Long before there was a waterproofing layer on houses, the old Dutch master Rembrandt apparently used one in his painting. New chemical research on his 1642 masterpiece The night guardpublished in the journal Sciencehe discovered that he gave the entire painting a lead-impregnated base coat, probably to protect it from the damp exterior wall where it was first mounted.
His painting of civilian soldiers marching to defend Amsterdam was originally over four meters by five meters and was commissioned to hang in the meeting room of the Kloveniersdoelen guild where these musketeers were based.
As part of the extensive Operation Night Watch project to restore the painting inside a glass case at the Rijksmuseum, scientists investigated a painting sample using a particle accelerator, the Petra III system in Hamburg. They compared it to a lead map of the paint created with an X-ray fluorescence macro scanner and discovered a previously unknown layer of lead.
“At first we were puzzled where the lead came from in this earth’s crust,” said Fréderique Broers, a research scientist at the Rijksmuseum. The Journal of Art. “Rembrandt often used white lead pigment and yellow lead-tin [in the paint], but we found a lot of lead in the dark background, especially at the top, where we wouldn’t expect these pigments to be present. In the sample, we clearly saw that the leadership came before the [quartz-clay] ground, so the hypothesis is that he used an impregnation layer that contained lead.
“In those days there used to be single brick houses, they had fewer tools to keep the temperature more constant, and of course in the Netherlands it rains, so the humidity is high.”
At the same time, the physician to English and French royalty, Sir Théodore de Mayerne, made a guide for painters based on the development of chemical knowledge. “He describes a painting hanging on the outside wall, and due to a lot of moisture and humidity, areas of the paint came off the canvas because it had glue on it. [base]” said Broers. “He suggests that if you have a painting that is going to be hung on an exterior wall, it is better to use an oil that contains lead instead of glue. So that knowledge was there, although we did not find it before in Rembrandt or in his contemporaries”.
However, a downside to the discovery is that even more care must be taken to minimize contact with cleaning solvents. Thanks to chemical reactions over the years and previous restoration efforts, the lead has reacted with the oil paint to form globules (small glass balls) that push to the surface of the paint and sometimes fall off. “This really explains the current state of the painting,” Broers said.
