Firing is the process that transforms enamel powder into a vitreous surface: without the kiln, there is no enamel, only powder. Grand Feu enamel — grand feu literally means great fire — requires temperatures between 750 and 900°C, achieved in repeated cycles that can range from five to over ninety passes depending on dial complexity. Each cycle follows the same pattern: I spread a thin layer of colored glass powder on the metal base, fire it, wait for fusion, extract it, flatten if necessary, and start again. The final color emerges only after the last pass.
The base must be in noble metal — yellow gold, white gold, or silver — because it must withstand thermal expansion without deforming and without reacting chemically with the enamel. 18k white gold is the most common choice for high-end watchmaking enameled dials precisely for its stability at those temperatures. Brass or steel bases are incompatible with Grand Feu.
The risk is constant. With each firing, glass and metal expand at different rates: this differential is the main cause of cracks, air bubbles, and detachment. Certain pigments — browns and some reds — are particularly unpredictable and can shift in tone from one cycle to the next. The rejection rate in specialized laboratories is high; there is no way to recover a dial that has cracked in the kiln.
Porcelain follows different logic. It is not enamel on metal: it is clay fired at much higher temperatures, around 1,300-1,400°C, which produces a compact ceramic body. Colors are applied after the first firing and fixed with subsequent firings at lower temperatures, around 900°C. The Meissen dial on the Senator and the Nabeshima discs follow this layered process, where each decorative intervention requires a new kiln pass.
The difference between enamel and lacquer is visible and tactile. Fired enamel has an optical depth that comes from within the glass surface, not from its external reflection. It does not become opaque over time, does not scratch as easily as a coating, does not react to solvents. From the bench, after forty years, I recognize an authentic Grand Feu dial by its non-uniform lustre: each layer has absorbed light slightly differently, and this leaves a visible trace that no lacquer can imitate.