Firing (Grand Feu Enamel)

Firing is the process that transforms enamel powder into a vitreous surface: without it, there is no enamel, only pigment. In Grand Feu — great fire, in French — the kiln temperature exceeds 750–850 °C, sometimes reaching 900 °C; at these temperatures the silica powder and metal oxides melt and bond to the base. A single cycle is not enough. The dial returns to the kiln five to fifteen times, often more: the Moritz Grossmann workshop reaches ninety firings distributed over several days. Each return to the kiln adds a layer, consolidates the color, and deepens the transparency.

The base must be compatible with the thermal expansion of the enamel. Gold is the preferred material — yellow gold for classic white enamel, 18k white gold when the project requires it — because the coefficient of thermal expansion remains close enough to that of glass to limit internal stress. Steel exhibits different expansion rates and makes the process less stable. Porcelain follows its own rules: firing reaches 1,300–1,400 °C, as in the Meissen dial of the Senator or in the Goldfeather Imari Nabeshima, which undergoes five firing phases and is reduced from a solid piece to a domed form one millimeter thick.

The risks are real and permanent. The differential contraction between glass and metal during cooling can produce microcracks, air bubbles, or separation. Browns and certain reds behave unpredictably: Kong Lingjun's workshop in Beijing spent months stabilizing the sand-chocolate gradient of the Yáo dial. When inscriptions — numerals, ornaments, signatures — are hand-painted with liquid enamel and then refired, each refiring is an additional risk to the entire already-completed dial.

The final result is a surface that does not become opaque over time. The visual depth achieved — that sensation of looking into the dial, not across it — depends on the accumulation of overlaid translucent layers, each fired separately. No lacquer and no varnish replicate this effect, because the physics is different: there a film is applied, here layers of glass fuse. From my bench I recognize authentic Grand Feu by the millimetric irregularity of the edge-view surface: it is never perfectly flat, and precisely for this reason it is alive.