A similar larger example with this type of glaze was sold at Christie's Hong Kong, 1 November 2004, lot 876.
The present 'peacock-feather' glaze with its characteristic blotches of turquoise and dark blue, is a rare version of the streaked copper-red glaze known as 'robin's egg'. The colour of both is derived from copper mixed with arsenic as an opacifier, although further research is needed to clarify the chemistry of these glazes, cf. R. Kerr, Chinese Ceramics, Porcelain of the Qing Dynasty 1644-1911, Victoria and Albert Museum, 1986, p. 88.
Compare with several other peacock-glazed vessels in important collections such as the Yongzheng-marked zun from the J.M. Hu and C.P. Lin collections, illustrated by R. E. Scott, Elegant Form and Harmonious Decoration, Percival David Foundation of Chinese Art and Sun Tree Publishing Ltd., 1992, pl. 151; a Qianlong jar of 'fish basket' form, illustrated in Kangxi Yongzheng Qianlong, Qing Porcelain from the Palace Museum collection, Hong Kong, 1989, p. 457, no. 139; and a Qianlong moonflask from the Robert Chang collection, sold at Christie's Hong Kong, Jade Shears and Shimmering Feathers, 28 November 2006, lot 1305. Compare also a Yongzheng-marked censer from the Edward T. Chow collection, sold at Sotheby's Hong Kong, 19 May 1981, lot 502.