Home Ruby Testing Rubies with a Diamond Tester: A Step-by-Step Guide

Testing Rubies with a Diamond Tester: A Step-by-Step Guide

by Madonna

Rubies, with their vibrant red hues and exceptional hardness, are among the most sought-after gemstones in the world. However, the market is flooded with both genuine rubies and their synthetic or simulant counterparts. To ensure the authenticity of a ruby, gemologists and jewelers employ a variety of testing methods, including using a diamond tester. In this article, we will delve into the process of testing rubies with a diamond tester, highlighting the key steps and considerations.

Understanding Diamond Testers and Their Principle

A diamond tester, also known as a diamond/moissanite tester, is a handheld device designed to distinguish between diamonds and other gemstones. It operates based on the principle that diamonds and moissanites, another type of gemstone, have different thermal conductivities. Diamonds, being excellent conductors of heat, disperse heat rapidly, while moissanites and other gemstones disperse heat at a slower rate.


Can a diamond tester measure rubies accurately?

Diamond testers use thermal conductivity to distinguish diamonds from other gemstones. While they can provide an indication, they’re not entirely accurate for identifying rubies. Rubies and other gemstones exhibit a range of thermal conductivity values, leading to potential false positives or negatives. For accurate identification, consulting a professional gemologist or using more advanced testing methods is recommended. Diamond testers can offer a preliminary insight, but their readings should be interpreted cautiously and verified by experts when dealing with valuable gems like rubies.


See Also: What Is the Price of Ruby per Carat: A Comprehensive Analysis


Step-by-Step Guide to Testing Rubies with a Diamond Tester

Testing rubies with a diamond tester involves using a device that measures thermal conductivity to distinguish between diamonds and other gemstones, including rubies. Here’s a step-by-step guide to help you through the process:

Step 1: Calibration

Before testing any gemstone, including rubies, it’s crucial to calibrate the diamond tester. Calibration ensures accurate readings and reliable results. Refer to the manufacturer’s instructions for your specific diamond tester model to perform the calibration process correctly.

Step 2: Preparing the Ruby

Ensure that the ruby is clean and free from any oils, dirt, or residues that might affect the test results. Use a soft, lint-free cloth to gently clean the surface of the gemstone.

Step 3: Performing the Test

1. Turn On the Tester:

Power on the diamond tester according to the manufacturer’s instructions. Allow it a few moments to stabilize and adjust to the ambient temperature.

2. Select the Mode:

Most diamond testers have different testing modes, including diamond, moissanite, and metal. Select the appropriate mode for testing gemstones.

3. Probe Placement:

Gently place the probe of the diamond tester against the surface of the ruby. It’s essential to make good contact between the probe and the gemstone for accurate results.

4. Observe the Reading:

The diamond tester will provide a reading on its display. If the reading indicates “diamond” or “moissanite,” it’s important to note that rubies should not display these readings.

Step 4: Analyzing the Results

Interpreting the test results requires careful consideration. If the diamond tester indicates “diamond,” it means that the gemstone is likely not a genuine ruby. However, if the reading is “moissanite” or “other gemstone,” it suggests the possibility of the gemstone being a ruby. Yet, this is not a definitive confirmation of authenticity.

Step 5: Additional Tests and Expert Evaluation

While a diamond tester can provide initial insights, further testing is recommended for a comprehensive analysis. Thermal conductivity is just one aspect of identifying rubies. Consult with a trained gemologist who can perform a thorough assessment using a combination of tests, including visual inspection, refractometer analysis, and spectroscopy.

See Also: Is Ruby-Zoisite Rare: The Rarity and Allure of Unique Gemstone

Considerations and Limitations

When using a diamond tester to assess rubies, several considerations and limitations should be kept in mind:

1. Synthetic Rubies

It’s important to note that some synthetic rubies, particularly those created using the flux-growth method, can have thermal conductivities similar to natural diamonds. This can potentially lead to false readings on a diamond tester. Therefore, using multiple testing methods and consulting with an expert is essential to confirm authenticity.

2. Treatments and Enhancements

Certain treatments, such as heat treatment, can affect a ruby’s thermal conductivity and skew the results obtained from a diamond tester. Always inquire about the gemstone’s history and any possible treatments before relying solely on the results of a single test.

3. Simulant Gemstones

Diamond testers are primarily designed to differentiate between diamonds and moissanites, which are diamond simulants. Other simulant gemstones, like garnets or spinels, may yield readings that are inconsistent with their actual identity. Always cross-reference the results with other tests.

4. Professional Expertise

While diamond testers are useful tools, they are not infallible. For a comprehensive and accurate assessment of a ruby’s authenticity, seeking the expertise of a certified gemologist is recommended. Professionals have access to a wide range of testing equipment and techniques that can provide a conclusive determination.


Testing rubies with a diamond tester can be a valuable preliminary step in identifying their authenticity. However, due to the complexity of gemstones, especially considering synthetic rubies and various treatments, relying solely on the results of a diamond tester is not sufficient. The use of multiple testing methods, along with the expertise of a qualified gemologist, is crucial to ensure the accuracy of the assessment. By following the steps outlined in this guide and exercising caution, both consumers and professionals in the gem industry can make more informed decisions when dealing with rubies.


Q1: How can I improve accuracy when testing rubies with a diamond tester?

A1: Ensure proper surface contact between the tester probe and the ruby. Use consistent pressure, control the gem’s temperature, and repeat tests for an average reading. However, professional gemological verification is advised.

Q2: What if the diamond tester shows a positive reading for a ruby?

A2: Positive readings might occur due to overlap in thermal conductivity values. Consult a gemologist or a gem testing lab for conclusive identification. Additional tests are needed to verify the gem’s authenticity.

Q3: Should I solely rely on a diamond tester for assessing gemstones?

A3: No, diamond testers offer preliminary insights but cannot provide definitive gemstone identification. Visual inspection, magnification, and spectroscopy are also crucial for comprehensive assessments.

Q4: Can fluctuating ambient temperatures affect tester accuracy?

A4: Yes, temperature differences can impact readings. Allow gems to reach a consistent temperature before testing and consider using the tester in a controlled environment.

Q5: How should I interpret borderline readings from a diamond tester?

A5: Borderline readings indicate uncertainty. Rely on other testing methods and consult experts for a conclusive identification. False positives/negatives are common with borderline readings.

Q6: Is a diamond tester a cost-effective tool for assessing rubies?

A6: While diamond testers are relatively affordable, their accuracy for rubies is limited. Investing in professional gemological services is crucial for accurate assessments of valuable gemstones.


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