct disclosure.
- No inscription proves nothing either way. Plenty of natural diamonds, and plenty of older or smaller stones, are not inscribed, and an inscription can be polished off.
2. Find the paperwork
A grading report, an appraisal, or an original receipt is often the most useful evidence you have. GIA’s laboratory-grown reports use a distinct format from its natural diamond reports, and state whether the stone was grown by the CVD (chemical vapor deposition) or HPHT (high pressure, high temperature) method. If a report names a growth method, you have your answer.
3. Date the setting
This is the check most guides skip, and for inherited jewelry it is often the strongest. Gem-quality synthetic diamond crystals were first produced by GE in 1970 and reported in 1971, and those early stones were yellow to brown. A center diamond sitting in an original mount that clearly predates that era, such as an old mine cut diamond in a hand-fabricated setting, is very unlikely to be lab grown.
Two cautions keep this honest. A stone can be reset, so the setting dates the mount, not necessarily the stone. And small accent stones deserve their own suspicion: reports of undisclosed synthetic melee (the small round stones framing a center diamond or lining a band) being found in set jewelry and trade parcels began emerging in 2013. A vintage-looking piece made or repaired recently can mix old and new.
4. Ask the right question when you buy
If you are buying rather than holding, the FTC disclosure rule does the work for you. Ask in writing: “Is this diamond natural or laboratory-grown?” A seller who will not put the answer on the receipt is telling you something.
Why it matters for value
This is where the distinction stops being academic. Natural and lab-grown diamonds of similar size and grade sell in different markets at different prices, and resale buyers treat them differently. Before you insure, sell, or pass a piece on, it is worth knowing which one you have, and for a significant stone that means a lab report.
A practical order of operations:
- Rule out simulants first with the checks in how to tell if a diamond is real.
- Look for an inscription and any paperwork.
- Date the setting and note whether the center stone looks original to it.
- For a stone that matters, get a laboratory report before you set a price.
The ring guide covers reading the rest of the piece, the metal marks and setting style, and our jewelry value guide explains how a lab result feeds into a realistic value range.
For a first read before any of that, GemPeek looks at your photos and gives you the likely stone type, cut style, setting era, visible condition, and an estimated value range, which helps you decide whether a piece is worth sending to a lab.