Last Updated on October 2, 2024 by Jason
Jewels in watches are used to create hard, smooth bearing surfaces, primarily to reduce friction in the fastest-moving parts of the mechanism, such as the balance wheel and escapement. Over time, watch jewels also came to be used in pivot bearings to extend the life of the movement by preventing wear.
Initially, watchmakers used fragments of real gemstones, such as diamonds and rubies, which were often leftover offcuts from gemstone cutting and considered of little value due to their small size. However, with advancements in technology, synthetic ruby and sapphire (composed of aluminium oxide) became the preferred materials.
The first recorded use of jewel bearings in watch movements dates back to 1704, when Nicolas Fatio de Duillier, along with Peter and Jacob Debaufre, received an English patent for their innovation. Initially, natural jewels like diamonds, sapphires, rubies, and garnets were used in the movements, marking a significant leap in horological technology.
Natural and synthetic jewels
In the 19th and early 20th centuries, watch jewels were primarily made from natural gemstones, mostly rubies and sapphires. Due to the difficulty of shaping and drilling these hard materials, they were initially used only for the balance staff’s bearings and endstones (cap jewels). However, as the benefits of jewel bearings in reducing friction and wear became clear, their use expanded to other parts of the watch movement.
In the 1880s, French chemist Auguste Victor Louis Verneuil (1856 – 1913) developed a method for producing synthetic gemstones, significantly increasing their availability for watchmaking. Verneuil started his work on ruby synthesis through flame fusion around 1886, and within six years, he had successfully created synthetic rubies. Although he deposited his findings with the Paris Academy of Science in 1891 and 1892, he officially announced his discovery in 1902. By the time of his death in 1913, Verneuil’s process was producing 10 million carats of synthetic rubies annually.
Jeweling in watches reduces wear and extends their lifespan by lowering friction. This is particularly important for the balance staff, which experiences more frequent rotation than any other wheel in the train, making it the first part to benefit from jewelled pivots. Reduced friction at the balance pivots is crucial, as it directly affects the watch’s timekeeping accuracy, which is why jewel bearings became integral to precise mechanical movements.
Types of jewels
In watch movements, several types of jewels are used as bearings to reduce friction and enhance the accuracy and longevity of the timepiece. Here are the main types:
Hole jewels
These are the most common types of jewels found in watch movements. They are pierced jewels with a hole in the centre, allowing the pivot of a gear or wheel to rotate smoothly. Hole jewels are typically used in pairs with cap jewels to form a pivot bearing.
Cap jewels
Also known as end stones, cap jewels are flat jewels placed at the end of a pivot. They work in conjunction with hole jewels to provide a smooth surface for the pivot to rotate against. This reduces friction and wear. The end stones also combine with the jewel hole to form an oil reservoir. The lubrication also helps to reduce friction.
Pallet jewels
These jewels are used in the pallet fork of the escapement mechanism. They engage and release the escape wheel, controlling the release of energy from the mainspring to the gear train. Pallet jewels are typically rectangular or brick-shaped.
Roller jewels
Also known as impulse jewels, these are mounted on the balance wheel and interact with the pallet fork. They transfer energy from the escapement to the balance wheel, helping to regulate the watch’s timekeeping.
How many jewels are necessary?
The first bearings to be jewelled, beginning in the early 18th century by Nicolas Fatio de Duillier, were those of the balance staff. These bearings are the most crucial in a watch, as accurate timekeeping relies on the balance wheel oscillating with minimal energy loss. A smaller impulse is needed to maintain the swing of the balance, which helps reduce any disturbance to the timekeeping. This need for precision explains why the balance staff pivots are made with such a small diameter. However, this also makes them prone to breaking. In high-quality watches, balance staff jewels are generally seen as essential, although many affordable watches have been produced successfully without them.
In watches using a lever escapement, the balance is largely unaffected by minor fluctuations in torque caused by friction in the train. Consequently, jeweling other parts of the movement is more about reducing wear and enhancing durability rather than improving the watch’s timekeeping accuracy. Although escape pallets experience significant sliding friction, watches like the Roskopf pin-pallet escapement, which uses no jewels, demonstrate that a watch can still function well without them.
In most jeweled watches, the jewels in the train serve to reduce wear and extend the movement’s life, with minimal impact on the watch’s timekeeping precision.
Jewel counts in a lever escapement
The balance staff, being the fastest-turning component in a watch, is the first and most critical part to receive jewel bearings. As a result, jewel counts in watches typically begin with the balance staff. Here’s how the jewel counts break down in jewelled watches:
7 Jewels: This consists of four jewels for the balance staff. There are two bearing jewels (jewel holes) and two end stones (cap jewels). Additionally, one jewel is used for the impulse pin, and two pallet jewels for the lever escapement. This gives a total of seven jewels.
15 Jewels: In higher-quality watches, jewels are also added to the pallet staff and train wheels. Two bearing jewels are placed on the pallet staff, and two each on the escape wheel, fourth wheel, and third wheel pivots. This adds eight more jewels to the previous seven. This totals 15 jewels, which is often referred to as “fully jewelled”.
Jeweling to the centre: Some watches are further “jewelled to the centre,” meaning they include jewel bearings for the centre wheel arbor. Since the centre arbor turns slowly, this doesn’t enhance timekeeping. However, it helps reduce wear on the centre bearing in the plate or bridge. In some cases, only the top bearing is jewelled, with the lower bearing left plain.
18 Jewels: Watches with 18 jewels typically include the 15 jewels mentioned above, plus an additional jewel for the top bearing of the centre wheel, along with end stones for the escape wheel arbor bearings.
While additional jewels are sometimes used in automatic winding mechanisms, there are cases where high jewel counts are purely for marketing purposes, with the extra jewels serving no practical function in the watch’s movement.
Quartz movements
Although quartz movements require fewer jewels compared to mechanical watches, they are still important for improving durability and performance, especially in the gear train and stepper motor. A typical quartz watch usually contains 4 to 10 jewels, though some may have as few as 1 or 2, depending on the complexity of the movement.
Simple, basic quartz watches tend to have fewer jewels (around 4), whereas more intricate quartz watches, especially those with complications or hybrid designs, may feature up to 10 jewels.
Related content
Jewel bearing at Wikipedia.