Magnet Test

The magnet test is among the fastest and cheapest methods of precious metal authenticity testing. It is based 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 the magnet, there is good reason to suspect base metal admixtures or a complete fake.

Physical background: magnetism of metals

Metals can be divided into three magnetic classes:

Gold is diamagnetic - it is even minimally repelled by a magnet, though this is imperceptible without a special measuring device. Silver behaves the same way. Platinum, on the other hand, is weakly paramagnetic, which means: a very strong neodymium magnet can attract platinum minimally, without this being taken as evidence of a fake. In practical authenticity testing of platinum, 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 craft supplies 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 = suspicion; no reaction = unremarkable.
4. Optional: let the coin slide down a slightly inclined surface and hold the magnet to the side - a ferromagnetic alloy slows or stops the coin.

Magnet test assessment:
  Strong attraction   →  ferromagnetic admixture - very likely fake
  Weak attraction     →  paramagnetic (normal for platinum, suspect for gold/silver)
  No reaction         →  diamagnetic - passed (gold, silver)

The limits of the magnet test: tungsten fakes

The most significant weak point of the magnet test is the so-called tungsten counterfeit: tungsten has a density similar to gold (tungsten: 19.25 g/cm³, gold: 19.32 g/cm³) and is likewise not ferromagnetic. Bars gold-plated over a tungsten core pass the magnet test easily - 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 reliable testing 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 measurement is recommended - three simple methods that together expose the most common types of fake.

The slide test as a special form

A variant of the magnet test is the so-called slide or Lenz test (also: magnetic balance): a strong magnet is moved rapidly past a silver or gold coin. In genuine precious metal the moving magnetic field generates an eddy current (Lenz's law) that causes 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 all metals and shows the strongest eddy current effect. Devices such as the "Sigma Metalytics" use this principle in digital form and can also estimate the fineness.

Application to coins vs. bars

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

Important note: the magnet test makes no statement about the fineness of the metal. A coin of 333 gold (8 carat) passes the magnet test just as one 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 precious metal item reacts strongly to a neodymium magnet, it is highly likely to be fake or heavily contaminated. If it remains unremarkable, that is a good sign - but no guarantee. Only the combination with weight, size and density checks provides a robust overall picture.