Jewelry Blog

How Do Diamond Testers Work?

How Diamond Tester Work

It has never been so easy to create a fake diamond, which is why it’s so challenging to tell them apart from genuine diamonds. While there are numerous ways to tell if your diamond is real, none of them are 100% reliable. That being said, the best way to do so is with a diamond tester.

Keep reading to find out how diamond testers work and how to find the best one. We’ll also talk about lab diamonds, moissanite, and CZ diamonds.

How Do Diamond Testers Work?

Customer testing Diamond Engagement Ring in Showroom

Real, natural diamonds and lab diamonds look absolutely the same to the naked eye. They even have the same chemical and physical properties. Artificial, lab-grown diamonds are created as a cheaper alternative to natural diamonds. Thanks to the development of modern gemology, lab diamonds mimic real diamonds to such an extent that telling them apart is quite the challenge.

The best way to check a diamond’s authenticity is with a diamond tester. This is a small, portable electronic device that is used to distinguish natural diamonds from fake ones. It usually has a heated metal needle-like tip, which is supposed to be placed on a diamond’s surface. The heat difference reveals whether the diamond is real. To be more precise, the speed and amount of heat that travels through the diamond is the key.

These factors reveal a diamond’s genuineness because thermal conductivity travels differently through fake diamonds. The results are revealed almost immediately.

More advanced diamond testers use electrical conductivity. They’re more accurate, and they have been proven to yield better, more reliable results. Another reason why diamond testers that use electrical conductivity are a better option is that they can identify moissanite. We’ll cover moissanite and what makes them harder to detect later.

What makes diamond testers a great investment is that they can be used for other gemstones, like rubies, emeralds, sapphires, and similar. While it might be easy to counterfeit gemstones, it’s even harder to tell them apart than it is with diamonds. The intensity and saturation of the gem’s color hide inclusions or any signs that the gem is synthetic.

How Much Do Diamond Testers Cost?

High Accuracy Diamond Tester

The price for diamond testers varies, depending on the device’s quality, conductivity, design, and manufacturer. Most diamond testers cost up to $20, while more cutting-edge diamond testers can go for a few hundred dollars. Diamond testers that use electrical conductivity are typically more expensive than those that rely on thermal conductivity.

While there are many diamond testers available on the market, here are our top 5 choices that you can find on Amazon:

1. Hqdz High Accuracy Diamond Tester Professional Jeweler for Novice and Expert

Diamond Selector 2 Diamond Tester

This high-accuracy diamond tester pen has an intuitive design with an LCD screen and LED indicators. It currently sells for $16.99, and it’s easy to use. Simply place the tester’s tip on your diamond and wait for it to make a sound. If it doesn’t sound off, this means that your diamond is real. It’s designed to differentiate genuine crystals from fake ones, like cubic zirconium (CZ) diamonds. The device requires one standard 9v battery, which comes with the diamond tester. It also comes with a leather pouch case, a testing platform, and a user manual.

2. HMKIS Diamond Tester Pen

HMKIS Diamond Tester Pen

This diamond tester uses thermal conductivity to differentiate diamonds and other precious and semi-precious gemstones from fake ones. It can detect CZ diamonds or fake diamonds made from glass. At a cost of $18.99, the HMKIS Diamond Tester Pen is an affordable, easy-to-use option that gets the job done. If you’re not sure how to use it, this device comes with instructions and information about test result analysis. It works not only for diamonds but also for gemstones, antiques, coins, stamps, and similar objects. The pen uses a 60X LED magnification microscope, and it comes with a protected leather bag and a testing platform.

3. HDE High Accuracy Professional Jeweler Diamond Tester

HDE Diamond Tester

The HDE diamond tester is a high-accuracy professional device that’s user-friendly, reliable, and affordable, coming in at only $13.99. You can use it for any type of diamond jewelry, including engagement rings, necklaces, earrings, bracelets, and loose diamonds. As it’s battery-powered, you only need one standard 9v battery. It features small and large switches, and it produces audible sounds every time you use it. This device has an ergonomic, compact, and easy-to-hold design that fits perfectly in your pocket.

4. Presidium Multi Tester III All-In-One Instrument for Testing Diamonds

Presiduim Multi Tester

This premium diamond tester sells for a higher price ($209), but you can use it to accurately test diamonds, moissanite, and all other diamond simulants. Thanks to its ergonomic handheld design and its clear LED display, this device is easy to use. The thin retractable probe tip of only 0.6 millimeters allows for an accuracy and speedy performance. It can even test small diamonds with as little as 0.02 carats. It comes with a metal stone rest, a user handbook, a warranty card, and a protective carrying case.

5. TANJIN Jewelry Diamond Tester with Case Portable Gemstone Selector II

Diamond Selector 2

This affordable diamond tester comes with a case-portable gemstone selector II. It currently sells for $12.98 and can be used to test the authenticity of diamonds, gemstones, currency, and documents. It’s completely safe to use, so you won’t risk damaging your diamond in the testing process. It’s powered by a DC 9V battery, which isn’t included.

How to Spot a Fake Diamond with a Diamond Tester?

Real vs. Fake Diamond

Diamond testers may look complicated to use, but they’re actually easy to figure out. Not all diamond testers look the same. Some have LED screens, while others just have two power bulbs that turn green or red, depending on whether the diamond is real.

Make sure you have a battery before you turn the device on, as diamond testers are usually battery powered. Most diamond testers come with a battery. Once it’s on, wait for at least 30 seconds for the probe to heat up. Some diamond testers light up or start beeping to signal the probe is heated and the device is ready to be used.

Afterwards, simply apply low pressure onto the diamond’s surface and wait for a couple of seconds. It’s important to hold the tip at the right angle to get the best results. Also, be sure to clean the probe thoroughly before turning the diamond tester on.

Depending on the type of diamond tester, the results will be displayed differently. Most of them come with a scale from 1 to 8. One-third of the scale is green, the middle is yellow, and the last part is red. If your diamond tester has a scale, you’ll want it to light up all the way to the end, to the red zone. This indicates that your diamond is real. If the scale lights up to the green or yellow zone, this means that your diamond isn’t real or that it’s another gemstone or diamond simulant.

Every diamond tester comes with instructions, so be sure to read them before you use the device.

Do Lab Diamonds Test as Real?

11091 Diamond Engagement Ring for 10000 in box

In general, most diamond testers won’t be able to detect lab grown diamonds. But before we get into lab diamonds, it’s important to understand the difference between lab-grown diamonds and diamond simulants. Even though these terms are often used interchangeably, they are actually not the same. Lab diamonds test as real, whereas fake diamonds, or diamond simulants, don’t count as real diamonds.

Common diamond simulants are moissanite, cubic zirconia, and white topaz, which we’ll cover in the next section.

There are many different names for lab diamonds, including man-made diamonds, cultured diamonds, and laboratory-grown diamonds. What makes them test as real are their chemical and physical properties, which match those of genuine, natural diamonds.

For this reason, lab diamonds can’t be detected by most diamond testers. Since lab diamonds have identical optical, chemical, and physical properties as earth mined diamonds, they’re considered real diamonds by gemologists and jewelers. The only difference is that they’re made in a controlled laboratory environment. Scientists replicate how they are made by applying extreme pressure and heat, mimicking their natural environment.

Another huge difference between lab diamonds and diamond simulants is the price. Lab diamonds are typically 20% to 40% more affordable than natural diamonds. On the other hand, diamond simulants are much cheaper, holding little to no value. What also differentiates lab diamonds from simulants is that real lab diamonds need to have an inscription on the girdle. In addition, they should come with a certificate that proves they were created in a lab.

Lab diamonds are the perfect choice for those who want a less expensive alternative to natural diamonds. People are also drawn to them because their creation doesn’t involve any type of forced labor, environmental hazards, or any other kind of abuse. Most variants are 100% ethically sourced and eco-friendly.

Do Moissanite and CZ Diamonds Test as Real?

Testing CZ and Moissanite

Moissanite, cubic zirconia diamonds, and white topaz all fall into the category of fake diamonds or diamond simulants, and therefore, they do not test as real diamonds. Diamond simulants can be synthetic, or they can occur naturally, just like diamonds.

Moissanite is a naturally-occurring silicon carbide that was mistaken for diamonds when it was first discovered. As opposed to what some people may assume, moissanite is actually a rare mineral. The reason it was, and still is, mistaken for a diamond is because they have similar optical properties and levels of hardness. More precisely, diamonds rank 10 on the Moth Scale, while moissanite scores 9.25 to 9.5.

They also have the same thermal conductivity, which is why standard diamond testers can’t tell them apart. Only diamond testers that use electrical conductivity can identify moissanite. Just because moissanite isn’t a real diamond, it doesn’t mean it’s not a beautiful gemstone. In fact, they make great engagement rings.

Cubic zirconia is a synthetic gemstone that’s usually colorless but can also come in a variety of colors. When you see a fake diamond, it’s most likely cubic zirconia. You can find them in almost any jewelry store, and they’re much more affordable than their naturally-occurring counterparts. As for their value, they’re worth almost nothing and have no market value.

White topaz is another common diamond substitute. It’s colorless in its purest form, but it can be found in a variety of other colors. It’s commonly used to imitate diamonds. Compared to cubic zirconia, which is synthetic, white topaz occurs naturally. The value and price of white topaz is only a fraction of a real diamond.

Other types of diamond simulants include high-leaded glass, which is otherwise known as rhinestone.

How Do Expert Laboratory Diamond Testers Work?

Selling a piece of jewelry online and examining with loupe

The diamond testers mentioned above can be purchased and used by anyone interested in checking whether their diamonds are real. However, expert laboratory diamond testers are much more innovative, developed, and accurate. Furthermore, this type of equipment can work on any type of diamonds, including colorless and colored diamonds, as well as other precious and semi-precious gemstones.

Gemologists use various high-tech equipment to test whether a diamond is real, including spectroscopes, X-ray machines, calibrated scales, diamond colorimeters, laser inscription equipment, and more.

Experts also use short-wave and long-wave ultraviolet light to test a diamond’s authenticity. Most diamonds display some level of fluorescence on a scale from 1 to 5 (none, faint, medium, strong, and very strong). Certain types of diamonds, like Type IaA and IaAB diamonds, absorb short-wave ultraviolet light. On the other hand, Type IIa and IIb transmit short-wave ultraviolet light.

GIA iD100 Gem Testing Device

GIA Tester Testing Diamond Ring

One of the newest, cutting-edge diamond testers available is the GIA iD100, developed by the Gemological Institute of America. This diamond tester uses fluorescence spectroscopy to identify whether a diamond is real, delivering automatic results in just two seconds. Not only can you use this testing device for colorless diamonds, but also near-colorless, blue, green, and brown diamonds.

Thanks to its thin, pinpoint probe tip, it can test diamonds that are 0.9 millimeters in diameter. No matter how well-crafted a lab diamond might be, the GIA iD100 will catch it. It’s incredibly easy to use. If the diamond is real, you’ll see the word “Pass” on the screen. If it isn’t, the message “Refer” will pop up.

Since this device is made for professional gemologists, it comes at a hefty price of $5,495.

Talk to a Diamond Expert

Afshin and Adira with Necklace in Showroom

Buying a diamond is a commitment, especially a diamond engagement ring that you will want to keep for the rest of your life. That’s why you should be certain you’re buying a ring with a genuine, natural diamond. Here at Diamond Estate Jewelry, we sell ethically-sourced diamonds of the highest quality. You can read more about our Ethical Guarantee here.

Before you buy a diamond engagement ring, it’s a good idea to consult with a diamond expert. With over 40 years of experience and a team of devoted professionals, we’ll help you find the perfect diamond for you or your significant other. If you have any questions about our services or diamonds in general, feel free to contact us.


About Afshin Shaddaie

Afshin moved to New York City in the 1980s, and a few years later, he began his career in the fine and rare jewelry scene. He teamed up with Michael Khordipour, and they've been curating vintage jewelry ever since. He also regularly contributes to Forbes, Rapaport, CNBC, The Knot, and Insider. Afshin constantly travels to international shows and private viewing events in the hope of finding rare vintage rings that will be important enough to make an impression. He is available for appointments at our New York showroom when he's not traveling. In 2019, Afshin authored his book called The Engagement Ring Guide for Men. He is considered one of the world's foremost authorities on vintage jewelry and antique diamonds. His favorite jewelry era is Art Nouveau, and he loves rare Italian jewelry from the 1950s - 1970s. The Natural Saltwater Pearl is his favorite precious jewel.