Finishing School: Six Key Movement Finishes
All you need to know about the different finishings used in your high-end mechanical timepiece.
At Patek Philippe, there is an ‘aesthetic committee’ comprising owners Philippe and Thierry Stern, that authorises the attractiveness of a movement before it goes into production. “The shape of the components, how they look together, and how well they are finished are crucial to the overall value of the watch,” says Philippe Barat, the brand’s director of watch development.
Perhaps this is why similar watches can have different price tags depending on whether they have open or closed casebacks. But it’s not all about making the movement look good. Quality movement finishing is essential to improving both design and performance. For instance, polish work helps reduce friction on parts that are constantly in contact, such as the barrel and barrel cover, as the smooth surfaces allow the mainspring to uncoil more consistently to ensuråe regular power transmission.
Conversely, poorly finished parts not only negate a watch’s luxury proposition, they could also affect its functionality. Roughly polished pinions cannot be properly adjusted, and can hinder the running of the gears and increase rate of wear-and-tear. Sharp and rough bridges can also make movement assembly or servicing a tedious affair. Here are some key movement finishes to look out for.
Anglage (or chamfering or bevelling) smoothens the edges of movement parts. This is done by filing the components at a 45-degree angle, and subsequently polishing them to high gloss. Look out for consistent smoothness and width on the edges. The most difficult type of anglage is found on interior angles, and can only be done by hand.
The overlapping circular patterns commonly found on top and base plates are the result of perlage, which gives the plates cleaner and smoother surfaces. The movement finisher applies emery paste of the end of a piece of peg wood, which is fitted on a rotating head. He then presses on the surface of the plate to create the pattern.
3. MIRROR POLISH
Mirror polish endows component surfaces with exquisite shine and smoothness. The highest level of mirror polish is ‘black polish’, which gives the component a totally smooth and unblemished black (or grey) appearance from certain angles, as it reflects light in only one direction.
4. CIRCULAR GRAINING, LINEAR AND SUNRAY FINISH
These techniques result in a matte, uniform graining on larger components such as bridges and plates. Linear graining is achieved by sliding the component over an abrasive paper. Circular and sunray patterns are made by using a bell grinding-wheel that draws straight lines across the metal from the centre.
5. CÔTES DE GENÈVE
Côtes de Genève (Geneva Stripes) feature a pattern of parallel lines and is a good way to hide any scratches or imperfections. Like other surface finishes, it also helps trap tiny dust particles to prevent movement damage. The pattern can be made using machines or hand, using a rectifying ruler that scratches the surface, or a lathe that moves back and forth.
Blued-steel screws not only look more regal but are harder and more resistant. The most traditional way to achieve this is to heat the screws over a high flame of precisely 310 degrees Celsius to achieve the perfect tint.
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