Silicon hairspring

A conventional hairspring is drawn from an iron-nickel alloy such as Nivarox. It works extremely well and has one obvious weakness: it is ferrous, so a strong magnetic field makes the coils cling to each other, shortening the effective spring and making the watch run fast. That is by far the most common reason a healthy mechanical watch suddenly gains minutes a day.

A silicon hairspring is etched photolithographically from a silicon wafer. Silicon is not magnetic, does not corrode, needs no lubrication where it is anchored, and can be produced to tighter geometric tolerances than a drawn wire. It can also be given an oxide layer that compensates for the temperature-driven change in elasticity.

How one is made

The spring is not wound or shaped at all. Its outline is drawn as a mask, transferred onto a single-crystal silicon wafer and cut clean through by deep reactive ion etching, so hundreds of springs come off one wafer with the same geometry to within a fraction of a percent. Terminal curves that a finisher would once have bent by hand are simply part of the drawing, which is why silicon springs can carry Phillips-style curves for isochronism without any manipulation.

The temperature trick is the clever part. Bare silicon becomes less stiff as it warms, which would make a watch lose badly with heat. Silicon dioxide behaves in the opposite direction, so the etched spring is oxidized to grow a controlled layer of glass on every surface, and at the right thickness the two effects cancel. For scale, the COSC thermal criterion allows 0.6 seconds a day per degree Celsius, and a compensated silicon spring is engineered to sit comfortably inside that.

What it buys

Magnetic immunity is the headline. The ISO 764 antimagnetic threshold is a field of 4,800 A/m, roughly 60 gauss, which many household magnets exceed at close range. METAS Master Chronometer certification requires the watch to keep running and keep its rate in 15,000 gauss, and that number is reachable only by building the oscillator from materials nothing can magnetize, not by shielding. It is why a watch can be certified to that level and still have a sapphire caseback.

The consistency is the quieter benefit. Metal springs are drawn, sorted and paired to balances by measurement; etched springs arrive within tight limits already, which cuts the adjusting work and makes a free-sprung balance cheaper to set up.

The trade-offs

Silicon is brittle. It does not deform and spring back the way metal does, so a severe shock is more likely to break it than bend it. It also cannot be manipulated on the bench: a watchmaker can nudge a metal hairspring back into shape, but a silicon one is replaced as a unit, from the brand, at brand prices.

In practice breakages are rare, since these movements pass the same shock testing as any other. The real cost is dependence. A metal spring from 1960 can be trued by anyone competent; a silicon spring can only be replaced, and only while the maker still supplies the part, which matters if you expect to own the watch for decades. A full service on a modern Swiss automatic runs an indicative US $350 to $600 before sales tax at a brand center, and a broken silicon spring is a parts order on top of that. Our guide to watch servicing and care covers what a service includes.

Who uses what

Ulysse Nardin put silicon escapement parts into a production watch in 2001, and Patek Philippe followed with its Spiromax spring in silicon-based material in the middle of that decade. Omega uses a silicon spring across its co-axial calibers, including the caliber 8800. Rolex uses its Syloxi silicon spring in some references but fits most of its range, including the caliber 3235, with the blue Parachrom spring, a niobium-zirconium alloy that is paramagnetic rather than silicon. Nivachron, used in the Powermatic 80 and elsewhere, is a titanium-based alloy made the traditional way: much less bothered by magnets than Nivarox, but a metal spring and not presented as immune.

Common confusions

Silicon is not silicone. One is a semiconductor element, the other a rubbery polymer used for gaskets and straps, and shop copy mixes them freely.

A silicon hairspring also does not make a whole watch antimagnetic. Unless the escape wheel, pallet fork and balance staff are non-ferrous too, those parts can still hold a field and add drag, which is why full magnetic resistance is specified for the watch rather than the spring. And silicon does not by itself make a watch more accurate: it removes one cause of drift and leaves regulation, positional error and servicing exactly where they were. Our guide to magnetism and watches and our answer on whether magnets can damage a watch cover the rest.