Why does enamel, after cooling down, often chip on curved surfaces?
Enameling on curved surfaces (Émail de ronde bosse) calls for special precautions.
After shaping the copper it should be properly annealed.
Degrease the metal thoroughly.
Apply a layer of nearly undiluted gum tragacanth, spread it with a feather to remove air bubbles. (Note: gum traganth is expensive, difficult to obtain and decays with time. Use any natural glue, such as gum arabic, glue for wallpaper, agarth, lavender oil, klyrfire or Blu-stic).
Dust the enamel evenly onto the surface (apply thin layers on top of each other rather than one thick layer).
Accurately adjust the kiln to the proper temperature.
Put the object in the kiln and remove it before it glows orange-red, otherwise the enamel starts dripping.
Let it cool down slowly, hence do not put it on metal.