Art researchers in Italy say they have found evidence that may lead to the uncovering of a lost masterpiece by Leonardo da Vinci.
They believes samples from a hidden wall in the Palazzo Vecchio in Florence contain traces of paint used only by the Renaissance master.
They say tiny probes sent through drilled holes in Giorgio Vasari's fresco "The Battle of Marciano in the Palazzo Vecchio" found black pigment of the same type used in the "Mona Lisa".
The project's leader, Maurizio Seracini, believes Da Vinci's unfinished fresco "The Battle of Anghiari" lies beneath Vasari's work.
Da Vinci started painting the fresco - considered by some to be his finest work - in 1504 but is thought to have abandoned it because of problems arising from his experimental oil painting technique.
The room was later renovated and Vasari painted his fresco in 1563.
Mr Seracini believes Vasari did not want to destroy Da Vinci's work and instead bricked it up behind a new wall on which he painted.
His theory was stimulated after finding a soldier on Vasari's work holding a small flag bearing the words: "He who seeks, finds."
Not everyone is convinced
But historians at a news conference in Florence have stressed the research is not conclusive, and further chemical analysis needs to be carried out.
The research has been controversial, with some art experts signing a petition to stop the investigation because the drilling is damaging Vasari's existing work.
An art historian who has led the opposition to the research, Tomaso Montanari, says he does not consider the findings credible.
"What do they mean by saying the findings are compatible with Leonardo?" he asks. "Any painting from the Renaissance would be. Anything from that era could be painted on that wall."