A new technique has been devised by researchers to save painter extraordinaire Leonardo da Vinci's portrait, which dates back to the early 1500s. The painting is fading fast and scientists have been feeling the need of developing a way to save it for a long time.

Widespread yellowing and browning of the paper has been caused by humid storage conditions for centuries. Now, an approach to non-destructively identify the concentration of light-absorbing molecules has been developed by researchers from Italy and Poland. The light-absorbing molecules are known as chromophores in ancient paper.

Chromophores are responsible for yellowing of the cellulose within ancient documents and works of art. The exposure to the combined actions of light, heat, moisture, metallic and acidic impurities and pollutant gases for centuries have modified the white color of ancient paper's main component, i.e. cellulose, said Joanna Lojewska, a professor in department of chemistry at Jagiellonian University in Krakow, Poland.

"Using a new 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", informed Adriano Mosca Conte, a researcher at University of Rome Tor Vergata in Italy.

Yellowing is a result of chromophores within cellulose absorbing the violet and blue range of visible light and largely scattering the yellow and red portions. This process leads to a yellow-brown hue, said Olivia Pulci, a professor in at University of Rome Tor Vergata.

The type of chromophores in da Vinci's self portrait is 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, CNR, in Rome, Italy.