Does the magnet test work on gold?

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Does gold stick to a magnet?

No. Pure gold is not magnetic.¹ Gold is a diamagnetic metal: it is very weakly repelled by a magnetic field.² This effect is so weak that it goes unnoticed in everyday life; with the magnet in your hand, you will feel neither a push nor a pull.³

What does the magnet test show?

The strong magnetic pull we feel in everyday life comes from ferromagnetic metals. The common ones are iron, nickel and cobalt, and their alloys.⁴ That is why a piece that sticks strongly to a magnet is not gold, or it contains some of these metals. In fact, the magnet test only shows whether there is iron in the piece.¹

Why is not sticking not enough?

Because gold is not the only metal that does not stick to a magnet. Copper and silver are diamagnetic, like gold.³ Aluminium and some types of stainless steel are not noticeably attracted to a magnet either.¹ Tungsten is paramagnetic; its attraction to a magnet is so weak that it can only be measured on a sensitive balance.⁵⁶

Tungsten matters for a particular reason: its density (19.25 g/cm³) is almost the same as that of gold (19.3 g/cm³), and gold-plated tungsten has been used to make fake bars.⁷⁶ Such a piece does not stick to a magnet, and on the scale it weighs as much as gold.

How is karat determined?

A magnet does not tell you the karat. Karat is determined by measurement. Of the methods used in the laboratory, fire assay damages the piece, while XRF (X-ray fluorescence) does not. The touchstone method, common at the jeweller, is also a simpler method that does little damage to the piece and gives quick results.⁸

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