How to Use a Cheap Diamond Tester: A Guide to Identifying Diamonds vs. Moissanite

Diamond testers are handy tools for anyone looking to verify the authenticity of a gemstone, whether you’re a jeweler, a collector, or just curious about that sparkly stone you found. While high-end testers can cost hundreds of dollars, affordable models (often under $50) can still get the job done if you know how to use them correctly. In this blog post, we’ll walk you through how to use a cheap diamond tester, the settings to use for checking diamonds, and how to distinguish a real diamond from a moissanite stone.

What Is a Diamond Tester and How Does It Work?

A diamond tester is a portable device that measures a gemstone’s thermal conductivity to determine whether it’s a diamond. Diamonds conduct heat differently than most other gemstones, including moissanite, cubic zirconia, or glass. Cheap diamond testers typically use a probe that you press against the stone to get a reading, often indicated by lights, sounds, or a digital display.

However, inexpensive testers aren’t foolproof. Moissanite, a popular diamond simulant, has thermal conductivity similar to diamonds, which can lead to false positives. We’ll cover how to spot moissanite later in this post.

Step-by-Step Guide to Using a Cheap Diamond Tester

Here’s how to use a budget-friendly diamond tester effectively:

1. Read the Manual

Every diamond tester is slightly different, so start by reading the user manual that comes with your device. It will explain the specific settings, indicators (e.g., green light for diamond, red for non-diamond), and calibration steps.

2. Prepare the Tester

•  Power On: Most cheap testers run on 9V batteries. Ensure the battery is fresh to avoid inaccurate readings.

•  Warm-Up: Turn on the tester and let it warm up for 30–60 seconds, as recommended by most manuals. Some models have a light or sound to indicate when they’re ready.

•  Calibrate (if required): Some testers need calibration using a test stone (often included) or by adjusting a dial to a specific setting. Follow the instructions to ensure accuracy.

3. Set the Tester for Diamond Testing

Cheap diamond testers usually don’t have multiple “settings” like professional models, but some allow you to adjust sensitivity or select a mode for diamonds. If your tester has a sensitivity dial:

•  Set it to the middle range for general testing. Too high, and you might get false positives; too low, and it might miss genuine diamonds.

•  If your tester has a “diamond/moissanite” switch, set it to “diamond” for now. (We’ll address moissanite testing later.)

4. Prepare the Gemstone

•  Clean the Stone: Dirt, oils, or residue can affect the tester’s accuracy. Wipe the gemstone with a soft, lint-free cloth. Avoid touching the testing surface with your fingers.

•  Ensure Proper Lighting and Stability: Place the jewelry or loose stone on a flat, non-metallic surface. Good lighting helps you see where to place the probe.

5. Test the Stone

•  Press the Probe Firmly: Gently press the tester’s probe tip perpendicular to the gemstone’s surface (usually the table, or flat top, of the stone). Apply even pressure but don’t push too hard to avoid damaging the probe.

•  Read the Result: Most cheap testers use lights or sounds:

•  Green light or steady beep: Indicates a diamond.

•  Red light or no/low beep: Indicates a non-diamond (e.g., cubic zirconia, glass).

•  Erratic or weak response: Could indicate moissanite or a need to retest.

•  Test Multiple Spots: Test different areas of the stone to confirm consistency, especially if it’s a larger gem.

6. Interpret with Caution

Cheap testers can misread moissanite as diamond due to its similar thermal conductivity. If you get a “diamond” reading, you’ll need additional steps to rule out moissanite (see below).

Tips for Accurate Testing

•  Test at Room Temperature: Extreme heat or cold can skew results. Let the stone and tester sit at room temperature (around 70–80°F or 21–27°C) before testing.

•  Avoid Metal Contact: If the stone is set in jewelry, ensure the probe doesn’t touch the metal setting, as this can cause false readings.

•  Test Known Stones First: Practice with a known diamond or non-diamond (like cubic zirconia) to get familiar with your tester’s responses.

•  Repeat the Test: If the result is unclear, clean the stone again and retest.

How to Tell If It’s a Moissanite Stone or a Real Diamond

Moissanite is a common diamond simulant that can fool cheap diamond testers because its thermal conductivity is close to that of a diamond. However, there are ways to distinguish between the two:

1. Use a Moissanite-Specific Tester

Some budget testers have a dual diamond/moissanite mode. If yours does:

•  Switch to the “moissanite” setting (if available).

•  Test the stone again. A moissanite reading will typically trigger a different light or sound (check your manual).

•  If your tester doesn’t have this feature, you’ll need to rely on visual or other tests.

2. Check for Double Refraction

Moissanite is doubly refractive, meaning it splits light into two rays, creating a “doubling” effect when viewed through the stone. Diamonds are singly refractive, so they don’t show this effect.

•  How to Check: Use a loupe (10x magnification) or magnifying glass. Look through the stone’s table at an edge or inclusion. If lines or facets appear doubled, it’s likely moissanite.

•  Note: This requires good lighting and some practice to spot.

3. Observe Sparkle and Fire

•  Moissanite: Has more colorful “fire” (rainbow-like flashes) than a diamond, especially under natural light. It can appear overly sparkly.

•  Diamond: Has a mix of white and colored light but is generally less “disco ball” than moissanite.

4. Weight Test (Loose Stones)

Moissanite is less dense than diamond. If you have a loose stone and a precise scale:

•  A moissanite stone will weigh slightly less than a diamond of the same size.

•  Example: A 1-carat diamond weighs 0.2 grams, while a 1-carat moissanite weighs about 10–15% less.

5. UV Light Test (Optional)

Some moissanites fluoresce under UV light (showing a greenish or yellowish glow), while most diamonds do not. However, this isn’t foolproof, as some diamonds also fluoresce.

•  Use a UV flashlight in a dark room to check for fluorescence.

6. Professional Verification

If you’re still unsure, take the stone to a jeweler with advanced equipment (like a spectrometer or electrical conductivity tester) for confirmation. Cheap testers are a great starting point but aren’t 100% reliable for moissanite.

Limitations of Cheap Diamond Testers

•  False Positives: Moissanite often reads as diamond on basic testers.

•  Inaccuracy with Small Stones: Stones smaller than 0.02 carats may not register accurately.

•  Build Quality: Cheap testers can be less durable or sensitive, so handle with care and replace batteries regularly.

•  No Clarity or Quality Assessment: Diamond testers only check authenticity, not the diamond’s cut, clarity, or value.

Final Thoughts

Using a cheap diamond tester is a great way to quickly screen gemstones, but it’s not a definitive tool, especially when distinguishing diamonds from moissanite. By following the steps above—calibrating properly, testing carefully, and using visual clues like double refraction—you can increase your confidence in identifying real diamonds. For critical purchases or appraisals, always consult a professional gemologist with advanced equipment.

Have a diamond tester and want to share your experience? Drop a comment below, or let us know if you’ve got tips for spotting moissanite