Is Your Diamond Real? Here’s How to Tell

Determining the authenticity of a diamond requires professional equipment and a highly trained eye. At-home tests do exist—from the fog test to the water-drop test—but the only way to be sure is by bringing your piece to a jeweler or buying a diamond that has third-party certification.

At a time when knockoffs and dupes have become increasingly ubiquitous, investing in a diamond can feel high stakes. Buying from a reputable jeweler who can provide certification from somewhere like the Gemological Institute of America (GIA), however, will always be your safest bet. This is because determining the authenticity of a gemstone requires a highly trained eye and advanced testing equipment in a professional setting. While at-home tests do exist (more on that later), most experts don’t suggest relying on them when considering a diamond purchase. Ultimately, the best way to tell if a diamond is real is to leave it to the pros.

• What Is a Diamond?
• Lab-Grown vs. Natural Diamonds
• Diamond Certification
• Diamond Simulants
• Jeweler Tests
• At-Home Tests

First things first: What is a diamond, and what makes it so special? The atomic structure of a diamond is unique because it’s the only gem made from a single element: carbon. It’s highly sought after for a few reasons. First, diamonds offer high dispersion of light (also known as fire), lending that vibrant sparkle they’re well known for. Diamonds are also a 10 on the Mohs scale, which measures a mineral’s hardness—meaning that they are the most resistant to scratching and are durable enough for everyday, lifelong wear. Lastly, diamonds tend to be very, very old; they form under incredibly high pressure and intense heat deep below the earth’s surface, with most dating back between one and three and a half billion years. In other words, to own a diamond is to own a piece of natural history.

In the middle of the 20th century, the first lab-grown diamond was created. Chemically and physically identical to diamonds, they are made in a laboratory by one of two methods: the high-pressure/high-temperature process (HPHT) or by chemical vapor deposition (CVD). Diamonds that come from the earth are rarer and thus have a higher resale value, but their lab-grown counterparts are still absolutely real diamonds.

Both lab-grown and natural diamonds are graded by the 4 C’s (cut, color, clarity, and carat), and certificates can be obtained for both. But how important is third-party diamond grading and certification?

“These reports are not essential for authentication but are especially important to provide customers with the specifications associated with quality and value,” says gemologist Christina Gandia Gambale, who is also the store owner of Greenwich St. Jewelers. “It’s essentially the diamond’s passport, giving you transparency and peace of mind that you’re buying exactly what you think you are.”

Over the years, a diamond certificate’s purpose has evolved. “They used to feel like the be-all and end-all because they gave you the grades and helped set the value,” says jeweler Susannah King, who points to GIA and International Gemological Institute as her preferred sources. “These days I see them more as a way of making sure a stone is natural rather than lab grown and giving buyers a bit of confidence that what they’re buying is genuine.”

“But,” King continues, “honestly, I don’t think the grades for color and clarity are the most important thing anymore. What really matters is the character of the diamond itself. Some of the most beautiful stones I’ve ever seen wouldn’t necessarily have the top marks on paper, but they’ve got that magic about them.”

Photo: Greenwich St. Jewelers

Diamond simulants are materials, both natural (like moissanite) and man-made (like cubic zirconia), that bear a strong visual resemblance to diamonds but don’t share the same chemical or physical properties. “Diamonds and diamond simulants can look strikingly similar to the untrained eye,” Gambale says. That said, there are some cues to keep an eye out for. “For me, it’s all about the way a diamond catches the light,” King says. “Real diamonds have this really steely, mirrorlike sparkle. The luster is so distinct once you know it. It’s not the same shine you get from other stones. There’s something sharper about it. That’s usually the first thing I look for when I’m figuring out if something’s likely to be a genuine diamond.” Simulants, on the other hand, often look overly glassy or rainbowlike in comparison. “But again, these differences are nuanced, which is why professional testing is so important,” Gambale says.

Though jewelers will inspect gemstones by sight to get a sense of whether a diamond is authentic, that’s only the first step. “Testing will use a combination of different technical processes,” jewelry designer Ellis Mhairi Cameron says. “We use loupes and microscopes to visually study any inclusions and growth patterns in closer detail, as these can be a giveaway. Thermal conductivity testers are also used to measure how a stone carries heat, as well as specialist lights to check how the diamond reacts under different conditions.”

For King, the only totally reliable way to know if a diamond is real is with X-rays. “Even those little handheld diamond testers can give you the wrong result sometimes, so they’re not foolproof,” she adds. “The proper machines in a professional setting are the only way to get a definite answer on whether a stone is natural or lab grown or a simulant.”

Ultimately, if determining the authenticity of a diamond were easy enough to do at home, there would be no need for third-party authenticators. “I wouldn’t really bother with at-home tests,” King warns. “There are so many stones out there that aren’t diamonds but have been made to trick those kinds of checks, so you can easily get a misleading result.”

But for those who can’t resist the urge to DIY, there are a few at-home tests you can try as a first step. “Popular at-home tests include the fog test, where you breathe on the stone to see if it stays misty, or the water-drop test, where you see if it sinks in water,” Cameron says. “These can give a general indication, but they aren’t super reliable because some simulant stones can pass and some real diamonds might not behave exactly as expected.” Instead, Gambale suggests approaching these at-home tests as curiosities: “fun to try, but not substitutes for a professional evaluation.”