NORTHWESTERN (US)—Could bronze sculptures have their own DNA-like fingerprint? Researchers are analyzing the alloy composition of works by artists such as Picasso and Matisse to pinpoint when and where the metal masterpieces were cast.

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 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, formerly a postdoctoral fellow in the lab of David Dunand, a professor at Northwestern—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 others.

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 researchers conclude.

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

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