The low estimate proved irresistible. The unsigned view of Venice's Grand Canal, which is thought to have been painted by a disciple of Canaletto - possibly Michele Marieschi - sparked a bidding war.

The opening bid immediately shattered the estimate at $25,000, and the bids came thick and fast from 13 interested parties. Nine of them were on the phone, and represented interest from England, Scotland, Italy and Sweden - but the winner was a floor bidder.

The 22 x 33 inch work, neither signed nor dated, was sold for $550,000 plus buyer's premium just before the end of the auction in Chevy Chase, Washington, US. It is thought to be a record breaking price for the Washington area.

The description of the piece was: "School of Giovanni Antonio 'Il Canale' Canaletto (Italian 1697-1768) Grand Canal, Venice, With a View of the Doge's Palace". Michele Marieschi never signed his works, which helps make the attribution plausible.

Although paintings 'of the school of' Canaletto have sold for up to six figures previously, Sloans and Kenyon auctioneers kept the estimate low as, with unsigned work, they let the market decide whether it's valuable.

The sale is impressive for a painting which was brought back from Europe simply as a souvenir in 1881.