Magazine article Science News

Cleaning Treasures: Safer Solvents for Restoring Frescoes

Magazine article Science News

Cleaning Treasures: Safer Solvents for Restoring Frescoes

Article excerpt

By suspending small amounts of solvents in nanoseale droplets, chemists have found an environmentally safer method of cleaning centuries-old frescoes and saving them from the unintended consequences of previous restorations.

The preservation of historic frescoes often involves firming up the paint and slowing its degradation by oxygen, light, and air pollution. In the 1970s, synthetic resins seemed like an ideal fix. Conservators began coating frescoes with protective layers of these acrylic polymers. However, the use of the synthetic chemicals created unforeseen problems, says Piero Baglioni, a chemist at the University of Florence.

For one thing, the polymers obstructed microscopic pores within the paint, preventing the natural perspiration of the underlying walls. This accelerated the accumulation of damaging salts, such as sulfates, under the coating.

Furthermore, within 2 decades, the protective layers themselves began to degrade. They often turned yellow from photooxidization, and they tended to shrink, creating stresses on the underlying paint, says Baglioni's collaborator Rodorico Giorgi.

Conservators began using solvents to remove the polymers. But the solvents were toxic materials such as aromatic compounds, which could be hazardous to the user. Moreover, the solvents couldn't clear the paint's pores, according to Baglioni. "It's impossible to remove these resins using a normal solvent," he says.

In the 1990s, Baglioni's team began replacing pure organic solvents with less toxic, water-based microemulsions of the aromatic compounds. That meant using surfactants to suspend the solvents in microscopic droplets of water. …

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