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For example: Scales, Engravers, Testers

5 Ways to Test a Diamond

5 Ways to Test a Diamond - Presidium Blog

Like all gemstones, diamonds have a distinguishing chemical structure and as such, they react to heat and electricity in different ways. If you are buying and/or selling precious stones, it is advisable to invest in reliable  gemological instruments such as diamond testers, refractive meters, gauges, and/or scales. 

But first, let’s define the terms: By “lab-grown” we mean diamonds that were developed in a laboratory, by experts. When we say “earth-mined” we mean diamonds that were excavated from deep below the earth—also called “natural” diamonds. However, both kinds of diamonds have an identical composition, hence, labeling one as “real” and the other “fake” would be inaccurate and misleading. 

Different gemological instruments and testing devices operate on different principles. They measure various properties, using different methods. By noting the differences, the device can identify the kind of gemstone that’s being tested, whether or not the diamond is lab-grown or earth-mined and how much the stone weighs, among others. Ready to learn more? Then read on!

1. Thermal Conductivity 

The most common type of diamond testers in the market today are those that check a stone’s thermal conductivity. These are typically handheld devices that measure the amount and speed of heat as it travels through the gem. 

Note that a diamond tester will identify a stone as a diamond whether it is earth-mined or laboratory-grown. Most diamond testers are easy enough to operate, and come with a user manual or instructional videos online. 

The Presidium Diamond Mate Tester (PDMT) is one such handy instrument that instantly verifies the authenticity of diamonds based on their thermal properties. As a first step, users can test an unknown colorless stone using the PDMT to help determine whether or not it is a diamond simulant. The PDMT comes in two versions: the battery-powered PDMT-A or the rechargeable PDMT-C.

If the PDMT registers a "Diamond" reading, another device can be used to further distinguish colorless diamonds from CVD/HPHT lab-grown diamonds or moissanites (D to J color). ARI by Presidium

can identify if it is a natural diamond, lab-grown CVD/HPHT diamond, or moissanite. ARI is a Presidium Diamond Verification Instrument®—a registered trademark of Presidium Instruments Pte Ltd.

2. Refractive Index

Testing for the refractive index of a diamond entails observing the properties of light as it passes through the stone. A refractive index meter is a device that measures the quantity of light reflected through the stone and as such, is able to identify if it is a diamond, moissanite, or other colored gemstones.

Unlike a traditional refractometer that has a limited range of refractive index (RI) measurements, the Presidium Refractive Index Meter II (PRIM II) measures a wider range of RI values, from 1.000 to ~3.000. This desktop digital tester can be used to test the RI of diamonds, moissanites, and diamond simulants  such as high zircon and strontium titanate.

In addition, a fast and clean test can be easily done with the PRIM II, without the inconvenience and messiness of using RI liquids, as you would in traditional refractometers. The PRIM II also comes with a downloadable software that provides a database of more than 50 gemstones with their various properties and possible origins. The program enables the user to enter known properties of the gemstone to ascertain what possible gemstone it is, based on the database information.

3. Carat

A carat is defined as a unit of weight that is used to measure the size of a diamond. According to GIA, 

“diamond carat weight measures how much a diamond weighs.” Carat is one of the 4Cs that determine the market value of a diamond—carat, color, clarity, cut. 

One carat weighs 200 milligrams, with each carat subdivided into 100 “points,” which lets us measure accurately to the 100th decimal place. A diamond that’s below one carat is usually classified by its points and as such, a 0.25-carat diamond is called a “25-pointer.” 

Meanwhile, the surefire way to measure carats is by using a reliable carat scale. One such device is the new and improved Presidium Carat Scale 100n (PCS-100n). PCS-100n measures diamond and gemstones up to 100.00 carats—without having to recalibrate each time the unit is turned off.

Each PCS-100n comes with its corresponding weight reference of 100.00ct/20g, for calibration. This compact and portable scale utilizes advanced circuitry design and surface-mount technology to weigh diamonds and precious gemstones up to 100.00ct. The PCS-100n can also be powered by a usb adaptor.

4. Lab-grown vis-a-vis Earth-mined

Today there are at least two types of lab-grown diamonds that very closely resemble earth-mined diamonds: the High Pressure High Temperature (HPHT) and CVD (Chemical Vapour Deposition) diamonds. Meanwhile, there are diamond simulants—cubic zirconia, glass, moissanite, quartz, white zircon, white topaz, white sapphire, white spinel, among others—that may look a lot like diamonds but have very different properties at the atomic level. 

Differentiating between diamonds that are laboratory-grown and earth-mined requires using gemological instruments, including screeners and gauges.

The Synthetic Diamond Screener II (SDS II) is a Presidium Diamond Verification Instrument® that can differentiate Type IIa colorless lab-grown diamonds (CVD or HPHT) from natural Type Ia colorless diamonds. The SDS II has been ASSURE TESTED by an independent third party through ASSURE program and achieved 100% Laboratory-Grown Diamond Referral Rate. 

On the other hand, the Presidium Electronic Gemstone Gauge (PEGG) is the industry’s first digital gemstone gauge and portable carat converter that can differentiate laboratory-grown Type IIa colorless diamonds from natural Type Ia colorless diamonds. The PEGG is recognized globally as the most reliable digital gauge for measuring gemstone dimensions. 

5. Thermoelectric Conductivity

In a thermal conductivity test, what’s being measured is the amount and speed of heat as it travels through the gem. In an electrical conductivity test, on the other hand, it’s all about the degree to which a diamond conducts electricity. 

These two types of diamond testers operate on the premise that gemstones react to heat and electricity in different ways. However, research has shown that thermoelectric conductivity diamond multi-testers have more advantages. 

Thermoelectric or thermoelectrical diamond testers can detect diamonds, moissanites, and simulants instantly. One such instrument is the lightweight and portable Presidium Adamas, for authenticating colorless diamonds as small as 0.01 carats.

An industry forerunner, Adamas diamond tester is the world’s first diamond and moissanite tester with a replaceable tip, and a micro probe tip. In the long run, a worn out or damaged probe can simply be replaced; you don’t have to buy a new diamond tester. 

Why Presidium for Diamond Testers?

Industry pioneers would have the most experience and expertise in producing gemological instruments. And if you are a serious buyer or seller of gemstones, then you need these tools as an added layer of protection for your investment.

Established in 1979, Presidium Instruments Pte Ltd is the world’s first company to launch gemological instruments catering specially to the jewelry industry.  Available in more than 40 countries, Presidium products include gemstone testers that determine refractive index, UV transmittance, thermal conductivity, and/or reflectivity. 

At the end of the day, there’s not one definitive test to determine the value of a diamond. Each test has its own parameters and expected results. To be on the safe side, it’s wise to do multiple tests for identifying different properties whenever possible, using reliable and industry-trusted gemological instruments.