Unusual PaintingUnusual Lead Compound

Micro and Macro X-Ray analysis detects lead formate in Rembrandt’s The Night Watch

Rembrandt van Rijn was one of the most important 17th century Dutch painters. His most famous painting The Night Watch
(1642) hangs in Amsterdam’s Rijksmuseum. An international team has now
identified lead formate-a compound very unusual for paintings-in various
areas of The Night Watch. The results presented in the journal Angewandte Chemie
provide clues about the pictorial practices of Rembrandt and the
reactivity of lead driers in the oil matrices of historical paintings.

Unusual Painting-Unusual Lead Compound - Micro and Macro X-Ray analysis detects lead formate in Rembrandt's <i>The Night Watch</i>

© Wiley-VCH, re-use with credit to ‘Angewandte Chemie’ and a link to the original article.

“Operation Night Watch” is a comprehensive research and
conservation project in which conservators, art historians, and other
scientists across various disciplines are collaborating closely on
Rembrandt’s Night Watch. As part of this project, the composition
and distribution of materials were examined by macro-X-ray powder
diffraction mapping. Synchrotron-based micro-X-ray powder diffraction
and infrared microscopy studies were also carried out in parallel on
tiny samples. This made it possible for the team from the Rijksmuseum,
the University of Amsterdam (the Netherlands), the CNRS, and the
European Synchrotron Radiation Facility (France), and the University of
Antwerp (Belgium), among others, to identify and map various lead
compounds present in Rembrandt’s paint layers.

Lead pigments were widely used by Rembrandt. The most common was white lead, a mixture of lead carbonates hydrocerussite Pb3(CO3)2(OH)2 and cerussite PbCO3.
Lead is also present in other pigments, and their associated alteration
products. However, one discovery made by the team headed by Victor
Gonzalez, Ida Fazlic, and Marine Cotte was more unusual: lead(II)
formate Pb(HCOO)2-a compound that has never before been found
in historical oil paintings. Lead formate, the lead salt of formic
acid, was found in several areas of The Night Watch-sometimes together with plumbonacrite Pb5(CO3)3O(OH)2, another rare lead compound.

To investigate the chemical origin of lead formate, the team produced
model paint layers according to old recipes. For example, siccative oil
was prepared by heating linseed oil, the most common binding agent for
paints at the time, with lead oxide PbO. Lead oxide is a metallic dryer,
causing paints to harden more quickly.

The study showed that PbO in oil paint can react to form lead formate. Even though no crystalline PbO was detected in The Night Watch,
the results support the hypothesis that an oil containing such a lead
dryer was used. But other hypotheses have to be considered. Past
conservation works on The Night Watch, notably the possible addition of an oil-based varnish in the 18th
century could have favored the formation of lead formate on the
painting. The team is now investigating the kinetics of lead formate
formation, and their stability in oil paint.

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