Magnet Test

The magnet test is one of the quickest and most affordable methods of authenticating precious metals. 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 a magnet, there is good reason to suspect base metal admixtures or an outright forgery.

Physical Background: Magnetism of Metals

Metals can be divided into three magnetic classes:

Gold is diamagnetic — it is even slightly repelled by a magnet, though this is imperceptible without specialist measuring equipment. Silver behaves in the same way. Platinum, however, is weakly paramagnetic, meaning a very strong neodymium magnet can attract platinum minimally — and this must not be interpreted as a sign of forgery. In practical authenticity testing of platinum, the magnet test should therefore be applied with caution.

Performing the Magnet Test

For a meaningful magnet test, a neodymium magnet of grade N52 is recommended — cheap ferrite craft magnets often fail to produce a 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 from the side.
3. Observe the reaction: noticeable attraction = suspicion; no reaction = inconclusive (passes).
4. Optional: let the coin slide down a slightly inclined surface and hold the magnet to the side — a ferromagnetic alloy will slow or stop the coin.

Magnet Test Assessment:
  Strong attraction   →  ferromagnetic admixture – very likely counterfeit
  Weak attraction     →  paramagnetic (normal for platinum; suspicious for gold/silver)
  No reaction         →  diamagnetic – passed (gold, silver)

The Limits of the Magnet Test: Tungsten Forgeries

The most significant weakness of the magnet test is the so-called tungsten forgery: tungsten has a similar density to gold (tungsten: 19.25 g/cm³, gold: 19.32 g/cm³) and is likewise not ferromagnetic. Gold-plated bars with a tungsten core pass the magnet test without difficulty — they raise no suspicion either by weight or magnetic attraction.

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

Overview of Complementary Testing Methods

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

The Swing Test as a Special Variant

A variant of the magnet test is the so-called swing or Lenz test (see also: Magnetic Scale / Swing Test): a strong magnet is moved rapidly past a silver or gold coin. In genuine precious metal the moving magnetic field induces an eddy current (Lenz's law), which creates 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 flux density
  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: Coins vs. Bars

With bullion coins (e.g. Krugerrand, Vienna Philharmonic) the magnet test is particularly common because coin forgeries are often made from iron alloys and react immediately. With bars — especially larger formats of 100 g and above — the magnet test alone is by no means sufficient; here, an 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 well as one made of fine gold (999), as long as no ferromagnetic alloying metals are present.

In Brief

The magnet test is an indispensable first rapid check: if a piece of precious metal reacts strongly to a neodymium magnet, it is in all likelihood counterfeit or heavily adulterated. If it shows no reaction, that is a good sign — but not a free pass. Only the combination with weight, dimension, and density checks produces a reliable overall picture.