The arms are those of Dom Pedro de Lancastre Silveira Valente, 5th Count of Vila Nova de Portimao (1697-1752). For a similar example see Nuno de Castro, Chinese Porcelain and the Heraldry of the Empire, Oporto, 1988, p. 52. The author discusses that this is from a later service that had corrected the coat-of-arms in a rudimentary fashion. The earlier two services were wrongly interpreted and incomplete and therefore rejected by the family. This is illustrated by Nuno de Castro, op. cit., p. 51. A similar vase was sold in our London Rooms, 28 April 1999, lot. 177.
The shape of this ewer probably copies Spanish or Italian Renaissance silver ewers of the sixteenth century and examples in Chinese porcelain are rare. It is particularly unusual to find a blue and white ewer of this form as most other known pieces were made in the famille verte palette.