Diamond testers are tools commonly used to determine the authenticity of gemstones, particularly diamonds. However, their reliability and effectiveness can vary depending on the type of gem being tested.

Let’s learn what diamond testers are, how they work, and what types of gemstones can pass or fail these tests.

What is a Diamond Tester?

Diamond testers are handheld devices, often shaped like a pen, that measure the thermal conductivity of a gemstone. This means they assess how quickly heat travels through the stone, which is a characteristic feature of diamonds due to their high thermal conductivity.

Thermal conductivity is crucial in determining the authenticity of a diamond. Since diamonds conduct heat exceptionally well, a tester can identify this property, helping to distinguish a real diamond from certain stimulants like cubic zirconia (CZ).

Do Diamond Testers Really Work?

Diamond testers are reliable to a certain extent but should not be the sole method of verifying a diamond’s authenticity. While they can effectively separate CZ from diamonds, they may not always distinguish between diamonds and other high-conductivity gems like moissanite.

Several factors can cause diamond testers to malfunction, including user error, low battery, or device wear and tear. It’s important to ensure that the metal point on the tester does not touch any metal surrounding the stone, as this can lead to inaccurate results.

How Do Jewelers Test Diamonds?

Jewelers often use multiple methods to verify a diamond’s authenticity. These include checking for single refraction, testing hardness, and confirming high thermal conductivity. Moissanite, for instance, is doubly refractive under magnification, which distinguishes it from diamonds.

Magnification is a crucial tool for jewelers. It helps in identifying features like double refraction in moissanite and assessing the quality of a diamond. Jewelers may also check for microscopic laser inscriptions that indicate the stone’s certification.

Types of Gemstones That Can Pass a Diamond Tester

Moissanite

Moissanite is the most well-known gemstone that can pass diamond testers as a diamond, especially on a standard thermal conductivity tester. It’s often used as a diamond alternative due to its remarkable brilliance and durability.

Moissanite has very high thermal conductivity, almost matching that of diamonds, which is why it can easily deceive basic diamond testers. Moissanite’s double refraction and slightly different optical properties can help distinguish it from diamonds when examined under magnification.

White Sapphire

While not as common, some high-quality white sapphires have been known to pass basic diamond testers under certain conditions. White sapphire has moderate thermal conductivity, and while it generally does not pass as diamond, specific testing conditions or slightly inaccurate testers can sometimes result in a false positive.

However, white sapphire’s lack of “fire” and different refractive index make it distinguishable from diamonds upon closer inspection.

High-Pressure High-Temperature (HPHT) Lab-Grown Diamonds

HPHT lab-grown diamonds are another type of gemstone that often passes diamond testers. Since these diamonds are chemically identical to natural diamonds, they conduct heat in much the same way.

However, the slight variations in crystal growth patterns can sometimes cause these diamonds to test incorrectly, particularly on older or less sophisticated testers. Despite this, they generally pass as genuine diamonds on most modern testing equipment.

Synthetic Rutile

Synthetic rutile is a lesser-known gemstone that has occasionally passed diamond testers, particularly older models. Like diamonds, synthetic rutile has high thermal conductivity, which can sometimes confuse basic testers.

However, its optical properties differ significantly from diamonds, making it easy to identify under magnification. The gemstone’s high dispersion and unusual color play are key indicators that it is not a diamond.

Garnet-Based Simulants

Some garnet-based diamond simulants can also pass certain types of diamond testers. These stimulants are designed to mimic the thermal properties of diamonds, allowing them to pass as the real deal on less advanced testers.

However, garnet’s different hardness and optical properties, such as its lack of brilliance compared to diamonds, make it distinguishable upon further examination.

Can Fake Diamonds Pass a Diamond Tester?

Moissanite, a man-made gem with high thermal conductivity, can pass as a diamond on a standard tester. This is why diamond testers alone cannot always differentiate between a diamond and moissanite, highlighting the need for additional tests.

Other diamond simulants, such as CZ, do not have high thermal conductivity and will not pass a diamond tester. Therefore, it is essential to use a combination of tests to confirm the identity of the stone.

Types of Diamond Testers

Diamond testers come in various types, including thermal, electrical, and combination testers. Each type has specific advantages for accurately identifying different diamond simulants.

Thermal Conductivity Testers

These testers are the most common and rely solely on measuring how quickly a stone disperses heat. They are particularly effective for distinguishing diamonds from glass, cubic zirconia, and other common imitations.

Electrical Conductivity Testers

These testers measure how well a gemstone conducts electricity. They are essential for identifying stones like moissanite, which can sometimes pass as diamonds on thermal conductivity testers alone.

Combination Testers

Combination testers use both thermal and electrical conductivity tests to provide the most accurate results. These devices are highly recommended for professionals who need to ensure the authenticity of a diamond with minimal risk of error.

Conclusion

Diamond testers are valuable tools in the initial stages of gemstone identification. However, they should not be solely relied upon, especially when distinguishing between diamonds and high-conductivity simulants like moissanite.

Multiple testing methods, including magnification, hardness tests, and checking for certification numbers, are essential for accurate gemstone identification. Whether you are a jeweler or a gemstone enthusiast, understanding the limitations and proper use of diamond testers will help you make more informed decisions.