The soaring ceilings of the upper Basilica of St. Francis in Assisi, Italy, were covered in cow's milk at the time they were frescoed, a new analysis of the vaulted dome has revealed.
The discovery was made after analysis of proteins in 13th-century fresco fragments recovered when an earthquake ravaged the church in 1997.
One of the most visited pilgrimage sites in Italy, the medieval shrine of St. Francis (1182-1226) was founded in 1228, two years after his death.
The complex comprises two basilicas: a darker, lower church built around the crypt housing St. Francis' tomb, with frescoes by Giotto and Simone Martini, and the bright upper church with a spectacular ensemble of frescoes by Giotto and Cimabue.
The masterpieces were thought to be forever lost when the earthquake sent vivid scenes of saints crashing to the floor in tens of thousands of puzzle-like pieces.
In an impressive feat of restoration, Giotto's fresco of St. Jerome, broken into 40,000 pieces, was pieced together in 2002. Cimabue's fresco of St. Matthew, reduced into 120,000 bits, was fully restored in 2005.
"It has been one of the most difficult pictorial conservation efforts in Italian history," Piero Pucci, professor of biochemistry at the University of Naples, told Discovery News. "As the restorers provided us with some tiny fragments of the collapsed frescoes, we thought to analyze them."
Pucci and colleagues identified the proteins in the artworks "without ambiguity," they reported at a recent conference in Rome.
"The fragments were recovered from the ground. Nevertheless, we have been able to suppress the interference arising from protein contaminations. We are absolutely certain about the proteins we have identified -- we can say that Giotto used cow milk as a binder in his frescoes," Pucci said.
Over the centuries, different organic binders have been used by artists. The concoctions have included eggs, milk and fish remains, used alone or mixed together with oils and other materials.
According to Gennaro Marino, who teaches chemistry and biotechnology at Naples University, the discovery is particularly important because it involves frescoes considered to be at the foundation of modern Western art. Widely considered the father of Renaissance painting, Giotto turned flat, iconic Byzantine figures into more realistic three-dimensional renderings.
"This non-invasive technology provides restorers and art historians with important information. Being able to determine the chemical composition of color layers is an essential step toward choosing a proper restoration technique as well as dating of art works," Marino said.
