"Long before it's in the papers"
January 27, 2015


Scientists in race against time to save vanishing Da Vinci “self-portrait”

May 29, 2014
Courtesy of the American Institute of Physics
and World Science staff

Sci­en­tists are try­ing to save a Leonardo da Vin­ci draw­ing, widely be­lieved to be a self-portrait, from slowly dis­ap­pear­ing. If they suc­ceed, the re­sults could help them save many oth­er an­cient art­works and doc­u­ments, they say.

The da Vin­ci portrait (Cred­it: M. C. Misiti/Cen­tral In­sti­tute for the Res­to­ra­tion of Ar­chi­val and Li­brary Her­it­age, Rome)

Cen­turies of ex­po­sure to hu­mid­ity or a closed en­vi­ron­ment has led to yel­low­ing and brown­ing of the pa­per with the red chalk draw­ing, so the col­ors no long­er stand out. A group of re­search­ers from Italy and Po­land is work­ing to find out wheth­er the de­grada­t­ion pro­cess has now slowed with ap­pro­pri­ate con­serva­t­ion, or if the ag­ing is still a prob­lem.

To do it, the team de­vel­oped a way to meas­ure the con­centra­t­ion of light-ab­sorbing mo­le­cules known as chro­mo­phores in an­cient pa­per—the cul­prits be­hind the “yel­low­ing” of the pa­per’s cel­lu­lose, or plant fi­ber. 

To­geth­er, “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 chem­ist at Jagiel­lonian Uni­vers­ity in Krakow, Po­land.

Chro­mophores form as a re­sult of chem­i­cal re­ac­tions with ox­y­gen. Yel­low­ing oc­curs when they ab­sorb vi­o­let and blue colors from vis­i­ble light “and largely scat­ter the yel­low and red portions—re­sult­ing in the char­ac­ter­is­tic yel­low-brown,” said Oliv­ia Pulci, a phys­i­cist at the Uni­vers­ity of Rome Tor Ver­gata.

Af­ter de­vel­op­ing a way to meas­ure the con­centra­t­ion of chro­mophores, re­search­ers used sim­ula­t­ions based on quan­tum me­chan­ic­s—which stud­ies nat­u­ral in­ter­ac­tions at the sub­a­tom­ic lev­el—to cal­cu­late what col­ors the chro­mo­somes ab­sorb most.

“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,” Leonar­do’s time, 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.”

They found that the type of chro­mophores in Leonar­do’s draw­ing are “si­m­i­lar to those found in an­cient and mod­ern pa­per sam­ples aged in ex­tremely hu­mid con­di­tions or with­in a closed en­vi­ron­ment, which agrees with its doc­u­mented his­to­ry,” said Mau­ro Mis­sori, a re­search­er at the In­sti­tute for Com­plex Sys­tems, in Rome. But re­search­ers must per­i­od­ic­ally re­peat the test to de­ter­mine how fast the pa­per is ag­ing, they added. “Our ap­proach can serve as a pre­cious tool to pre­serve and save not only this invalua­ble work of art, but oth­ers,” Conte said.

The work is de­scribed in the jour­nal Ap­plied Phys­ics Let­ters.

* * *

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Scientists are trying to save a Leonardo da Vinci drawing, widely believed to be a self-portrait, from slowly disappearing. If they succeed, the results could help them save many other ancient artworks and documents, they say. Centuries of exposure to humidity or a closed environment has led to yellowing and browning of the paper with the red chalk drawing, so the colors no longer stand out. A group of researchers from Italy and Poland is working to find out whether the degradation process has now slowed with appropriate conservation, or if the aging is still a problem. To do this, in a study described in the journal Applied Physics Letters, the team developed a way to measure the concentration of light-absorbing molecules known as chromophores in ancient paper. These are the culprits behind the “yellowing” of the cellulose, or plant fiber, in the paper. Together, “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 chemist at Jagiellonian University in Krakow, Poland. Chromophores form as a result of chemical reactions with oxygen. 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,” said Olivia Pulci, a physicist at the University of Rome Tor Vergata. After developing a way to measure the concentration of chromophores, researchers used simulations based on quantum mechanics—which studies natural interactions at the subatomic level—to calculate what colors the chromosomes absorb most. “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,” Leonardo’s time, 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.” They found that the type of chromophores in Leonardo’s drawing are “similar to those found in ancient and modern paper samples aged in extremely humid conditions or within a closed environment, which agrees with its documented history,” said Mauro Missori, a researcher at the Institute for Complex Systems, in Rome. But researchers must periodically repeat the test to determine how fast the paper is aging, they added. “Our approach can serve as a precious tool to preserve and save not only this invaluable work of art, but others,” Conte said.