“Translucent” enamel upon reliefs known as _de basse taille_ is the art of enamelling reliefs of silver or gold that have previously been chased or engraved with the design required. The enamel is laid on in various degrees of thickness, according to the strength of shading or depth of tone required. The transparent varieties of enamels are selected for these works, and opaque varieties avoided. “Painted” enamels were suggested by the translucent enamels upon reliefs. The extensive demand for the latter variety, and the great number executed, gave rise to the invention of using enamel colours as in oil-painting; that is, instead of engraving the subject or design previously on the metal, the method of expressing with the brush the drawing and the light and shade with the enamel colours direct was resorted to, on grounds specially prepared upon copper surfaces. Labarte believes that the modification in the art of glass painting introduced in the fourteenth century had the effect of causing enamel painters to experiment in painting with the enamel colours direct, as in painting on glass. About this time the method of painting on glass was introduced, which formerly was decorated by simply using the pieces of _stained_ or coloured glass as in mosaic work, the only difference between the superficial glass painting and the painting in enamels being that in the latter the opaque enamel colours are used instead of the transparent as in glass painting. It was, however, a considerable time from the introduction of painting on enamels before any good specimens of the art were executed. Among the earliest specimens of Cloisonné enamels was the golden altar given to the cathedral of Sta. Sophia at Constantinople by Justinian. [Illustration: Fig. 94.—Altar Tray and Chalice, Cloisonné Enamel; Sixth Century (?).] This altar was dismantled and divided amongst the Crusaders at the taking of Constantinople in 1204. The next important works in date are the gold altar of Ambrose at Milan, made by Volvinius in 825; the votive crown of St. Mark, Venice, 886-911; the Limburg reliquary made for Basil II. (the Macedonian), 976; and the famous altar, the Pala d’Oro, in St. Mark’s, Venice, 976-1105, made at Constantinople, and brought from there to Venice by order of the Doge Ordelafo Faliero. This altar had precious stones added to it and was enlarged in 1209 and in 1345. If the crown of Charlemagne (Fig. 96) was used at his coronation it would make the date of the four enamelled gold plates with the figures of Solomon, David, and Our Lord between two seraphim and Esaias and Hezekiah, anterior to the year A.D. 800, when he was crowned. These enamels are enclosed in filigree bands and sunk into the metal in the Greek manner. The sword of Charlemagne, made in the ninth century, has the golden scabbard inlaid with filagree Cloisonné enamels. Both the sword and crown are in the Imperial treasury at Vienna.