Painting dumped in attic identified as a Van Gogh

Olaf Kraak | AFP | Getty Images

A previously unknown oil painting by Vincent Van Gogh that was dumped in an attic has been found and confirmed by experts as authentic.

The painting, "Sunset at Montmajour," is the first full-size Van Gogh to emerge for 85 years. It had been banished to a Norwegian attic for more than a century because its owner believed it to be a fake.

According to letters from the Dutch master to his brother Theo, the painting was done in 1888, when Van Gogh was living in Arles, in southern France. However, the notoriously self-critical artist wrote that he did not like the painting and that it was "well below what I'd wished to do." As such, he did not put his signature on it.

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Sunset at Montmajour (1888),  by Vincent Van Gogh
Photographer | Collection | Getty Images
Sunset at Montmajour (1888), by Vincent Van Gogh

The painting was listed in Theo's personal collection before he sold it to a Norwegian industrialist, Christian Mustad, in 1908. It is believed that Mustad was told at some point that it was a forgery or false attribution. It was sold to a private collector when he died in 1970.

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When the collector asked the Van Gogh Museum in Amsterdam for an opinion on the painting in 1991, researchers concluded it was a fake because of its lack of signature. Thanks to modern technology, however, researchers could correlate the literary evidence and artist's style and technique with an analysis of the materials used to prove it was authentic.

"Stylistically and technically there are numerous parallels with other Van Gogh paintings from the summer of 1888," senior researchers Louis van Tilborgh and Teio Meedendorp said Monday when the work was unveiled at the museum.

The painting will be on display in the museum for a year. It could fetch millions at auction, as other works by Van Gogh have done, such as the famous "Sunflowers" piece, which sold for $39.9 million in 1987.

—By CNBC's Holly Ellyatt, follow her on Twitter @HollyEllyatt