Gold coins and bars carry a lot of value in a small piece, which makes them a target for clever fakes. A common trick is a core of a cheaper, heavy metal such as tungsten, covered with real gold. The surface tests as gold. This guide explains how to check coins and bars properly, without damaging them.
Why a surface test is not enough
An XRF analyzer is the standard way to read gold purity, and it is excellent for jewellery. But X-rays read the outer layer of the metal. If the outside is real gold and the inside is not, a surface reading alone can look fine. For coins and bars, you need a second test that looks deeper.
How a conductivity tester works
Every metal conducts electricity at its own rate. A conductivity tester places a small magnetic field into the coin, which makes tiny electric currents flow inside the metal. The tester measures how easily they flow and shows the result in MS/m, next to the value that metal should give.
| Metal | Approximate conductivity (MS/m) |
|---|---|
| Fine gold | 45 |
| 22K (916) coin gold | 9.7 |
| Fine silver | 61 |
| Tungsten | 18.8 |
Tungsten does not match fine gold or 22K gold, so a coin or bar hiding tungsten reads off target. On 916 gold, the tester reads up to about 0.65 mm into each side.
A simple routine for coins and bars
- Check size and weight against the official figures for that coin or bar.
- Read the alloy with XRF to confirm the gold percentage at the surface.
- Check conductivity on both sides to look below the surface.
- Compare the reading with the expected value for that metal.
- Record the results before you pay.
If either test is off, do not buy until the piece is checked further.
What each method can and cannot do
- XRF analyzer: gives the gold percentage and the other metals, but reads the surface.
- Conductivity tester: looks below the surface and can test through a capsule, but shows no karat number. Pieces thinner than about 0.8 to 1 mm are not suitable.
- Together: they cover each other's blind spots.
Semsons Tech machines for coin and bar testing
- Gold coin testing machine (conductivity tester): for gold, silver, platinum and palladium coins and bars, reads through capsules up to about 3 mm, ₹1,35,000 including GST.
- Signet-PC and Signet FSDD XRF analyzers: for the gold percentage and full alloy.
Buying old jewellery too? See our counter routine for old gold.
Where to see and buy it
These are the Semsons Tech machines for this job. The store links let you book online; the other links open the full specifications or a quotation request.
| Machine and where to buy | Key facts |
|---|---|
| Gold coin conductivity tester Buy or book on our store Full specifications | Checks the metal below the surface of coins and bars Reads through capsules up to about 3 mm ₹1,35,000 incl. GST |
| Signet-PC XRF gold analyzer Buy or book on our store Full specifications | Benchtop XRF with a Si-PIN detector as standard Installation and operator training included ₹6,45,000 incl. GST; book for ₹50,000 |
See both tests on a real coin. Book a demonstration or call +91 98216 12340.
