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A primer on Anti-magnetic Watches. How magnetic are you?

by Sharon Tan on July 8, 2020

We take a brief survey on the story of anti-magnetic watches. This will kick off a series reviews of watches which offer anti-magnetism as a property. We begin here with this introduction to anti-magnetic watches.

Magnetism and watches

It’s been a long history in watch making, starting from perhaps the 16th century. Even centuries on, watchmakers continue to push boundaries to strive for more accurate movements. Early watchmakers would improve on hairsprings shapes, create tourbillons, use tuning forks, quartz crystals and probably many other tricks and tweaks to gain that extra second of accuracy. But watchmakers had to deal with making the watch robust as well to withstand daily wear that could be peppered with some physical activity. Watches started getting water resistant, and then got waterproof up to depths that humans wouldn’t normally go to. But one thing that plagued watchmakers for the longest time was magnetism. Most of us already know the detrimental effects a strong magnetic field could have on watches, especially vintage ones. But modern watches of perhaps the last decade onwards, are practically impervious to magnetic fields. How did we arrive at a solution to this problem?

Classical Solution – Soft Iron Shield

The modern Rolex Milgauss

The earliest foray into a deliberate attempt at making anti-magnetic watches dates back to the 1950s. That was the age of the famous Rolex Milgauss, Omega Railmaster, Jaeger LeCoultre Geophysic, Patek Philippe Ref. 3417 and IWC Ingenieur Ref. 666A. We will also do a review of the modern renditions of these watches in upcoming articles.

Back then, the reliable approach for an anti-magnetic watch was to encase the whole movement in a soft iron shield. This is an approach still used by modern antimagnetic watches such as Rolex Milgauss. Rolex was possibly the first to the gate when the Oyster Perpetual Milgauss, ref. 6451 was introduced as early as 1956. Soft iron refers to iron which attracts and contains magnetic fields. When the watch is exposed to a magnetic field, the magnetic field would be attracted to and contained within the soft iron shield, thus going around the watch movement rather than going through it. The downside of such a design is that a bigger capacity (thicker) shield will be needed to contain stronger magnetic fields. This approach remained practical for magnetic fields of up to 1,000 Gauss (see note 1) or 80,000 A/m [online conversion table]. That was also how the conjugated name Milgauss was derived.

The modern Rolex Milgauss Ref. 116400GV. Full hands-on review soon.

Note 1: To put things into perspective of just how strong 1,000 Gauss is; Most household appliances such as speakers and hair dryers produce magnetic fields of maybe 20 Gauss. A typical fridge magnet would produce about 50 Gauss. To move to the thousands of Gauss, a good visual would be a junkyard magnet which produces 10,000 Gauss. The human body begins responding to magnetic fields at 16,000 A/m (or 200 Gauss) if they are direction-changing.[see source ]. Static fields have much lesser effect on humans.

New Approach

Before we get into the technicalities of achieving higher magnetism resistance, we want to understand why there was even a demand for such a function.

We are intrigued with IWC’s approach to solved this problem and will turn our attention for the moment to focus on the Ingenieur. IWC launched the Ref 666A in 1963 which was proudly designed, built and even named for engineers working in laboratories with strong magnetic fields. Given the practical success of the Ingenieur (Ref. 666A), it was perplexing why IWC continued developing a movement to survive 500,000 A/m (or 6,270 Gauss)? We initially thought this project was driven by perfectionist (or egoistical) engineers wanting to show off some technical flex, because who would ever need to be subjected to such a magnetic field? This was not the case.

The original requirement for such a watch came from the military. Yes, you read that right. It was a military demand. It was meant to be a specialised tool watch for underwater anti-mine operations. We found out from IWC engineers of that era, that the requirement wasn’t exactly 500,000 A/m. It was more like the watch was supposed to be completely amagnetic and have no interaction or emission of any sort of electromagnetic waves. The rationale was that these small emissions of waves (say from a quartz watch or disturbances to the magnetic fields from moving components) could set off the underwater mines. Now everything started to make sense. The antimagnetic movement was developed for underwater anti-mine specialists and only 50 were produced for that purpose [see IWC forum on BUND watches].

IWC Ocean BUND (image from https://www.iwc.com/en/forum/ocean-bunds.html)

With the changing of components to be made of non-magnetic materials, it just could not be magnetized and easily met the rating of 500,000A/m. Although the original intent was never to strive for any anti-magnetic rating, it was a measure that most people could understand.

The Ingenuity

The concept of using a soft iron shield was no longer practical for such a high anti-magnetic rating as it would be unusually thick and heavy. Also, it would not meet the Marines’ requirements of being non-magnetic as there could be residual magnetic fields in such a construct.

With the cal. 3759, IWC had to toss the entire shielding concept, and make the movement itself insensitive to magnetic fields. One important component to redesign was the hairspring. The hairspring was a metallic (and usually magnetic) component that was moving all the time, affecting and being affected by magnetic fields.It was also at the heart of the entire time-keeping chain. When a hairspring becomes magnetized by external magnetic fields, it would stick to itself and stop moving. To overcome this, IWC developed hairsprings drawn from Niobium Zirconium alloys. If this alloy sounds familiar, that’s because this family of alloy is currently used in Rolex’s blue parachrom hairspring. Niobium Zirconium alloy is completely paramagnetic (see note 2) and unaffected by magnetic fields.

Note 2: Materials are generally classified as diamagnetic, paramagnetic and ferromagnetic. Diamagnetic and paramagnetic materials are very slightly, if at all, affected by magnetic fields and do not retain any magnetic properties once the external magnetic fields are removed. Diamagnetic materials include gold and copper, paramagnetic materials include titanium and niobium. Ferromagnetic materials have magnetic domains resulting from their atomic structures and electron spins. They are highly affected by external magnetic fields and are able to retain magnetic properties even when the field is removed. Examples are iron and nickel. For the ease of reading, we will only categorize materials as nonmagnetic and magnetic in the rest of the article.

Now that the main timekeeping component is taken care of, almost all other large steel components had to be replaced with nonmagnetic materials. It sounds like a simple replacement of materials, but there were other considerations such as hardness and thermal sensitivity considered when redesigning the components. All in all, it was no simple feat and took IWC years to finish the development of this nonmagnetic movement.

Technical Stumbles of Niobium Zirconium hairsprings

IWC did not have their own hairspring production and had to rely on external specialists to draw these extremely fine hairsprings, which also left them with very little control over the quality of the hairsprings. When the hairsprings were delivered to IWC, the engineers had a hard time working with them as they were sensitive to temperature changes. Chronometer grade allows for variation of 0.5s/day per °C which was also the standard that IWC would adhere to. These nonmagnetic hairsprings ended up having variations of a few seconds per °C! The variation was not entirely due to the choice of materials, the quality of the drawing process played a part too. The only thing IWC could do was to individually rework and calibrate these springs and send the whole lot to be tested. The manual calibration of these springs were also off the standard procedure that the watchmakers were familiar with, and every piece would need to be specially inspected. After the watchmaker’s best attempt to salvage the hairsprings, the whole lot would be tested, and only those that could pass the chronometer test would be used for production pieces. You could imagine the high cost and low yield of such a process, and naturally was not a sustainable one for continued production.

Word has it that the company that provided these hairsprings shut down after delivering the first (and only) batch of niobium zirconium hairsprings to IWC. After which, IWC kept the raw niobium zirconium alloy rods for some years, though never finding another specialist to make the hairsprings. We didn’t manage to find out exactly where these rods went in the end.

The Rolex Parachrom hairspring is also made of niobium zirconium.

It remains a mystery to us how Rolex managed to overcome the temperature sensitivity problem in their version of the parachrom hairspring, first released in 2000. Hoping some metallurgist watch collector could shed some light on the science behind temperature sensitivity in these alloys. It could have been as simple as modifying the percentage contents of the alloy, or perhaps some post-treatment after drawing the fine wires. Well, it could also be the pick-and-choose method that IWC used long ago.

Modern Antimagnetic Watches

The pursuit for antimagnetic watches did not stop there. IWC’s concept of using nonmagnetic materials remained an attractive concept to overcome magnetism as the overall watch size could be kept small. It was only a matter of time that watchmakers discovered choice materials for making components. Fast forward to 2001, Ulysses Nardin launched the Freak, the first production wristwatch to use a silicon escape wheel.

The Ulysse Nardin Freak. This model was introduced in 2013.

Silicon is non-magnetic and can be grown to net shape parts and cut with extreme precision. It was the first time silicon was used in mechanical watch parts. No surprise that many other brands such as Omega jumped on board, and silicon hairspring became a staple among many brands. Omega’s Master Chronometer watches that carry the METAS chronometer certification are rated to 15,000 Gauss (or about 1,200,000 A/m), and are achieved by developing non-magnetic movements rather than using soft iron shields. The most notable would be the Omega Seamaster <15,000 Gauss which exceeded the METAS standards.

Omega Seamaster Aqua Terra > 15,000 Gauss.

The use of this modern man-made material was a breakthrough. While we are focused on anti-magnetic properties in this article, we cannot help but mention the numerous other advantages of Silicon. Silicon was not only completely nonmagnetic, it was also corrosion resistant, thermally stable and very much lighter than it’s metallic counterparts. Silicon could improve efficiencies and lengthen the life of movements.

Even newer materials were discovered in the late 2010s. Zenith and Hublot revealed the use of more advanced materials such as carbon composite for their hairspring, with claims of higher accuracy, better shock-resistance, better thermal stability and higher efficiency due to it’s lighter weight. Yes, it’s anti-magnetic too, but that was no longer considered an innovation but a norm.


With the use of these nonmagnetic materials, testing these watches might as well be compared to testing plastic’s reaction to magnets. Nonetheless, tests must be done to prove the watches’ resistance to magnetism. We take a step back in time to look at how IWC tested the Ingenieur 500,000 A/m prototype.

We got our hands on some old press release kit of the Ingenieur 500,000 A/m, dated Nov 1989. There’s a chapter in it detailing the test procedures and test results. This test was performed at Fällanden,Zürich on their early prototype. A probe attached to the movement to measure the magnetic field during the test. The watch and attached probe was then fastened vertically (such that the magnetic field would go head-on with the movement) onto a plastic rail and moved into the test section. The magnetic field was then increased way beyond the required 800,000 A/m (1000 Gauss) to a maximum of 3,700,000 A/m (46,550 Gauss) for about 20-30s, and the movement was happily ticking away. Immediately after the test, the accuracy was checked to have a small deviation of +1s to +3s per day. It was also interesting to read that one of the other challenges faced was to document the test. Cameras couldn’t work properly when placed too close to the test, so they had to find a camera that could focus on the watch from about 8m away. Stefan Ihnen told us that he was not sure how IWC did in-house tests for the production pieces, but guessed that an equipment similar to an MRI machine was used. IWC now use large water-cooled coils to produce 600,000 A/m (7,500 Gauss) magnetic fields on a daily basis to test their watches.

The slim case of the IWC 3508 with a hard-earned 500,000 A/m stamp on the side.

To date, the highest magnetic field used to test a watch is likely for Omega’s Seamaster Aqua Terra prototype. It was tested to some insane magnetic fields of 160,000 Gauss. The prototype has survived the test and is now being exhibited at the Omega Museum. Production pieces are tested at a much lower level in-house. Omega uses a 1.5 tonne magnet to produce 15,000 Gauss of magnetic field in a small testing tunnel of 70mm [Omega’s Master chronometer Test ]

And just for fun, the good people at Hodinkee have experimented with two iconic antimagnetic watches so you don’t have to. They sat a Rolex Milgauss and an Omega Master Chronometer 15,000 Gauss on a very strong (and heavy) neodymium magnet, and hoped nothing bad happened.

Beyond Magnetism

In the centuries past, watch making and movement engineering has evolved. In solving the problem of magnetic interference, watch designers have explored new design concepts which led to discovering of nonmagnetic materials that were in many ways superior to conventional metals. It would be silly to not take advantage of these materials. With magnetism out of the way, we can expect engineers to devise and discover more technology in pursuit of a perfect watch, if there’s ever such a thing.

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