After the 13th century, fine Venetian glass was decorated with gilding and fired enamels. Decorating a cristallo goblet with enamel was an elaborate process executed by specialists. Finely powdered glass, colored with metallic oxide and suspended in an oily medium, was applied to a vessel with a brush. As the glass was fired in the furnace, the medium burned away. Sometimes, several firings were required to fuse the various colors of an ornately enameled object. During the Renaissance, decorative motifs derived from classical antiquity were inspired by the discovery of ancient Roman wall paintings. These motifs, interlaced with vines or ribbons, included fantastic creatures, flowers, and coats of arms. The glass decorator probably used contemporary engravings as a source for these designs.