The paints used in many works of art contain additives that are often sensitive to cleaning solvents, so art conservators must weigh the risks of damaging works against the benefits of cleaning them. To ease this burden, Piero Baglioni and colleagues at the University of Florence have created poly(vinyl alcohol) (PVA) gels that can be placed directly on paintings, absorb soil, and be removed without damaging the texture or pigment (Proc. Natl. Acad. Sci. U.S.A. 2020, DOI: 10.1073/pnas.1911811117).
First, researchers mix high- and low-molecular-weight PVAs in an aqueous solution, then subject the mixture to one or three freeze-thaw cycles. During the freezing process, ice grows in dendrite-like needles. Because the mixture consists of two types of PVA, these ice needles are disordered, allowing for the formation of large, disordered pores, similar to those of a sponge. The pores remain after the mixture is thawed. Baglioni says the resulting product—called a twin-chain polymer hydrogel—has never been previously synthesized. “This is a new class of gel,” he says. In collaboration with the Peggy Guggenheim Collection, the researchers tested the gels on two solvent-sensitive Jackson Pollock paintings. The gel removed soil without damaging the pigment. Baglioni says his team’s next paper, to be published in Heritage Sciencelater this year, will describe cleaning the Picasso painting L’Atelier.