A jewel bearing is a hard, polished stone — historically ruby or sapphire, both forms of corundum — pierced or cupped to support a pivot, pallet stone or impulse jewel with far less friction and wear than a bare metal pivot running in a metal plate.
Early jewelling used natural stones, hand-selected, cut and drilled by specialist jewellers, which made a fully jewelled movement expensive and jewel count a genuine indicator of grade and cost. Watches described as jewelled in small numbers in the eighteenth and early nineteenth centuries generally jewelled only the most critical bearings: the balance staff and sometimes the pallets.
The Verneuil flame-fusion process, developed around the turn of the twentieth century, allowed synthetic corundum boules to be grown industrially, chemically identical to natural ruby or sapphire but produced in bulk and at far lower cost. Its adoption by the watch industry through the twentieth century made higher jewel counts affordable across grades that had previously used unjewelled or minimally jewelled trains.
This changed what a jewel count actually signals. A pre-industrial natural-stone movement with seven jewels in the balance and pallets may represent careful, expensive work; a mid-twentieth-century watch with an inflated jewel count, including jewels placed in positions that do little functional work, can be a marketing exercise rather than a mechanical improvement. See the companion article on reading jewel counts for the identification implications.
Jewels perform different jobs depending on shape and placement: hole jewels support radial pivot loads, cap or end-stone jewels absorb end-shake and axial thrust (particularly important on the balance staff), and pallet and impulse jewels are shaped stones doing escapement work rather than simple bearing duty. Counting jewels without identifying their function tells a researcher less than examining what each one does.
Because natural and synthetic corundum are optically and chemically extremely similar, distinguishing them in a finished watch generally requires laboratory examination rather than visual inspection; for most collecting purposes, jewel material is inferred from period and grade rather than tested directly.