The manufacturing of an enamel dial begins with a thin metal disk whose edge has been turned up. The metal varies according to the planned value of the finished product. The least expensive version is made of copper. Small, temporary feet are first soldered onto the disk. The disk is then flattened to make sure it is straight and the feet true.
Impurities are removed in an acid (nitric, hydro-chloric, sulfuric) bath. Larger pieces can be burned-off or annealed to remove any protective oil coating before the acid bath. A dirty base plate can crack the enameling or make it por-ous. The pickled base plate must be rinsed well. Acid contamination can make transparent colors cloudy.
Cadrans Donze S.A. receives the enamel powder in big barrels from central Europe. Mr. Vermot-Donze sieves the powder and then washes it in a large glass bowl. As you remember, enamel is glass and using a metal or plastic container or stirring rod would contaminate the enamel with pieces of the container or stirrer. The enamel is washed repeatedly, up to 30 times, until the water remains clear and the enamel in the bowl sparkles. Without washing, the baked enamel could look grainy, cloudy or dirty. Because prolonged exposure to water will cause the ground enamel to deteriorate quicker than normal atmospheric conditions, it is advisable to wash only the amount that is needed for that day.
The next step in the process is to spread an even Optical pyrometer amount of less pure enamel over the underside of the disk. The enamel powder is dusted on through a sieve and then laid onto an asbestos sheet. The sheet is placed into a preheated oven and left in for a few minutes until the powder has melted and formed a glossy layer. The counter enameling, or backing enamel, is necessary to prevent the finished dial from cracking or the enamel from later peeling off.
The temperature inside the oven is about 850° C (1530° F). Experienced enamellers preheat the oven to a temperature 10°-50° C (18°-90° F) higher than needed, because of the heat loss that occurs when the oven door is opened. The oven temperature can be monitored with a pyrometer, but they can sometimes stick or require re-calibration. Thus the direct obser-vation of the firing and the furnace color is the craftsman’s best monitor. With experience, it never fails.
The final judging of the firing time lies in the mind of the enameller, because it depends on such things as the size or insulation of the oven, inside and outside temperatures of the oven, the size of the enameled piece, as well as on the enamel and the enameller’s work speed when placing items in the oven.
The upper (front) side of the dial black is dusted with a very fine grade enamel powder. This is repeated several times over and the black is fired after every coat. The number of coats depends on the required thickness of the finished dial. The usual minimum is three coats. Too thick a coat can cause the enamel to crack or flake. Too thin a coat will burn.
The watch brand and numerals are printed with a dial printing machine. Its principle is the same as in any dial factory. The image (numerals, logo, name, etc.) is engraved or etched into a steel plate. Black enamel mixed with binding agent (usually an oil) is applied into the etched areas and picked up from them with a soft gelatin cushion. When the cushion is pressed against the dial black, it leaves the image on it. The image must be fired to make it permanent, but the temperature will be about 100° C (180° F) less because a higher temperature would turn the black enamel brown cool watches.
After being fired a few times, the enameled piece may become warped. This can be corrected by rubbing the dial with a flat charcoal brick when the dial comes out of the oven. This stage requires experience, because if the dial is still too hot, rubbing will spoil the still-soft surface. If the dial cools off too much (below 540° C/1000°F), the enam- el may crack when pressed.