After two and a half years of research, Operation Night Watch, the Rijksmuseum’s investigation into Rembrandt van Rijn’s iconic painting, has revealed its findings. The museum announced on Wednesday that analysis of the colossal Militia Company of District II under the Command of Captain Frans Banninck Cocq—more commonly known as The Night Watch—has afforded new insight into the Dutch master’s process, as well as pointers for how to restore the picture as best as possible.

Using imaging technology techniques, researchers discovered a hidden sketch beneath the painting that revealed Rembrandt’s original composition, which experts said was placed directly onto the canvas. The research team found that Rembrandt made only minor tweaks to it in his final composition. A central sword and several spears were added (and later removed in the final version), the leg position of a soldier was adjusted, and a sword was painted between Captain Frans Banninck Cocq and his lieutenant Willem van Ruytenburch. Also, feathers visible on the helmet of militiaman Claes van Cruijsbergen in the sketch were painted over by Rembrandt.

"We always suspected Rembrandt must have made a sketch on the canvas before embarking on this incredibly complex composition, but we didn’t have the evidence," Taco Dibbits, director of the Rijksmuseum, said in a press conference on Wednesday. "We are currently able to look beneath the surface of the paint better than ever before, and now we have the proof, giving us a real understanding for the first time of how the painting was made.

"We have discovered the genesis of The Night Watch," he added.

Researchers also discovered a pigment containing poisonous arsenic that was used in the painting. That pigment can be detected in still lifes featuring lemons that were painted during the era, but Rembrandt didn’t rely on it often. In The Night Watch, the pigment appears in the portion portraying Van Ruytenburch’s coat and sleeves. The Rijksmuseum also said that certain colors in The Night Watch, such as one known as "smalt blue" that is derived from blue cobalt-based glass, have faded over the years. A dog appears to have discolored, revealing the sketch underneath, and a militiaman’s face is similarly obscured by decay.

Some of the changes made to The Night Watch over the years can’t only be attributed to the passage of time. Researchers said that there are pronounced deformations in top left of the painting, and that they may have been caused in the 2000s, when The Night Watch was moved during renovations at the Rijksmuseum. Petria Noble, head of paintings conservation at the Rijksmuseum, said in the press conference that the team will immediately begin a restoration to fix deformations. Within two to three months, the painting will likely be good as new.

"The painting will be taken off its current wooden stretcher, [which] we strongly feel is contributing to the problem because it reacts differently to the canvas," Noble said. "It will then be put onto a new strainer, a non-reactive material that we feel will be much more stable. This is very important for the long-term preservation of the painting."

In 2019, a team of conservators, scientists, and curators at the Rijksmuseum, where The Night Watch has been on display since 1808, commenced the investigation. The painting, an iconic work of the Dutch Golden Age, depicts ​​the militia company led by Frans Banninck Cocq and Willem van Ruytenburch. It is Rembrandt’s largest work, and one of his most dynamic ones, with a strong sense of motion.

Since its completion in 1642, the painting has endured repeated affronts. In 1715, the monumental canvas was trimmed to fit between the narrow columns of Amsterdam’s Town Hall, an alteration that led to two characters being cropped out. The fragments that were cut off have never resurfaced. The painting was also knifed twice, in 1911 and 1975. In 1990, the painting was sprayed with acid by an escaped psychiatric patient.

Earlier this year, the Operation Night Watch team succeeded in using A.I. to reconstruct the missing sections of the painting, which included two militiamen and a boy on a bridge on the painting’s left side, as well as a space without figures toward the bottom of the frame. The technology paired high-resolution images of the remaining composition with artificial neural networks that mimicked Rembrandt’s techniques. A copy of the work painted by Gerrit Lundens between 1642 and 1655 also proved critical to the reconstruction.

"An all-encompassing approach such as this would have been impossible even a few years ago, which means Operation Night Watch is setting a new standard for the study of painting," Noble said. "All these discoveries now prompt us to look at Rembrandt’s other paintings with different eyes. We now know what we should be looking for."