A Lost Picasso? Alloy Composition Profiles Could Help Identify, Date And Authenticate Bronzes

Researchers from Northwestern University, together with collaborators from the Art Institute of Chicago, have completed the first comprehensive survey of the alloy composition of a large number of cast bronze sculptures by major European artists from the first half of the 20th century.

The researchers classified the unique composition profiles of 62 modern sculptures by linking data from the alloy composition of these sculptures with parameters from art history, including artist, foundry, casting methods and casting date.

These profiles -- where a sculpture’s metal composition is akin to DNA’s genetic information -- could be used as another method to identify, date and even authenticate sculptures.

The study is published online in the journal Analytical & Bioanalytical Chemistry.

The foundries of the early 20th century were quite secretive about the bronze composition they used, to prevent other foundries from producing a superior product. This suggests that alloy composition may be sufficient to identify which foundry cast a particular sculpture.

Bronzes are copper alloys containing various amounts of tin, zinc and other metals whose presence alter the alloy’s melting temperature and fluidity, the strength and hardness of the sculpture, its resistance to corrosion, and its color and patination (the chemical process by which a patina forms).

Not all sculptures carry a foundry mark or have documentary evidence to identify where and when they were cast. In some cases, the same sculpture was cast at various dates, with gaps spanning years or even decades. An in-depth knowledge of bronze composition is therefore important to the art historian and connoisseur studying 20th century sculptures and trying to address questions of authenticity, origin and artist intention.

The research team, led by Marcus Young while a postdoctoral fellow in the lab of Northwestern Professor David Dunand, used a form of optical emission spectroscopy called ICP-OES to determine the metal composition of 62 bronze sculptures cast in Paris during the first half of the 20th century.

The sculptures studied, from the collections of the Art Institute of Chicago and the Philadelphia Museum of Art, included works by Matisse, Picasso, Renoir and Rodin, among other masters.

The researchers showed that the sculptures consist of copper, with zinc and tin as major alloying elements, varying over a broad range of compositions. They were able to group the sculptures into three distinct types: high-zinc brass, low-zinc brass and copper-tin bronze.

These three groups show good correlations with the artist, the foundry, the casting date and the casting method. For example, the high-zinc brass alloys correspond to most of the Picasso sculptures cast in lost-wax at the Valsuani foundry after World War II.

“By expanding the ICP-OES database of objects studied, these material correlations may become useful for identifying, dating or possibly even authenticating other bronzes that do not bear foundry marks,” the authors concluded.

In addition to Young (now at Ruhr-University Bochum in Germany) and Dunand, James N. and Margie M. Krebs Professor of Materials Science at Northwestern’s McCormick School of Engineering and Applied Science, other authors of the paper are Joseph Lambert, professor of chemistry in the Weinberg College of Arts and Sciences at Northwestern, and Francesca Casadio, A.W. Mellon Conservation Scientist, and Susie Schnepp, associate conservator of objects, both of the Art Institute.

The research is part of the McCormick School’s ongoing collaboration with the Art Institute of Chicago, which is led by Katherine T. Faber, Walter P. Murphy Professor of Materials Science and Engineering, for Northwestern, and Casadio, for the Art Institute.