CAPILLARITY

Capillarity is the phenomenon by which a liquid rises, falls or moves within a narrow space — tube, gap, Set between two surfaces — under the effect of surface tension and wetting, independently of gravity. It depends on the surface tension of the liquid, the contact angle it forms with the solid, and the radius of the gap, according to Jurin’s law. A wetting liquid, like most watchmaking oils, forms a concave meniscus and spontaneously advances into the finest spaces.

In watchmaking, capillarity is both harnessed and feared. The oil reserves of the Oil of the jewels pivoting are designed to retain the Lubricant by capillarity, as close as possible to the point of friction. But an excess quantity, a poorly polished jewel, or the absence of epilame treatment around the reservoir causes the oil to migrate away from its location, contaminating neighboring surfaces, disrupting the running and accelerating wear. Mastering capillarity, through precise dosing with the oil pick, is thus one of the conditions for the proper running of a mechanical movement.