Widespread use of a damaging conservation technique has seen many of Italy鈥檚 Renaissance frescoes darken and crumble. That degradation can now be stopped in its tracks.
In the 1960s conservators began coating frescoes in clear acrylic polymers to preserve them, but the treatment has had the opposite effect. 鈥淭he acrylic makes the fresco look brilliant and well preserved initially,鈥� says Piero Baglioni, a chemist at the University of Florence. 鈥淏ut as the plaster can no longer breathe, degradation beneath the coating actually speeds up, due to calcium salt and humidity build-up.鈥�
The iron-based pigments in the frescoes react with the calcium salts and water, causing them to fade and crumble all the quicker. The acrylic itself also degrades and darkens, altering the colour of the paintings, such as those at the Santa Maria Della Scala museum in Siena (pictured), lending an unnatural, plasticky sheen.
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So Baglioni鈥檚 team has developed a way to strip frescoes of acrylic without resorting to a concentrated solvent that could damage the pigments. They used a microemulsion of xylene, an oil in which acrylics are only weakly soluble. The xylene droplets are just nanometres wide, so the solvent has a large surface area. 鈥淪o the weakness of the solvent simply doesn鈥檛 matter,鈥� says Baglioni.
By soaking an inert cellulose powder in the microemulsion and applying the resulting paste to the painting for around 30 minutes, the researchers can remove the offending acrylics. They can then set to work with safer, more sustainable conservation measures.
