Key points
- No single method is perfect – combine several.
- A precision scale and a caliper are the most important tools on the go.
- Tungsten has almost the same density as gold – catching it takes conductivity or ultrasound tests.
- For large amounts, testing at a specialist dealer is worth it.
1. Visual inspection
Look closely at the strike, edges and reeding. Genuine bullion coins have sharp details, even lettering and a clean surface. Bars show the refiner, weight, fineness and usually a serial number. Check whether the refiner is accredited by the LBMA.
Important: stamps and certificates can be faked. A visual check is a start, not proof.
2. Weighing and measuring
With a precision scale (0.01 g) and a digital caliper, compare weight, diameter and thickness with the mint's official specifications. Because gold is so dense, a fake made of another metal can hardly match both the weight and the dimensions.
| Coin | Weight | Diameter |
|---|---|---|
| Krugerrand 1 oz | 33.93 g | 32.77 mm |
| Maple Leaf 1 oz | 31.10 g | 30.00 mm |
| Vienna Philharmonic 1 oz | 31.10 g | 37.00 mm |
| Swiss Vreneli 20 francs | 6.45 g | 21.00 mm |
You will find further specifications on the websites of the respective mints. Small deviations from wear are normal for old circulated coins, but not for new bullion coins.
3. Magnet test
Gold is not magnetic. If a piece sticks to a strong neodymium magnet, it is certainly not a genuine gold coin. The reverse proves little, though: copper, lead and tungsten are not magnetic either. The magnet test only filters out crude fakes with an iron or steel core.
4. Ping test
Genuine gold coins ring with a bright, long tone when tapped lightly. Fakes made of other alloys often sound duller and shorter. There are apps that compare the sound with reference recordings. The test only works without a capsule and takes some practice.
5. Density test
Pure gold has a density of 19.3 g/cm³. You can measure it with a scale and a glass of water: weigh the piece in air, then hanging from a thin thread in water. Density = weight in air ÷ (weight in air − weight in water). Alloyed coins such as the Krugerrand come out lower, at about 17.5.
The limit: tungsten, at 19.25 g/cm³, has almost the same density as gold. A bar with a tungsten core passes this test.
6. Electronic testers
Devices that measure electrical conductivity also detect pieces with a tungsten core – often even through a capsule or foil. For bars, ultrasonic devices reveal inclusions inside. Such devices are expensive; many bullion dealers use them and test for a fee.
7. Acid scratch test
For jewellery, a scratch test on a touchstone with testing acids is common. It shows the approximate fineness of the surface. It is unsuitable for bullion coins and bars because it leaves marks and cannot detect a gold-plated core.
8. Professional analysis
- X-ray fluorescence (XRF): non-destructive, shows the alloy within seconds – but only at the surface.
- Fire assay: the most accurate method, but it destroys part of the sample. Used by refiners, mostly for scrap gold.
Which method for what?
| Method | Detects | Misses |
|---|---|---|
| Weighing and measuring | Most fakes made of lighter metals | Carefully matched tungsten fakes |
| Magnet | Iron and steel cores | Copper, lead, tungsten |
| Density | Lead, copper, brass | Tungsten |
| Conductivity / ultrasound | Tungsten cores too | — |
| XRF | Surface alloy | What lies beneath the surface |
This guide is general information and does not replace investment, tax or legal advice. No guarantee of accuracy; rules can change. Updated: 30 September 2026.