An oil painting has been proven to be one of Claude Monet's - after scientists discovered the artist painted over his own signature. The 1891 painting, titled 'A Haystack in the Evening Sun', was largely unknown and its origin had never been verified. But a team of researchers from the University of Jyväskylä in Finland painstakingly  unearthed the signature. Scroll down for video . An 1891 oil painting - titled 'A Haystack in the Evening Sun' - has been proven to be one of Claude Monet's despite the artist painting over his own signature . The painting has been owned by the Gösta Serlachius Fine Arts Foundation, also in Finland, for more than 50 years. It is thought to be part of a wider series by Monet with all the pieces illustrating stacks of hay in fields after the harvest season. The painting was verified after a special camera was used to examine the composition of the work. This allowed researchers to see different layers  including a previous signature by  Monet. It is thought to be part of a wider series by Monet (above) with all the pieces illustrating stacks of hay in fields after the harvest season . Ilkka Pölönen, a researcher, said the camera scans one 'line' at a time. He told ArtDaily: 'When the camera is moved using the scanner an image of the whole picture can be obtained.' The Fine Arts Foundation said the artwork  is the first Monet painting to be held in a Finnish public collection. The other paintings from the series are held at various galleries including the Art Institute of Chicago, the National Gallery of Scotland and the J. Paul Getty Museum in California. X-ray fluorescence (XRF) is a non-destructive technique, which can identify the presence of certain pigments. It was first used in the 1940s and applied to paintings in the 1950s. The technique involves bombarding the artwork with x-rays so powerful that they cause atoms in the picture’s layers to emit ‘florescent’ x-rays of their own. XRF can be used to identify the colours of hidden paintings or to see earlier versions of famous pieces. By mapping the x-rays of copper, for blue and green, iron, for yellow, orange and brown, and mercury, for red, scientists can see full-colour 'maps' of previous versions. In this case a special camera was used to examine the composition of the work. This allowed researchers to see different layers  including a previous signature - verifying that the painting was by Monet.
Oil-painting titled 'A Haystack in the Evening Sun' is from 1891 . Researchers in Finland used special technique to unearth signature .