A diamond tester is a small electronic device used to determine whether a gemstone is a real diamond. It works by measuring how the stone conducts heat or electricity—properties diamonds possess in very distinctive ways.
To use a diamond tester correctly, the stone must be clean, room temperature, and tested directly on its surface using the probe tip. When the tester touches a genuine diamond, the device registers a positive reading because diamonds transfer heat extremely efficiently.
While the device itself is simple, accurate results depend on proper technique and interpretation. At acredo, we occasionally help clients test stones they purchased elsewhere or inherited, and the difference between a correct and incorrect test often comes down to small details people don’t realize matter.
Understanding how to use a diamond tester—and what it can and cannot tell you—can help you avoid common mistakes when identifying diamonds.
What A Diamond Tester Actually Measures
Most diamond testers work by measuring thermal conductivity.
Diamonds conduct heat extremely well—much better than most other gemstones. When the tester’s probe touches the stone, the device measures how quickly heat moves through it.
If the stone conducts heat at the rate expected for diamond, the tester signals a positive result.
Modern testers may also combine electrical conductivity tests to distinguish diamonds from stones like moissanite, which can sometimes behave similarly in thermal tests.
This is why jewelers often use dual testers that measure both properties.
Gem Fact
Diamonds conduct heat five times better than copper, which is why thermal testers are so effective at identifying them.
Preparing The Stone Before Testing
Proper preparation is critical for accurate results.
Before using a diamond tester, jewelers typically make sure the stone is:
-
Clean and free of oils or residue
-
Completely dry
-
At room temperature
Accessible so the probe touches the stone, not the metal setting
If oils from fingerprints or lotion remain on the stone, they can interfere with heat transfer and produce inaccurate readings.
For this reason, jewelers often clean the diamond with alcohol or jewelry cleaner before testing.
Expert Tip
If a diamond is mounted in a ring, the probe must touch the stone itself, not the metal prongs or band. Metal can produce incorrect readings.
Step-By-Step: How To Use A Diamond Tester
Using the tester itself is straightforward, but each step matters.
Turn On And Calibrate The Device
Most testers require a brief warm-up period. Many models include a calibration indicator to ensure the device is ready.
Jewelers typically test the device on a known diamond sample to confirm accuracy.
Hold The Stone Steady
The stone should remain completely still during testing.
Movement can cause inconsistent readings because the probe may lose full contact with the surface.
If the stone is loose, jewelers often place it on a soft pad or hold it with gem tweezers.
Touch The Probe To The Stone
The probe tip is gently placed against the flat surface of the diamond.
The key is light but firm contact.
Pressing too hard can damage delicate stones, while too little pressure may prevent the tester from registering.
Within a second or two, the tester will display a reading.
Interpret The Result
Most testers indicate results through lights, sounds, or digital displays.
Typical outcomes include:
-
Diamond
-
Moissanite
-
Not Diamond
If the result is unclear, jewelers usually repeat the test several times on different areas of the stone.
From The Jeweler’s Bench
Professional jewelers rarely rely on a single test. When identifying gemstones, we confirm results using multiple methods.
Common Mistakes When Using Diamond Testers
Many incorrect readings happen because the tester is used improperly.
Some of the most common mistakes include:
Testing A Dirty Stone
Oils or residue can interfere with heat transfer.
Touching Metal Instead Of The Stone
Metal settings can affect readings.
Testing Stones That Are Too Small
Very small diamonds may be difficult for some testers to read accurately.
Testing Extremely Cold Or Hot Stones
Temperature differences can affect conductivity readings.
Understanding these factors helps ensure more reliable results.
What A Diamond Tester Cannot Do
Although diamond testers are very useful, they do have limitations.
A diamond tester cannot determine:
-
Diamond quality or clarity
-
Whether a diamond is natural or laboratory-grown
-
The diamond’s value
Both natural diamonds and lab-grown diamonds typically register as diamonds on a tester because their physical properties are nearly identical.
Professional gemological instruments are required to distinguish between them.
Expert Insight
A diamond tester answers one question only: does this stone behave like a diamond? Identifying origin or value requires deeper gemological analysis.
When Professional Testing Becomes Important
If you are considering purchasing a diamond—or verifying an important stone—it is wise to combine tester results with professional evaluation.
At acredo, jewelers may examine a stone using:
-
Magnification tools
-
Diamond testers
-
Advanced gemological instruments
This approach ensures the stone is properly identified before it becomes part of custom-designed jewelry or handcrafted rings.
The acredo Perspective
Diamond testers are helpful tools, but they are only one part of the identification process.
Professional jewelers rely on experience, magnification, and specialized equipment to understand a gemstone fully.
At acredo, many clients exploring loose stones or inherited diamonds enjoy learning how these tools work during a personalized consultation. Understanding the science behind diamonds often adds a deeper appreciation to the jewelry design process.
Once a diamond is confirmed and evaluated, it can then become part of something much more meaningful—a unique piece of handcrafted jewelry created specifically for you.
Discover The Craft Behind Every Diamond
Whether you are verifying a diamond, exploring gemstone options, or imagining a piece of custom-designed jewelry, understanding how professionals evaluate stones is part of the journey.
At acredo, we invite you to explore our customization options, design your perfect ring, or schedule a creative sit-down near you to experience how diamonds become part of unique jewelry creations.
Because every remarkable piece of jewelry begins with knowing exactly what you are working with—and then transforming it into something extraordinary.