Why Watch Movements Have Jewels

More important than how many jewels a movement contains, of course, is what the precious stones actually do. So, let’s look at what jewels we are talking about and why they are featured in watches in the first place. With few exceptions, the stones used are so-called jewel bearings. These flat, cylindrical stones typically house rotating gear or lever pins. Three escapement components are also made of jewels, including the pallets that come into contact with the escape wheel and the impulse pin, which animates the movement’s balance wheel.

Historically, watchmakers used rare precious stones like diamonds, rubies, or sapphires. The latter two are both naturally-occurring colored variants of the mineral corundum. Today, many movements make use of synthetic corundum. The stones are aluminum oxide, and the differing tones are a result of adding certain elements. Red corundum stones most frequently serve as jewel bearings in watch movements. The color of these so-called synthetic rubies is analogous to that of true rubies. However, the color is optional and some brands opt for transparent bearings instead, including Moritz Grossmann. It’s now probably occurred to you that the sapphire crystal protecting countless dials is none other than colorless corundum. Since jewels play a primarily functional role in movements and synthetic stones can get the same results for a fraction of the price, there has never really been a push to use exclusively natural stones, as is the case in the luxury jewelry industry.

To understand why jewel bearings are the preferred solution in watches, you have to look at the alternatives. A very simple solution is a bearing with tapered sides that accommodates a pointed shaft. The movement plate has a hole in it that is slightly wider than the tip of the shaft. This type of bearing system can often be found in older alarm clocks. Since both components in this scenario are made of metal, and the pointed end exerts significant force, the contact points tend to wear down quickly. Thus, this is not a reasonable solution for high-quality, long-lasting watch movements.

One way to reduce the amount of force is to replace the pointed shaft with cylindrical shaft, a so-called cone or pivot bearing. Minimizing friction is key here, so the cylindrical end typically is typically narrower than the rest of the shaft, as friction increases with size. Boring a cylindrical hole in the base plate gives you a simple pivot bearing. This type of mechanism is sufficient for a slow-moving gearwheel. Bear in mind, however, that many shafts are made of steel and the bearing surface is typically the same as the rest of the base plate, oftentimes brass. Thus, even larger reductions in friction are necessary for faster-moving movement components, such as the balance wheel, escape wheel, and more. This is where jewels come in. Watchmakers still use the basic principles of the pivot bearing, but instead of drilling a corresponding hole in the base plate itself, jewels with a hole in their surface are used instead. The stones are embedded into the movement’s base plate and tend to remain there for the life of the watch. Since the jewel surfaces are much harder and more durable than the steel shafts, the latter typically require periodic replacement. This is quite easily done during routine maintenance. If the bearing surface itself is worn, which was often the case prior to the introduction of jewel bearings, more complex repair or replacement of the base plate is required.https://www.fanreviewwatch.com