What is Magnetic Shielding?

Magnetic shielding refers to the set of protective measures and materials used in watchmaking to defend a timepiece against the disruptive effects of magnetic fields. It is one of the most important technical features in modern horology, ensuring precision and reliability in an increasingly magnetised world.

From smartphones and computers to power lines and electronic devices, magnetic fields are ubiquitous in everyday life. They pose a serious challenge to mechanical watches, whose balance wheels and escapements depend on delicate ferromagnetic components that can easily become magnetised. Magnetic interference can cause significant timing errors or even stop a watch entirely.

The concept of magnetic shielding in watches emerged as a direct response to this problem. Over the decades, it has evolved from simple mechanical protection to sophisticated engineering solutions involving innovative materials and design strategies.

The Impact of Magnetism on Watches

To understand the importance of magnetic shielding, it is essential first to grasp how magnetism affects a watch’s movement. A traditional mechanical watch relies on a balance wheel and hairspring to regulate timekeeping. The hairspring, usually made from steel or similar alloys, is extremely thin and sensitive. When exposed to magnetic fields, its coils can become magnetised and stick together, altering its elasticity and oscillation rate.

This change in behaviour causes the watch to run faster or slower, sometimes gaining or losing several minutes per day. In severe cases, the movement may stop entirely if the escapement components can no longer function freely.

While even weak magnetic fields can affect accuracy, exposure to stronger fields, such as those found near speakers, electric motors, MRI machines, or airport security scanners, can result in lasting damage. With the growing number of electronic devices surrounding us, the risk of magnetisation has never been greater.

The problem of magnetism became particularly significant during the mid-20th century, as industrialisation and technological progress exposed professionals to stronger magnetic environments. Engineers, pilots, scientists, and military personnel all required timepieces that could withstand such interference.

Early Efforts in Anti-Magnetic Watchmaking

The pursuit of magnetism-resistant watches began in the early 20th century, when watchmakers started experimenting with special materials and design techniques to reduce susceptibility.

One of the earliest milestones was achieved by Vacheron Constantin in 1915, which introduced a pocket watch designed to resist magnetic interference. Later, in 1930, Tissot produced the world’s first fully non-magnetic wristwatch, incorporating non-ferrous materials such as palladium and nickel-chrome.

However, the breakthrough came in the 1950s, a decade marked by rapid advances in science and engineering. Several watch manufacturers introduced professional-grade anti-magnetic watches designed for use in technical and industrial settings.

1. Rolex Milgauss (1956)
   The Rolex Milgauss, whose name is derived from “mille gauss” (one thousand gauss), was built specifically for scientists and engineers working at CERN (the European Organisation for Nuclear Research). It featured a soft-iron inner case that formed a Faraday cage around the movement, protecting it from magnetic fields up to 1,000 gauss.

2. IWC Ingenieur (1955)
   IWC developed the Ingenieur for similar purposes, equipping it with an iron shield surrounding the movement. Its design balanced technical resilience with understated elegance, making it one of the most recognisable anti-magnetic watches in history.

3. Omega Railmaster (1957)
   Created for railway workers and electricians, the Omega Railmaster used a double-case system with soft-iron protection. It became part of Omega’s legendary trilogy of professional watches, alongside the Seamaster and Speedmaster.

These pioneering models established the foundations of magnetic shielding in watchmaking, setting a standard that continues to influence design today.

The Faraday Cage Principle

The most common and effective form of magnetic shielding in mechanical watches relies on the Faraday cage principle. Named after the English scientist Michael Faraday, this principle involves surrounding the watch movement with a closed, conductive enclosure made from soft iron or other ferromagnetic material.

When exposed to an external magnetic field, the cage distributes magnetic forces around its exterior, preventing them from penetrating the interior and affecting the movement. In practical terms, this means that even if the case is subjected to magnetic interference, the delicate escapement components remain unaffected.

Typically, the Faraday cage consists of three parts:

• A soft-iron dial

• A soft-iron movement cover

• A soft-iron inner case back

These components form a complete protective shell that diverts magnetic energy away from the movement. While effective, this approach has one limitation: it requires space, making such watches thicker than standard models.

Despite this, the Faraday cage remains a proven and reliable method of protection, particularly in professional and field watches.

The Role of Non-Magnetic Materials

As materials science advanced, watchmakers began developing alternative strategies to combat magnetism. Instead of relying solely on protective enclosures, they turned to non-magnetic materials that could be used directly within the movement itself.

The most critical development was the introduction of non-magnetic hairsprings. Early versions were made from alloys such as Nivarox (a blend of nickel, iron, and chromium) and Elinvar, which offered partial resistance to magnetism. Later, the advent of silicon technology revolutionised the field.

Silicon is inherently non-magnetic, lightweight, corrosion-resistant, and extremely stable in temperature fluctuations. These properties make it ideal for balance springs, escapement wheels, and other key movement components. Brands such as Patek Philippe, Omega, and Breguet have adopted silicon components in their high-end movements, achieving exceptional anti-magnetic performance without the need for bulky shielding.

In 2013, Omega introduced the Seamaster Aqua Terra >15,000 Gauss, the first watch capable of withstanding magnetic fields up to 15,000 gauss without a protective case. This remarkable achievement demonstrated the effectiveness of silicon-based technology and marked a new era in magnetic resistance.

Measuring Magnetic Resistance

Magnetic resistance in watches is typically measured in gauss (G) or amperes per metre (A/m), both units representing the strength of a magnetic field. A typical household magnet may produce around 100 gauss, while professional instruments or industrial machinery can generate fields of several thousand gauss.

The International Organisation for Standardisation (ISO) introduced the ISO 764 standard to define criteria for anti-magnetic watches. According to this standard, a watch must resist magnetic fields of at least 4,800 A/m (equivalent to around 60 gauss) without its timekeeping deviating by more than 30 seconds per day.

While this threshold provides basic protection for everyday use, modern watches far exceed it. Many professional and luxury models offer resistance ranging from 1,000 to 15,000 gauss or even higher.

Modern Approaches to Magnetic Shielding

Contemporary watchmaking employs a variety of strategies to achieve magnetic resistance, combining traditional shielding methods with cutting-edge materials and design.

1. Soft-Iron Inner Case Construction
   This traditional approach remains effective, especially for tool watches. Brands such as IWC, Sinn, and Ball Watch Company continue to use soft-iron inner cases in models designed for engineers, pilots, and divers.

2. Use of Non-Magnetic Components
   Silicon, titanium, Glucydur (a beryllium bronze alloy), and other non-ferrous materials are now common in balance wheels, escapement components, and even mainsprings. This approach allows manufacturers to design slimmer, more elegant cases without sacrificing performance.

3. Hybrid Systems
   Some watches combine both strategies, offering soft-iron shielding alongside non-magnetic movement components. This ensures protection even in extreme environments while maintaining traditional craftsmanship.

4. Advanced Testing and Certification
   The METAS (Swiss Federal Institute of Metrology) certification, introduced by Omega, tests watches for performance under magnetic fields up to 15,000 gauss. The COSC chronometer standard also includes magnetic resistance assessments, ensuring precision under varying conditions.

Magnetic Shielding in Quartz and Electronic Watches

While mechanical watches are particularly vulnerable to magnetism, quartz and electronic watches also face certain challenges. The coils and circuits in quartz movements can be affected by strong fields, potentially disrupting oscillation frequency or damaging components.

Manufacturers of quartz tool watches, such as Casio and Citizen, design their movements with shielding materials or layout optimisations to reduce interference. However, quartz watches are generally less sensitive than mechanical ones due to their reliance on electronic rather than mechanical oscillators.

Design and Aesthetic Considerations

Magnetic shielding also influences watch design. Traditional soft-iron cages add bulk, requiring robust and often sporty case designs. This explains why many anti-magnetic watches belong to tool-oriented categories such as pilot, field, or engineer models.

Conversely, the use of non-magnetic materials allows for greater flexibility. Silicon-based movements have enabled slimmer, more refined watches that still offer exceptional resistance, merging technical innovation with elegance.

Aesthetically, the anti-magnetic concept often becomes part of a watch’s identity. The Rolex Milgauss, for example, is known not only for its resistance but also for its distinctive lightning bolt seconds hand, symbolising the triumph of precision over magnetic disruption.

The Importance of Demagnetisation

Even with magnetic protection, watches can still become magnetised through prolonged or intense exposure. Fortunately, demagnetisation is a simple process. Watchmakers use small electronic devices that generate an alternating magnetic field to neutralise residual magnetism.

In recent years, portable demagnetisers have become available for enthusiasts, allowing quick and safe restoration of accuracy. However, the development of non-magnetic components has significantly reduced the need for such maintenance in modern timepieces.

The Future of Magnetic Resistance

The future of magnetic shielding lies in continued innovation in materials science and movement design. As technology advances, fully non-magnetic mechanical watches are becoming the standard rather than the exception.

Manufacturers are exploring advanced ceramics, composites, and carbon-based materials that offer both resilience and visual appeal. Silicon and other synthetic elements will likely remain central to this evolution, complemented by precision manufacturing techniques such as microfabrication and laser processing.

At the same time, the aesthetic and philosophical appeal of anti-magnetic watches endures. They symbolise resilience, technical mastery, and adaptability in a world filled with invisible forces.

Conclusion

Magnetic shielding is one of the most significant technical achievements in modern watchmaking. From the early experiments of the 1930s to the advanced silicon movements of today, the quest to protect watches from magnetic interference reflects the industry’s relentless pursuit of precision and reliability.

What began as a practical solution for scientists and engineers has evolved into a defining feature of high-performance timepieces. Whether through the invisible protection of a Faraday cage or the innovation of non-magnetic materials, magnetic shielding continues to ensure that mechanical watches remain accurate, functional, and enduring in a world saturated with magnetism.

In its essence, magnetic shielding represents more than technical defence; it embodies the harmony between scientific progress and the timeless art of watchmaking.