BURNISHING

Burnishing is a finishing operation that consists of polishing a surface while cold working it, that is, crushing and hardening its surface layer. It is carried out using a burnisher, a very hard and perfectly polished tool (steel hardened, agate, or hard metal) that is slid under pressure over the workpiece: rather than removing material like an abrasive, the burnisher smooths and compresses it, closing the pores and increasing the hardness and wear resistance. It is notably through burnishing that pivots of the wheels are finished, an operation then called pivot rolling, which gives them a mirror polish and an ideal cold-worked surface to turn in the jewels with minimal friction. Burnishing thus improves both the appearance, the glide, and the longevity of the bearings. It illustrates the finishes that, beyond aesthetics, condition the performance and durability of the Movement.