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As devices that are powered by the energy stored by winding the spring, it is critical for mechanical watches to retain as much energy as possible. This naturally means that friction should be avoided – what jewels are designed to do. 

Ever since watches have been created in the early 1500s, efforts have been made to increase the accuracy and efficiency of the movement. The invention of Jewel bearings by Nicolas Fatio de Duillier, Peter Debaufre, and Jacob Debaufre, around 1702 was one of the most important findings to improve minimizing friction and thus achieve better operation of the movement. 

So, how do these jewels work?

First, let’s talk about the choice of material of the jewels. At the beginning (until around the 20th century), jewel bearings were ground into shape using materials like quartz and garnet for most watches and sapphire and ruby for luxury watches. Now, almost all watches use jewels made from artificial sapphire or ruby, which is significantly more cost-effective yet just as efficient. The reason why these materials are used is that their slick surface is unique for their low coefficient of friction with metals. 

By using these jewels, it improves mechanical movements in two ways: they improve the accuracy of the watch and increase the lifespan of the bearings. By decreasing the energy lost in friction, the slight discrepancies in impulses applied to the balance spring can be minimized, which can accumulate to create a noticeable difference in time-keeping accuracy. Furthermore, the jeweled bearings can ensure that the gear will not jam and stop the watch. 

Types of Jewels

Pallet Jewel – Rectangular jewels used at the end of the arms of the pallet forks. 

Hole Jewel- donut shaped jewels mounted as support on the shaft of wheels.

Capstone/Cap Jewel – cylinder shape jewels with no hole used as supports to be placed at the end of the wheel arbors. 

Impulse Pin/Roller Jewel – D shaped pin mounted on the roller table as part of the balance wheel assembly. 

The standard watch movement makes use of 17 jewels. The 17 jewels are most commonly placed in the movement in these parts:

1: Balance Wheel Assembly (impulse jewel)

2-5: Balance Staff Pivot Bearings (two pairs of jewels – a hole jewel and cap jewel)

6-7: Escape Lever Pallet (one pair of pallet jewels)

8-9: Center Wheel (one pair of escape level pivot bearings)

10-11: Escape Lever (one pair of jewels – a hole jewel and cap jewel)

12-13: Escape Wheel (one pair of jewels – a hole jewel and cap jewel)

14-15: Fourth Wheel (one pair of jewels – a hole jewel and cap jewel)

16-17: Third Wheel (one pair of jewels – a hole jewel and cap jewel)

As stated, this is the standard number of jewels used in a mechanical watch. However, the number of jewels varies heavily depending on the function and design of the watch. For example, chronographs and automatic winding movements are just a few that require more than 17 jewels. 

 

Written by Sudona Barton of the Rotate Watches team.