Many different types of polishing techniques belong to the sophisticated repertoire of finishes that adorn Lange movements. The time invested in these processes is truly impressive, but so are the talents of Lange’s finisseurs. For example, it takes several months of practice to apply an immaculate flat polish.
It is a skill that calls for keen vision and true virtuosity. Machines do not qualify for this kind of work: they can neither smoothly lift out a chamfer in a tongue nor change its angle to produce a visually uniform width.
Up to two hours of precision work are needed to mirror-polish the surfaces of a whiplash spring, the endpiece of an escape wheel, and other parts of the movement. To flat-polish a component, the finisseur presses it into the pith of an elderberry shoot and guides it in figures of eight on films coated with progressively finer diamond powder.
This process requires the utmost in concentration. Even a tiny grain of dust between the part and the polishing film, or excessive pressure on the part, can wipe out hours of work in a second.
SPECULAR POLISHING.
Only very few and select parts are decorated with the intricate specular polishing technique, among them the tourbillon bridge of the TOURBOGRAPH “Pour le Mérite”. This process can take several days. Using special abrasive pastes, the respective parts are manually polished on a zinc or tin plate until they appear to be black at a certain angle of incident light.
At A. Lange & Söhne, all of the edges of plates, bridges, and levers are chamfered, a process which involves both bevelling and polishing. Lange’s finisseurs demonstrate their skills by producing chamfers with a consistently uniform width and angle on virtually every edge in a movement that is finished with this technique.
The bevels are also polished entirely by hand. Movement parts made of softer materials are prepolished with progressively smoother rubber tools and then finished with a polishing brush. Harder steel parts are polished with a rotating wooden wheel.
POLISHING INTERNAL ANGLES.
The degree of perfection of a timepiece comes to the fore in discreet but salient details. Connoisseurs look for them first: the internal angles of bridges and levers. If they are precisely defined and straight, they are unquestionably polished by hand, because only a human hand can execute the linear polishing motion needed to obtain such a result. If the internal angle is rounded, it is justifiable to assume that it was machine-finished.
Lange’s finisseurs use a pencil-like hard metal tool to polish internal angles. They cut and finish such angles entirely by hand.
