Are Diamond Testers Accurate?

At Espling Jewelers, we understand the importance of trust and reliability when it comes to purchasing jewelry. As you explore the world of diamonds and gemstones, you may come across the question: are diamond testers accurate? In this article, we delve into the intricacies of diamond testing, providing you with a comprehensive guide to understanding the accuracy of diamond testers.

How Diamond Testers Work

  • Thermal Conductivity: Diamonds have high thermal conductivity, meaning they can quickly conduct heat away from the probe of the tester. In contrast, simulants like cubic zirconia or moissanite have lower thermal conductivity, causing heat to be retained longer at the probe's tip.
  • Probe Design: The probe of a diamond tester is typically made of a material with high thermal conductivity, such as metal. When the probe comes into contact with the stone, heat is transferred from the probe to the stone.
  • Heat Source: The diamond tester includes a heat source that heats up the probe. The heat is then transferred to the stone through the probe.
  • Sensor and Display: The device contains a sensor that measures how quickly heat is conducted away from the probe. This information is then displayed on the device, indicating whether the stone is a diamond or a simulant.

Factors Affecting Accuracy

While diamond testers are generally reliable, several factors can affect their accuracy:

  • Quality of the Tester: The quality and calibration of the diamond tester can significantly impact its accuracy. Higher-quality testers are more likely to provide reliable results.
  • Type of Diamond: Some types of diamonds, such as synthetic diamonds, may have thermal conductivity properties similar to natural diamonds, making them challenging to differentiate using a diamond tester alone.
  • Environmental Factors: Temperature and humidity can affect the accuracy of a diamond tester. Extreme temperatures or high humidity levels may impact the device's performance.
  • Presence of Metal Settings: Diamonds mounted in metal settings may not conduct heat as effectively as loose stones, potentially affecting the tester's results.

How to Use a Diamond Tester

Using a diamond tester correctly is crucial for obtaining accurate results. Here is a detailed guide on how to use a diamond tester effectively:

  1. Choose the Right Tester: There are different types of diamond testers available, such as thermal conductivity testers and electrical conductivity testers. Ensure you have the right type for your needs.
  2. Prepare the Diamond Tester: Before using the tester, ensure it is properly calibrated according to the manufacturer's instructions. This calibration ensures accurate readings.
  3. Calibration: Diamond testers need to be calibrated correctly to ensure accurate results. Calibration adjusts the device to account for variations in the thermal conductivity of different materials.
  4. Prepare the Diamond: Clean the diamond to remove any dirt, oil, or debris that could affect the test results. Ensure the diamond is dry before testing.
  5. Perform the Test: Place the diamond tester probe on the surface of the diamond. Apply slight pressure to ensure good contact. For electrical conductivity testers, a light indicator will show if the diamond is a conductor (likely a diamond) or a non-conductor (likely a simulant).
  6. Interpret the Results: The tester will provide a reading or indicator light that corresponds to whether the diamond is genuine or a simulant. Follow the manufacturer's guidelines for interpreting the results.
  7. Repeat if Necessary: For accurate results, it may be necessary to test the diamond multiple times from different angles or positions.
  8. Verify with Other Tests: While diamond testers are generally reliable, it's a good practice to verify the results with other tests if possible, such as using a loupe to examine the diamond's facets or seeking a professional appraisal.
  9. Store the Tester Properly: After use, store the diamond tester in a safe place and follow the manufacturer's instructions for maintenance and storage.

Variations on Diamond Testers

There are different types of diamond testers available, including those that use electrical conductivity or ultraviolet light to test diamonds. Each type of tester operates on a different principle but aims to achieve the same goal of distinguishing between diamonds and simulants.

Thermal Conductivity Testers

Thermal conductivity testers, also known as diamond testers, are widely used for distinguishing between diamonds and simulants. These testers measure the rate at which heat is conducted through a stone, with diamonds conducting heat more effectively than most simulants. By measuring this heat conductivity, thermal conductivity testers can provide an indication of whether a stone is likely to be a diamond or a simulant.

Electrical Conductivity Testers

Electrical conductivity testers use the principle that diamonds are typically poor conductors of electricity, while most simulants are better conductors. These testers apply a small electrical current to the stone and measure its conductivity. Diamonds will generally show low conductivity, while simulants may exhibit higher conductivity. However, it's important to note that some synthetic diamonds may have similar electrical conductivity to natural diamonds, making this method less reliable for distinguishing between them.

Ultraviolet Light Testers

Ultraviolet (UV) light testers rely on the unique fluorescence properties of diamonds. When exposed to UV light, some diamonds emit a characteristic blue fluorescence, while many simulants do not. UV light testers illuminate the stone with UV light and observe any fluorescence emitted. While this method can be effective for identifying some diamonds, not all diamonds exhibit fluorescence, and some simulants may fluoresce as well.

Combination Testers

Some diamond testers combine multiple testing methods, such as thermal conductivity and UV fluorescence, to enhance accuracy and reliability. These combination testers offer users the versatility to perform different tests and cross-reference results to make more informed assessments.

Limitations of Diamond Testers

Diamond testers, while effective for most situations, have limitations. Some advanced synthetic diamonds and treated diamonds can mimic natural diamonds' thermal and electrical conductivity, potentially leading to false positives. 

Additionally, unusual diamonds with atypical properties might confuse standard diamond testers, necessitating further testing by a gemologist. Furthermore, some simulants, like moissanite, closely resemble diamonds in thermal conductivity, making them challenging to differentiate with diamond testers. User error, such as incorrect probe placement or settings, can also impact the accuracy of diamond testers.

Are Diamond Testers Accurate? The Verdict

Diamond testers are valuable tools for quickly distinguishing between diamonds and most simulants, offering convenience and efficiency in gemstone identification. However, their accuracy is not foolproof and can be influenced by various factors.

Overall, diamond testers are generally accurate for identifying natural diamonds in most cases. They rely on the principle of thermal conductivity, which diamonds exhibit differently from most simulants. This makes them effective for distinguishing between diamonds and common simulants like cubic zirconia or moissanite.

However, there are limitations to consider. Diamond testers may struggle with certain synthetic diamonds that closely mimic natural diamonds' properties. Additionally, user error and factors such as incorrect settings or unusual diamond properties can affect their accuracy. In these situations, it's advisable to seek further testing by a professional gemologist.

While diamond testers are useful and accurate for most scenarios, they are not infallible. It's essential to use them correctly and understand their limitations, especially when dealing with unusual or synthetic diamonds. For the most accurate and reliable results, consulting a qualified gemologist is recommended.


In conclusion, diamond testers are valuable tools that can aid in distinguishing between diamonds and simulants, offering convenience and efficiency in gemstone identification. While they are generally accurate for identifying natural diamonds, it's important to be aware of their limitations and seek further testing by a professional gemologist when necessary. At Espling Jewelers, we are dedicated to providing you with the highest quality jewelry and expertise to ensure that your purchase is both meaningful and valuable.