Sigma Metalytics
Also: Sigma Device, Sigma Tester, Conductivity Tester
Sigma Metalytics refers to a product line of portable testing devices that measure the specific electrical resistance of precious metals via electromagnetic induction, reliably exposing counterfeits.
Sigma Metalytics is an American brand that manufactures handheld devices for the non-destructive authentication of precious metal coins and bars. The devices operate on the principle of electromagnetic induction: a coil generates a high-frequency alternating field that penetrates the metal being tested and measures its electrical conductivity and permeability. The result is compared with stored reference values for gold, silver, platinum and palladium.
Operating Principle and Product Variants
The measurement principle is based on the penetration depth of the electromagnetic field (skin effect): depending on the frequency selected, the field reaches different depths within the material. This makes it possible to detect plated objects in which a layer of genuine metal conceals an inferior core — such as the dangerous tungsten forgery, where tungsten cores are encased in gold.
Sigma Metalytics offers two main variants:
| Model | Target Group | Key Feature |
|---|---|---|
| Precious Metal Verifier (PMV) | Dealers, private investors | Compact, multiple probes for different coin thicknesses |
| Professional Series | Commercial testers | Extended frequency range, higher measurement accuracy |
The probes are calibrated to common coin diameters and thicknesses (e.g. 1-oz coins such as the Krugerrand or Maple Leaf). An incorrectly chosen probe can lead to measurement errors.
Strengths and Limitations
Advantages over simpler methods:
- Non-destructive, no chemicals (unlike the acid test)
- Measurement in seconds without removing the coin from its capsule
- Detects tungsten cores that may slip through the magnet test and density determination
Limitations:
- Coins must be tested without packaging or in thin capsules
- Very thick precious metal plating can prevent the EM field from penetrating deep enough into the core — a forgery approach using a particularly thick gold casing can distort the result
- Not a replacement for X-ray fluorescence analysis (XRF) for full material analysis
- The device must be regularly calibrated
For a comprehensive test, it is recommended to combine the Sigma test with weight and dimension checks (using the coin weight checker and coin dimensions checker) and, if required, a professional XRF analysis.
In Brief
Sigma Metalytics devices are the tool of choice for quickly and without chemicals detecting tungsten-core forgeries and plated items. For the ultimate assurance of authenticity on large holdings, a combination of several testing methods remains the gold standard.