University of California, San Diego, researchers said samples taken from a stone wall hidden behind a fresco in the Palazzo Vecchio in Florence, Italy, appear to contain a black pigment similar to the one Leonardo used on his masterpiece "Mona Lisa," while other samples contained a red lacquer-like substance and a beige material apparently applied with brush strokes, both consistent with the presence of a painting concealed behind the fresco.
The missing da Vinci masterpiece, "The Battle of Anghiari," might have been intentionally spared by fellow artist Giorgio Vasari when Vasari later decorated the palazzo with his own frescoes, the researchers said.
Maurizio Seracini, the UC San Diego researcher who has led the search for the Leonardo for three decades, called the findings "very encouraging."
"The evidence does suggest we are searching in the right place," Seracini told the Los Angeles Times.
In the early 1500s, Leonardo was commissioned to decorate the palazzo hall with scenes of Florentine military victories, but he abandoned his partially completed painting when his experimental technique -- oil painted on a base of plaster mixed with wax or linseed oil -- failed as the plaster began to separate from the wall.
Seracini's search stirred controversy last fall when Italian conservation authorities allowed his team of researchers to drill holes through Vasari's fresco to insert tiny probes into the wall in areas where Vasari's original paint was already missing.
Hundreds of leading art historians from Europe and the United States denounced Seracini's work, saying he was destroying a known masterpiece in a problematic quest to find a missing one.