Circular graining

Circular graining is a mechanical finish applied to flat surfaces of watch movement components — plates, bridges, rotors — using a rotating abrasive tool that leaves an impression of overlapping concentric circles. Each circle has a constant diameter; the overlapping marks create a uniform texture that diffuses light softly, without directional reflections. It is not polishing: the surface remains matte, but alive.

The English term is circular graining; in French you often encounter perlage, although technically classical perlage produces smaller and denser circles, almost overlapped like scales. The difference is subtle but real. Those who work at the watchmaking bench learn early to distinguish them with the naked eye: perlage has a more granular and satin appearance, circular graining tends toward wider and more legible circles.

The technique is executed with a mandrel mounted on a drill or pantograph, with hard wood, felt, or brush tips loaded with diamond paste or aluminum oxide. The operator applies the tip to the surface, rotates it for an instant, then moves the piece by a fraction of a millimeter and repeats. Controlled overlapping is everything: if the circles do not touch, the surface appears pitted; if they touch too much, regularity is lost. On a plate of medium size, the work can take hours.

Traditionally, circular graining covers surfaces that the designer does not want to leave raw but which do not justify mirror polishing — which would cost more in time and highlight every minor imperfection. On main plates it often appears alongside anglage on edges and Côtes de Genève on upper bridges: the three finishes alternate, creating texture contrasts without material contrasts.

Today some manufacturers produce circular graining numerically on CNC-controlled machines. The visual result is almost indistinguishable from manual execution on simple pieces, but on complex geometries or soft metals like the german silver of Minerva movements, the hand remains irreplaceable: the operator's variable pressure compensates for material irregularities. When the finish is truly hand-executed, the slightest irregularity of the circles — perceptible only with a lens — is actually the mark of quality.