A red chalk sketch from around 1512 CE, long believed to be a self-portrait by Leonardo da Vinci, has a glowering, bearded man’s face emerging from a swarm of brown spots. Kept safely in the vaults of the Biblioteca Reale in Turin, the portrait’s power, despite the imperfections, has even gained rumors of supposedly magical powers. That foxing, as the mottled deterioration is called, has been a serious concern for conservators. New research may have identified the fungal culprit, which could assist in its protection.

A research team led by Guadalupe Piñar at the University of Natural Resources and Life Sciences in Vienna (or BOKU) published their findings in the December issue of Environmental Microbiology Reports, and the report is also available for open-access reading on Wiley Online Library. The researchers write that due to the “non-culturability of the microorganisms inhabiting the portrait,” identifying the exact fungus causing the foxing wasn’t possible. New non-invasive sampling for DNA analysis with scanning electron microscope (SEM) imaging and molecular techniques revealed the fungus Eurotium halophilicum from the phylum Ascomycota in the foxing spots. There was also “a high abundance of lichenized Ascomycota, while the membrane filters showed a dominance of Acremonium sp. colonizing the drawing.”

Jeffrey Marlow reports for Discover magazine that for “conservationists [sic], the message is mixed,” as the research both points to waiting for less invasive conservation technologies — he adds that if “earlier researchers had had their way in 1987, Leonardo’s drawing would have been soaked in ethylene oxide” — and taking action with available technology now. In other words, while the cause of the foxing is better identified, knowing how to address it is another problem to be solved.

According to the BOKU team, through examining photographs of the drawing, “by 1952, clear alterations comprising reddish-brown colour spots of microbial origin were already visible on the edge of the sheet,” although these didn’t seem to increase after that year. During World War II, the drawing was hidden to keep it out of Nazi hands, although whether this had any impact on its condition in the 1950s isn’t addressed. Mold on art has its own sort of beauty, if you’re into organic patterns and decay, but identifying and addressing Leonardo’s fungus condition will help assure the drawing’s presence in future centuries of our artistic canon.

h/t Mental Floss

“Amid the possible causes of a very famous foxing: molecular and microscopic insight into Leonardo da Vinci’s self-portrait” by Guadalupe Piñar, Hakim Tafer, Katja Sterflinger, and Flavia Pinzari is available to read at Wiley Online Library.