The uniform strips of the ribbing quarter decorating the three-quarter plate and the caseback sides of the bridges of a Lange calibre, are produced by a slightly inclined, rotating grinding wheel that is guided along the component in straight, parallel lines.
The decorative finish applied to the mainspring barrels and other larger round surfaces or wheels, consist of spiral arms of solarisation. This is formed by rotating the part and the grinding wheel in opposite directions.
Applied to the inside surfaces of plates and bridges as well as to the invisible dial side of the main plate, the cloudlike decoration is generated from a rotating abrasive peg that only briefly stipples the component. Each stipple overlaps the previous one to give the final finish.
Applied especially to the steel clicks, springs and yokes, straight graining decoration is produced with abrasive paper across which the part is drawn in a longitudinal direction. The component is should be drawn in straight but cautious movements to assure that the delicate linear pattern is applied to even the furthermost corners.
This technique is applied to the smaller wheels. The regular circular contours are produced when the part is rotated on abrasive paper.
The vertical edges of the frame elements of a Lange movement are manually pressed against the side of the abrasive peg to give the desired finish.
Probably the most time-consuming and patience-demanding technique of all. Flat Polishing is used to mirror-polish the surfaces of a whiplash spring, the endpiece of an escape wheel and other parts of the movement. The process includes pressing the component into the pith of an elderberry shoot and guiding it in figures of eight on films coated with progressively finer diamond powder.
Using special abrasive pastes, a limited number of parts are decorated using the intricate black polishing technique – manually polishing on a tine plate – such that the components appear to be black when placed at a certain angle of incident light. This was done on the tourbillon bridge of the Tourbograph “Pour La Merite” piece.
A process which involves both bevelling and polishing, chamfering is a technique used on all the edges of plates, bridges and levers.
Polishing of internal angles
The internal angles of bridges and levers are polished by hand in order to correctly execute the linear polishing motion required to achieve the desired result.