Mar 10, 2020
 6 minutes

Why Watch Movements Have Jewels

By Tim Breining
CAM-1044-Edelsteine-2-1

Why Watch Movements Have Jewels

Watches and jewelry have a certain affinity – at least that’s what most jewelry shop displays would have you believe. Men’s watches are sometimes described as the only piece of masculine jewelry, and classic women’s watches are frequently adorned with precious stones, mother-of-pearl dials, and other luxurious materials. Women’s watches are slowly but surely expanding beyond this niche; however, that doesn’t mean they’re losing all their glittering gems. Jewels are much more than just pretty decoration when it comes to watches. For hundreds of years, clock and watchmakers have taken advantage of the unique characteristics of precious stones, employing them in timepiece movements. In this article, we’ll explain why watch movements feature jewels and dispel some common myths surrounding the topic.

7, 17, or 21 Jewels: What’s the difference?

7, 17, 21, or more: Many older watches list the number of gemstones or jewels that its movement contains on the dial. Nowadays, that information is most often engraved on the movement itself. The fact that the number of jewels is so prominently displayed gives us a sense of these small stones’ significance. Over the years, various brands’ marketing departments have certainly sent the message that more is better when it comes to jewels. This has paved the way for some seriously extreme creations, such as a Waltham watch that boasts 100 jewels. It turns out only 17 of those actually serve a purpose, the others were simply mounted on the rotor for no apparent functional reason. Questionable cases like this led to the introduction of an ISO standard that prohibits promoting non-functional jewels in watch movements. Ever since, you can rest assured that any jewels advertised serve as a more reliable source of information about the movement itself.

But what are the jewels for?

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.

Moritz Grossmann Atum

The number of jewels necessary for any given movement depends on the number of components that require bearings. Seven jewels tends to be the absolute minimum for more affordable movements, while 21 is considered a fair number for a modern, three-hand automatic caliber. If additional friction points are outfitted with precious stones, such as the barrel, those numbers climb even higher. Increased numbers of jewels are often necessary for more complex mechanisms, seeing as additional wheels and levers present new opportunities for bearings to be used within the movement.

Why (Synthetic) Jewels?

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.

The unique shape of the jewels gives them additional functionality as a lubricant reservoir. This means that lubricant will remain at the appropriate point even after years of operation. These factors, together with cost-effective mass production, automated grinding, and laser-drilling technologies, means that even the most affordable mass-produced mechanical watch movements are often equipped with jewel bearings. Luxury watch brands distinguish themselves by placing their jewel bearings in gold settings, so-called chatons. Historically, watchmakers utilized these soft metal settings as a way to adjust the imperfect hand-cut jewels. While this is no longer the case, it still adds to the watch aesthetically and is a mark of the best in haute horlogerie. You’ll often find chatons in timepieces from brands with traditional design philosophies, such as A. Lange & Söhne.

When are jewel bearings superfluous?

As mentioned previously, jewel bearings aren’t necessary for every shaft or movement component. In fact, there are some situations in which they are far from the optimal choice. One such example is the most recognizable bearing in automatic watches: the rotor bearing. With few exceptions, you will find the rotor surrounded by tiny ball bearings. In this case, ball bearings have a quicker movement impulse, whereas a jewel bearing would have to build up lubrication every time the rotor moved. Moreover, the large diameter of the ball bearing better protects the rotor from tilting or hitting against the rest of the movement. To achieve the same stability with a jewel bearing, you would have to increase the size so much that it would no longer be efficient.

Moreover, jewel bearings require a certain amount of looseness (or “play”) so that the shafts can tilt slightly. Ball bearings, on the other hand, can be preloaded (i.e., fitted with no looseness), allowing for one-way bearing. A similar concept is employed for flying tourbillons. This negates the need for a visually-distracting bridge on the upper side of the mechanism. Some super thin watches with ball bearings are able to do away with a base plate altogether. The Piaget Altiplano Ultimate Concept, for example, features several ball-bearing mechanisms integrated into the case itself, including the barrel.

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About the Author

Tim Breining

My interest in watches first emerged in 2014 while I was studying engineering in Karlsruhe, Germany. My initial curiosity quickly evolved into a full-blown passion. Since …

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