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Analytical Chemistry

Plastic film decodes the chemistry of priceless art objects

Noninvasive method samples the surfaces of historical paintings, frescoes, and more.

by Sarah Webb
March 20, 2017 | APPEARED IN VOLUME 95, ISSUE 12

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Credit: Anal. Chem.
This plastic film containing hydrophobic and ion-exchange resins captures molecules on the surface of art.
Credit: Anal. Chem.
This plastic film containing hydrophobic and ion-exchange resins captures molecules on the surface of art.

Beyond their beauty and cultural significance, art objects are covered with chemicals that provide a window into their history—how they were created, taken care of, and where they’ve been. But conservators have limited options for analyzing the surface chemicals without damaging the irreplaceable artwork. In a bid to help, a research team has reported an updated version of a noninvasive method for removing molecules from a range of surfaces and analyzing them using mass spectrometry (Anal. Chem. 2017, DOI: 10.1021/acs.analchem.6b03722). Pier Giorgio Righetti of Politecnico di Milano and his colleagues previously developed an extruded plastic film made from ground-up hydrophobic and cation-exchange resin beads contained in a poly(ethylene-vinyl acetate) binder. They’ve now added anion-exchange beads to expand the range of compounds that can be detected. They dampen a strip of the film with water and set it on a surface of interest to draw chemicals into the film for analysis. The researchers next elute proteins with an ammonium acetate buffer, and they recover dye molecules with a mixture of methanol and formic acid. Then they analyze the compounds using LC/MS. The team tested the method on parchment, canvas, bone, and linens. In addition, they analyzed two 16th-century frescoes and a 14th-century wood painting and found proteins and dyes consistent with the times. Tests of reference molecules on control materials showed that the process removes no more than 10% of the compounds, meaning the technique is noninvasive, the researchers say.

Credit: Anal. Chem.
To find the origin of its red pigment, researchers sampled a small area (blue square) on this 68.5 cm by 78.5 cm 14th century wood painting, “San Francesco, Santi, Madonna che allatta il Bambino, San Pietro, San Paolo, Santi, la Trinità, San Giovanni Battista, Santo Vescovo, San Gerolamo,” by Pietro Gal gallo.
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