Artists are constantly using new pigments and oils to produce more vibrant, luminous and interesting colors. Rembrandt van Rijn was no different. The Dutch Old Master had technique, creativity and painstaking labor going for him. He also had chemistry. A new analysis of his works shows he used a rare compound in some of his paints, which helped him pull off his signature impasto technique, Henri Neuendorf at artnet News reports.
Historians already knew that Rembrandt used readily available compounds such as lead white pigment and oils like linseed oil to make the paste-like paints he piled in thick layers to give his work a three-dimensional appearance. When a team of researchers from The Netherlands and France subjected tiny paint samples from three of his best-known works—"Portrait of Marten Soolmans,” “Bathsheba” and “Susanna”— to X-ray analysis at the European Synchrotron in Grenoble, France, however, they detected another compound they weren't expecting: a lead carbonate mineral called plumbonacrite, Pb5(CO3)3O(OH).
The finding in his impasto mix was especially surprising since plumbonacrite is generally found in 20th-century works onward, though it did pop up in a sample of a Vincent van Gogh red lead pigment sampled from “Wheat Stack under a Cloudy Sky” (1889). That being said, Rembrandt was painting in the first half of the 1600s.
“We didn't expect to find this phase at all, as it is so unusual in Old Masters paintings,” Victor Gonzalez, lead author of the study and scientist at the Rijksmuseum and Delft University of Technology says in a press release for the study, which appears in the journal Angewandte Chemie International Edition.
So where did this unusual compound come from? After studying historical texts and determining what would have been available to a 17th-century Dutch artist, they believe he intentionally added the compound in the form of lead oxide or litharge to his oils to make a paste-like paint. “[O]ur research shows that its presence is not accidental or due to contamination, but that it is the result of an intended synthesis,” says Gonzalez.
Knowing the composition of the artist’s palette will help conservationists figure out how to best preserve his artworks over time. The team now has plans to re-create Rembrandt’s impasto paint and artificially age it in high CO2 and CO2-free conditions to better understand how humid and dry conditions impact the paints.
They also hope to look at other paintings by Rembrandt and fellow Dutch Golden Age painters to see if the use of plumbonacrite-bearing compounds was more widespread than previously thought.
“We are working with the hypothesis that Rembrandt might have used other recipes, and that is the reason why we will be studying samples from other paintings by Rembrandt and other 17th century Dutch Masters, including Vermeer, Hals, and painters belonging to Rembrandt's circle,” co-author Annelies van Loon, a painting research scientist at the Rijksmuseum and the Royal Picture Gallery Mauritshuis, says in the release.
This isn’t the only artistic secret revealed by X-rays in recent years. In 2016, a synchrotron helped unveil a previously unseen painting beneath Degas' “Portrait of a Lady” and last year researchers used x-rays to show Picasso painted over a canvas by a friend to produce the work “Crouching Beggar.”