Van Gogh’s wilting flowers

AMSTERDAM •Theyellow petals and stems of Vincent van Gogh’s January 1889 version of Sunflowers in the Van Gogh Museum in Amsterdam are microscopically wilting, say researchers at the University of Antwerp in Belgium and the Technical University of Delft in the Netherlands.

After examination of the pigments of the famous painting, researchers concluded that one of two chrome yellow pigments he used is sensitive to light and has a tendency to turn from pale yellow to an almost olive green or ochre over time.

This effect cannot yet be seen with the naked eye, said Frederik Vanmeert, a researcher and doctoral candidate in the chemistry department of the University of Antwerp, but they could become more visible over time. He was one of the authors on a technical study published in Angewandte Chemie, a scientific journal, on Monday.

The unstable chrome yellow was encountered “in the pale yellow background and the bright yellow petals, but also in the green stems and flower hearts, thus indicating their higher risk for past or future darkening,” the report said.

The researchers were able to examine “Sunflowers” in 2016 using a new process of chemical mapping called Macroscopic X-ray Powder Diffraction, which allows them to detect materials within the pigments of a painting without ever touching the painting. They received permission from the Van Gogh Museum to do the study and collaborated with the museum on the results.

Van Gogh, the 19th-century postimpressionist artist, used synthetic paints that came in tube form and were new to the market during his era, including three types of chrome yellow — two of which seem to have a tendency to deteriorate in certain kinds of light. For Sunflowers, he used two of these, one of which is the sensitive pigment, Vanmeert said.

The Dutch artist and his contemporaries used the chrome yellow pigments in his series of Sunflowers paintings and in other paintings as well, but it is not yet known how many of his paintings may be affected by the microscopic degradation, Vanmeert said. There has already been a comparative investigation with the Sunflowers in the National Gallery in London, he added, “and they are expecting to see the same problem there too.”

In 2013, researchers at the Van Gogh Museum discovered that one of the red pigments that van Gogh used for many of his works had a tendency to fade to white. His famous The Bedroom (1888), which currently has blue walls, originally had purple walls, according to museum officials, before the red pigment faded.

Marije Vellekoop, head of collection and research at the Van Gogh Museum, said that van Gogh had used the chrome yellow a lot in his paintings, and that the museum is considering the results and looking for ways to address the problem.

“The recent research helped us to understand where in the painting this type of chrome yellow is present, so we know which parts to monitor closely,” she said in an email.