Magnet Test

The magnet test is one of 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 are grounds to suspect base metal admixtures or a complete counterfeit.

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 not perceptible without special measuring equipment. Silver behaves the same way. Platinum, on the other hand, is weakly paramagnetic, meaning: a very strong neodymium magnet can attract platinum minimally, without any counterfeit indication being derived from it. In practical authenticity testing of platinum, the magnet test must therefore be applied with caution.

Performing the magnet test

For a meaningful magnet test a neodymium magnet of grade N52 is recommended – cheap ferrite magnets from hobby supplies often deliver no clear result.

Step by step:

1. Place the bar or coin on a smooth, non-magnetic surface.
2. Slowly bring the neodymium magnet closer from above or from the side.
3. Observe the reaction: noticeable attraction = suspicion; no reaction = unremarkable.
4. Optionally: 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 evaluation:
  Strong attraction  →  ferromagnetic admixture – very likely fake
  Weak attraction    →  paramagnetic (platinum normal, for gold/silver: suspicion)
  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 also not ferromagnetic. Bars with a gold-plated tungsten core pass the magnet test without problem – 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 uncover the most common counterfeit types.

The slide test as a special form

A variant of the magnet test is the so-called slide or Lenz test (also: magnetic scale): 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), which causes a measurable braking resistance. A coin made 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 even estimate the fineness.

Application to coins vs. bars

For bullion coins (e.g. Krugerrand, Vienna Philharmonic) the magnet test is particularly widespread, because coin fakes are often made of iron alloys and react immediately. For bars – especially larger formats from 100 g – 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 made of 333 gold (8 carat) passes the magnet test just as one made of fine gold (999) does, as long as no ferromagnetic alloying metals are contained.

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 with high probability fake or heavily contaminated. If it remains unremarkable, that is a good sign – but no free pass. Only the combination with weight, size and density testing gives a robust overall picture.