“Cerca Trova” (Seek and Find) appears on a banner on Vasari’s mural of the Battle of Marciano

Only 15 surviving paintings are generally attributed in whole or in part to Leonardo. His responsibility for another six is disputed.

Dr. Maurizio Seracini, an engineering professor from UC San Diego, had been pursuing a quest to recover Leonardo Da Vinci’s largest painting, a 1505 fresco depiction of the 65 year earlier Battle of Angiarhi between Florence and Milan which once ornamented the Hall of Five Hundred in Florence, which disappeared in the course of a mid-16th century remodeling by Giogio Vasari, for a number of years.

The New York Times reports that scientific instruments are now ready to test Seracini’s hypothesis that Vasari simply walled-up the Da Vinci fresco.

“The Battle of Anghiari,” (was) 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? …

(N)ew 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.” …

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. …

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.

Rubens chalk, ink, and water-color copy of Da Vinci study for “The Battle of Anghiari,” Musée du Louvre