FLORENCE (AP).- Researchers may have discovered traces of a lost mural by Leonardo da Vinci by poking a probe through cracks in a 16th-century fresco painted on the wall of one of Florence's most famous buildings.

The latest findings Monday still leave much mystery in the hunt for the "Battle of Anghiari," a wall mural painted by Leonardo in Florence's storied Palazzo Vecchio, and possibly hidden behind a fresco done by Giorgio Vasari decades later.

The hunt for the unfinished mural has captivated art historians for centuries, and took on fresh impetus in the last years with the employment of state-of-art scientific tools.

Some believe Leonardo's mural, which he began in 1505 to commemorate the 15th-century victory by Florence over Milan at the medieval Tuscan town of Anghiari, may be hidden behind a newer wall, which was frescoed over decades later by Giorgio Vasari. Leonardo's "Battle of Anghiari" was unfinished when Leonardo left Florence in 1506.

Maurizio Seracini, an Italian engineer from the University of California, San Diego, told reporters that the fragments of color retrieved by the probe in the palace's Hall of the 1500s are consistent with pigments used by Leonardo. He said an analysis showed that the red, black and beige paint found is consistent with the organic paint Leonardo used on his frescoes.

But the paint could also have been used by Leonardo's contemporaries in Florence, which is awash in Renaissance art. Seracini called the results "encouraging" but preliminary.

To find samples of pigment of the wall behind a space previously discovered under the Vasari, work, experts slipped probes through areas where paint on the outer wall's fresco was either cracked or flaked off, noted Cristina Acidini, the head of Florence's cultural heritage and museums.

For one sample, a probe was slipped into a spot near a downward thrusting sword in Vasari's work. For another sample, the probe went through a point near the head of a horse, with its eye open wide as if startled.

Seracini was inspired by the word's "Cerca, trova," ("seek and you shall find") which were painted on a tiny flag in Vasari's painting depicting a different battle. Those who think Leonardo's work might be hidden behind the later wall painting contend it is unlikely that Vasari, famed for his biographies of Renaissance artists, would have destroyed any masterpiece by Leonardo.

"We have found these very special black pigments, and there are some traces of red," Seracini told reporters. The red is a kind of lacquer "used for oil painting. And this element matches Leonardo's plan to paint his Battle of Anghiari' with an oil technique," Seracini contended.

The hunt for the missing Leonardo mural is being led by the National Geographic Society and the University of California, San Diego, in partnership with the city of Florence. Experts from Florence's world renowned art restoration institute, Opificio delle Pietre Dure, also were involved.

"These data are very encouraging," said Seracini, a National Geographic Fellow. "Although we are still in the preliminary stages of the research, and there is still a lot of work to be done to solve this mystery, the evidence does suggest that we are searching in the right place," said a National Geographic statement quoting Seracini.

Seracini and his colleagues note that some black material found behind Vasari's wall shows a chemical composition similar found in brown glazes in two Leonardo works, "Mona Lisa" and "St. John the Baptist."

Flakes of red material that were found appear to be organic pigments, the researchers said. A study of high-definition endoscopic images "suggests" that a beige material spotted on the original wall was applied by a paint brush, the researchers aid.

Previously, using radar and X-rays, Seracini and his team found a cavity behind Vasari's fresco that they think could indicate a space between two walls.

Florence Mayor Matteo Renzi said one plan aims to remove some parts of the Vasari fresco which were restored in the 19th and 20th centuries, to look behind them. "We are sure that the "Battle of Angiari' is behind" Vasari's work, he said.

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Frances D'Emilio contributed from Rome



Copyright 2012 The Associated Press.