How Jewels Make a Watch Movement More Precise: An Examination of Mechanical Advancements

Jewels, typically made from synthetic rubies or sapphires, play a critical role in enhancing the precision and longevity of mechanical watches. Their inclusion is a testament to the relentless pursuit of perfection in the horological world.

The Importance of Reducing Friction

Jewels in watch movements are not merely decorative; they serve several essential functions. One of the primary reasons for their use is to reduce friction. Friction between moving parts is one of the main issues that can destabilize a watch's precision. By using synthetic rubies or sapphires, watchmakers minimize this friction, which in turn extends the lifespan of the components and helps maintain accuracy over time.

Pivot Points and Lubrication

Jewels are often used as pivot points for gears and other moving parts. This design allows for smoother rotation and movement, which is crucial for achieving precise timekeeping. Additionally, these pivot points aid in retaining lubrication. Because they are non-porous and have a very low coefficient of friction, they can hold oil more effectively than metal surfaces, ensuring that the moving parts remain lubricated longer. This further reduces friction and wear.

Temperature Stability and Vibration Damping

Beyond minimizing friction, jewels also enhance temperature stability. Metals expand and contract with changes in temperature, which can affect a watch's performance. Synthetic materials like rubies and sapphires are less affected by these changes, ensuring that the watch maintains consistent performance regardless of environmental conditions.

Jewels can also serve as vibration dampers. As a watch movement operates, small vibrations occur. These vibrations can be detrimental to accuracy. By absorbing some of these vibrations, jewels help reduce the impact of shocks and movements that could otherwise affect the watch's precision.

The Evolution of Jewels in Watches

The use of jewels in watches has a long and fascinating history. From the earliest attempts to counter the ill effects of friction, where ancient civilizations used grease and oil to lubricate moving parts, to the introduction of synthetic rubies and sapphires, the quest for precision has driven constant innovation.

Before the advent of synthetic stones, oils and lubricants made from natural materials were used. These oils, however, were subject to degradation over time, leading to the need for frequent disassembly, cleaning, and re-oiling. This process was laborious and costly, driving watchmakers to seek more effective solutions.

The pivotal moment in this evolution came with the work of scientists like Nicolas Fatio and the Debaufre brothers around 1702. They introduced the use of natural gemstones to watches, significantly reducing friction and enhancing precision. The static coefficient of friction of steel-on-steel is about 0.58, whereas that of sapphire-on-steel is 0.10-0.15, making a significant difference in the overall performance of a watch.

Jewels in the Watch Movement

In a mechanical watch, jewels serve multiple critical functions. They reduce friction, which is one of the main issues in any mechanism. The effects of friction on mechanical parts are well understood, and for centuries, lubricants have been used to mitigate this. However, as watches became more complex, the need for better control over friction became critical.

In watches, you find sliding friction in pivotal points like the pallets and impulse pins, where the rubies or sapphires act as “ends” of the prongs that interact with the teeth of the escape wheel. Rotating friction, a more critical issue, is found in bearings, where jewelled hole jewels and capstones are employed to support the arbor shaft of the wheels. This arrangement not only reduces friction but also ensures that the mechanism can be lubricated effectively.

Typical Configurations and Usage

While jewels are a refinement that is not mandatory, certain configurations and numbers are commonly seen in watches. For example, a 7-jewel lever watch includes an impulse pin and two pallets, while a 11-jewel watch adds two lever bearings and two escape wheel bearings. As the watch becomes more complex, more jewels are added. A 23-jewel watch might include additional capstones and barrel bearings, while self-winding watches can have up to 27 jewels to ease the movement of the rotor.

Over-Jewelling and Industry Standards

While the inclusion of jewels is beneficial, the practice of over-jewelling has become a contentious issue. Since 1974, the International Organization for Standardization (ISO) and the Normes de l'Industrie Horlogère Suisse (NIHS) have published a standard (ISO 1112) that prohibits manufacturers from including non-functional jewels in jewel counts for advertising or sales literature. Despite this, the association of jewels with quality continues to prompt some manufacturers to over-jewell their watches, a practice that is often unnecessary and potentially misleading.

For a deeper dive into the world of horology and watchmaking, I recommend my book, The Watch Manual. You can find it in my bio. If you enjoyed this content, I hope you will check out my Quora bio for more insights.