Polissage
This is a surface treatment of steel components, which according to watchmaking tradition, is reserved for the rarest and finest haut de gamme timepieces. There are actually several names in use to describe this surface treatment: poli mirroir, poli noir, poli bloc. It is interesting that two of the names are descriptions of the appearance and the third of the method for achieving it.
It is seldom applied to components upon which other parts are mounted as the surface treatment can be slightly uneven, risking a reduction in the precision of the placement of any added components.
On the other hand, as it is an embellishment meant to be seen, why should it be hidden under other components?
At Breguet, côtes de Genève are applied by pulling a wooden burnisher multiple times across the top surface of the bridge component.
Each pass with the burnisher creates a stripe. The sharpness of the stripe and the width, angle, depth, and fineness of the brushed areas are all determined by the wood which is used, the abrasive material applied to the burnisher, and, of course, the skill of the watchmaker hand applying the finish.
