The Hidden Technique Uncovered through X-rays in Rembrandt's The Night Watch

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In Rembrandt's monumental 17th-century painting "The Night Watch," a group of Dutch civilian soldiers assembles in a dimly lit room, ready to head out to protect their city. Known for his skill in playing with light and darkness, Rembrandt artfully highlighted the expressive hands and faces of his subjects, while keeping the room's details hidden and many of the guardsmen's bodies obscured in shadow.

Researchers recently discovered that the famous painting "The Night Watch" was hiding more than originally thought. Upon using X-rays to examine beneath the varnish and paint, conservators found an unexpected layer filled with lead.

For the first time in the 400-year history of the paintings, researchers combined X-rays with spectroscopy of a paint sample and 3D digital reconstructions. The study revealed a lead-rich layer that had never been seen before in Rembrandt's works, as reported Friday in the journal Science Advances.

Rembrandt and his artist contemporaries usually began a painting by coating the canvas with a stiffening layer of glue, then applying a base coat of underlying pigment, known as a ground layer, to prepare the canvas.

"The Night Watch" did not have a glue layer. It is possible that a lead-saturated layer was used instead to provide better protection for the canvas, as suggested by the study authors.

Upon completion in 1642, the painting was displayed in Amsterdams Kloveniersdoelen, a musketeers' shooting range, on a wall opposite a row of windows, making it susceptible to potential moisture damage.

Frédérique Broers, a research scientist of microscopy at the Rijksmuseum in Amsterdam, where "The Night Watch" is displayed, suggested that Rembrandt may have been inspired to reinforce his canvas with lead after reading a publication about the chemistry of painting written by Théodore de Mayern, a physician from Geneva. Mayern wrote about observing a painting that had been prepared with glue, but the paint and glue layers had separated after the artwork hung for several years on a damp wall. He recommended using a foundational layer of lead-rich oil in such circumstances. According to Broers, the researchers believed that Rembrandt chose to use lead because it had better drying properties compared to the normal glue layer for preparing the canvas.

Whether the inspiration came from Mayern or discussion among painters, Rembrandt likely embraced the uncommon technique as a promising safeguard for a painting that he knew would be displayed in a humid spot, Broers said. The new findings suggest that Rembrandt was open to exploring unconventional methods that deviated from his standard practices, in order to execute his unique artistic vision.

A previously unknown lead-containing layer was discovered in Rembrandt's The Night Watch after a paint sample was analyzed using different techniques.

Fréderique Broers/Rijksmuseum

The researchers conducted detective work as part of Operation Night Watch, a conservation and analysis project initiated by the Rijksmuseum in 2019. Originally named "Militia Company of District II under the Command of Captain Frans Banninck Cocq," the painting became known as "The Night Watch" in the 18th century, partly due to the darkening varnish and the passage of time. Over the years, the varnish yellowed and darkened with dirt, leading viewers to mistakenly believe that the scene depicted a nighttime setting.

The varnish layers were removed during a 1940s cleaning, lifting much of the darkness, but much work remained to restore and analyze the artwork. Operation Night Watch is the largest and most wide-ranging research and conservation project in the history of Rembrandt's masterpiece, with the goal of delving deeper into his process than ever before and preserving the painting for decades to come, according to the Rijksmuseum's website. The researchers combined data from large-scale scans of the painting using X-ray fluorescence and powder diffraction, as well as reflective imaging spectroscopy to create visualizations of chemical elements and molecules, revealing their distribution and showing where crystalline structures formed.

Analysis of a small paint sample taken from the Mona Lisa has uncovered a rare compound, unveiling a new revelation, according to a recent study. The minute sample, measuring just 55 micrometers wide and 160 micrometers long, was removed from the painting, scanned, and digitally modeled in 3D. This innovative method provided a deeper understanding of how the iconic artwork was created, as stated by Broers.

For years, specialists were puzzled by the sudden appearance of small "pimples" made of lead crystals that seemed to emerge out of thin air on the painting's surface. Although lead is typically found in the white pigment used in paintings, there was very little bright white in "The Night Watch."

The presence of these tiny lead specks in the darkest areas of the painting added to the mystery, according to Broers. However, with the discovery of a lead-rich layer covering the canvas, this puzzle has finally been solved.

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A significant discovery from previous investigations revealed the composition of the ground layer above the lead layer, which consisted of quartz and clay. This was the earliest evidence of Rembrandt using this mixture, which he continued to use, albeit not exclusively, throughout his career.

Before this, Rembrandt had primed his canvases with a double ground layer: one of red earth and another of white pigment. However, "The Night Watch" was much larger than his other works, measuring 12.5 feet (3.795 meters) high and 14.9 feet (4.535 meters) long. The study suggests that a single ground layer was lighter, more flexible, and cheaper than his usual double layer.

Operation Night Watch's success is attributed to a comprehensive approach to its preservation and protection, according to Broers. X-ray scan data was analyzed in conjunction with findings from cleaning and conservation experts, while curatorial interpretation offered a historical context for the chemical components found in the paint and primer layers. The collaboration of these diverse disciplines ensures that "The Night Watch" will be appreciated by generations of art enthusiasts in the modern age. "We really needed all of the expertise from the whole team of Operation Night Watch to bring it into context," remarked Broers.

Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American and How It Works magazine.