Bacteria help restore ageing Italian frescoes
A strain of bacteria has successfully restored 14th century frescoes belonging to what was once the most extensive cycle of medieval paintings in the world, Italian researchers have announced.
The bacteria, known as Pseudomonas stutzeri, degraded the organic compounds present in the frescoes, making it possible to see figures that previously had appeared like ghosts in a thick mist.
The restored artwork, "Conversion of St. Efisio" by Tuscan artist Spinello Aretino, is part of the 14th and 15th century cycle of frescoes that decorated about 2,000 m square of the interior wall in the Camposanto cemetery in Pisa, near the Leaning Tower.
Featuring artists such as Buonamico Buffalmacco, Piero di Puccio, Antonio Venziano, Spinello di Aretino and Benozzo Gozzoli, the frescoes were regarded as masterpieces of sacred art by the pre-Raphaelite painters, and became extremely popular in the 18 and 19th century with the English aristocrats on the Grand Tour.
But in 1944, Americans forces accidentally dropped a bomb on the Camposanto. As a large restoration project began soon after the war, the paintings were detached from the walls and glued onto canvas stretched across asbestos frames.
The glue, the exposure to weather and, in a recent controversy, the use of ammonium carbonate as a cleaning solvent in the ongoing restoration, caused much of the paint to dissolve.
"Spinello Aretino's painting was in desperate condition," said Dr Claudia Sorlini of the University of Milan. "Colour pigments would have certainly vanished when using a chemical solvent Thus, we thought to use Pseudomonas stutzeri bacteria as they quickly degrade organic compounds. The result is amazing."
Found in soil and sediment Pseudomonas stutzeri is a rod-shaped organism that essentially eats nitrogen. Strains of the species have shown the ability to degrade one of the world's most serious pollutants, tetrachloroethylene - a chemical used for dry cleaning and metal degreasing.
"Pseudomonas stutzeri is a very resourceful organism, making a living in rather nutrient-poor environments, such as soil," said Dr Tom Lewis University of Vermont, a microbiologist who has carried out extensive research on the bacteria.
"They have evolved great diversity in the kinds of compounds that they are able to use for their growth, making them good candidates for breakdown of the compounds that have accumulated on very old artwork," he said. This is the first time a strain has been used in an art restoration project, he said.
Sorlini and colleagues cultured "Pseudomonas stutzeri strain A29 in the laboratory and, after specific diagnostic tests, applied them on the painting surface using compresses.
"In about 6 to 12 hours, the bacteria cleaned up to 80% of the painting. Leftovers were then removed with enzymes," Sorlini said. The treatment ended with a delicate washing of the frescoes.
Researchers are now planning to use bacteria like "Pseudomonas stutzeri on limestone and marble monuments in the attempt to remove the black crust that forms on them. Work will begin soon in Greece, at the Theatre of Epidaurus.
"This is an interesting challenge combining an interest in microbiology and beautiful works of art," Lewis said.