Are you looking to confidently identify gemstones, especially diamonds? Whether you’re a budding enthusiast, a seasoned collector, or simply curious about a new piece of jewelry, a gem tester can be an invaluable tool. In the world of precious stones, mistaking a simulant for a genuine gem can lead to significant financial missteps. This article will equip you with the knowledge and skills to correctly use your gem tester, ensuring more accurate initial identifications and helping you avoid common pitfalls.
Understanding Your Gem Tester: How It Works
Before we begin the test, let’s first understand the scientific principles behind gemstone testers.
The Core Principle: Thermal Conductivity
Most handheld gem testers, particularly those designed for diamonds, operate by measuring thermal conductivity. This means they assess how efficiently a material conducts heat. Diamonds are exceptional heat conductors, making this property a reliable indicator for distinguishing them from many common simulants like cubic zirconia (CZ) or glass, which have much lower thermal conductivity.
The Key Distinction: Moissanite and Electrical Conductivity
Here’s where it gets tricky: moissanite shares a very similar thermal conductivity to that of a diamond. This means a basic thermal diamond tester alone cannot reliably distinguish between diamond and moissanite.
To differentiate between these two, you need a more advanced gem tester that can also measure electrical conductivity. Diamonds are generally not electrically conductive (with very rare exceptions), while moissanite is electrically conductive. This difference in electrical properties is the key to telling them apart.
Different Types of Testers
You’ll typically find two main types of testers on the market:
- Thermal Conductivity Only: These are often simpler diamond testers that are great for weeding out most fakes but will struggle with moissanite.
- Thermal + Electrical Conductivity (Multi-Testers): These more sophisticated gem testers provide both thermal and electrical readings, making them essential for distinguishing between diamonds and moissanite.
Preparation is Key: Ensuring Test Accuracy
Accurate results start with proper preparation. Don’t skip these crucial steps!
Read Your Tester’s Instructions
Every gem tester is unique, so always start by reading the manufacturer’s instruction manual. Different models have subtle variations in calibration, operation, and how you interpret their readings.
Clean Your Gemstone
Dirt, oil, and grime are your enemies when testing. They can create a barrier between the tester’s probe and the gemstone, leading to inaccurate readings. Gently wipe the stone clean with a soft, lint-free cloth before testing.
Calibrate Your Tester
Many gem testers require calibration before each use, or periodically. This usually involves setting the device against a known diamond or a specific calibration point as per the instructions. Calibration ensures your tester is reading accurately and consistently.
Choose a Suitable Environment
Conduct your tests in a stable, room-temperature environment. Avoid areas with strong drafts, extreme temperature fluctuations, or direct sunlight, as these can affect thermal readings. Also, keep the testing area free from other metals, which might interfere with the tester’s sensitive probes.
Secure Your Gemstone
- Loose Stones: If you’re testing a loose stone, place it in a non-conductive holder or a small, non-metallic tray (some testers come with one). This isolates the stone and prevents interference.
- Mounted Gems: When testing a stone set in jewelry, be extra careful. Ensure the tester’s probe only touches the gemstone itself and never the metal setting.
Correct Testing Steps: A Step-by-Step Guide
Once prepared, follow these steps for effective gemstone identification.
Turn On and Preheat
Switch on your gem tester and allow it to warm up as indicated by the manufacturer. This usually takes a few seconds, preparing the internal components for accurate measurement.
Correct Holding Technique
Hold the tester firmly by the body. If your model has designated metal contact points or a grounding plate on the side, ensure your fingers are touching them.
Precise Probe Placement
- Vertical Touch: Gently and steadily press the probe tip perpendicularly onto a clean, flat surface (a facet) of the gemstone. Avoid tilting the probe or dragging it across the stone, as this can give inconsistent results or even damage the stone over time.
- Avoid Metal Contact: Double-check that the probe is making contact only with the gemstone and not with any part of the metal setting. Metal will conduct heat and/or electricity, causing the tester to give a false positive, indicating a diamond.
Observe the Reading
- Indicator Lights/Sounds: Most gem testers use a combination of indicator lights and audible beeps to show results. For a diamond, you’ll typically see a specific light (often green) illuminate and/or hear a continuous beeping sound.
- Identifying Moissanite with Multi-Testers: If you’re using a multi-function tester that measures both thermal and electrical conductivity, pay close attention to both readings. A diamond will show high thermal conductivity but no (or very negligible) electrical conductivity. Moissanite, on the other hand, will show high thermal conductivity and clear electrical conductivity. This dual reading is your definitive clue for moissanite.
Repeat the Test
For more reliable results, repeat the test on different facets of the gemstone. Consistency across multiple points increases your confidence in the reading.
Interpreting Results and Understanding Limitations
While powerful, your gem tester isn’t a magic wand. Be aware of its limits.
Limitations of Thermal Conductivity Testers
As mentioned, standard thermal diamond testers excel at ruling out common simulants like CZ, glass, or quartz. However, they cannot distinguish between diamond and moissanite due to their similar thermal properties. If you’re encountering a stone that tests as “diamond” on a basic thermal tester but you suspect it might be moissanite, you’ll need additional methods.
The Importance of Electrical Conductivity Testers
This is where electrical conductivity testers (or multi-testers) become indispensable. If a stone passes the thermal test but then also registers as electrically conductive, it’s almost certainly moissanite, not a diamond.
Not for All Gemstones
Remember, most gem testers are specifically optimized for diamonds. While some higher-end gem testers might offer limited identification for other stones, a diamond tester may give ambiguous or misleading readings for other gems like rubies, sapphires, or emeralds. Their thermal and electrical properties are distinct from diamonds.
Understanding False Readings
Several factors can lead to false positives or negatives:
- Probe Contamination: A dirty probe or stone.
- Environmental Interference: Drafts, extreme temperatures, or vibrations.
- Metal Contact: Touching the setting instead of just the stone.
- User Error: Incorrect holding, insufficient pressure, or tilted probe.
User Skill Matters
Your technique directly impacts accuracy. Practice makes perfect. Consistent, gentle pressure and precise probe placement are key to getting reliable readings from your tester.
Beyond the Tester: A More Comprehensive Identification Approach
Your gem tester is an excellent preliminary tool—your first line of defense in gem identification. However, for definitive verification, especially for high-value gemstones, it’s always best to combine its readings with other methods.
Combine with Visual Observations
- 10x Magnifying Loupe: Use a jeweler’s loupe to examine the stone for inclusions (internal characteristics), abrasions, or unique optical properties. For moissanite, a common giveaway is facet doubling, where you’ll see a slight double image of the facet lines through the stone, something not typically seen in diamonds.
- “Fire” (Dispersion): Observe the stone’s “fire” – the colorful flashes it emits. Moissanite generally exhibits significantly more “fire” or rainbow flashes than a natural diamond.
- Perspective Effect (Reading Test): For loose, unmounted stones, place them table-down (flat side down) on a piece of paper with fine print or a drawn line. If you can read the print or see a clear straight line through the pavilion (bottom) of the stone, it’s likely a simulant. A well-cut diamond‘s facets will refract light in such a way that you won’t be able to see through it clearly.
Seek Professional Appraisal
For any high-value gemstone or if you have lingering doubts, the most reliable course of action is to consult a professional gemologist. They possess advanced equipment (like refractometers, microscopes, and spectroscopes) and specialized training to accurately identify gemstones, detect treatments, and confirm whether a stone is natural or synthetic. This expert opinion provides the ultimate peace of mind.
Conclusion
Mastering your gem tester is a valuable skill for anyone interested in gemstones. By understanding how your tester works, preparing properly, following precise steps, and interpreting results with an awareness of its limitations, you significantly enhance your ability to identify diamonds and other gems. Remember, while your gem tester is an essential preliminary tool, it’s part of a larger identification toolkit. Always combine its readings with careful visual observation, and for absolute certainty with valuable pieces, don’t hesitate to seek the expertise of a professional gemologist. Your informed approach will safeguard your investments and deepen your appreciation for the world of precious stones.