Transparent glasses are tinted with the silica-based cobalt pigment smalt. It has been used since the Middle Ages to make smalt, a blue-colored glass. Smalt, normally now discoloured, is common in European paintings from the 15th to 17th centuries. "Cyanus" denotes a blue low-fired glass-paste or smalt. During the Victorian Era, zaffre was used to prepare smalt and to stain glass blue. Smalt was widely used to color glass and as pigment for paintings.