Pocketwatch 101™ – Learn about Vintage and Antique Pocket Watches
Why do watches have jewels?
Why are jewels used in watches, and what are the jewels in a watch worth?
The Purpose of Jewels in Watches
When a watchmaker speaks of the jewels in a watch, he or she is not talking about the decorative jewels that may adorn the exterior of the watch case; the watchmaker is referring to jewels which are used within the mechanism of the watch itself. The purpose of the jewels in the watch is to reduce friction. Jewels provide a very smooth, very hard, long-lasting bearing surface at various points within the watch in order to reduce friction and increase running efficiency.
Types of Watch Jewels
The basic materials used in the manufacture of synthetic ruby are sulphates of aluminum and ammonia. These undergo various chemical, mechanical and thermal treatments and are turned into dark-red ruby in the form of a "boule". After this, the machining of the stone requires as many as 50 different manufacturing operations, from the sawing of the boule to the final polishing of the jewel.
There are several different types of jewels that are commonly used in watches as described below. Illustrations of jewel types are greatly enlarged, of course. Actual jewels are a few millimeters in size, and the holes in the jewels are measured in fractions of a millimeter... quite tiny!
These are tiny "donuts" of synthetic ruby or garnet which have a carefully sized and shaped hole through their center. The cross-section of the hole in the jewel can be straight-sided (plate-jewel) or rounded (olive-hole jewel). The pivot (the polished tip) of a wheel arbor (the "axle" for each of the gears in the watch) rides in the hole of the jewel, and the jewel provides a smooth, hard surface which when lubricated is also very low friction. This allows the watch to run with less mainspring power, and protects the moving parts of the watch from wear.
Cap-jewels (also called end-stones):
These are tiny disks of jewel which cover the hole jewel. They always occur in pairs with hole jewels, i.e. you can't have a cap jewel unless there is already a hole jewel in that position. If the jewel is capped, then the wheel pivot will be conical in shape, whereas it is square-shouldered if the jewel is uncapped. In a capped jewel, the wheel pivot will ride on the cap jewel, and will be prevented from wandering sideways by the hole jewel. This has the effect of further reducing friction, and also prevents outside contamination of the tiny drop of oil that lubricates the jewel and pivot. Capped jewels on the escapement of a watch will, in theory, provide for more consistent performance in a wider range of positions than just a hole jewel alone.
These small, angle-faced jewels are attached to the pallet fork (with melted shellac) and interact with the teeth on the escape wheel. There are two pallet jewels, commonly called the entry and exit jewels, which take turns "locking" the gear-train of the watch and then transferring impulse power (through the impulse jewel) to the balance. In a typical 18,000 beat-per-hour watch, this locking function occurs five times per second.
Impulse (roller) jewel:
This is a ruby or garnet "pin" jewel, usually D-shaped when viewed end-on. A typical watch has one impulse jewel, which is located on the roller-table of the balance. As the balance turns, the impulse jewel oscillates back and forth, contacting the pallet-fork on each swing. This unlocks the pallet, allowing the escape wheel to advance one tooth, thus regulating the escapement of the watch. The roller-jewel is the single point of contact between the balance and the rest of the gear train. On vintage watches, the impulse jewel is held in place with melted shellac.
Typical Jewel Placement in Watches:
As a general rule, the higher the jewel count the higher the quality-grade of the watch. A more highly-jeweled watch has a mechanism that, at least in theory, runs more efficiently than one with fewer jewels. All other things being equal, this is true, but there are many factors which can affect the proper functioning of a watch... jewelling is only one such factor.
The following are typical placements of jewels in various watch grades.
- 7 jewel: 1 impulse jewel, 2 pallet jewels, 2 balance staff hole-jewels, 2 balance staff cap-jewels.
- 11 jewel: add 2 hole-jewels for pallet fork and 2 hole-jewels for escape wheel.
- 15 jewel: add 2 hole-jewels each for 3rd and 4th wheels
- 17 jewel: add 2 center-wheel hole-jewels
- 19 jewel: add 2 cap-jewels on the pallet
- 21 jewel: add 2 cap-jewels on the escape wheel.
- 23 jewel: add 2 mainspring barrel jewels
Auto-winding watches can add 2 - 4 (or more) jewels in the winding mechanism. Complicated movements may have additional jewels as needed for the various complications (calendar, moon-phase, repeaters, etc). Prior to WWII, a 15-jewel Swiss watch was considered "fully jeweled." Post-WWII, a fully-jeweled watch was defined as having 17-jewels.
Keeping up Appearances:
Some watches were jeweled asymmetrically; there would be a jewel on the visible side of the watch movement but only a brass bushing on the other non-visible side of the watch (see photo below). There are many Waltham and Elgin watches which have jewels visible on the 3rd, 4th and escape wheels, but when you remove the dial there are only bushings on the other side. Clearly this was done to make the watch appear to have a higher jewel count than it actually had.
Are more jewels better?
The presence of a higher number of jewels does not, in itself, guarantee a higher-quality watch, but there is certainly a correllation between higher-quality watches and more highly-jewel watches. Watches which do not have jewels on the wheels of the gear-train are subject to long-term wear from the steel "axle" or arbor of the gear grinding and cutting its way into the brass plate, thus enlarging the holes and causing the arbor to shift, which can render the watch inefficient or inoperable. Jeweled bearings present a smooth, hard finish which won't wear the way a brass bushing will.
In general, a jeweled watch allows for more efficient transfer of power from the mainspring to the escapement, which means that a longer and thinner mainspring can be used in the watch, which in turn produces longer running times. In general, we advise collectors and watch buyers to stick with "fully-jeweled" watches... 15-jewels or higher... and leave the 7-jewel "fixers" for the next guy. This problem is described in greater detail in our article "The Problem with seven-Jewel Watches".
"A watchmaker stole the jewels from my watch!"
We're always surprised when we still hear this ridiculous old myth! The fact is that no watchmaker has any reason to steal any jewels from a watch. First, the jewels in a watch have little or no monetary value. None. Nada. Zilch. They are small polished fragments of man-made ruby that have little value other than their mechanical value within the mechanism of a watch as a friction bearing. They are NOT precious gemstones. Second, if the watchmaker took all the jewels out of your watch, the watch wouldn't work anymore. This would be a problem that the owner of the watch might notice!
The watchmaker would then have to repair the watch to make it work again before they could return it to its owner. How would they repair it? They would have to put the jewels back in all the places where they were removed which would take a LOT of time and a lot of work... far more work than the jewels are worth! It simply makes no sense. It would be like trying to sneak the engine from someone's car to get a fraction of a gram of platinum out of the spark plugs.
Finally, and most importantly: watchmakers are, on the whole, an honest, hard-working group of skilled craftsmen and women whose primary interest is taking care of all the wonderful little time-keeping machines that keep our world running smoothly. We have neither the time nor the inclination to engage in less than honorable pursuits like stealing jewels from watches.
So next time you hear this old myth about a dishonest watchmaker stealing jewels from watches, please set the record straight!