Mainplate

The mainplate is the structural foundation of a mechanical movement: everything else — bridges, axes, wheels, escapement — is built upon or around it. It is not merely a support surface. It is the load-bearing architecture of the caliber, and every choice regarding its material, shape, and finishing affects both mechanical resistance and the visual readability of the movement.

From the workbench, I have seen mainplates in gilded brass, in German Silver (nickel-silver alloy without gold, also called Maillechort), in Grade 5 titanium, and in stainless steel. German Silver remains the classical reference for Swiss and German haute horlogerie: it does not oxidize, machines well, and holds a bevel. Titanium is lighter and harder, but responds poorly to hand finishing work — those who use it do so to reduce caliber weight, not to facilitate decoration.

Finishing on the mainplate is one of the true measures of manufacturing quality. Côtes de Genève — parallel milled lines — are the most common finishing on Geneva movements and are instantly recognizable through a sapphire caseback. In Glashütte, the so-called Glashütte ribbing is used: wider and deeper fluting, executed by hand, which is one of the most recognizable signatures of the Saxon tradition. Perlage — a motif of overlapping circular pearls — finishes internal surfaces that remain invisible. Tremblage creates an irregular grain on German Silver mainplates, worked by hand with a vibrating chisel. Anglage, or beveling, works the edges: on high-end pieces it requires hours per single component.

When the mainplate is opened — stripped of excess metal to reveal the movement beneath — one enters the territory of skeletonization. Selective material removal is not merely aesthetic: it changes structural rigidity and demands a redesign of the architecture. In shaped movements, the mainplate follows the case perimeter rather than being circular or rectangular, and the structural challenge becomes even more complex. I have seen shaped calibers from the seventies and eighties where the mainplate was reduced to the thinnest profile: holding them in hand made clear how difficult it was to maintain axis coplanarity.

Mainplate coating — rhodium plating, DLC treatment, chemical blackening — modifies appearance but not structure. The côte unique, which carries a single continuous line across multiple adjacent mainplates, is the most difficult finishing to execute: one mistake and you start over.