Like Mona Lisa’s smile, the origin of the unidentified white smudge staining Edvard Munch’s The Scream is one of art’s greatest mysteries. For decades, the puzzling substance was rumored to be bird poop, but recent analysis points the blame elsewhere.

As Artnet News reports, scientists at the University of Antwerp in Belgium have traced the white splatter on the painting to wax drippings from a candle. Researchers came to the conclusion after examining it with a machine of their own invention called a Macro-X-ray fluorescence scanner. After ruling out white paint or chalk, they detected the tell-tale signs of wax indicating that the mess had likely been made by accident inside the artist's studio.

Munch had been known to paint outdoors and would often leave his works exposed to the elements. This habit of his helped spread the idea that a bird flying overhead left the stain, and as the University of Antwerp puts it, “literally added another layer of meaning to Munch's masterpiece.”

The painting bearing the white smudge is the first of four versions Munch composed in the late 19th century—it currently resides at the Norwegian National Museum in Oslo. The meaning of the artwork may still be ambiguous, but at least we can say with confidence that the subject probably isn’t screaming about a bird pooping on his shoulder.

[h/t Artnet News]

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