Rembrandt covered the canvas of his largest and most famous work, popularly known as The Night Watch, with a layer of lead-rich oil to protect it from moisture, according to a study published Friday in the journal Science Advances. It is the latest find of Operation Night Watch, a project that since 2019 wants to know every detail of the painting, as well as the techniques, styles and pigments that the painter used. The final goal is to find the best strategy that guarantees its conservation.
The lead was leading the researchers. Some light pigments, such as certain yellows and whites, contain this element which, over time, tends to gather in small bumps that distort the pictures. However, in Rembrandt's masterpiece, these bubbles are everywhere, even in unexpected areas.
In order to investigate its origin, the international team of scientists who carried out the work analyzed a strip of paint thinner than a hair in the light of a synchrotron. These particle accelerators can produce X-rays so concentrated that they allow analysis on a microscopic scale. The result is a kind of photo of the sample in which each chemical component is highlighted.
The researchers exposed the fragment of the work to this light beam and took measurements with two different detectors, one which allows to know the chemical elements present (titanium, lead, iron, strontium and calcium), and another which analyzes oil and quartz particles. "After doing a scan, we rotated the sample one degree and repeated the process, and so throughout the 360 degrees", explains in an email to La Vanguardia Fréderique Broers, researcher at the University of Amsterdam and first author of the article. In total, each detector provides 360 images, one for each angle, which, combined, allow a 3D reconstruction of how the ingredients of the paint are distributed.
This three-dimensional view, never seen before (at least with this level of detail), "contributes a lot of information about the composition of the paint, and the shape and sizes of the particles of each pigment", says the expert. And in this 3D replica, the researchers identified that, in the deepest layers of the work, there was an unexpected large amount of lead.
“Then we scanned the entire Night Watch, and we saw that the lead is all over the surface of the painting, even in dark areas. This suggests the use of a layer impregnated with a product that contained lead throughout the paint. In addition, a second fragment of paint collected from the ground after the knife attack on the painting in 1975 shows, under the microscope, this layer that contains lead", summarizes the expert.
“We also have a historical source [a 17th-century manuscript] that suggests the use of an oil impregnation layer containing lead instead of an adhesive layer [the usual practice], if you have a painting that it will be hung on an outside wall”, he continues, as was the case with Rembrandt's work. The evidence left no doubt: the painter used an unusual technique to protect his largest painting from moisture. The researchers trust that the find will contribute to improving the conservation capacity of the work which, with 400 years of history, requires careful conservation in order to continue to delight visitors to the Rijksmuseum in Amsterdam.
