The discovery that the color was madder is the earliest evidence for the complex chemical knowledge needed to extract the dye from a plant and turn it into a pigment, Leona reports in Tuesday's edition of Proceedings of the National Academy of Science.
The find is some 700 years earlier than any previously known use of madder, which became highly popular in the Middle Ages and provides many of the red shades and glazes in the work of the Dutch painter Johannes Vermeer.
"Tracing the use of organic colorants offers a way to follow trade routes, identify relations among archaeological objects, detect forgeries and attribute works of art," Leona wrote.
Leona refined a technique called Raman spectroscopy, which relies on the scattering of light to study materials. That process is not generally suitable for studying madder or some other dyes, but Leona enhanced the result using tiny metal particles that could amplify the findings and detect even very low levels of chemicals.
In addition to tracing madder, he was able to identify as kermes the red in the painting "St. John the Baptist Bearing Witness," from the workshop of Francesco Granacci in the early 1500s in Florence, Italy. Kermes was a dye made from the bodies of insects and was common in Europe before the importation of cochineal from the New World.
And the red color in the Morgan Madonna, dated at between 1150 and 1210, turned out to be based on lac dye, which originated in Asia and may have been imported to southern Europe by Muslim traders.
This is the first documented example of lac dye in European art before the 15th century, according to Leona. He noted that this sculpture was originally housed in the French region Auvergne, which borders Provence, where commercial records from a few decades later record importation of lac.
Karen Trentelman of the Getty Conservation Institute in Los Angeles welcomed the findings.
Such work demonstrates how "fundamental scientific research of works of art and cultural heritage materials can impact our understanding of past societies and cultures," said Trentelman, who was not involved in Leona's research.
The research was funded by the National Science Foundation, the Camille and Henry Dreyfus Foundation, the David H. Koch Foundation and the Andrew W. Mellon Foundation.
--- On the Net: Proceedings of the National Academy of Science: http://www.pnas.org