Bridges

Bridges are the metal plates fixed on the mainplate that close from above the axes of the gear train components, holding them in position and ensuring their alignment. Without them the movement doesn't work: every shaft needs two supports, one below in the mainplate and one above in the bridge. This is the starting point, everything else comes after.

From the workbench I've learned that the bridge's shape tells the era and the watchmaking school. In nineteenth-century pocket watches, finger bridges were used—elongated structures that resemble outstretched fingers, each dedicated to a single shaft. The three-bridge design of Girard-Perregaux, with its three horizontal gold blades running parallel across the caliber, is the most famous example of this philosophy brought to system: architecture and decoration coincide. The pillar movement architecture, used by manufactures like Moritz Grossmann, is another solution: mainplates and bridges work together with columns, featuring the wide ribbing typical of the Glasshutte school.

The material changes function and appearance. German silver—cupronickel—a copper-nickel-zinc alloy without actual silver, was the historical standard of German manufactures because it performs well under the tool and holds finishes for a long time. Today titanium and exotic alloys are also used, often treated with PVD to obtain black or anthracite surfaces that create visual contrast in open movements.

The finishes on bridges are the most direct index of a manufacture's level. Côtes de Genève are parallel stripes engraved across the entire surface; traits tirés are a subtler variant adopted, among others, by Audemars Piguet on the Code 11.59. Vacheron Constantin's côte unique creates an even tighter pattern of lines. Parmigiani's Côte de Fleurier is a proprietary geometric finish. De Bethune's random guilloché, with its irregular wave-like pattern, breaks the repetitive logic of all the others. None of these finishes improve precision: they exist to declare how much work is inside.

Skeletonization works precisely on the bridges: metal is removed from non-structural zones, leaving sufficient ribbing to support the shafts. Doing it well requires rethinking the architecture from scratch, as Hermès did with the H1978S, where bridges and mainplate follow the contours of the square case from the original design. Doing it poorly produces fragile bridges that deform over time. When I receive a skeletonized movement to restore, the first thing I look at is the residual cross-section of the bridges: that's where you can tell if the work was done with proper judgment or just for effect.