Restoring artwork with nanostructured fluids

The first step in framing a watercolor, charcoal sketch, or other work on paper is to mount it on a mat by means of hinges. In the 19th century and earlier, hinges were made of paper backed with glue. By the middle of the 20th century, framers began to use the newly available pressure-sensitive tape or, to use a more familiar name, sticky tape. Old sticky tape can discolor an artwork, and if it was misapplied, disfigure it. Removing old tape is tricky. Pulling it off could damage the paper. Using a solvent to dissolve the tape risks leaving a watermark. To tackle the challenge, Nicole Bonelli of the University of Florence and her collaborators have developed an approach based on a hydrogel and nanostructured droplets. The hydrogel consists of a covalently linked polymer network that holds water. A conservator can shape a rectangular piece of the gel so that it fits exactly over the piece of sticky tape to be removed. The nanostructured droplets consist of a solvent covered with surfactant molecules. Confining the solvent in both the gel and the droplets ensures that it does not spread beyond the tape and that just the right amount is used. Lab tests demonstrated that for two types of tape used in galleries and museums today, the droplets made their way to the tape’s backing and dissolved it. Among the first artworks to receive the new treatment was a 16th-century sketch that resembles one of the male figures in Michelangelo’s fresco The Last Judgment (a detail of which is shown here). When a piece of tape at the bottom of the sketch was removed, the words “di mano di Michelangelo” (“from Michelangelo’s hand”) were revealed. Why would anyone conceal proof of provenance? Possibly because Michelangelo rarely signed his works, so it could have been an attempt to pass the sketch off as genuine. (N. Bonelli et al., Proc. Natl. Acad. Sci. USA 115, 5932, 2018, doi:10.1073/pnas.1801962115 .)