This shape represents one of the group of ritual or sacrificial vessels recreated during the 18th Century on the basis of much earlier ritual bronze forms, especially dou, zun, gui and fu. It is quite possible that the ceramic models were based on the printed illustrations in the Song Dynasty catalogue of early bronzes, Hsuan-ho Po-ku t'u lu. A set of five (white-glazed) vessels comprising the basic shapes is in the National Palace Museum, Taipei, illustrated by Liu Liang-yu, A Survey of Chinese Ceramics, vol.5, pp.38-9; it is also illustrated and discussed by Beurdeley and Raindre, op. cit., no. 220, where the Emperor's critical comments in 1756 are recorded. The nature of the ritual, the form of the vessels, and the five appropriate colours, are discussed by M. Medley, Ceremonial Paraphernalia of the Ch'ing Dynasty, Transactions of the Oriental Ceramic Society, vol.31, 1957-9. A yellow-glazed fu, according to other scholars, would have been set at the centre of an altar within white, blue, green, black and red vessels, on the occasion of Earth or Agriculture-related sacrifices either in Spring or at a form of Imperial Harvest Thanksgiving ceremony. It would probably have contained grain, rice, millet, and vegetables. Beijing under the Qianlong Emperor was full of such altars within the Forbidden City