How Does A Diamond Tester Work?

Many buyers and jewellery enthusiasts ask the question: how does a diamond tester work? Understanding the answer is key to knowing how professionals and consumers can distinguish diamonds from their imitations.

What Are Diamond Testers

Diamond testers are handheld instruments used to determine whether a gemstone is a genuine diamond or an imitation. They work by measuring the stone’s physical properties, most commonly conductivity. Diamonds conduct heat extremely efficiently, unlike materials such as cubic zirconia or glass, which makes this property useful for identification.

Some testers also measure electrical conductivity to help distinguish diamonds from moissanite, which shares similar heat conductivity but differs in its electrical behaviour. By using these measurable differences, diamond testers provide a quick and practical way to identify diamonds without laboratory equipment.

Types of Diamond Testers

There are several kinds of diamond testers, each designed to apply these principles in different ways.

Thermal conductivity testers – the most common devices, which measure how quickly heat moves through a stone. A heated probe touches the surface, and the instrument records the speed of heat transfer. Diamonds disperse heat far more rapidly than materials such as cubic zirconia or glass, making them easy to identify with this method.

Electrical conductivity testers – designed to solve the problem of moissanite, which conducts heat almost as efficiently as diamond. These testers apply a mild electrical current. Diamonds are poor electrical conductors, while moissanite conducts electricity, allowing for accurate separation.

Multi-testers – modern devices that combine both thermal and electrical conductivity methods. By using dual measurements, they reduce the chances of false readings and provide higher accuracy when testing a wide range of gemstones.

How to Use a Diamond Tester

Using a diamond tester is straightforward, but accuracy depends on following the correct steps.

First, the stone should be clean and free of grease, dust, or oil, as surface residues can interfere with the probe’s contact. The tester also works best when the stone is at room temperature, since extreme heat or cold may affect readings.

The device is switched on and allowed to warm up, usually indicated by a light or beep. A metal probe attached to the tester is then gently placed on the surface of the stone, preferably on the table facet. The instrument measures the stone’s response and displays a result, often through lights, sounds, or digital readings, indicating whether the stone is a diamond or a simulant.

Care must be taken to avoid touching the probe to the metal setting, as this may give an inaccurate reading. Testing multiple points on the stone can also increase reliability.

Accuracy and Limitations

Diamond testers are generally reliable tools, but they are not foolproof. Thermal conductivity testers can easily separate diamonds from most simulants such as cubic zirconia and glass, yet they struggle with moissanite due to its similar heat transfer properties. This is why electrical conductivity testers or multi-testers are often preferred in professional settings.

Environmental conditions can also affect accuracy. If the stone is too cold or has just been handled, the temperature difference may alter the reading. Likewise, dirt, oils, or moisture on the surface can interfere with the probe’s contact and give false results.

Another limitation is size. Very small stones may not provide enough surface area for the probe to measure effectively, making readings less reliable. In addition, testers cannot assess a diamond’s quality, origin, or authenticity as natural or lab-grown; they simply confirm whether a stone exhibits diamond-like conductivity.

For these reasons, while diamond testers are useful for quick checks, they should be supported by professional gemmological analysis or certification when full verification is required.

Alternatives to Diamond Testers

While diamond testers are convenient, they are not the only way to determine whether a stone is genuine. Several other methods are used in gemmology to confirm identity and provide a fuller picture of a stone’s characteristics.

One of the most reliable approaches is gemmological certification. Laboratories such as GIA and IGI use advanced equipment to analyse stones in detail, confirming whether they are natural diamonds, lab-grown diamonds, or simulants. A grading report provides definitive assurance beyond what a handheld tester can offer.

Microscopic inspection is another common technique. Under magnification, gemmologists can look for internal inclusions, growth patterns, or features unique to diamonds that are not present in cubic zirconia, glass, or moissanite.

Other advanced methods include spectroscopy and X-ray examination, which measure how stones absorb light or react to radiation, offering precise identification. These tools are typically found in professional laboratories rather than retail environments.

Together, these alternatives highlight that while diamond testers are practical for quick checks, professional analysis remains the gold standard for accuracy and reliability.