What Do Jewels In A Watch Movement Do?

 
Robin J. from Breskens, Netherlands asks:

I own mechanical and automatic watches but I have never understood what they mean when they talk about stones or jewels in the specifications.

For example, my Theorema Toronto mechanical watch has a mechanical movement with 17 Stones. Or my Ingersoll Grand Canyon automatic movement with 35 Jewels.

So my question is, what do they mean with a movement with stones or jwwels and what is the difference how many stones or jewels are used?

Stones or jewels were developed in watches to reduce friction at the points of heaviest wear. When metal rubs against metal and when oil breaks down, the damage to pivots and bearings can be rapid and devastating in terms of watch repairs. So in a nutshell, in order to reduction wear and friction between two pieces of metal that rub against one another, watch makers use (today synthetic rubies) hard stones as friction points as they last a lot longer than metal.

To combat metal-on-metal wear watchmakers needed to find a substance that was harder than metal and so began the use of jewels within watches. The jewels that are hard enough are diamonds, sapphires and rubies. The latter two were cheaper than diamonds and could be synthetically created, Rubies are used because they have a hardness on the mohs scale similar to diamonds. These days these are synthetic rubies created for the express purpose of use in watches. As it was initially quite difficult to create and set these jewels, the amount of jewels in a movement was an indicator of it’s quality.

In most watches these jewels are used for all the pivot points in the gear train, as well as in the anti-shock settings (whether these be Incabloc or some other version). Those watches with complications also use jewels to reduce friction and over time, as watches became complicated, the amount of jewels gradually increased.

This is where it all became rather unscrupulous. As jewels became easier to produce and set, some brands used to include jewels in places where they weren’t needed, sometimes even to the detriment of the movement. They then heavily marketed this fact so consumers would think their relatively inexpensive watch was of a higher quality.

Your two watches may have different amounts of jewels due to specific movement design. Also, as one is automatic it will have additional moving parts that would require jewels to reduce friction. The automatic works are under heavy wear as the rotor spins almost constantly and transmits power to the mainspring.

In conclusion, jewels ensure a watch can function for longer periods between servicing and also ensure that the damage to high wear points is greatly reduced. It is worth noting, some brands have brought back the use of chatons (a difficult technique where small brass or gold settings are used to fit the jewel into the movement plate) and in some watches the setting of jewels is almost an art form.

Last, it is important to note that while it is true the that amount of jewels in a movement once spoke to its quality or complexity, today that isn't so much true. Watch collectors are much less interested in jewels as they are easy to include and produced from synthetic materials.

Robin sent us a pic of his watch which inspired his question - nice!

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  • Early on,  I used to try to count the visible jewels but I always came up short. Later I found out that the pallet stones (bearing surfaces on the escapement lever (fork) are also jewels and count (even though they are not the doughnut shaped bearing I was otherwise looking for).

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  • MarkCarson the other jewel everyone always forgets is the ruby impulse pin on the balance roller 😉 .  

    One of my proudest watch nerd moments was at a group discussion with the senior watchmaker for one of the Big Three –we were talking about their rattrapante complication, and somebody asked where the extra (odd numbered) jewel was.  The watchmaker furrowed his brown and couldn’t quite sort out where the extra jewel was and then I remembered that there’s a ruby roller on the return-t0-zero level for the rattrapante hand.

    Got major points for that one.

  • Eames

    Has there been a watch movement that uses sapphire or synthetic diamonds in all, rather than metal components?