"Sunset at Montmajour" depicts a dry landscape of twisting oak trees, bushes and sky, and it was done during the period when Van Gogh was increasingly adopting the thick brush strokes that became typical of his work in the final years of his short life, experts at the Van Gogh Museum in Amsterdam said Monday.
It can be dated to the exact day it was painted because Vincent described it in a letter to his brother, Theo, and said he had painted it the previous day — July 4, 1888.
"At sunset I was on a stony heath where very small, twisted oaks grow, in the background a ruin on the hill and wheat fields in the valley," Van Gogh wrote.
"It was romantic...the sun was pouring its very yellow rays over the bushes and the ground, absolutely a shower of gold."
But then Vincent confessed that the painting was "well below what I'd wished to do," and later he sent it to Theo to keep.
Museum director Axel Rueger, at an unveiling ceremony in the museum, described the discovery as a "once-in-a-lifetime experience".
"This is a great painting from what many see as the high point of his artistic achievement, his period in Arles, in southern France," he said. "In the same period he painted works such as 'Sunflowers,' 'The Yellow House' and 'The Bedroom'."
Van Gogh struggled with bouts of mental distress throughout his life, and died of a self-inflicted gun wound in 1890. He sold only one painting while he was alive, though his work was just beginning to win acclaim when he died.
According to a reconstruction published in The Burlington Magazine by three researchers, the painting was recorded as number 180 in Theo's collection, and given the title "Sun Setting at Arles." It was sold to French art dealer Maurice Fabre in 1901.
Fabre never recorded selling the work, and the painting disappeared from history until it reappeared in 1970 in the estate of Norwegian industrialist Christian Nicolai Mustad.
The Mustad family said that Christian had purchased the work in 1908 as a young man in one of his first forays into art collecting, but he had soon after been told by the French ambassador to Sweden that it was a fake. Embarrassed, Mustad banished it to the attic.
After Mustad's death in 1970, art dealer Daniel Wildenstein said he thought the painting was either a fake Van Gogh or possibly the work of a less-known German painter, and the painting was sold to a collector. The museum said it will not disclose who purchased it, or whether it has been resold since then.
In 1991 the museum itself declined to authenticate the painting.
"That may be a painful admission, given that the same museum is now attributing it to Van Gogh, but it is understandable" as experts had no information about what the painting depicted, the Burlington Magazine article said.
Teio Meedendorp, one of three experts who worked on the project, said his predecessors might also have been confused because the painting was done at a "transitional" moment in Van Gogh's style.
"From then on, Van Gogh increasingly felt the need to paint with more and more impasto (thick strokes using lots of paint) and more and more layers," he said.
The painting was unsigned. Some parts of the foreground were not "as well-observed as usual." And part of the right side of the painting used a different style of brush strokes — possibly the same reasons Van Gogh himself considered the painting a failure.
But when the museum took a fresh look at the work in 2011, they had the advantage of a newly edited and published compendium of all Van Gogh's letters, and were able for the first time to identify the exact location "Sunset" depicts: Monmajour hill, near Arles, France. The ruins of Monmajour abbey can be seen in the background on the left side of the painting.
Van Gogh mentioned the painting in two other letters the same summer.
The number 180 on the back of the canvas was an important clue, and new techniques of chemical analysis of the pigments showing they were identical to others Van Gogh used on his palette at Arles — including typical discolorations.
Meanwhile, an X-ray examination of the canvas showed it was of the same type Van Gogh used on other paintings from the period, such as "The Rocks," which hangs in Houston's Museum of Fine Arts.
Rueger described "Sunset" as ambitious, because the canvas is relatively large, at 93.3 by 73.3 centimeters (36.7 by 28.9 inches) — and because Van Gogh himself felt the result didn't live up to his imagination of what it was meant to be.
The artist made similar remarks about some of his most famous paintings, including the 1889 "Starry Night" that hangs in the Museum of Modern Art in New York.
Meedendorp said that "Sunset" belongs "to a special group of experimental works that Van Gogh at times esteemed of lesser value than we tend to do nowadays."
Meedendorp said it's not impossible that another unknown or lost Van Gogh could be found someday. The artist destroyed some works himself when he wasn't satisfied with the results, but others that are mentioned in his letters or early collection of his work have since disappeared. He is believed to have completed more than 800 works, painting at an accelerating pace before his death aged 37.
The Van Gogh Museum, which houses 140 paintings, receives more than a million visitors annually. Van Gogh paintings are among the most valuable in the world, selling for tens of millions of dollars on the rare occasions one is sold at an auction.
Follow Toby Sterling on Twitter http://www.twitter.com/lbsterling
Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.