A 600-year-old Leonardo da Vinci drawing has been slowly disappearing over time. Though scientists are trying to stop or slow this process, they first have to figure out what exactly is causing it.

This is Leonardo da Vinci's self-portrait as acquired during diagnostic studies carried out at the Central Institute for the Restoration of Archival and Library Heritage in Rome, Italy. (Image source: M. C. Misiti/Central Institute for the Restoration of Archival and Library Heritage, Rome)

This is Leonardo da Vinci’s self-portrait as acquired during diagnostic studies carried out at the Central Institute for the Restoration of Archival and Library Heritage in Rome, Italy. (Image source: M. C. Misiti/Central Institute for the Restoration of Archival and Library Heritage, Rome)

A team from Italy and Poland determined the paper’s growing discoloration — its yellowing — due to oxidation is “responsible for severe visual degradation in ancient artifacts,” like this one.

“During the centuries, the combined actions of light, heat, moisture, metallic and acidic impurities, and pollutant gases modify the white color of ancient paper’s main component: cellulose,” Joanna Lojewska, a chemistry professor at Jagiellonian University in Krakow, Poland, said. “This phenomenon is known as ‘yellowing,’ which causes severe damage and negatively affects the aesthetic enjoyment of ancient art works on paper.”

The team measured and quantified the compounds known to cause the change in color in cellulose, using a non-destructive technique that relied upon light reflectance to gather their data.

What the team found specifically is that extreme humidity or a closed environment was the likely cause of the discoloration that is leading the red chalk self-portrait to disappear over time.

“The sadly poor state of preservation that characterizes Leonardo’s self-portrait today is the result of the inappropriate conditions in which it was historically stored,” the researchers wrote in the study published in Applied Physics Letters. “Unfortunately, a lack of sufficient knowledge, both physical and chemical, of the mechanisms responsible for paper degradation prevented good conservation strategies from being adopted in the past.”

Going forward, the team wants to conduct further optical analysis of the portrait over time to quantify the degradation rate of the drawing and estimate its “life expectancy.” Such continued observation, they wrote, would also be applicable to knowledge of degradation of other historical items as well.

“Needless to say, such information is invaluable to restorers and conservators. Our method has allowed us to gain a clear insight into this iconic artwork’s current state of preservation and represents an important contribution to ensuring that it will survive and be appreciated by future generations,” they wrote.

(H/T: Popular Science)