The only generally recognized self-portrait of Leonardo da Vinci, ravaged by time over five centuries and considered by many as beyond repair, may be saved with new technology, scientists say.

The red chalk drawing, which has been the victim of fungi and has been marred by spots and blotches since the 1500s, was created on paper made of cotton, linen and hemp that is slowly changing color.

The paper is turning yellow and brown with age, and as it does so the contrast level between the paper's color and the colors of chalk used to create the image is reduced, causing the drawing's visibility to slowly fade.

Experts in Poland and Italy set themselves the task of analyzing molecules in the ancient paper called chromophores, which absorb light and have caused the yellowing in many examples of ancient works of art and documents.

"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," says chemist Joanna Lojewska at Jagiellonian University Poland.

Comparing their findings on the da Vinci work with studies of other examples of paper from various centuries, researchers said they garnered insights into the conditions under which the portrait has been stored over the years.

 "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 study authors reported in the journal Applied Physics Letters.

Determining exactly how much degradation the portrait has experienced over its lifetime and the conditions that have led to it will help preservationists in their efforts to save the fading work from further damage, the researchers said.

For several decades in the 20th century, the portrait was framed and on public display in Italy in Turin's Royal Library, where it was exposed to sunlight.

The portrait, which art historians say was likely done in Turin, is currently stored in a humidity- and temperature-controlled vault in the library in an attempt to arrest further yellowing and damage from light.

Not all art experts believe to the work to be a self-portrait of Leonardo; they point out that at the time the work was completed, sometime around 1510, he was in his 50s, while the work's subject appears to a man much older.

Some experts have suggested it could be a portrait of da Vinci's father or an uncle.

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