Jewels have been used as bearing surfaces in clocks and watches since the early 18th century. Their purpose is to reduce friction and because of their hardness to minimise wear thus improving the life of the timepiece. Originally natural rubies were used but corundum, the mineral source of both rubies and sapphires is readily synthesised and synthetic rubies, first produced in the mid 19th century became available on a commercial scale at the start of the 20th century.
Since then they have been widely used as the bearing surfaces in escapement gear trains. A fully jewelled watch will contain at least 15 jewels with a usual maximum of 21 although the quality of a watch is rather more dependent upon the shape and finish of the jewels rather than the number.
Inverted CalibreJumping Hours