Chinese porcelain used smalt glazes from the Tang dynasty onwards, though Chinese cobalt glass is found from the Zhou dynasty (1122–221 BC). Cobalt was used as a pigment in Central Asia from the 13th century. A fragment of a mud painting in the ancient Tangut city of Khara-Khoto has been found to contain smalt, judged to be dated between the 11th and 13th centuries. A large quantity of smalt was purchased for the decoration of the gallery of Francis I of France at Fontainebleau in 1536. Smalt, normally now discoloured, is common in European paintings from the 15th to 17th centuries. For example, it is found in Hans Holbein the Younger's portrait of Sir William Butts (ca. 1540), in Michael Pacher's painting "The Early Fathers' Altar" (ca. 1483), and in the frescos of Domenico Ghirlandaio (1449–1494).