No single test can guarantee a coin is authentic. The best approach combines multiple methods that probe different properties. Here's everything you need to know about each testing method—and how to use them together.
Why Multiple Tests Matter
A coin has two categories of properties you can verify:
- Geometry: Diameter, thickness, weight, density
- Material properties: Composition, conductivity, elasticity, magnetic response
Each testing method reveals different information. A sophisticated fake might pass one test but fail another. The more properties you verify, the higher your confidence.
The Complete Testing Methods Comparison
| Method | Tests Geometry | Tests Material | Destructive | Cost | Accuracy | Catches Tungsten |
|---|---|---|---|---|---|---|
| Visual Inspection | ✅ | ❌ | No | Free | 60-70% | ❌ |
| Weight Test | ✅ | Indirect | No | $20-50 | 85% | ❌ |
| Dimension Test | ✅ | ❌ | No | $10-30 | 80% | ❌ |
| Magnet Test | ❌ | ✅ | No | $5-10 | 50-60% | ❌ |
| Ping Test | ✅ | ✅ | No | $0-29/yr | 80-90% | ✅ |
| Specific Gravity | ✅ | ✅ | No | $30-50 | 90%+ | ❌ |
| Conductivity (Sigma) | ❌ | ✅ | No | $700-2000 | 98%+ | ✅ |
| XRF Analysis | ❌ | ✅ | No | $5000+ | 90% | ⚠️ Surface only |
| Acid Test | ❌ | ✅ | Yes | $10-20 | 85% | ✅ |
| Ultrasound | ✅ | ✅ | No | $300+ | 95% | ✅ |
Method-by-Method Breakdown
Visual Inspection
What it tests: Design details, edge lettering, surface quality, color
How it works: Compare against known authentic coins looking for die marks, font consistency, detail sharpness, and color accuracy.
Catches: Low-quality counterfeits with obvious design flaws, wrong fonts, blurry details, or incorrect coloring.
Misses: High-quality fakes with accurate dies, any material substitution that looks right.
Cost: Free
Best for: First-line screening before other tests.
Weight Test
What it tests: Mass (geometry-dependent)
How it works: Weigh the coin on a precision scale (0.01g accuracy minimum) and compare to official specifications.
Catches: Fakes made from lighter or heavier materials that weren't precisely calibrated.
Misses: Tungsten fakes (tungsten density ≈ gold density), carefully calibrated fakes.
Cost: $20-50 for a precision scale
Best for: Quick screening—wrong weight is an immediate red flag.
Specifications for common coins:
| Coin | Official Weight |
|---|---|
| 1 oz Gold Eagle | 33.93g |
| 1 oz Gold Maple Leaf | 31.10g |
| 1 oz Krugerrand | 33.93g |
| 1 oz Silver Eagle | 31.10g |
| 1 oz Silver Maple Leaf | 31.10g |
Dimension Test
What it tests: Diameter, thickness (geometry)
How it works: Measure with calipers and compare to specifications.
Catches: Fakes with incorrect dimensions—common in cheap counterfeits.
Misses: Correctly-sized fakes made from wrong materials.
Cost: $10-30 for digital calipers
Best for: Confirming geometry matches official specs.
Magnet Test
What it tests: Ferromagnetic properties (material)
How it works: Pass a strong neodymium magnet over the coin. Gold, silver, and platinum are not magnetic and should show no attraction.
Catches: Fakes with iron, steel, or other ferromagnetic cores.
Misses: Fakes made from non-magnetic base metals (copper, zinc, lead, tungsten).
Cost: $5-10 for a neodymium magnet
Limitations: Many counterfeit materials are non-magnetic too. A passed magnet test means little; a failed test is conclusive.
Best for: Quick screening to eliminate obvious ferromagnetic fakes.
Ping Test (Acoustic Resonance)
What it tests: Material elasticity AND geometry simultaneously
How it works: Tap the coin and analyze its resonance frequencies. Different materials produce distinctly different sounds based on their Young's modulus (stiffness).
Catches: Wrong material composition—including tungsten fakes. Tungsten has completely different acoustic properties than gold, producing a dead "thud" instead of a ring.
Misses: Genuine coins with internal defects may produce unusual results. Some coins of different types have overlapping frequencies.
Cost: Free (manual), $0-29/year (Pingcoin app)
Best for: Detecting tungsten fakes that pass weight tests. First-line screening with scientific backing.
Learn more: The Complete Guide to Coin Ping Testing
Specific Gravity Test
What it tests: Density (geometry + material)
How it works: Weigh the coin in air, then suspended in water. The difference reveals density using Archimedes' principle.
Catches: Wrong material if density differs significantly from precious metals.
Misses: Tungsten-gold composites (tungsten density: 19.3 g/cm³, gold: 19.32 g/cm³—nearly identical).
Cost: $30-50 for equipment
Accuracy: 90%+ for detecting most base metal fakes
Limitations: Requires careful technique. Trapped air bubbles affect results.
Conductivity Testing (Sigma Metalytics)
What it tests: Electrical conductivity at depth (material)
How it works: Sends electromagnetic waves into the coin and measures how they're absorbed. Different metals have different conductivity signatures.
Key advantage: Measures ~180 microns deep—deeper than plating thickness.
Catches: Plated fakes, wrong core materials, tungsten fakes.
Cost: $700-2000+ for Sigma Metalytics device
Accuracy: 98%+
Best for: Professional dealers, serious collectors, high-value authentication.
XRF Analysis
What it tests: Elemental composition (material surface)
How it works: X-ray fluorescence identifies which elements are present in the sample.
Catches: Wrong surface composition, karat verification.
Critical limitation: Only penetrates ~70 microns—won't detect a gold-plated tungsten core.
Cost: $5000+ for portable units, or pay per test at a dealer
Best for: Verifying surface composition and gold purity, not detecting plated fakes.
Acid Test
What it tests: Chemical composition (material surface)
How it works: Apply acid to the coin. Different metals react differently—gold resists most acids while base metals corrode.
Catches: Plated fakes (reveals base metal underneath).
Major drawback: Destroys the tested area. Not suitable for collectible coins.
Cost: $10-20 for acid test kit
Best for: Absolute last resort on non-collectible items.
Ultrasound Testing
What it tests: Internal structure (geometry + material)
How it works: Sound waves travel through the coin and reflect off internal features. Different materials transmit sound at different speeds.
Catches: Internal inconsistencies, layered fakes, tungsten cores.
Cost: $300+ for equipment
Best for: Professional authentication, detecting sophisticated internal forgeries.
The Optimal Testing Stack
For different scenarios, here's what to combine:
Casual Buyer (< $500 purchases)
| Test | Why |
|---|---|
| Visual inspection | Catch obvious fakes |
| Weight test | Verify basic specs |
| Magnet test | Eliminate ferromagnetic fakes |
| Ping test (app) | Detect material issues including tungsten |
Total cost: $30-80 + free app
Confidence level: 90%+
Serious Collector ($500-5000 purchases)
| Test | Why |
|---|---|
| All of the above | Foundation |
| Dimension test | Verify geometry |
| Specific gravity | Additional density verification |
Total cost: $80-150
Confidence level: 95%+
Professional Dealer / High-Value Authentication
| Test | Why |
|---|---|
| All of the above | Foundation |
| Sigma Metalytics | Professional-grade conductivity |
| Ultrasound (if available) | Internal structure |
Total cost: $1000-2500
Confidence level: 99%+
Why the Ping Test Deserves Special Attention
Most testing methods either test geometry OR material properties. The ping test is unique in testing both simultaneously through acoustic physics.
More importantly, it's one of the few affordable methods that catches tungsten fakes. A tungsten-core gold coin will:
- ✅ Pass weight tests (same density as gold)
- ✅ Pass visual inspection (gold surface)
- ✅ Pass magnet tests (tungsten isn't magnetic)
- ✅ Pass specific gravity (nearly identical density)
- ❌ Fail the ping test (tungsten sounds completely different)
For most people, the combination of weight + dimensions + magnet + ping test provides excellent protection at minimal cost.
Conclusion
No single test is perfect. Counterfeiters continuously adapt, and testing methods have inherent limitations. The key is layering multiple tests that probe different properties.
For the average precious metals buyer, a sub-$100 testing kit (scale, calipers, magnet, Pingcoin app) provides 90%+ confidence. For high-value purchases, investing in professional equipment like Sigma Metalytics makes economic sense.
When in doubt, start with the free tests (visual, magnet) and work up to more sophisticated methods as value increases.
Related: The Complete Guide to Coin Ping Testing | Is Counterfeiting Getting Easier?