How are metallic oxides used to produce colours in enamelwork?

In enamelwork, metallic oxides serve as the primary agents for creating color. These oxides are introduced into a molten base of clear glass, known as flux or frit, which is composed of flint or sand, red lead, and soda or potash.1

The resulting color is determined by a combination of the specific oxide used and the chemical composition of the flux. Rather than simply changing the quantity of the oxide, craftsmen often achieve different hues by adjusting the proportions of the flux components themselves. For instance, the black oxide of copper can produce a turquoise-blue enamel when mixed with a high proportion of carbonate of soda, or a yellowish-green enamel if the proportion of red lead is increased.1

Once the colored enamel is cooled, it is pulverized into a fine powder, washed, and applied to a metal base. The piece is then fired in a furnace until the enamel fuses and adheres to the metal.1