Hi, this is model RSW232 or SG232 I believe - the RSW standing for Ronald Stennett Willson, the designer, of course. The Wedgwood England sand blasted mark was introduced in 1971 after the representation of the Portland Vase was dropped. It was maintained until Wedgwood Glass closed, so anytime from late 1971 to the end of the century I am afraid. They made a lot of ducks - a bit like English batsmen!