Watch companies used semi-precious gems like garnets, rubies and sapphires as bearings to reduce friction for the steel pivots of the gear train, instead of softer bronze bushings. Learn the different kinds of jewels, their function and location, and how to determine the jewel count of a watch simply by looking at it.
The two primary types are hole and cap jewels, and both have functions on the balance assembly and in the gear train. Loose jewels are are those that have not been mounted in a setting. Think of the difficulty involved in making these tiny parts after mining the raw materials and cutting them into usable shapes.
Both hole and cap jewels could be mounted in a setting made of brass, bronze, and even gold. The setting was a ring with an inside shoulder to hold the jewel in place, while a press crimped the metal edges of the setting over the jewel, securing it.
Diamonds were used as cap jewels on the balance staff and on the escapement of the very highest grades. While they increase its value, the diamonds themselves do not increase its accuracy.
Which watch had the most? Waltham's legendary Riverside Maximus came with 3 pairs of diamond jewels, for a total of six.
Sometimes referred to as the impulse jewel, this stone trips the pallet fork in the opposite direction by every arc of the balance wheel, absorbing millions of impacts during its service life. The roller jewel is mounted to the roller table of the balance wheel with shellac, a gummy resin secreted by the female lac bug.
For more information on roller tables visit the Advanced page.
These stones were also mounted with shellac to the pallet fork, momentarily halting the gear train at every tooth of the escape wheel and pushing the balance wheel through its oscillations.
It's the precisely angled faces of those two stones, driven by the mainspring, that impels the balance wheel into its next cycle.
Hole jewels were used as bearings for polished steel pivots that generated very little friction when properly oiled, relying on the flat face to control end shake, which is vertical travel. They were made from industrial-grade precious stones, so they were much harder than the steel gear train pivots but even more brittle.
Cap jewels provide a rebound surface for the pivot tips, eliminating the need for the flat surface found on hole jewels. Paired hole and cap jewels trap the staffs by their pivot tips, generating far less friction than hole jewels alone because smaller surface areas come in contact with each other.
Jewels were also used in lever escapements, which was the eventual design choice of most watch factories. The roller jewel, mounted on the balance wheel, gives the impulse to the pallet fork, alternately locking and releasing the entry and exit pallet stones. This allows the escape wheel to rotate one tooth at a time, gradually letting down the mainspring until it's spent.
Bushings are not jewels.
They are holes drilled into both upper and lower plates for the escapement, gear train and mainspring. The contact between all of the parts is metal on metal, and unless they're properly maintained the bushings will enlarge and become ruined.
Holes with stops were milled into the plates, an unmounted jewel inserted into the hole, and then the plate metal was rolled over the edges of the jewel, trapping it in place. These are not meant to be replaced, and they must be shattered before they can be removed and a new jewel fitted in its place.
These jewels were mounted in settings and then seated from the inside so they can't fall outward, fabricated with precision to end up flush with the plate surface. Friction keeps the setting tightly in place, so they're easily changed if necessary. This is also known as an "interference fit".
Unlike friction-fit jewels, these kinds of settings were almost always screwed in from the top side of the plate, though there are several exceptions. The settings were carefully milled flush with the plate so they couldn't interfere with the oscillation of the balance wheel on full-plate designs.
Sometimes called "smokestack" jewels, these settings were made of gold and were again screwed in from the top. The purpose of raised settings was partly for show, but they also did a better job of retaining oil because of their cupped shape, so that it didn't migrate onto the plates, staining them.
These are also raised for oil retention but are pressed in from the inside of the upper plate to prevent them from falling out. They are used for a clean look on only the higher grades and are almost always gold. Any cap jewels, which must be installed first, are not a snug fit and are kept in place by the friction-fit hole jewel, which is installed second.
There are seven gear train components in any American railroad-era watch, no matter the size or model, making for seven jeweling locations. The exceptions are 5th pinion designs by Illinois and Aurora, which converted hunting movements to open-face.
The pallet fork utilizes two pairs of hole/cap jewels and two stones on a higher-count watch, while any balance wheel uses two pairs of hole/cap jewel plus the roller jewel.
A few companies that had produced hunting movements with a standard gear train chose to modify their existing design to achieve an open-face watch, rather than go back to the drawing board and come up with a completely new model.
The 4th wheel on a hunting movement (yellow arrow) carries the second hand, and to convert it to open-face the factory simply added an extra idler (red arrow) 90 degrees away so that it was opposite the winding stem and mounted the seconds hand there.
5th pinions can also be jeweled, singly and in pairs, adding to the count.
For decades the railroad companies had generally accepted any 15-jewel watch for service, but in 1891 the rules changed. The new standards required a minimum of seventeen for a fully-jeweled watch - a total of seven jewels for the balance assembly and a pair for each piece of the gear train for ten more. Not long after that the Hampden Co introduced the first 23-jewel pocket watch in America, and the jewel race was on. Factories added jewels anywhere they could put them, like the mainspring arbor and extra pivot caps.
There were combinations that added up to different totals and combinations that added up to the same totals, and once the count gets above seventeen it can get confusing. Here are the most common designs by the numbers:
Seven was the lowest total for the vast majority of American watches, and was the basis for all higher counts. There were no jewels in the gear train and the regulator is usually a simple one.
The purpose of hole and cap jewels was to reduce friction between the gear pivots and the plates in which they rotated. In a 7-jewel watch the entire gear train used bushings instead of jewels. Over time the pivots and the bushings can wear badly, especially with poor maintenance, and once these bushings become enlarged the watch is essentially ruined.
Several factories made 7-jewel watches with glass cap "jewels" on top of every pivot, along with false jewel counts and railroad motifs stamped on the plates. Underneath are metal bushings, though the glass caps may keep a certain amount of dust out of the pivots. The micro-regulator on the balance is functional.
All the jewels are visible on the upper plate, with none under the dial. The tip-off between an 11 and a 15-jewel watch is that the lower count will usually have only a simple regulator.
Again, all of the gear train jewels are on the upper plate, with corresponding metal bushings on the pillar plate.
The tip-off between a 15 and an 11-jewel watch is that the one with higher count will usually have a micro-regulator.
All the components are jeweled except for the mainspring, which rotates too slowly to generate any appreciable friction.
External barrel jewels make it easier to wind the watch.
Arbor jewels allow the mainspring to unwind more smoothly.
For more on mainspring barrels, visit the Advanced page.
Jeweled banking pins artificially inflated the count and did not increase accuracy. This design is found on the Howard Series O.
Why are they non-functional? Because there is virtually no friction between the pallet arm and the banking pins, which act as stops for the pallet as it swings rapidly back and forth.
24-jewel models are rare, with few factories making them.
Only the Columbus, Illinois, Rockford and Seth Thomas factories made 25-jewel watches as regular production pieces.
Who made the fewest? Rockford, with only a dozen.
Who made the most? Seth Thomas, with roughly 720.
Illinois was the only company to offer a 26-jewel watch, and roughly 250 of those were produced in just three grades: the Bunn Special, Benjamin Franklin and Pennsylvania Special.
Pennsylvania Special photo courtesy of Jones & Horan.
It would've been possible to add three more jewels to a standard watch, assuming none are used for banking pins. There could have been a cap jewel on the upper center wheel and an internal pair on the mainspring arbor inside the barrel.
For years the Shugart Guide printed the existence of a 28-jewel watch, which would've been the highest count of any American pocket watch during the railroad era. This piece was examined in detail and is fully explained on the Model 5 page at Seth Thomas Research.