Ping Test
Also: Ring test, Ping test, Coin ping, Bell test
The ping test is a non-destructive authenticity check that uses the characteristic ringing sound a coin makes when lightly struck to tell genuine precious-metal coins from fakes.
The ping test is one of the oldest and simplest methods of checking the authenticity of precious-metal coins. Silver, gold and platinum possess a characteristic acoustic property thanks to their crystalline metal structure: when lightly struck, they vibrate at a high, long-lasting frequency, giving a bright, clear tone that rings on for several seconds. Counterfeit coins made from inferior alloys or with a tungsten core produce instead a dull, short sound with no sustain. Additional test methods such as the density test or the magnet test should be used alongside it.
The physics behind it
A coin's sound is determined by its natural frequency, which depends on material, mass, geometry and alloy composition. Precious metals such as silver and gold have a high speed of sound within the solid and low internal damping (damping coefficient). The result is a long, bright sustain. Counterfeit materials such as copper-zinc alloys, lead or tungsten damp the sound more strongly, so the tone comes out noticeably lower, shorter or tinny.
| Metal | Speed of sound (approx.) | Sound character |
|---|---|---|
| Silver (999) | 3,650 m/s | Bright, long ringing |
| Gold (999) | 3,240 m/s | Warm, medium-length ring |
| Copper | 3,810 m/s | Similarly bright, but shorter decay |
| Tungsten | 5,180 m/s | High, hard tone - no harmonic decay |
| Lead | 1,210 m/s | Very dull, no sustain |
Note: the tungsten sound is not trivial to distinguish. Because tungsten has a density very close to that of gold (tungsten: 19.25 g/cm3, gold: 19.32 g/cm3), the ping test is only of limited use on gold-plated tungsten fakes. Here the ultrasound test or X-ray fluorescence analysis are essential.
How it is done
The ping test is possible with no tools at all, but a smartphone app can make it far more precise:
- Freehand method: balance the coin on a fingertip or fingernail (minimal damping from body contact). Tap it lightly with the edge of another coin, a pencil or a fingernail. Listen to the tone and pay attention to its length, pitch and clarity.
- App-assisted method (recommended): apps such as Bullion Test or CoinScan record the tone through the microphone and compare the frequency spectrum with reference values for known coin types. A deviation of more than a few hertz in the fundamental can indicate a fake.
- Comparison method: place a genuine reference coin of the same type and weight alongside and compare the two sounds directly.
Fundamental frequency f ~ (speed of sound v) / (2 x coin diameter d)
Example silver ounce (d ~ 40 mm): f ~ 3,650 m/s / 0.08 m ~ 45,625 Hz (overtone spectrum)
The actually audible fundamental lies well lower because of the complex coin geometry (typically 1,000-6,000 Hz for common bullion coins), but the principle stays the same.
The limits of the method
The ping test is a useful quick filter, not conclusive proof. It fails with:
- Tungsten-gold fakes (identical density, similar acoustic properties for certain geometries)
- Coins with core damping from air pockets or cavities (rare high-quality fakes)
- Damaged or heavily oxidised coins, whose sound properties are altered
- Coins in a capsule or blister, when the test is muffled by packaging material
For a robust verdict the ping test should always be combined with a coin weight check, a size check and, where possible, the coin authenticity check. For high-value pieces, professional procedures such as X-ray fluorescence or ultrasound at a recognised refinery are advisable.
Key takeaway
The ping test is a quick, free first check for precious-metal coins and gives good indications of obvious fakes on gold and silver coins. It does not, however, replace instrument-based testing, especially not for tungsten-based fakes or high-quality numismatic pieces.