Enamels like this plaque are created by fusing powdered glass to a copper sheet. Metal oxides are added to the clear, molten glass to produce a variety of colors, which are affected by both the composition of the glass and the concentration of the metal oxide used, as well as the atmospheric conditions in the kiln. Enamels are fired multiple times, requiring enormous skill to control the different temperatures necessary for the various colors and layers. Techniques developed during the fifteenth and sixteenth centuries permitted a wider range of opaque and translucent colors. Enamelers increasingly exploited the overlay of one color on another in thin layers or, with subtle shading, manipulated them to reveal what lay beneath. For instance, to achieve a more naturalistic flesh tone, early enamelers sometimes applied mulberry beneath the white to create warm undertones. To enhance details in the composition or delineate features in the face, a technique known as enlevage was employed, in which white powdered glass was manipulated with a fine tool to expose the darker fired layer beneath. Grisaille was also used to produce subtle modeling in shades of gray. Final touches of oxide color or gilding, brushed on and lightly fired, added expression and richness. This particular plaque depicts St. Vitonus in victory over a dragon and converting two pagans.
