A German museum has discovered that its prized Monet painting The Seine at Port Villez is a fake.A spokesman for the Wallraf-Richartz Museum and Foundation Corboud in Cologne in western Germany says a research project carried out as part of an upcoming exhibition revealed that the work was not painted by the impressionist master."Our restoration department examined some 70 paintings with X-rays, with infrared technology and paint tests to deconstruct and explain the painters' techniques for an exhibition starting in two weeks," Stefan Swertz told AFP."There were several things that made us take a closer look at The Seine at Port Villez and we have absolutely no doubt that it was not painted by Monet," he said.One of the things that unmasked the fake Monet was the fact that the painter's name was not signed just once, but later retraced to be darker."This does not happen with an original. The artist just throws his signature onto the canvas. Also, the painting was made over a drawing that was clearly not in Monet's style," he said.The museum says the third clue was a colourless substance applied to the canvas to make it look older.Mr Swertz says the museum was philosophical about the discovery."We are, as we say in German, crying with one eye and laughing with the other. It is a terrible loss, but also an achievement. We are very proud of our research that could discover this," he said.The work was donated to the museum, the oldest in Cologne, in 1954. It will remain part of both the upcoming exhibition and the permanent collection "but with its provenance clearly explained," Mr Swertz said.The museum still has five Monet originals in its collection."We have of course checked all of them and they are all authentic," said Mr Swertz.