New X-ray imaging analyses of the masterpiece indicate an unexpected lead layer, possibly applied as a precaution during the canvas preparation, according to a new research paper published in Science Advances. The work was part of the Night Watch conservation process at the Rijksmuseum, the largest interdisciplinary research and preservation project for the famous Rembrandt painting, dedicated to the long-term preservation of the artwork.
Previous Analyses of Rembrandt’s Paintings
Previous analyses of Rembrandt’s paintings indicate his use of several pigments in his works, including lead white, ochre, bone black, vermilion red, madder red, azurite, smalt blue, madder yellow, and lead tin yellow, among others. The artist rarely used pure blue or green pigments, except for the Belshazzar’s Feast. The Rembrandt database serves as a good source for comprehensive documentation of the various investigative reports.
Discovery of the New Lead Layer
Earlier this year, researchers involved in the Night Watch conservation process discovered rare traces of a compound called lead formate in the painting. They scanned approximately half a square meter of the painting’s surface using powder-dispersive X-ray imaging (along with other methods) and analyzed small fragments of the painting using micro X-ray scanning devices. This revealed the presence of lead formate – which is surprising in itself – but the team also identified this formate in areas where there were no lead, white, or yellow pigments. It may be possible that lead formate can disappear relatively quickly, which could explain its absence in works by Dutch artists thus far. But if this is the case, why did lead formate not disappear in the Night Watch? And where did it come from in the first place?
New Analyses and Conclusions
This new paper sheds further light on the painting by focusing on the preparatory layers applied to the canvas. It is known that Rembrandt used a base of quartz clay for the Night Watch – something he likely did for the first time, perhaps because the enormous size of the painting “prompted him to seek a cheaper, lighter, and more flexible ground layer” than the red earth and lead white and cerussite he was known to use in his earlier works, the authors suggest.
According to the authors, this is the first time that three-dimensional X-ray imaging techniques have been employed: the fluorescent X-ray technique and the nano X-ray imaging technique using ptychography. The authors point out that the analysis of small volumes of historical paintings usually relies on two-dimensional imaging techniques (such as optical microscopy, scanning electron microscopy, and synchrotron X-ray spectroscopy), which provide only partial information about the size, shape, and distribution of pigment particles beneath the visible surface.
Three-dimensional imaging methods capture more details in comparison, revealing the presence of the previously unknown (and unexpected) lead-containing layer located directly beneath the ground layer. The authors note that this could be due to the use of a lead compound added to the oil used to prepare the canvas as a drying agent – perhaps to protect the painting from the harmful effects of moisture. (An adhesive is typically applied before the ground layer.)
The Night Watch was originally hung in the “Great Hall” of the Amsterdam militia training school and faced the windows. The authors note that since the Middle Ages, red lead in oil has been used to preserve stone, wood, and metal against moisture, citing a contemporary source that mentions the use of oil rich in lead instead of traditional glue to prevent the canvas from separating after years of exposure to wet environments. The newly discovered lead layer may be the reason for the unusual lead prominence in areas of the Night Watch that lack other lead-containing compounds in the paint. It may be possible that the lead migrated to the ground layer of the painting from that underlying lead oil preparatory layer.
Source:
Science Advances, 2023. 10.1126/sciadv.adj9394
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