An unusual compound is found in Rembrandt’s The Night Watch

An international team of scientists from the Rijksmuseum, CNRS, ESRF, European Synchrotron, University of Amsterdam and University of Antwerp has discovered a rare compound of lead (called lead formate) in Rembrandt’s masterpiece The Night Watch. This discovery, the first in the history of the scientific study of the paintings, provides new insight into the technique of painting in the seventeenth century and the history of painting preservation. The study has been published in International edition of applied chemistry.

The Night Watch, painted in 1642 and today on display at the Rijksmuseum Amsterdam (Netherlands), is one of Rembrandt’s most important masterpieces and the largest work of art. Under Operation Night Watch 2019, the largest research and Preservation project Ever for Rembrandt’s masterpiece, an international research team has joined forces to study how it works painting Substances react chemically and over time.

The team of scientists combined multi-scale imaging methods for the chemical study of the materials Rembrandt used in The Night Watch. An X-ray scanning instrument developed at the University of Antwerp (Belgium) was applied directly to the plate, while small fragments taken from the plate were studied using synchrotron micro-X-ray probes, at ESRF, the European Synchrotron (France), and the PETRA-III facility (Germany).

These two types of analyzes revealed the presence of an unexpected organometallic compound: lead formate. This compound has not been previously detected in historical paintings. “In paintings, lead formations were only reported once in 2020, but in model paintings (mock-ups, fresh paints). And there… we not only detect lead formate, we identify it in areas where there is no pigment from Lead, white, yellow. We think they probably disappear quickly, which is why they have not been detected in ancient main plates yet,” explains Victor Gonzalez, CNRS researcher at the Laboratory of Photonics, Major Molecular Physics and Photochemistry (PPSM) (CNRS / ENS) Paris-Saclay ) and the first author of the paper.

So why has this not gone away? For Catherine Keon, Head of Science at the Rijksmuseum and Professor at the University of Amsterdam (Netherlands), this discovery is the key to better understanding Rembrandt: “In the process of night observation we focus on Rembrandt’s painting technique, the condition of the painting and how we can better understand it. It better preserves them for future generations. Lead formate gives us valuable new clues about the potential use of lead-based oil paints by Rembrandt and the potential influence of oil-based varnishes from earlier preservation treatments, and the complex chemistry of historical oil paintings.”

What is the origin of this compound? Can it provide information on Rembrandt’s workshop recipes, or shed light on the chemical mechanisms active in the layers of old paint? To answer these questions, the scientists studied fragments taken from The Night’s Watch and model samples prepared in the laboratory to simulate the painter’s installations.

They worked with the hypothesis that Rembrandt used an organic medium (linseed oil) containing dissolved lead oxide (PbO litharge) to enhance its organic properties. “Thanks to the unique analytical performance of ESRF, the world’s brightest synchrotron light source, we can map the presence of formes at a micrometer scale, and follow their formation over time,” explains Marin Kott, a scientist at ESRF.

The spatial organization of compounds at the molecular level and the dynamics of their formation allowed the researchers to propose new hypotheses about the chemical conditions for their in situ crystallization in ancient coating layers.

“In addition to providing information on Rembrandt’s photographic techniques, this research opens up new avenues on the interaction of historical pigments, and thus on heritage preservation,” explains Koen Janssens, a professor at the University of Antwerp.

The team’s next step is to further study the origin of these formics and see if they could also originate from previous recovery therapies.