In pirate stories, the pirate always bites down on a gold coin to tell if it’s real. Gold is a fascinating metal: both strong enough to hold gemstones securely, yet soft enough to dent if it’s bitten (or banged on the side of a counter, as I, unfortunately, know all too well). We don’t advise biting on gold jewelry to test it, as it will be permanently damaged, not to mention that your dentist will have a fit.
But you can use your teeth to tell if pearls are real or fake. The pearl “tooth test” is simple, and even your dentist will approve. Gently rub the pearl/s across the front of your teeth. Real pearls will feel slightly rough, owing to the microscopic layering of the nacre, whereas faux pearls don’t have that cuticle and will glide smoothly. Under a microscope, the surface of a real pearl and the surface of a human hair are similar.
There’s no tooth test for diamonds. Unfortunately, there’s no DIY test that guarantees a diamond is real without sending it to an independent gemological lab, such as GIA. I’ve heard all the Internet ones you have—breathe on it, try to scratch it, try to read through it, drop it in water to see if it floats, etc., so I decided to call up the folks at GIA and see what they had to say.
What they said was, “There are no easy and reliable at-home tests that will conclusively tell you if your gemstone is a natural diamond or some other material. Your best course is to take your jewelry to a trained jeweler for examination and, if necessary, request to have the gemstone tested by an independent gemological laboratory.”
You’ve probably heard a lot about lab-grown diamonds recently. Technology exists to grow diamonds and other gems in a reactor by adding the same elements that occur in nature and mimicking the heat and pressure of the earth. The difference is that they’re done in a few weeks instead of a few billion years.
Lab-grown diamonds are diamonds. They’re physically, chemically, and optically identical to diamonds found in the earth, so any diamond test will identify them as a diamond. Additional tests can quickly identify whether the stone is natural or manmade, but those can only be done in a gemological lab, not yet even in most jewelry stores.
Synthetic diamonds are pretty but they’re not rare, and they’re not going to be as valuable as a natural diamond. In fact, as technology advances and their manufacture becomes more economical, chances are their cost will go down, not up.
Diamond simulants, on the other hand, are not diamonds, they’re other materials that are meant to look like a diamond. Common materials used to simulate diamonds include cubic zirconia (CZ), synthetic moissanite, white sapphire, white topaz, and glass.
Here’s what the gemologists in GIA’s library told me:
While it’s not always possible to distinguish between a diamond and a simulant with the untrained eye, there are some visual differences:
So let’s chat about some of the things you might have heard about DIY diamond testing.
You can buy a low-end one for less than $20 if you just want to test a few pieces. Or say you’re big on going to estate sales where there might be jewelry, invest in a high-end or professional grade tester that’s going to run you at least a few hundred dollars, especially because newer varieties of moissanite can fool older diamond testers. But even if it tests real, if it’s of any significant value, still get it evaluated by a professional.
Nope, this guarantees that your stone gets wet, but not necessarily that it’s real. GIA says diamonds and simulants both will sink.
While a high-end setting is no guarantee that the stone is real—sadly, there are instances of stone swapping—a low-end setting is a clue that it may not be real. If the setting is gold-filled or gold plated, or even 10 karat gold, that’s a low-end setting. Sterling silver is trickier: sometimes diamonds are set in silver. A designer piece (like David Yurman, John Hardy, Lagos, etc.) is likely to have real diamonds, but cheap silver will likely have diamond simulants.
Here are some common metals and fineness marks:
|Metal||Fineness Marks, US System||Fineness Marks, International|
|9 or 10 karat gold||9K or 10K (Note: 9K gold was not allowed to be sold as “gold” in the United States until very recently, but it is in the UK.||375 (37.5% gold) or 417 (41.7% gold), respectively.|
|14 karat gold||14K||585 (58.5% gold)|
|18 karat gold||18k||750 (75% gold)|
|24 karat gold||24K||999 (99.9% gold)|
|Platinum||PT: Platinum must be at least 95% pure to be marked PT with no numeric qualifier. Between 85% (850) and 95% the piece will have PT with the additional number. Anything below 850 must also show the other alloys.||950|
|Sterling Silver||Sterling or 925||925|
|Fine Silver (infrequently used for jewelry)||999||999|
The fog test sort of works, but it’s not reliable. If you breathe on the diamond, like you would to clean your eyeglasses, either it won’t fog or the fog will dissipate almost instantly, whereas it will linger for a few seconds on other materials. This is because diamond is a very effective conductor of heat.
It won’t hurt your jewelry, but GIA gemologists say ambient humidity can affect your results (so don’t try this in Florida) and besides if you need reading glasses for everything else, how can you even see if a stone is foggy? I can’t! Plus newer varieties of synthetic moissanite also dissipate heat quickly too. So fog it up for a quick buff if you must, but that’s it—and it’s not a substitute for a real cleaning, either.
Back to diamonds. There are more tests written about online (most of which neither we nor GIA advise trying, such as a heat test or a scratch test), but the reading test is at least harmless and kind of fun, if nothing else. Put a loose diamond flat side down on a newspaper or draw a little black dot on a piece of white paper. If you can read or see the dot through the stone, it’s not a diamond.
The reason why diamonds sparkle so much is their refractive properties, so the light will bounce around too much to be able to read through it. The catch, says GIA, is that many variables can affect the test, such as lighting, cleanliness of the stone, and your own eyesight. If you’re a trained and experienced gemologist it’s a good start, and it brings me to the next point, which is that simulants can sparkle too, so that’s not necessarily a test either.
Refractive index is a comparison measure of the speed of light from one medium to another (i.e. stone to air). Diamond’s refractive index is 2.417 (2.42 rounded up), meaning that light travels through a diamond 2.417 times slower than it travels through air.
Refractive indices of diamonds and common simulants:
|Synthetic moissanite (virtually all moissanite on the market is lab-grown)||2.65 – 2.69 (although higher than a diamond, moissanite’s color is slightly different and it can have a disco-ball effect in a larger stone)|
|Cubic Zirconia (CZ)||2.17|
|White topaz||1.60 – 1.64|
Hint: take it to a jeweler. That’s all.
Fun fact: Did you know that rubies and sapphires are the same thing? When corundum is deep red, it’s called ruby and when it’s any other color, it’s called sapphire. Corundum is almost—not quite—as hard as a diamond. It’s a 9 on the Mohs hardness scale; diamond is a 10. Don’t try to scratch it, though as you might damage either the stone or the mounting or both. Inclusions aren’t a clue, either, because glass can have gas bubbles that look like gem inclusions, says GIA.
Natural emeralds have a lot of inclusions, so if your deep green stone has a lack of inclusions, more than likely it’s not natural. You might be very lucky and have an extremely rare and valuable gem on your hands, but more than likely you’ll find out you have a lab-grown stone or simulant instead. And GIA’s gemologists also point out that a lab-grown emerald also can have a lot of inclusions, although a gem lab can tell by the inclusions whether the gem is natural or manmade.
The upshot? Diamond and gem identification is not a DIY. When you’re dealing with something potentially valuable, always trust it to a professional gemologist jeweler or independent gem lab.
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