A diamond tester is a device used to distinguish real diamonds from fake diamonds or other simulants. It works by using various methods to detect the properties and characteristics of real diamonds that are difficult to replicate in fakes. The key things a diamond tester picks up on are thermal conductivity, electrical conductivity, fluorescence, and optical properties.
Thermal Conductivity
One of the main things a diamond tester checks for is the thermal conductivity of the stone being tested. Thermal conductivity measures how well a material conducts heat. Diamond has extremely high thermal conductivity, significantly higher than most other gemstones and diamond simulants like cubic zirconia and moissanite.
When a diamond tester heats up the tip of its thermal probe and applies it to the stone, the heat will dissipate through a real diamond very rapidly. The tester detects this rate of heat transfer and uses it to determine if the stone is a diamond or not. Materials like cubic zirconia, moissanite, and glass have much lower thermal conductivity, so the heat does not transfer away from the probe tip as quickly. This is one of the quickest and easiest ways for a diamond tester to weed out fakes.
How Thermal Testers Work
There are a few different methods diamond testers use to check thermal conductivity:
– Thermal probe testers have a heated tip made of metal or diamond that gets applied directly to the stone being tested. The tester monitors how quickly the heat transfers from the probe into the stone. Real diamonds conduct heat rapidly, while simulants do not.
– Cooling plate testers place the stone on a plate cooled to a set temperature below room temperature. An infrared camera or thermal sensor monitors how quickly the stone warms to room temperature. Real diamonds will heat up faster due to their higher thermal conductivity.
– Dual probe testers have two thermocouple probes that both contact the stone at once. One probe gets heated while the other stays at ambient room temperature. The tester measures the temperature difference between the two probes over time as heat is conducted through the stone. The rate of heat transfer indicates if the stone is a good thermal conductor like diamond.
Advantages of Testing Thermal Conductivity
– It is very accurate for detecting diamonds and easy for anyone to perform.
– The test takes just 1-2 seconds.
– It does not require any advanced knowledge or settings – simply touching the probe to the stone is enough.
– Results are easy to interpret – either the stone conducts heat well (diamond) or poorly (not diamond).
– Testers are inexpensive and portable. Probes work on stones of any size.
– Non-destructive and does not require pre-treating or handling the stone excessively.
Electrical Conductivity
Diamond testers may also look at the electrical conductivity of a stone. Diamond is an excellent electrical insulator, meaning it does not conduct electricity well at all. In contrast, cubic zirconia and moissanite are semiconductors that will conduct some electricity. Glass and crystal are also poor electrical insulators compared to diamond.
To test electrical conductivity, diamond testers pass a small electrical current through the stone and measure its resistance. Real diamonds will have extremely high resistance, while fake diamonds and other stones will conduct electricity better and have lower resistance.
Electrical Conductivity Methods
– Metal probe testers touch two metal probes directly to the stone to pass a current through it. An ohmmeter measures the resistance.
– Contact plate testers have the stone stand on a metal contact plate while another probe is touched to it. This also passes a current and measures resistance.
– Advanced testers induce an alternating electric field around the stone without direct contact, then detect its conductivity through the field. This avoids any risks of damaging delicate stones.
Advantages of Electrical Conductivity Tests
– Accuracy is very high, close to 100% for diamond simulants like cubic zirconia.
– Results are quick and do not require advanced training or adjusting settings.
– Minimal handling is required – just brief contact with probes or plates.
– Testers are portable and stones do not require pre-treatment.
– Useful for detecting some simulants thermal probes may miss.
Fluorescence
Some diamond testers also inspect the fluorescence of stones under ultraviolet light. About 20-35% of natural diamonds exhibit some level of fluorescence under UV light, usually blue or sometimes yellow, green, etc. This fluorescent glow occurs because impurities in the diamond crystal structure get excited by the UV radiation.
Simulants like cubic zirconia and glass may also fluoresce under UV, but usually much more strongly than diamond. Coating diamonds to enhance their apparent whiteness can also produce unnaturally strong fluorescence. Thus, excessive fluorescence under UV can be a sign that a stone is not a natural diamond.
Fluorescence Testing Methods
– Standard UV lamp testers shine shortwave or longwave UV light on the stone and observe the color and intensity of any visible fluorescence.
– Advanced fluorescence viewers use filters and digital sensors to accurately measure the intensity of UV-induced fluorescence. They compare this to known diamond fluorescence levels.
– Specialty reagents can be applied to diamonds to cause distinctive fluorescence colors and patterns not seen in other stones.
Benefits of Fluorescence Testing
– Quick, simple, and portable – requires only a UV lamp.
– Non-destructive – no contact or pre-treatment needed.
– Provides additional verification alongside other tests like thermal conductivity.
– Can detect diamond simulants and potentially treated/coated diamonds.
– Longwave UV is safe for diamonds, handlers, and equipment.
Optical Properties
Diamond testers may examine the optical properties of stones as well. The high refractive index of diamond causes it to bend and reflect light in very distinctive ways. Tools that measure optical characteristics can identify these patterns to verify real diamonds. Properties tested may include:
– Refractive index – diamonds have very high refractive indices of 2.417. Most other stones are below 2.
– Dispersion – diamonds have strong dispersion, separating white light into the full color spectrum.
– Single refractive beams – light only refracts once when entering and leaving a real diamond.
– Crystal structure – diamonds reflect internal flaws in organized octahedral growth patterns.
– Polarization – diamonds do not display pleochroism or double refraction under polarization filters.
Optical Testing Methods
– Refractometers measure refractive index precisely by detecting the bending of light through the stone.
– Spectroscopes disperse light into a rainbow spectrum to check a stone’s dispersion.
– Microscopes with polarizing filters can detect double refraction and examine internal crystal growth patterns.
– Fiber-optic lights shine into the stone and reveal single refraction and crystal flaws.
Advantages of Optical Testing
– Very accurate for identification when testers include multiple optical properties.
– Detects diamond characteristics that other tests may miss.
– Non-destructive and does not require direct contact with the stone.
– Provides detailed information beyond just “diamond or not”.
– Equipment like microscopes and spectroscopes are common and easy to use.
What About Moissanite?
Most standard diamond testers are designed to distinguish real diamonds from cubic zirconia, glass, and crystals, which have very different thermal, electrical, and optical properties compared to diamond. However, moissanite is a special case that can potentially fool some diamond tests.
Moissanite is a rare mineral that is also exceptionally hard and has certain diamond-like qualities. In thermal conductivity tests, moissanite conducts heat nearly as well as diamond, so thermal probe testers may misidentify it as diamond. Moissanite’s electrical conductivity is slightly higher than diamond though, so electrical tests can detect this difference.
While moissanite has some similarities to diamond, its refractive index, dispersion, fluorescence, and other optical properties are still noticeably different when measured carefully. Diamond testers that combine electrical and thorough optical testing are generally able to distinguish moissanite from diamond. Using multiple types of tests together provides the most accurate identification of moissanite and eliminates the risk of misidentification.
Common Diamond Simulants
Cubic Zirconia (CZ)
Cubic zirconia is by far the most common and believable diamond simulant, used extensively in jewelry. However, CZ has much lower thermal conductivity and electrical resistance compared to diamond, so it is easily identified by diamond testers. It may also fluoresce under UV.
Moissanite
As a rare mineral, moissanite can resemble diamonds visually and has some similar properties, but sensitive electrical and optical testing can distinguish moissanite from diamond.
Glass
Glass has very poor thermal and electrical conductivity compared to diamond, making it simple for testers to identify. Glass also fluoresces strongly under UV light.
Crystals
Crystals like quartz and crystal have different electrical and optical qualities that diamond testers can pick up on. Crystal is also prone to double refraction.
Coated stones
Diamonds or simulants with surface coatings still retain their base properties, so thermal and electrical testing reveals their core identity. Heavy coatings may produce unusual fluorescence.
Synthetic diamonds
Synthetic diamonds have virtually identical properties to natural diamonds, making them indistinguishable to standard diamond testers. Advanced spectroscopic analysis can sometimes identify synthetics.
Interpreting Diamond Tester Results
When using a diamond tester, it helps to understand how to interpret its readings and results properly. Here are some guidelines:
– Most testers have indicator lights or audible tones to signal diamond or not diamond. Look for clear positive vs negative results.
– Repeat tests 2-3 times in different spots on the stone for consistent readings. Vary pressure and placement.
– Compare readings against calibration standards for your device to ensure accurate results.
– Consider any ambiguous or borderline readings as potential diamond simulants deserving of further testing.
– Do not rely on just one test – use multiple electrical, thermal, and optical checks for best accuracy.
– Refer to manufacturer guides for your specific tester’s required thresholds and result interpretation.
– Document test results from each method and check for contradictions or inconsistencies.
– Have a qualified jeweler investigate any stones that produce confusing or conflicting test results.
Caring for Diamond Testers
Diamond testers are precision instruments that require some care and maintenance for best accuracy and longevity:
– Handle testers gently and avoid dropping or shocking them.
– Keep components clean and free of dirt, oil, and residues. Follow manufacturer cleaning guidelines.
– Store in a secure box or pouch to prevent damage.
– Use soft cloth to gently wipe thermal probe tips when needed.
– Replace batteries/charging as required to maintain power.
– Have testers calibrated annually by the manufacturer.
– Do not leave testers exposed to extreme cold, heat, humidity or moisture.
– Use included components and accessories only – no substitutes.
– Follow all operational and care instructions provided by the manufacturer.
With proper use and care, a quality diamond tester should provide years of reliable service. Calibrating and servicing the tester as needed helps keep it in top working order.
Conclusion
Diamond testers use a variety of clever techniques to distinguish real diamonds from convincing fakes like cubic zirconia and moissanite. By testing the unique thermal, electrical, and optical properties of diamond, these devices can accurately and reliably determine true diamonds in seconds. Diamond testers pick up on the exceptional heat and electrical conductivity, fluorescence, refractive qualities that are nearly impossible to duplicate in simulants. Using multiple types of diamond testing together provides the most certainty and minimizes the risks of misidentification. With the right knowledge and care, diamond testers are invaluable tools for quickly verifying the authenticity of diamonds.