The creation of a soft, porous gel made it possible to blot dirt off the rough, textured surfaces of oil paintings by a leading twentieth-century painter without leaving a trace.

Museum conservators must tread a thin line between washing away an artwork’s contaminants and scrubbing off its paint. Piero Baglioni at the University of Florence in Italy and his colleagues sought a solvent-free method to clean artworks that would minimize the risk of damage.

The researchers developed a hydrogel — a soft, jelly-like solid filled with water — for the job. This involved freezing a mixture of long- and short-chain polymer molecules in water for 16 hours, during which time the molecules linked up to form a network. The shorter chains interfered with ice formation, preventing ice crystals from guiding the longer chains into neat rows. Thawing yielded a milky gel with irregular pores like those of a sponge.

When the hydrogel comes into contact with a painting, it conforms closely to even rough surfaces, and most dirt migrates into the gel’s pores. The authors dabbed dirt off two of US painter Jackson Pollock’s masterpieces, Two and Eyes in the Heat, restoring the paintings’ bright colours.