(8 Dec 2014) LEADIN:
Leonardo da Vinci's self-portrait has survived 500 years of yellowing, staining, and fading.
To assess its health without touching it, Italian scientists have developed a new technique that could become the golden standard in paper preservation.
STORYLINE:
Sitting under dim lights at the Royal Library in Turin, Leonardo da Vinci's iconic, self-portrait is a high-profile patient for paper conservationists.
The paper on which Leonardo laid his hand to draw his face is as tired and worn-out, as the old man in it.
Blemishes dot his nose, cheeks and forehead - a dark stain marks his beard. Scientists say, the result of 500 years of poor care.
"The main problem of the paper, on which Leonardo drew his self-portrait, is the diffused yellowing, and the presence of localised stains that we call foxing," says physicist Mauro Missori. "In our opinion, such a phenomenon was caused by an inappropriate conservation of the self-portrait during its life, especially in highly humid environments and probably in closed containers," he adds.
Turin Royal Library archives suggest that great damage was caused in 1929-1930, when the self-portrait was moved to a new frame, and hung in front of a window, awash with morning sunlight.
World War II then forced the Leonardo sketch into exile in Rome, to avoid the risk of aerial bombardment. Another tough trip for the delicate work.
Missori's findings were published in the Scientific Journal of Applied Physics Letters last June. His results resonated throughout the conservation world. Reaching a definitive diagnosis however, was no easy feat. Missori and his team were not allowed to sample, swab or even touch the paper.
They could only rely on its looks.
This instrument called a multi-channel spectrometer, measures the exact colour of paper. New paper looks white because the cellulose -which makes up the paper- is intact and can reflect the entire spectrum of light. Yellowed paper instead, absorbs the blue spectrum and reflects only yellows and oranges.
This means the paper has started deteriorating under the effect of humidity, visible light and UV rays, pollution and microorganisms. Cellulose breaks down. In turn, new molecules called chromophores appear.
Since 1998, the Royal Library in Turin keeps Leonardo's portrait inside a special underground vault - like a bunker for the arts, that only opens on special occasions.
This month until mid January 2015, visitors of the library will have the opportunity to see this and other Leonardo sketches with their own eyes.
"Here, there is a constant temperature of 20 degrees Celsius, a constant relative humidity of 55 percent, with minimum variations," says Turin Royal Library director, Mauro Saccani. "This allows the best conservation for our documents."
The portrait's fragile state has also caused debate among art historians. The "foxing" and fading have put in doubt the identity of the man in the portrait. Art historian Paola Salvi says it's definitely Leonardo da Vinci.
"The eyes (in the self portrait) are rotated in the same way that a person would have if he were looking into a mirror with his head rotated by three quarters. This detail is not immediately visible because of the alterations in the paper; alterations that you can see with UV florescent light."
"Also, a direct comparison to the side portrait preserved in Windsor, has shown that the two subjects depicted are in fact the same person. Here, at about age 50, and in the Turin paper, about 65 years old," she adds.
Salvi calls Missori's research groundbreaking.
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