Public Release: 14-Jan-2019
The secret to Rembrandt’s impasto unveiled
Rembrandt van Rijn revolutionized painting with a 3D effect using his impasto technique, where thick paint makes a masterpiece protrude from the surface. Thanks to the ESRF, the European Synchrotron, Grenoble, France, three centuries later an international team of scientists led by the Materials Science and Engineering Department of the Delft University of Technology and the Rijksmuseum have found how he did it. The study is published in Angewandte Chemie .
Impasto is thick paint laid on the canvas in an amount that makes it stand from the surface. The relief of impasto increases the perceptibility of the paint by increasing its light-reflecting textural properties. Scientists know that Rembrandt, epitome of the Dutch Golden Age, achieved the impasto effect by using materials traditionally available on the 17thcentury Dutch colour market, namely lead white pigment (a mixture of hydrocerussite Pb3(CO3)2(OH)2 and cerussite PbCO3), and organic mediums (mainly linseed oil). The precise recipe was, however, unknown until today.
Plumbonacrite, Pb5(CO3)3O(OH)2 is the mysterious, missing ingredient of the impasto effect, researchers from The Netherlands and France have discovered. It is extremely rare in historic paint layers. It has been detected in some samples from 20th century paintings and in a degraded red lead pigment in a Van Gogh painting. “We didn’t expect to find this phase at all, as it is so unusual in Old Masters paintings”, explains Victor Gonzalez, main author of the study and scientist at the Rijksmuseum and Delft University of Technology. “What’s more, our research shows that its presence is not accidental or due to contamination, but that it is the result of an intended synthesis”, he adds.
The European Synchrotron, ESRF, played an essential role in these findings. The team sampled tiny fragments from the Portrait of Marten Soolmans (Rijksmuseum), Bathsheba (The Louvre) and Susanna (Mauritshuis), three of Rembrandt’s masterpieces. Using the ESRF’s beamlines, they quantified the crystalline phases in Rembrandt’s impasto and in the adjacent paint layers, modelled the pigment crystallites morphology and size and obtained crystalline phase distribution maps at the microscale.
The samples were less than 0.1mm in size, requiring the small and intense beam delivered by the synchrotron. The scientists analysed them on two ESRF beamlines, ID22 and ID13, where they combined High-angular Resolution X-Ray Diffraction (HR-XRD) and micro-X-Ray Diffraction (μ-XRD) . “In the past, we have already successfully used the combination of these two techniques to study lead-white based paints. We knew that the techniques can provide us with high quality diffraction patterns and therefore with subtle information about paint composition”, explains Marine Cotte, scientist at the ESRF, 2018 Descartes-Huygens Prize laureate for her research on art conservation.
The analysis of the data showed that Rembrandt modified his painting materials intentionally. “The presence of plumbonacrite is indicative of an alkaline medium. Based on historical texts, we believe that Rembrandt added lead oxide (litharge) to the oil in this purpose, turning the mixture into a paste-like paint”, explains Cotte.
The breakthrough yields the path for the long-term preservation and conservation of Rembrandt’s masterpieces. However, the number of samples studied is not extensive enough to assess if lead white impastos systematically contain plumbonacrite. “We are working with the hypothesis that Rembrandt might have used other recipes, and that is the reason why we will be studying samples from other paintings by Rembrandt and other 17th Dutch Masters, including Vermeer, Hals, and painters belonging to Rembrandt’s circle”, explains Annelies van Loon, scientist at the Rijksmuseum.
In addition to this, the team will reconstruct specific impasto-like samples, preparing and ageing them under CO2 rich and CO2 free atmospheres (to assess the origin of carbonates in plumbonacrite) and in humid and dry conditions (to assess the effect of water). This work, led by the Materials Science and Engineering Department of the Delft University of Technology and the Rijksmuseum is a collaboration between academia (Institut de Recherche de Chimie Paris, Sorbonne University and University of Amsterdam), Cultural Heritage research institutes (C2RMF: Centre de Recherche et des Restauration des Musées de France), museums (Rijksmuseum and Mauritshuis) and the ESRF.
Delphine CHENEVIER, Head of Communications, ESRF, email@example.com, +33 (0)6 07 16 18 79
Victor Gonzalez, Rembrandt Rijksmuseum: V.Gonzalez@rijksmuseum.nl
Marine Cotte, ESRF: firstname.lastname@example.org
Here’s some additional info of the issue of Plumbonacrite from Natural Pigments founder George O’Hanlon (posted to his Painting Best Practices Facebook page):
Plumbonacrite—Secret of Painting Like Rembrandt?
“Plumbonacrite is closely related to hydrocerussite, but has a different chemical composition (less carbonate). Both minerals are forms of lead white. The traditional, more ancient lead white is trilead dicarbonate dihydroxide, which is also referred to as ‘basic lead carbonate’. Its formula is the same as that of the mineral hydrocerussite. Lead carbonate, which has the same formula as the mineral cerussite, often occurs as a minor component in lead white. Why the excitement recently about finding plumbonacrite in three of Rembrandt’s best-known works—"Portrait of Marten Soolmans,” “Bathsheba” and “Susanna”?
Plumbonacrite was believed to be a modern synthetic pigment, until the mineral was reclassified in 2012, and is now recognized to form in nature. Plumbonacrite has received scarce attention regarding its geochemical formation and behavior. Previous methods to synthesize it were based on complex experimental conditions that frequently yielded this mineral mixed with the more common hydrocerussite. Plumbonacrite has been identified in paint samples from twentieth-century paint and paintings. It was found in commercial grounds from the colourman Lefebvre-Foinet (Paris) used in several paintings by the Canadian artist Jean-Paul Riopelle (1923–2002).
According to the scientists who discovered it in Rembrandt’s paintings, it appears to be an intentional addition to his paint and may have formed in situ within the impasto layers, in alkaline conditions of lead oxide (litharge) in an alkaline environment, and is one reason for the excitement among conservation scientists. However, some artists recently got excited probably thinking it will give them access to the painting techniques of Rembrandt. Poppy ■■■■! As though using a specific material will make you a better painter, much less paint like Rembrandt.
When exposed to carbonate rich solutions, litharge becomes unstable and converts to plumbonacrite. This mineral is stable in alkaline solutions above 10 pH. Since the plumbonacrite form of lead white has a different basicity than the hydrocerussite form (which is the more common form of lead white), it may have an influence on the drying rate of oil and the formation of soaps. Since the formation of plumbonacrite likely occurs during drying of the paint, it is unlikely that it would directly influence the behavior of the paint. What is interesting about this finding is how this form of lead white may influence the drying and stability of the paint, not its initial handling properties.
Will this secret ingredient help artists paint like Rembrandt? Not likely. It is interesting and certainly understanding the materials of old masters can add to the arsenal of modern painters, and perhaps help them to produce contemporary masterpieces. Regardless, I love it when a mineral or pigment can get artists excited about painting. Anything that gets artists excited about their materials and work is a good thing in my book.
Source: Victor Gonzalez, Marine Cotte, Gilles Wallez, Annelies van Loon, Wout de Nolf, Myriam Eveno, Katrien Keune, Petria Noble, Joris Dik, “Identification of Unusual Plumbonacrite in Rembrandt’s Impasto by Using Multimodal Synchrotron X‐ray Diffraction Spectroscopy,” Angewandte Chemie International Edition, 7 January 2019.”