The vanishing violet in van Gogh’s Irises

On May 8, 1889, painter Vincent van Gogh checked himself into a psychiatric hospital near Saint-Rémy-de-Provence, France, during a major mental health crisis. The hospital director, Théophile Peyron, allowed van Gogh to bring his paints, and he even set aside studio space for the artist, hoping that painting the natural beauty in the hospital’s surroundings would help van Gogh with his recovery. In a letter to his brother Theo van Gogh dated May 9, the artist wrote that he had begun painting the “violet irises” that grow on the parklike hospital grounds.

Violet. It’s a small but revealing detail. Anyone who has ever seen one of van Gogh’s studies of the flowers—either in person or as one of the many reproductions that appear on posters, tote bags, dresses, and blank books—will tell you that the irises in these paintings look blue. But the irises on the grounds of the hospital in Saint-Rémy-de-Provence, which have changed little in the past 135 years, are a vivid violet.

What has given van Gogh’s irises the blues?

That’s the question at the heart of Ultra-Violet: New Light on Van Gogh’s Irises, an exhibition that opened at the J. Paul Getty Museum in Los Angeles on Oct. 1 and runs through Jan. 19, 2025. The exhibition details a study that Getty scientists and conservators began in 2020 of what is probably van Gogh’s most famous version of Irises.

“One of the challenges with Irises as a subject of study is that it’s one of the most popular paintings in our collection, and it is literally always on view. So it’s difficult to get it off of the wall and into the lab or into the conservation studio,” says Catherine Patterson, a chemist who works at the Getty Conservation Institute.

But in 2020, as the museum closed its doors to visitors because of the COVID-19 pandemic, Getty researchers realized they had an opportunity to study the painting in way they had never been able to before—even as they donned masks and kept socially distant from one another. “This project really was one of those silver linings of the pandemic era, if only because the museum had to close,” Patterson says.

Patterson and her colleagues’ study of the painting revealed what many have long suspected: a light-sensitive paint van Gogh used called geranium lake has degraded over the years, removing the red color that he mixed with blue to achieve violet.

Geranium lake is made from eosin Y dye—a brominated organic chromophore. To turn the water-soluble dye into an insoluble pigment that artists could paint with, paint makers used what’s known as the lake process, which combines the dye with a binder.

Other conservation scientists have identified geranium lake degradation as the culprit for the loss of reds and pinks in many of van Gogh’s works, including other paintings he made of irises while at Saint-Rémy-de-Provence. But until this latest work, researchers could not say if the same was true for the most famous of the Irises paintings.

The loss of color in van Gogh’s works has inspired studies into the mechanism behind geranium lake’s degradation in recent years. For example, a team led by the University of Perugia’s Aldo Romani proposed that geranium lake loses its color when exposed to light and oxygen in the air (Dyes Pigm. 2020, DOI: 10.1016/j.dyepig.2020.108600).

Light prompts eosin Y to form its long-lived triplet state. The triplet grabs a hydrogen radical from the fatty acids in the paint’s binder and forms a colorless semireduced eosin Y radical. The radical can recombine with hydrogen atoms to re-form eosin Y, or it can react with atmospheric oxygen and break down into two colorless compounds: 2-(3,5-dibromo-2,4-dihydroxybenzoyl)benzoic acid and 2,6-dibromobenzene-1,4-diol.

Patterson says mechanistic studies like Romani’s help her understand what happened to the colors in Irises. “A lot of the work that I do is fundamentally analytical chemistry,” she says. Her team favors noninvasive techniques to identify materials without touching the painting, whenever possible.

For the study of Irises, the Getty researchers used X-ray fluorescence spectroscopy to make an elemental map of the painting. One of the elements they were able to detect was bromine.

Although that finding alone doesn’t tell them exactly what molecules are on the canvas, it’s a good indicator of where geranium lake was used, Patterson says. That’s because geranium lake is one of the few pigments that contain bromine, and it’s the only bromine-containing paint that was available to van Gogh.

Van Gogh and his contemporaries knew that geranium lake was prone to fading, says Devi Ormond, a conservator at the Getty Museum. But they used it anyway. Ormond says that van Gogh wrote in a letter to Theo that he applied thick layers of the pigment, hoping the color would last longer. Alas, the color still faded.

But that doesn’t mean modern viewers can’t get a sense of what Irises looked like when its paint was still wet. For the Ultra-Violet exhibit, Getty scientists and conservators collaborated with the cultural heritage nonprofit Factum Foundation for Digital Technology in Preservation to re-create Irises in its original hues.

The Getty team scanned the original Irises using high-resolution photogrammetry, and the Factum team used the data to create a textured surface that captures van Gogh’s thick paint application and distinctive brushstrokes. That surface was then molded into a flexible skin that the Factum group color printed, using a color palette Getty’s team developed. The whole re-created painting was then stretched over a canvas and varnished.

“What Catherine and I really wanted to do was capture the tactility of van Gogh’s work, which is often missed when you just see it on the screen,” Ormond says.

Patterson agrees that the color-corrected re-creation is one of the most satisfying parts of the exhibit. For visitors, she says, “there’s a lot of head swiveling as they look back and forth between that and the original.”