That brings us to another trait of finely finished watches: mirror polishing. Mirror polished parts can take up to ten times the amount of labor to produce rather than leaving the part unpolished.
Mirror polished parts are of course smoother than non-mirror polished parts and as such are much more beautiful to behold. The most desirable form of mirror polish is often called ‘black polish’ as it describes the state where the metal is so perfectly smooth that it appears black from certain angles. 
IWC is known among watch collectors as a very technical brand, and finishes its watches well to improve its functionality in addition to improving the aesthetics.
Again, mirror polishing is not all about show, it has been utilized to improve the functions of a watch. The smoothness of the inner wall of a mainspring barrel affects the unwinding of the coiled mainspring; i.e. the smoother the inner barrel wall, the smoother and more consistent the uncoiling of the mainspring, which of course results in a more regular power supply to the gear train. As an example, IWC practices this “engineering approach” to movement finish, as evidenced in its Portuguese watch, where the large single barrel houses a mainspring that stores up to 7 days of power reserve.
Mirror polishing is an arduous process. A single craftsman sits down with a tube of diamond paste, a flat bench with a layer of paste laid on it, and then a mat on which the polishing begins. To mirror polish screw heads, a watchmaker could be rubbing the screws in a circular motion for hours. The craftsman has to make sure that the polish is even, and certain watch companies insist that the area underneath the head has to be mirror polished as well – to facilitate smooth positioning of the screw. Considering that a watch can easily have 40 screws in its movement, many of which may not be seen other than by the watchmaker who assembles and disassembles it, it’s a lot of dedication for something so small. |