Leonardo's lost mural

A

According to historical records, in 1502 Florentine statesman Piero Soderini commissioned the artist Leonardo da Vinci to paint a fresco on the inside wall of the Hall of the Five Hundred - a room named after the 600 members of the Republic of Florence's Grand Council - which now serves as the city hall. The painting, six metres long and three metres tall, was to depict the scene of the knights of the Italian League defeating an army from Milan near the Tuscan town of Anghiari. Da Vinci, it is said, used the opportunity to try out a new oil-painting technique, but it was not very successful, possibly because of the high humidity in the hall. He never completed the mural.

B

In the 1550s, biographer and artist Giorgio Vasari was commissioned to remodel the Hall of the Five Hundred and paint several enormous murals, each four or five metres high. One mural - picturing the same battle - was to be painted over Leonardo's unfinished work, but at least one source describes Vasari as a Leonardo fan who couldn't bring himself to destroy the work.

C

Maurizio Seracini, an art diagnostician at the University of California, San Diego, has spent around 40 years on a quest to find out what happened to da Vinci's painting. He has said, 'I'm convinced it's there'. A break came in the 1970s, when he climbed a scaffold in front of Vasari's painting and spied two words inscribed on a banner one of the knights is carrying: 'cerca trova; it said, which roughly translates as 'seek and find'. Seracini took it as a clue that rather than doing what had been asked, Vasari had built a false wall in front of da Vinci's work and painted his mural on that surface instead.

D

A team led by Seracini eventually got permission to scan the entire building with high-frequency surface-penetrating radar. The scanning revealed some sort of hollow space directly behind the section of mural where the inscription had been found. To peek behind Vasari's fresco, the team planned to drill 14 strategically located centimetre-wide holes in the work. But an outcry ensued after journalists publicised the project. Some 300 Italian scholars petitioned the mayor of Florence to halt the work. But the team was making little boreholes some nine to twelve metres above the ground,' said art historian Martin Kempof of Oxford University, who wasn't involved in the work. ‘That kind of damage can be repaired invisibly.'

E

Despite the public protests, in late 2011 Seracini and his team were given permission to continue their work - but not in the 14 spots they'd originally hoped to investigate. To avoid damaging original portions of Vasari's painting, museum curators permitted them to drill only into existing cracks and recently restored spots. This time the researchers struck gold: a hollow space behind 17 centimetres of fresco and brick. They inserted an endoscopic camera into the space and took video footage of rough masonry work as well as spots that appear to have been stroked by a brush. A substance removed from the void was analysed with x-rays, and the results suggested it contained traces of black pigment.

F

Based on the x-ray data, Seracini thinks the black pigment, which is made up of an unusual combination of manganese and iron, is similar to those found in brown glazes of what is probably da Vinci's most famous painting, La Gioconda (Mona Lisa). That Seracini found components unique to Renaissance painting leads him to call the results 'encouraging evidence', yet he complained that further samples couldn't be collected because he was only permitted to work on the project within a very narrow time period. 'Unless I get hold of a piece of it, and prove that it is real paint, I cannot say anything definite, and that's very frustrating,' he said.