Antimagnetic

A watch doesn't become antimagnetic by decree: it becomes so through how its movement is constructed, or how it's shielded. The distinction matters, because these two approaches have different consequences for maintenance, case thickness, and the longevity of the protection.

The problem of magnetism is as old as precision watchmaking itself. A sufficiently strong magnetic field magnetizes the steel components of the oscillator — the hairspring and balance wheel above all — altering frequency and consequently isochronism. In the 1930s, pilot watches like the Spezialuhr für Flieger from 1936 already had to contend with interference from on-board instruments. The classical solution was to interpose a soft iron shield between the movement and the outside: a ring, a cover, or an internal drawer functioning as a Faraday cage, deflecting field lines without allowing them to pass through. The Rolex Milgauss ref. 6543 used a soft iron ring around the movement; its successor ref. 6541 added a drawer above the caseback to improve coverage. The IWC Ingenieur, the Vacheron Constantin Overseas Tourbillon in Grade 5 titanium, the Laventure Marine Type 3, and Bremont's Trip-Tick case — developed in 2007 to exceed Martin-Baker ejection seat testing — all work on this perimeter logic. The limitation is thickness: the soft iron ring takes up space, which is why the Ingenieur 35 eliminated it to drop to 9.4 mm with a sapphire caseback.

The other approach, more recent, acts from within: vulnerable components are replaced with intrinsically non-magnetic materials. Silicon is paramagnetic by nature — silicon hairspring, lever, and escape wheel don't magnetize, reduce friction, and extend service intervals. Omega pursued this path in parallel with developing the Co-Axial escapement; Rolex uses the Syloxi silicon hairspring in the Perpetual 1908; Breguet equips the Calibre 1896 with a complete silicon escapement. TAG Heuer developed the TH-Carbonspring in carbon fiber, created to solve silicon's porosity issues and proposed as a solid industrial alternative.

Swatch Group took a third path with Nivachron: a patented synthetic alloy, non-magnetic and thermostable, used for hairsprings in ETA Powermatic 80 calibers and various Rado, Tissot, Certina, and Mido calibers. It's neither silicon nor soft iron: it's an engineering compromise designed for mass production.

The most demanding reference standard today is Omega's METAS Master Chronometer certification, which imposes resistance to fields of at least 15,000 gauss with the movement fully assembled in the finished watch — not on the bench, in the actual case. Before this certification, many manufacturers claimed values measured on a naked movement, which tell us nothing about the watch's behavior on the wrist.