Matteo Renzi, mayor of Florence, tells reporters a fresco lost for five centuries may be hidden in city hall [Reuters]

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 on Monday still leave much mystery in the hunt for the "Battle of Anghiari", a wall mural painted by Da Vinci in Florence's storied Palazzo Vecchio, and possibly hidden behind another fresco.

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 Da Vinci'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.

Da Vinci's "Battle of Anghiari" was unfinished when the artist left Florence in 1506.

'Cerca, trova'

Maurizio Seracini, an Italian engineer from the University of San Diego, told reporters that the fragments of colour retrieved by the probe in the palace's Hall of the 1500s are consistent with pigments used by Da Vinci.

He said an analysis showed that the red, black and beige paint found is consistent with the organic paint Da Vinci used on his frescoes.

But the paint could also have been used by Da Vinci'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 Da Vinci'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 Da Vinci.

Pigment clues

"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 Da Vinci's plan to paint his 'Battle of Anghiari' with an oil technique", Seracini contended.

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 Da Vinci works, "Mona Lisa" and "St John the Baptist".

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.