Enamel in watchmaking is not just a material: it's a family of techniques distinguished first by firing temperature, then by substrate structure, then by layering. Clarifying these differences is the first job to do, because the term enamel appears on dials that have almost nothing in common with each other.
The fundamental distinction is between grand feu and petit feu. Grand feu—great fire—means firing at high temperature, generally above 800 °C. The result is a vitreous layer that fuses intimately with the base metal, usually copper or silver. It does not fade, is not altered by UV light, and resists chemically far superior to any varnish. Petit feu fires at lower temperatures and allows you to deposit fine details—numerals, indices, text—without burning what is already underneath. In the Breguet Classique Souscription, the white background is grand feu, the Arabic numerals are petit feu: the two fires do different work on the same dial.
The number of layers varies enormously. A basic white dial requires five or six firings; a deep black can reach thirty, because every imperfection becomes visible on the dark surface and each layer must be checked before the next. The Moritz Grossmann Enamel Roman Vintage exceeds ninety working phases spread over several days. Any crack or bubble stops everything and you start from scratch: there is no partial recovery.
The substrate structure changes the technique. In champlevé, cells are carved into the metal and filled with colored enamel: the metal edges remain visible and define the design. In plique-à-jour, the enamel is translucent and suspended in cells without a metal back, and light passes through it like in a stained glass window. In paillonné, extremely thin metal elements—tiny stars, leaves, silver shards—are inserted between successive layers of translucent enamel, creating an optical depth that no printing can reproduce.
One thing I often see poorly described is cold enamel, which is not enamel in the technical sense: it is not fired, does not vitrify, it is a colored resin. It is more fragile, ages differently, and should not be confused with grand feu even when the aesthetic result approaches it. I recognize it immediately from the workbench: true enamel has a hardness and depth that resin does not reach.
Grand feu can also be applied to casebacks and plates, not just dials. Guilloché engraving under translucent enamel—a technique visible on many Moser dials—is a case where mechanical and vitreous decoration multiply each other: the engraved texture lives beneath a layer that amplifies it instead of hiding it.