Large "sacrificial" blue monochrome porcelain bottle vase, China, 18th century The unusually large vase is glazed in a dark blue overglaze that spreads in a thicker layer around the foot, forming drips and some shrinkage, leaving the heel visible. The neck rim and interior are glazed in white. The unglazed base is brown. Height: 69.5 cm Firing fels and chips on the neck. Sacrificial blue" porcelain - ji lan you - was produced as early as the Yuan period in Jingdezhen, and continued under the Ming and Qing, reaching its peak under Qianlong. This color was obtained through the specific use of cobalt oxide, which was very stable in the kiln, even though it was fired at high temperatures, to obtain an intense, brilliant blue. The use of cobalt was reserved for luxury items and strictly controlled, produced for imperial use and as tableware for ceremonial rituals at the Altar of Heaven. In the Temple of Heaven, crockery, tiles and fabrics were all blue.