Vitreous glaze (or glass) is composed of sand or other siliceous matter fused with potash or soda; this is ground and mixed with water, forming a liquid in which the clay biscuit ware is dipped, and afterwards fired, in order to make it impermeable to liquids. Oxide of lead in considerable quantities is added to the vitreous glaze, which increases its fusibility, but still keeping it transparent; this is what is known as a _plumbeous_ glaze. This glaze may be coloured yellow by the addition of iron oxide; green by copper oxide; blue by cobalt; and black by manganese. All these coloured glazes were known to the ancients. A further addition of the oxide of tin to the vitreous or plumbeous transparent glaze, in comparatively small quantities, produces the opaque enamel known as a “stanniferous” or tin glaze. This is the enamelled glaze of the Della Robbia ware, of the Hispano-Moresque, and of the Italian maiolica. From recent analysis of the enamel on Assyrian tiles and bricks it has been ascertained that the oxide of tin was used by the enamellers of that early time, but not to the same extent as the vitreous glaze. Persia was the natural inheritor of the art of the ancient land of Mesopotamia, and the beautiful siliceous and probably the stanniferous glaze, and also metallic lustres, have been used in that country from very early times. The Arabs, or Saracens, evidently brought the workmen from the East, and imported many pieces of Damascus ware during the independent Caliphate of the Damascus Caliphs in Cordova in Spain, which lasted from the eighth century to the year 1235, when the Moors drove the Arabs out of Spain. The Arabs (says Riaño) had, as early as the beginning of the twelfth century, if not before, established the industry of metallic-lustred pottery in Spain. Edrisi, the Arab geographer, wrote in 1154, in describing Calatayud in Spain: “Here the gold-coloured pottery is made, which is exported to all countries.” This gold-coloured pottery is likely to have been similar to the siliceous glazed ware of the East. The next reference to lustred pottery is made by Ben Batutah, a celebrated Arab traveller, when travelling from Tangiers to Granada, and when passing Malaga (1349-57) he says: “At Malaga the fine golden pottery is made, which is exported to the furthermost countries.” The golden pottery here referred to is the tin-glazed Hispano-Moresque. At Manises, in the kingdom of Valencia, the famous lustred pottery _fabriques_ or workshops were in a flourishing state in the fifteenth century, when Eximenus, in his “Regiment de la cosa publica,” quoted by Riaño, speaking of the excellent things made in his time at Manises in Valencia, says: “Above all, the beauty of the gold pottery, so splendidly painted at Manises, which enamours every one so much that the Pope, and the cardinals, and the princes of the world obtain it by special favour, and are astonished that such excellent and noble works can be made out of the earth.”