Enamel is glass ground into powder, applied to metal and then fired in a kiln. The term “Grand Feu” refers to this high-temperature firing, generally around 800 °C depending on the enamels used. Under the heat, the grains fuse into a vitreous layer that adheres to the base. As it cools, it solidifies, revealing its colour and lustre.
As early as the 17th century, enamellers in Blois and Paris decorated watch cases and dials with miniature painted scenes.
Enamel is a glass made from mineral materials and metal oxides that give it its colour. Depending on its formulation, it may be opaque or transparent, covering the metal or revealing the details engraved on its surface.
Before application, the enamel is ground into fine grains, then carefully washed several times. The powder is kept moist to form a mixture that the enameller can pick up and apply with a brush. This step allows the grains to be distributed precisely over the prepared metal base.
The water is used only for application and must evaporate before firing.
For UKIYO dials, five layers are needed to achieve the right colour intensity. They give a thickness of 0.35 mm on the front as well as on the back.
Each firing requires great precision: a small difference in enamel density between the two sides causes distortion and means starting again.
Cooling reveals the result, allowing the colour, surface and quality of the firing to be assessed.
With transparent enamel, the decoration of the metal remains visible beneath the colour. Light passes through the coloured layer and is reflected by the metal. The perlage shown here produces different shades depending on the lighting and the angle of the watch.