Mother-of-pearl clouds over Lørenskog, near Oslo, Norway, half an hour after sunset.
Mother-of-pearl clouds over Lørenskog, near Oslo, Norway, half an hour after sunset. Credit: Svein M. Fikke

Art is on the minds of some scientists this week at Europe’s largest annual geosciences meeting. For two of the world’s most famous paintings, researchers say scientific clues lurking in their portrayals of rock layers or moist air raise new questions about the inspiration for one iconic work of art and the authenticity of another.

One of four versions of the 1893 painting The Scream, by Edvard Munch.
One of four versions of the 1893 painting The Scream by Edvard Munch. Credit: In the public domain in countries with a copyright term of life of the author plus 70 years or less.

A poster presentation Monday by a Norwegian meteorologist shed doubt on the current favorite theory of what inspired the striking red and orange sky over Oslo seen in the painting The Scream by Edvard Munch. Today, an Italian American scientist will present geological and botanical reasoning in a talk arguing that a painting in the National Gallery in London attributed to Leonardo da Vinci, called The Virgin of the Rocks, cannot be from the hand of that Renaissance painter. The researchers are making their cases at the General Assembly of the European Geosciences Union (EGU) in Vienna, Austria.

Regarding The Scream, it’s not dust from the 19th century eruption of Krakatoa volcano that gave the sky the appearance that awed Munch so much, said Helene Muri of the Department of Geosciences of the University of Oslo in a Monday press conference about the poster. More likely, it’s a rare breed of cloud. “This is a painting that is known worldwide, and we are just not convinced by the previous hypotheses, that it was Munch’s internal turmoil or that is was the Krakatoa eruption,” Muri said.

As for the supposed Leonardo masterpiece, it’s the far superior scientific accuracy of a second version of The Virgin of the Rocks at the Louvre Museum in Paris that has convinced Ann Pizzorusso, an independent scholar who is both a geologist and an expert on the Italian Renaissance, that the London painting is by someone else. She spoke with Eos earlier this week.

Layered Rocks and Layered Clouds

Looking at the Louvre painting is like being in the field.

Looking at the Louvre painting is like being in the field, Pizzorusso told Eos. “If I look to the foreground, there’s marvelous bedded sandstone. With his sfumato technique, Leonardo made visible the layers and texture,” she said, referring to the artist’s practice of shading colors gradually into one another to produce blurred, softened outlines. She also noted a sill, an intruded layer, of a different kind of rock, diabase. “And above it, you can see spheroidally weathered sandstone, which again his painting technique allows you to accurately identify.”

The new Munch hypothesis that Muri unveiled at the EGU meeting came from her late colleague Jón Egill Kristjánsson. The 1883 eruption of Krakatoa, in what is now Indonesia, injected dust into the stratosphere, and the particles formed a thin, homogeneous layer that caused colorful sunrises and sunsets. However, they didn’t produce the wavy texture seen in Munch’s painting, Kristjánsson had contended.

Another natural phenomenon, polar stratospheric clouds, also called nacreous or mother-of-pearl clouds, looks very much like the sky in Munch’s painting, Muri offered. The sky’s look so affected Munch that he wrote a poem about the spectacle before depicting it on cardboard.

Mother-of-pearl clouds arise when stormy weather drives moist air up against a mountainside into the normally parched stratosphere Muri explained. On the leeward side of the mountain, as the air cools, ice crystals form. Too thin to be visible by day, those crystals are lit from below just after sunset or before sunrise and will display the exact color and texture that Munch captured, she said. The phenomenon occurs rarely enough—about four times a year, Muri estimated—to trigger surprise and awe.

Botanical Clues

Pizzorusso has harbored doubts about the London Leonardo for about 20 years, advocating for her point of view in articles and in a popular geology book, Tweeting Da Vinci. In Vienna, she is presenting her analysis of new, high-quality photographs of the Louvre version that have become available. “On those you can see fossil imprints on the front of the sandstone and geologic features that would have been caused by sedimentation,” she told Eos.

Two Virgin of the Rocks paintings attributed to Leonardo da Vinci.
(left) The Virgin of the Rocks by Leonardo da Vinci at the Louvre Museum in Paris. (right) Another Virgin of the Rocks painting at the National Gallery in London, attributed by the museum also to Leonardo da Vinci. Geologist and Italian Renaissance scholar Ann Pizzorusso will argue this week at the European Geosciences Union meeting in Vienna, Austria, that the London painting is not by Leonardo. Credit: In the public domain in its country of origin and other countries and areas where the copyright term is the author’s life plus 100 years or less.

She also noted what botanists have said about the plants in both versions. Those in the National Gallery painting do not even exist in nature, she said. “The plants are correct in the Louvre version, Iris germanicus, for example. And they are growing in the soft, sandy soil, whereas a lot of the plants in the London version are trying to grow out of hard diabase, where it’s very hard for roots to take hold.”

Pizzorusso noted that the existence of two Virgin of the Rocks paintings goes back to a dispute about payment between Leonardo and two coworkers and the religious organization that ordered the painting. It is thought that Leonardo sold the first version he made, the Louvre one, to someone else and eventually delivered the London version as fulfillment of his contract. If the London version isn’t his, it is possible that his coworker Giovanni Ambrogio de Predis made the painting after Leonardo’s example.

Even with help from science, a definitive answer may prove elusive.

Looking at that painting in London, however, it’s obvious to see that its creator shared none of Leonardo’s urge to draw nature as perfectly as possible, Pizzorusso told Eos. “Basically, the rocks are unidentifiable,” she said. “You cannot tell whether they are sandstone or limestone. It almost looks like a stage setting, with Styrofoam rocks.”

In either of these art-sleuthing cases, even with help from science, a definitive answer may prove elusive. However, as Muri of the new proposal about The Scream contends, advancing an unprovable hypothesis is good science if it can replace another hypothesis that is less plausible. “We researchers ask questions; that is our job,” she said. “We’re not trying to sow confusion, but to clarify what the cause could be.”

—Bas den Hond (email:, Freelance Science Journalist


den Hond, B. (2017), Science offers new clues about paintings by Munch and da Vinci, Eos, 98, Published on 27 April 2017.

Text © 2017. The authors. CC BY-NC-ND 3.0
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