Magnetism is a plague. Much like syphilis, it will slowly drive a watch adjuster to a wretched state of madness if not diagnosed and treated in time.
The symptoms of magnetism are so diverse that it is wise to routinely demagnetize your watches before adjusting them. Most of the parts in a vintage watch are non-magnetic, but many are made of steel and can easily become magnetized. These parts will cause erratic timing, and some of them—like steel hairsprings—will have calamitous effects.
Why Do Watches Get Magnetized?
The modern world has so many electronic devices that give off fields that magnetism is inevitable. When you a buy a vintage pocket watch off eBay, for example, it goes through dozens of devices that weigh, scan, measure, image, probe, and transport it between the seller’s door and yours. And once you have your pocket watch, it might share a pocket with your smartphone.
Your tools, if magnetized themselves, can magnetize the parts they touch. When I bought my staking set, for example, it was a boiling ball of magnetism that could power a small MRI coil. Inexplicably, my anti-magnetic tweezers occasionally get magnetized. Such is the modern world.
Many of watchmaking’s great innovations were designed to prevent magnetism. The use of Faraday cages to enclose a movement (e.g., Rolex’s Milgauss) and magnetism-resistant hairspring alloys are the big ones. In modern watches, the shift toward silicon hairsprings greatly increases a watch’s resistance to magnetism.
But your 1917 Illinois pocket watch has none of that new-fangled stuff, so we’ll need to learn to identify and remove magnetism from our vintage movements.
Signs of Magnetism
A magnetized watch won’t run well, but there’s no single timing-machine signature of magnetism. Its effects depend on the magnetized part and where it is in relation to the escapement.
If the hairspring is magnetized, its coils might stick together and slap against each other as they unstick, which would be apparent as erratic timing traces. If the coils stay stuck, the effective length of the hairspring will be much shorter than normal, causing the watch to run abnormally quickly.
As an example, here are some odd Timegrapher traces: loopy and bulbous, with a consistent high-frequency period.
When faced with wavy traces, we know to measure the period of the wave—the time between the peaks. A wave with a 60-second period, for example, suggests a flaw in the fourth wheel, which rotates once every 60 seconds. But these waves have a fast period, much faster than the escape wheel rotates, so it isn’t that.
I’m not sure what part was magnetized, but a zap with the demagnetizer (literally) straightened out the timing traces.
Because magnetism’s effects can be subtle and diverse, it’s wise to always demagnetize a watch before measuring its rates or attempting to adjust or regulate it. Otherwise, you could chase the rates in circles. I always run a watch through the demagnetizer when I first receive it and before I adjust it.
How to Demagnetize a Watch
You demagnetize a watch with a demagnetizer. (The mind recoils, I know.) These have been around forever, so you have a choice between many different kinds. Like all watchmaking tools, demagnetizers run the range from cheap stuff from China to solid equipment to poor value-for-money equipment with a Swiss name stamped on it.
The two most common kinds work differently.
- The first kind—represented by the ubiquitous “little blue box” unit made in China—requires you to slowly move the watch through an alternating field. To use it, hold the watch an inch over the center of the unit, press the ON button, and keep the button depressed as you slowly move the watch away from the unit. Let go of the ON button when the watch is arm’s length from the unit. One or two zaps should suffice.
- The second kind is a classic degausser. If you were an A/V geek back in the day and had a shoebox-sized device (occasionally with sweet wood-grain decals on the side) that you used to erase VHS and reel-to-reel tapes, you know what I mean. (In fact, those old magnetic-tape erasers are excellent for watches.) You set the watch down on on the unit, press the button, and zappo—the deed is done. If you’re demagnetizing a small part, a strong demagnetizer might shoot it across the room, so it’s wise to hold or cover it. There are plenty of new degausser-style units, but keep an eye out for vintage Bulova “Elimag” units, which pop up for sale on eBay occasionally.
If you’re curious to see both types in action, this video from Mark’s inestimable Watch Repair Channel shows both of them in use at the 60-second mark:
Compared to other watchmaking tools, demagnetizers are inexpensive and essential, so they deserve a place of pride on the bench. And if yours has wood-grain decals, it’s extra proud.