By Eric Moll, Updated Mar 24, 2022

Although the name suggests otherwise, a "tin can" is rarely pure tin. The alloy and metal coatings used in modern food containers give them a subtle but measurable attraction to magnets. This attraction is rooted in the paramagnetic properties of the constituent metals, not in any “tin‑specific” magnetic behavior.

Invention

The first sealed metal food container was patented by British inventor Peter Durand in 1810. Durand’s design featured iron coated with a thin layer of tin to resist corrosion and keep food fresh.

Evolution

Over the past two centuries, the composition of these containers has shifted several times:

• Early 19‑century: Iron with a tin coating.
• Late 19‑century: Tinplate steel – steel sheets wrapped in a very thin tin layer.
• 1957: Aluminum introduced for the bottom of the can, while the cap remained tinplate steel.
• 1965: Some manufacturers began coating steel cans with chromium instead of tin, yet the term “tin can” remained common.

Today, most commercial food cans are made from a combination of tinplate steel, aluminum, and occasional chromium, with the total tin content usually below 2 % by weight.

Magnetism

All the metals that appear in a modern tin can – iron, steel, tin, aluminum, and chromium – are paramagnetic. Paramagnetic materials do not generate their own magnetic field but become temporarily magnetized when exposed to an external magnetic field. As a result, a typical tin can will be gently attracted to a strong magnet.

In practice, the attraction is weak enough that most household magnets won’t lift a can, but it is detectable with a laboratory magnet or a magnetometer. The effect is purely a physical property of the metals and has no bearing on the safety or quality of the food inside.

References

• History of the Can
• Chemistry: The Molecular Nature of Matter and Change; Martin Silberberg; 2004