Here’s How Researchers Determined a Long-Lost Van Gogh Painting Is an Original

The first newly discovered Vincent Van Gogh painting since 1928, “Sunset at Montmajour,” spent years collecting dust in a Norwegian attic. Experts assumed that the large canvas was painted by another artist, but when art historians took a closer look, they reconsidered. To confirm the painter’s identity, they used a number of techniques and lines of evidence. The Associated Press reports:

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 painted it the previous day — July 4, 1888.

He said the painting was done “on a stony heath where small twisted oaks grow.”

Van Gogh’s word alone, however, did not authenticate the painting. Two years of intense research were required to give the painting the final stamp of approval. “Since 1991 the museum has developed a number of new techniques for identifying and authenticating works of art,” the New York Times reports. (Here’s a run-down.) And according to the museum’s senior researcher, they used “all those methods” in this round of research.

The Van Gogh Museum tested pigments in the painting to ensure they matched with other known works Van Gogh produced at the time. Researchers use a variety of microscopic techniques to study pigments likes these, including transmission electron microscopes, scanning electron microscopes, optical microscopy and polarized light microscopy. The Museum explains how the latter method aids in this process:

This investigative tool enables pigments and fibres to be identified. The particles to be examined, generally between 1 and 20 μm (microns) in size – smaller than one-thousandth of a millimetre – are placed under a microscope and a polarized light source is shone through them from underneath. Each type of pigment and fibre reacts differently to these polarized light rays so that every single particle can be identified.

The museum also determined, using X-ray analysis, that the canvas used for this work matches the type of canvas that Van Gogh used for another work in the same period.

“Everything supports the conclusion,” the Museum writes in a statement. “This work is by Van Gogh.”

Van Gogh told his brother that he considered the painting to be “a failure in several respects,” the AP notes. The Van Gogh Museum director, however, disagrees. Describing the painting’s merits in the Museum’s statement, he writes: “What makes this even more exceptional is that this is a transition work in his oeuvre, and moreover, a large painting from a period that is considered by many to be the culmination of his artistic achievement, his period in Arles in the south of France.”

More from Smithsonian.com:

Van Gogh’s Night Visions
The Secret Behind Van Gogh’s Fading Sunflowers

Rachel Nuwer | | READ MORE

Rachel Nuwer is a freelance science writer based in Brooklyn.