Fire enamelling

Fire enameling is one of the very few decorative techniques in watchmaking where the final result is never completely predictable until the kiln is opened. Enamel — a mixture of finely ground mineral oxides — is applied in successive layers on a metal base, usually copper or brass, and fired each time at temperatures between 750 and 850°C. Every firing can alter what was done in the previous one. Minimal variations in humidity, ambient temperature, or even the composition of the paste force the craftsman to adapt every step in real time.

There are distinct technical variants, and confusing them is a common mistake. In classic Grand Feu, the enamel is spread across the entire surface and fired repeatedly until achieving a uniform, luminous layer with an optical depth that no print can replicate. In champlevé, the metal is first engraved, the depressions filled with colored enamel layer by layer, then each layer is fired separately; pictorial details arrive only at the end, painted by hand. In cloisonné, the operation begins with the partitions: extremely thin strips of gold or silver are soldered to form cells that delimit the color fields, then filled with a brush using different enamels and fired up to twenty times. On a dial of 18 millimeters in diameter, as in the case of certain pieces created in collaboration with Genevan craftsmen, this operation occupies entire days of work.

Miniature painting on enamel is an even more extreme variant: the drawing is traced in ink, then covered by twenty or more layers of pastel color thin enough to let light pass through them. Each layer requires firing. For a dial of average size, you easily reach 35 hours of actual work, not counting pieces discarded for defects that emerge during firing.

From my workbench, I've seen enameled dials arrive with micro-cracks invisible to the naked eye but evident under magnification: defects that emerge months after delivery, generated by cooling too rapidly or by a metal base not perfectly prepared. This is why serious ateliers discard a substantial percentage of production and don't publish the figures. Enameling does not forgive approximations or speed.