See another blue-glazed dou in the Victoria and Albert Museum illustrated by M. Medley, 'The Illustrated Regulations for Ceremonial Paraphernalia of the Ch'ing Dynasty', T.O.C.S., vol. 31, 1957-1959, pp. 95-105, pl. 39a. Medley notes, p. 100, that in the Winter Solstice sacrifice to Heaven in 1748, blue porcelain vessels were used for the first time as stipulated by Emperor Qianlong, and these sacrificial rites continued throughout the Qing dynasty. See, also, the similar blue-glazed Qianlong-marked dou sold in our Hong Kong rooms, 7 July 2003, lot 609.