Compare the very similar ewer illustrated by C.J.A. Jörg, Oriental Porcelain, A Choice from the Boymans-van Beuningen Museum Collection, Rotterdam, 1997, no.4, pp.19 and 20, where the author suggests the form of these ewers is taken from European earthenware or stoneware ewers. He also points out the similarity between the human heads and similar motifs appearing on an early 17th Century vase in the British Museum, which was made for the Jesuit College of Saint Paul in Macao, and exhibited, Chinese Trade Ceramics, Taipei, 1994, catalogue no.7, pp.26 and 27. He adds that similar human head motifs also appear on apothecary bottles of a slightly later date, such as the one also in the British Museum included in the same exhibition, ibid., catalogue no.11, pp. 36 and 37. Another Transitional blue and white ewer, also with human masks, is in the Ashmolean Museum, Oxford, and is illustrated by J. McClure Mudge, Chinese Export Porcelain in North America, New York, 1986, pp.140 and 141, fig. 206.