How to Tell If a Diamond Is Real, and What Testers Can't Tell You

You can't reliably tell if a diamond is real at home. Breath and newspaper tricks don't give consistent results, and handheld testers can mistake moissanite for diamond, or some lab-grown diamonds for moissanite. A lab-grown diamond is diamond, so telling it from a mined one takes a gemological laboratory. When you buy, look for a grading report you can verify, and make sure the stone can be matched to it.

Can you tell if a diamond is real at home?

Not with any confidence. GIA's own guide says that much of the Internet advice on this is wrong, and some methods can even damage your gem. Here is how the popular checks hold up.

• The fog test. You breathe on the stone and watch whether it fogs. GIA says this cannot be replicated with consistent results. GIA notes that online advice doesn't specify how long to breathe or how large the stone must be, and humidity can affect the result. Natural and lab-grown diamonds also react in exactly the same way.
• The newspaper test. The idea is that a well-cut round diamond bends light so much that you can't read print through it. GIA calls this problematic and says it should never be used as a definitive test. Lighting, dirt, the stone's shape and proportions, whether it is mounted, and your own eyesight all affect what you see.
• Looking for inclusions. Some people believe imitations are always flawless. GIA says it is a myth that imitations will not have inclusions. Glass can have gas bubbles that look like natural inclusions, and some diamonds are flawless anyway.
• Sharp facet edges. Molded imitations, such as plastic and some glass, may have less-sharp edges, but edge sharpness alone is not a reliable test. Cut simulants have sharp edges too, and any stone can have abraded facet junctions from wear.
• The setting. Gold or platinum proves nothing. GIA notes that diamonds are sometimes set in silver, and a rough setting can simply be wear and tear.

What about holding a flashlight to the stone and judging the sparkle? GIA explains that sparkle, brightness and fire together give a diamond its look. All three depend heavily on cut, and a dirty stone won't sparkle at all. An emerald-cut diamond won't flash the way a round imitation does, and moissanite has more than twice the fire of diamond and slightly more brilliance.

A trained eye can pick up a few visual clues. In moissanite, GIA says viewers will see a double image of its back facets, and its intense fire in sizes of one carat or more may give it away. Cubic zirconia, GIA notes, will yellow in color over time.

Do diamond testers work, and can a diamond tester tell lab-grown?

Handheld testers are a step up from home tricks, but they aren't proof. IGI is clear about their limits.

According to IGI, the most common handheld testers measure thermal conductivity. You place the warm tip against the stone, and the device measures how fast heat travels through it. The catch is moissanite. IGI says thermal testers frequently give false positives with moissanite, because diamond and moissanite handle heat in similar ways.

Electrical testers measure how much electricity travels through the stone, and how fast. IGI says these have historically been considered more reliable, since they can distinguish between natural diamonds and moissanite. They have a blind spot of their own: they can mistake certain lab-grown diamonds for moissanite. HPHT growth uses a metal catalyst, and traces of that metal can make the stone conductive. IGI adds that natural or lab-grown fancy blue diamonds can conduct too, because they contain boron.

So can a diamond tester tell lab-grown from natural? Not these. IGI describes them as tools for separating diamond from simulants such as cubic zirconia and moissanite, and says separating lab-grown from natural is a job for a laboratory.

Why does a lab-grown diamond test as diamond?

Because it is diamond. GIA explains that lab-grown diamonds have the same crystal structure as natural diamonds, made of tightly bonded carbon atoms, with nearly the same chemical, optical and physical properties. By eye, GIA says, the two can be indistinguishable.

That is what separates lab-grown diamonds from simulants. Cubic zirconia, moissanite and glass are, in GIA's words, completely unrelated to diamonds at the atomic level. A loupe won't help: GIA says you cannot spot one through a loupe, and the only way to tell is by laboratory testing. Its FAQ adds that traditional gemological observations and instrumentation are not able to tell them apart.

For a fuller side-by-side, see our guide to lab-grown diamond vs. moissanite vs. cubic zirconia. For what "lab-grown" means on paper, see the lab-grown diamond glossary entry.

How laboratories separate lab-grown from mined

The difference lies in how the stone grew, not in what it is made of. GIA says natural and lab-grown diamonds differ in how the crystal was produced and the environment it was exposed to since growth. Tiny atomic-level irregularities and impurities, called defects, reveal which is which.

GIA describes two main stages in its laboratory:

1. A stone submitted as a diamond with a specific gravity of 3.52 is presumed to be diamond and goes through the GIA DiamondCheck, which reads nitrogen impurities in its infrared spectrum. Diamonds come out as "Pass" (type I) or "Refer" (type II and lab-grown diamonds). Anything else is treated as a non-diamond and sent for identification.
2. Senior gemologists examine the referred stones using photoluminescence spectroscopy, which helps identify CVD and HPHT lab-grown diamonds and detect post-growth treatment.

For jewelers, GIA built the GIA iD100, a desktop instrument that helps separate natural diamonds from lab-grown diamonds, simulants and some treated diamonds in under two seconds. IGI likewise says that separating lab-grown from natural is best done by a gemological laboratory capable of modern spectrometry, UV, photoluminescence and other testing methods. For the detail on the two growth methods, see our CVD vs. HPHT explainer.

A grading report, matched to the stone

A grading report records what a laboratory found when it examined a particular stone. GIA says it tests every diamond to verify that it is, in fact, a diamond, and does not issue grading reports for simulants. Its lab-grown report also states whether there is evidence of post-growth treatments.

The report describes the stone the laboratory examined. It doesn't, on its own, prove that the stone in your hand is that stone. Two checks help close the gap:

• Verify the report. GIA explains that you can enter the report number on GIA Report Check, its online database, and compare the grading details with the paper.
• Link the stone to the report. GIA laser-inscribes each lab-grown diamond's girdle with the report number and a statement identifying it as lab-grown. If your stone carries an inscription, a jeweler can read it under magnification and check it against the report. A match is a strong cross-check, not a fresh laboratory identification.

IGI says the fast pace of change in growing technology makes it important for diamonds to be accompanied by a grading report from a gemological institute whenever they change hands.

Already own a stone with no report? GIA's advice is to ask your local fine jeweler to send it to GIA for you. The jeweler will know the shipping and insurance requirements and can explain the report when it comes back. A report identifies and grades a stone; it doesn't put a price on it. We don't value stones, and diamonds are not investments. If you are insuring a piece, your insurer may ask for an independent appraisal.

Our certificate glossary entry walks through how to read a report line by line.

The sensible way to spend

Buy a diamond with a report you can verify, and have the stone matched to that report.

Every diamond we sell comes with a GIA or IGI grading report. Once the paperwork checks out, your budget can go to the things you can actually see.

A lab-grown diamond can look the same as a natural one by eye and usually costs less than a comparable natural stone, so we'd point most people toward lab-grown. We'd put the savings into the cut, which drives the sparkle you were trying to judge with that flashlight. There's rarely a reason to pay more for a grade your eye can't see.

When you're ready to compare, browse our center stones for engagement rings. Check each stone's listed details against its report, and ask how the stone can be matched to it. Our returns policy sets out what happens if a stone isn't right for you.