We all take it for granted that mechanical watches have jewels in them as part of the essential operation of the movements – as you’ll see through the back of any watch with a display caseback. But the question is, when and why did jewels become widely used"   
By Andrew Hildreth

The purpose of jewels in watch movements is to reduce friction – that’s the easy part. Their use dates back to the start of the eighteenth century, in London, when the manufacturing skills were developed to fasten the jewels to the metal plate; and more importantly, how to drill a precise hole through the jewel, or into the jewel so that it is smooth and uniform. If jewels are going to be used in watch movements to hold a pivot (bearings and endstones), these were the two problems to surmount. Before gemstones the pivots ran directly into the plate.  Friction was the main problem and this was solved at the time with a variety of oils with varying viscosity.  Accurate timekeeping required that at least the degree of friction be known; and that friction was consistent.  The caseback of a Nomos Glashutte Lambda, showing several synthetic rubies
But the more interesting part of the story has little to do with horology and everything to do with politics, subterfuge and human nature. And the ultimate irony is that the widespread use of jewels was only guaranteed thanks to an effort to restrict their use. 
Clockmaking in London, at...