Magnet Test

The magnet test is one of the fastest and cheapest methods of checking the authenticity of precious metals. It rests on a fundamental physical principle: the precious metals gold, silver and platinum are not ferromagnetic — a strong magnet does not noticeably attract them. If a bar or coin reacts clearly to a magnet, there is good reason to suspect base-metal additions or an outright counterfeit.

The physics: magnetism of metals

Metals fall into three magnetic classes:

Gold is diamagnetic — a magnet even repels it very slightly, though this is imperceptible without specialist equipment. Silver behaves the same way. Platinum, however, is weakly paramagnetic, which means a very strong neodymium magnet can attract it minutely without that being a sign of a fake. When testing platinum in practice, the magnet test must therefore be applied with caution.

Carrying out the magnet test

For a meaningful magnet test a neodymium magnet of grade N52 is recommended — cheap ferrite magnets from a craft shop often give no clear result.

Step by step:

1. Place the bar or coin on a smooth, non-magnetic surface.
2. Slowly bring the neodymium magnet close from above or the side.
3. Observe the reaction: noticeable attraction = suspicious; no reaction = unremarkable.
4. Optionally: let the coin slide down a gently tilted surface while holding the magnet to the side — a ferromagnetic alloy will slow or stop the coin.

Magnet test evaluation:
  Strong attraction  →  ferromagnetic addition – very likely fake
  Weak attraction    →  paramagnetic (normal for platinum; suspicious for gold/silver)
  No reaction        →  diamagnetic – passes (gold, silver)

The limits of the magnet test: tungsten fakes

The biggest weakness of the magnet test is the so-called tungsten forgery: tungsten has a density very close to that of gold (tungsten: 19.25 g/cm³, gold: 19.32 g/cm³) and is also not ferromagnetic. Bars with a tungsten core plated in gold pass the magnet test with ease — they stand out neither by weight nor by magnetic attraction.

The same applies to fakes made of brass, bronze or gold-plated copper fitted with a non-magnetic core. The magnet test therefore does not rule out these variants. For a reliable assessment it must always be combined with further methods.

Complementary testing methods at a glance

For beginners, the combination of magnet test, coin weight check and density test is recommended — three simple methods that together expose the most common types of fake.

The swing test as a special form

A variant of the magnet test is the so-called swing or Lenz test (also: magnetic scale): a strong magnet is moved quickly past a silver or gold coin. In genuine precious metal, the moving magnetic field induces an eddy current (Lenz's law), which produces a measurable braking resistance. A coin of base metal without this property shows no such effect.

Eddy-current formula (simplified):
  P = (σ · d² · B² · ω²) / k

  σ = electrical conductivity of the metal
  d = thickness of the conductor
  B = magnetic field strength
  ω = angular velocity of the relative motion
  k = geometry factor

Silver has the highest electrical conductivity of any metal and shows the strongest eddy-current effect. Devices such as the "Sigma Metalytics" apply this principle digitally and can even estimate the fineness.

Use with coins versus bars

For investment coins (e.g. Krugerrand, Vienna Philharmonic) the magnet test is especially common, because coin fakes are often made of iron alloys and react immediately. For bars — particularly larger formats from 100 g upward — the magnet test alone is by no means sufficient; here the Archimedes test or ultrasound is essential.

Important note: the magnet test says nothing about the fineness of the metal. A coin of 333 gold (8 karat) passes the magnet test just as one made of fine gold (999) does, as long as it contains no ferromagnetic alloying metals.

In brief

The magnet test is an indispensable first quick check: if a piece of precious metal reacts strongly to a neodymium magnet, it is very probably fake or heavily contaminated. If it stays unremarkable, that is a good sign — but not a free pass. Only combining it with weight, dimension and density checks yields a dependable overall picture.