Researchers struggling to solve a longstanding Leonardo da Vinci mystery -- the fate of a lost masterpiece known as the "Battle of Anghiari -- have found intriguing traces of paint hidden behind a 5-inch-thick frescoed wall in Palazzo Vecchio, Florence's 14th-century city hall.
The color is consistent with that used by the Renaissance creator of the Mona Lisa, suggesting that Leonardo's artwork has remained hidden behind that frescoed wall for more than 500 years.
Known as the "Battle of Marciano," the mural was painted by the renowned 15th-century painter, architect and writer Giorgio Vasari (1511-1574) in the imposing Hall of the Five Hundred. The hall was a room built at the end of the 15th century to accommodate the meetings of the Florentine Council.
Right behind that wall could lie one of the biggest discoveries in the history of art, according to art diagnostic expert Maurizio Seracini, director of the Center of Interdisciplinary Science for Art, Architecture and Archaeology at the University of California, San Diego, who has been searching for the lost masterpiece since the 1970s.
Three months ago Seracini's team drilled six tiny holes into Vasari's fresco, inserted a 0.15-inch-wide probe and micro-cameras and collected samples of red, white, orange and black material.
Analysis with a scanning electron microscope revealed the black material had an unusual chemical makeup of manganese and iron.
The compound corresponds to the "black pigment found in brown glazes on Leonardo's 'Mona Lisa' and 'St John the Baptist,'" Seracini said on Monday at a press conference in the Hall of Five Hundred.
Red material, most likely red lacquer, was also found. The researchers said that this kind of material is unlikely to be present in an ordinary plastered wall. High definition endoscopic images also revealed a beige material which "could only have been applied by a paint brush," the researcher said.
"Evidence suggests we are searching in the right place," Seracini said.
"The Battle of Anghiari" has a mysterious history. It was conceived in 1503, when Leonardo and Michelangelo received twin commissions to paint on opposite walls of the Palazzo Vecchio.
Both murals were to represent historic Florentine victories, and the commissions reinforced the intense rivalry between the two artists.
While Michelangelo never got past a sketch of his "Battle of Cascina," Leonardo began to paint the "Battle of Anghiari" on June 6, 1505, when he was 53. The mural would celebrate the Florentines' victory over Milanese troops in 1440.
In his 1550 book "Lives of the Artists," Vasari said that Leonardo painted only a portion of the 12- by 15-foot fresco. It was a battle known as the "Fight for the Standard," which represented "the rage and fury both of the men and the horses," Vasari wrote.
He also said that Leonardo abandoned the project because of technical problems arising from his experimental mixing of oil paint and fresco.
Historians, however, have questioned Vasari's conclusion. Some speculated that he made up the story, and that the fresco actually was completed.
Hailed by Leonardo's contemporaries as his finest work, the "Battle of Anghiari" now survives in several preparatory drawings and sketches by the master himself and in a Rubens drawing which was inspired by an anonymous copy of the fresco.
Ten years after writing his account of the "Battle of Anghiari," Vasari was hired to modify the council room into the Hall of Five Hundred, a hall dedicated to the ruling Medici family.
In the course of this work, Leonardo's mural disappeared.
It wasn't the only artwork to dissolve. Working on the city-wide renovation plan devised by Duke Cosimo I to celebrate the Medici family, Vasari had to sacrifice masterpieces such as Masaccio's Trinity in the church of Santa Maria Novella.
Yet he did not destroy the work; he just bricked it over and added his own fresco, the "Madonna of the Rosary."
Masaccio's work remained obscured until 1861, when Vasari's wall was removed.
In 2000, at a da Vinci conference, leading scholar Carlo Pedretti proposed that Vasari saved Leonardo's masterpiece just as he had Masaccio's.
The conference prompted Seracini to carry out sophisticated tests that involved the use of laser scanners, X-ray machines, and thermographic and radar equipment.
The only nonfictional living character mentioned in "The Da Vinci Code," Seracini found a Dan Brown-like clue in the wall housing the "Battle of Marciano."
There, on a tiny painted green flag, Vasari wrote: "Cerca, trova -- seek and you shall find."
A radar survey carried out last year revealed the presence of a hollow space between Vasari's "Battle of Marciano" and the original stone wall.
The existence of the air gap was confirmed by the team's probe, strongly pointing to the bricked-up theory. "No other gaps exist in the Hall of Five Hundred," the researchers said.
Matteo Renzi, the mayor of Florence, said he had asked the Italian government for permission to carry out further drilling in over a dozen areas where the Vasari's fresco no longer exists.
"We need to know how much is left of the painting. We are not some crazy art vandals. We are curious people who are not afraid of solving one of art history's greatest mysteries," Renzi said.