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Vanishing da Vinci

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SOURCE Applied Physics Letters

Studying a Famous Leonardo Self-Portrait, a Team of Scientists Has Developed a New, Nondestructive Way to Gauge Degradation of Ancient Paper Art and Docs

WASHINGTON, June 3, 2014 /PRNewswire-USNewswire/ -- One of Leonardo da Vinci's masterpieces, drawn in red chalk on paper during the early 1500s and widely believed to be a self-portrait, is in extremely poor condition. Centuries of exposure to humid storage conditions or a closed environment has led to widespread and localized yellowing and browning of the paper, which is reducing the contrast between the colors of chalk and paper and substantially diminishing the visibility of the drawing.

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A group of researchers from Italy and Poland with expertise in paper degradation mechanisms was tasked with determining whether the degradation process has now slowed with appropriate conservation conditions -- or if the aging process is continuing at an unacceptable rate.

To do this, as they describe in Applied Physics Letters, from AIP Publishing, the team developed an approach to nondestructively identify and quantify the concentration of light-absorbing molecules known as chromophores in ancient paper, the culprit behind the "yellowing" of the cellulose within ancient documents and works of art.

"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," explained Joanna Lojewska, a professor in the Department of Chemistry at Jagiellonian University in Krakow, Poland. "This phenomenon is known as 'yellowing,' which causes severe damage and negatively affects the aesthetic enjoyment of ancient art works on paper."

Chromophores are the key to understanding the visual degradation process because they are among the chemical products developed by oxidation during aging and are, ultimately, behind the "yellowing" within cellulose. Yellowing occurs when "chromophores within cellulose absorb the violet and blue range of visible light and largely scatter the yellow and red portions -- resulting in the characteristic yellow-brown hue," said Olivia Pulci, a professor in the Physics Department at the University of Rome Tor Vergata.

To determine the degradation rate of Leonardo's self-portrait, the team created a nondestructive approach that centers on identifying and quantifying the concentration of chromophores within paper. It involves using a reflectance spectroscopy setup to obtain optical reflectance spectra of paper samples in the near-infrared, visible, and near-ultraviolet wavelength ranges.

Once reflectance data is gathered, the optical absorption spectrum of cellulose fibers that form the sheet of paper can be calculated using special spectroscopic data analysis.

"Using our approach, we were able to evaluate the state of degradation of Leonardo da Vinci's self-portrait and other paper specimens from ancient books dating from the 15th century," said Adriano Mosca Conte, a researcher at the University of Rome Tor Vergata. "By comparing the results of ancient papers with those of artificially aged samples, we gained significant insights into the environmental conditions in which Leonardo da Vinci's self-portrait was stored during its lifetime."

The article, "Visual degradation in Leonardo da Vinci's iconic self-portrait: a nanoscale study" is authored by A. Mosca Conte, O. Pulci, M.C. Misiti, J. Lojewska, L. Teodonio, C. Violante, and M. Missori. It will appear in the journal Applied Physics Letters on Tuesday, June 3, 2014 (DOI: 10.1063/1.4879838). After that date, it can be accessed at: http://scitation.aip.org/content/aip/journal/apl/104/22/10.1063/1.4879838

ABOUT THE JOURNAL
Applied Physics Letters features concise, rapid reports on significant new findings in applied physics. The journal covers new experimental and theoretical research on applications of physics phenomena related to all branches of science, engineering, and modern technology. See: http://apl.aip.org

Jason Socrates Bardi
+1 240-535-4954
jbardi@aip.org

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