If you believe, as Maurizio Seracini does, that Leonardo da Vinci’s greatest painting is hidden inside a wall in Florence’s city hall, then there are two essential techniques for finding it. As usual, Leonardo anticipated both of them.
First, concentrate on scientific gadgetry. After spotting what seemed to be a clue to Leonardo’s painting left by another 16th-century artist, Dr. Seracini led an international team of scientists in mapping every millimeter of the wall and surrounding room with lasers, radar, ultraviolet light and infrared cameras. Once they identified the likely hiding place, they developed devices to detect the painting by firing neutrons into the wall.
“Leonardo would love to see how much science is being used to look for his most celebrated masterpiece,” Dr. Seracini said, gazing up at the wall where he hopes the painting can be found, and then retrieved intact. “I can imagine him being fascinated with all this high-tech gear we’re going to set up.”
Dr. Seracini was standing in the Palazzo Vecchio’s grand ceremonial chamber, the Hall of 500, which was the center of Renaissance politics when Leonardo and Michelangelo were commissioned to adorn it with murals of Florentine military victories. On this July day of 2009, it remained the political hub, as evidenced by the sudden appearance of Florence’s new mayor, Matteo Renzi, who was rushing from his office to a waiting car.
The scientific lecture ceased as Dr. Seracini moved quickly to intercept the mayoral entourage. He was eager to use the second essential strategy for retrieving a Leonardo painting in Florence: find the right patron.
That has always been a good tactic in the home of the Medicis and bureaucrats like Machiavelli, a friend of Leonardo’s who signed the contract commissioning the battle mural. Dr. Seracini, an engineering professor at the University of California, San Diego, had spent years in bureaucratic limbo waiting to try his neutron-beam technique, but he saw this new mayor as his best hope yet for finding Leonardo’s work.
The quest had begun more than three decades earlier with a clue fit for a Dan Brown novel. In 1975, after studying engineering in the United States, Dr. Seracini returned to his native Florence and surveyed the Hall of 500 with a Leonardo scholar, Carlo Pedretti.
They were looking for “The Battle of Anghiari,” the largest painting Leonardo ever undertook (three times the width of “The Last Supper”). Although it was never completed — Leonardo abandoned it in 1506 — he left a central scene of clashing soldiers and horses that was hailed as an unprecedented study of anatomy and motion. For decades, artists like Raphael went to the Hall of 500 to see it and make their own copies.
Then it vanished. During the remodeling of the hall in 1563, the architect and painter Giorgio Vasari covered the walls with frescoes of military victories by the Medicis, who had returned to power. Leonardo’s painting was largely forgotten.
But in 1975, when Dr. Seracini studied one of Vasari’s battle scenes, he noticed a tiny flag with two words, “Cerca Trova”: essentially, seek and ye shall find. Was this Vasari’s signal that something was hidden underneath?
The technology of the 1970s did not provide much of an answer. Dr. Seracini went on to make his name with scientific analyses of other works of art, and to found the Center of Interdisciplinary Science for Art, Architecture and Archaeology at U.C.S.D. In 2000 he returned to the hall with new technology and a new financial patron, Loel Guinness, a British philanthropist. By taking infrared pictures and laser-mapping the room, Dr. Seracini’s team discovered where the doors and windows had been before Vasari’s remodeling.
The reconstructed blueprint, combined with 16th-century documents, was enough to locate the spot painted by Leonardo. It also offered a potential explanation for Michelangelo’s failure to do anything more than an initial sketch for his mural: He must have been miffed that Leonardo was assigned a section of the wall with much better window light.
“This room is huge, but it wasn’t big enough for both Michelangelo and Leonardo,” Dr. Seracini said. (Visit nytimes.com/tierneylab for more details.)
The new analysis showed that the spot painted by Leonardo was right at the “Cerca Trova” clue. The even better news, obtained from radar scanning, was that Vasari had not plastered his work directly on top of Leonardo’s. He had erected new brick walls to hold his murals, and had gone to special trouble to leave a small air gap behind one section of the bricks — the section in back of “Cerca Trova.”
But how could anyone today know what lay behind the fresco and the bricks? How could anyone peer six inches into the wall without harming the historic fresco on the surface?
Dr. Seracini was stymied until 2005, when he appealed for help at a scientific conference and got a suggestion to send beams of neutrons harmlessly through the fresco. With help from physicists in the United States, Italy’s nuclear-energy agency and universities in the Netherlands and Russia, Dr. Seracini developed devices for identifying the telltale chemicals used by Leonardo.
One device can detect the neutrons that bounce back after colliding with hydrogen atoms, which abound in the organic materials (like linseed oil and resin) employed by Leonardo. Instead of using water-based paint for a traditional fresco in wet plaster like Vasari’s, Leonardo covered the wall with a waterproof ground layer and used oil-based paints.
The other device can detect the distinctive gamma rays produced by collisions of neutrons with the atoms of different chemical elements. The goal is to locate the sulfur in Leonardo’s ground layer, the tin in the white prime layer and the chemicals in the color pigments, like the mercury in vermilion and the copper in blue pigments of azurite.
Developing this technology was difficult, but not as big a challenge as getting permission to use it. Dr. Seracini kept running into political and bureaucratic dead ends. So when he saw the new mayor dashing across the Hall of 500 that July afternoon, Dr. Seracini rushed at the chance for a personal to appeal to Mr. Renzi, who had been a fan of the project before his election.
With the politesse of a Medici, the mayor paused and listened, then promised to further this artistic endeavor once he had dealt with his first batch of election pledges.
“My dream is to see this discovery very soon,” Mr. Renzi said. “Soon” can be a highly relative term in Italian bureaucracies, but the mayor did indeed go on to restart the approval process and meet with one of the current patrons of the project, the National Geographic Society. Last week, the mayor said he expected it to proceed shortly.
“We are very willing to give Professor Seracini permission,” Mr. Renzi said Thursday. “The only issue that remains concerns timing — who does what. Within a week or two it should get the go-ahead.”
Once he gets permission, Dr. Seracini said, he hopes to complete the analysis within about a year. If “The Battle of Anghiari” is proved to be there, he said, it would be feasible for Florentine authorities to bring in experts to remove the exterior fresco by Vasari, extract the Leonardo painting and then replace the Vasari fresco. Of course, no one knows what kind of shape the painting might be in today. But Dr. Seracini, who has extensively analyzed the damages suffered by many Renaissance paintings, said that he was optimistic about “The Battle of Anghiari.”
“The advantage is that it has been covered up for five centuries,” he said. “It’s been protected against the environment and vandalism and bad restorations. I don’t expect there to be much decay.”
If he is right, then perhaps Vasari did Leonardo a favor by covering up the painting — and taking care to leave that cryptic little flag above the trove.