Scrolls, manuscripts, old books … all have in common a characteristic smell and the yellowish color of their pages. Scientists have long known that this yellowing is due to the fact that cellulose, the main component of paper, oxidizes over time. However, until now it was not known in which part of this molecule the color change occurred. A study published in Physical Review Letters solves the mystery.
The researchers compared the wavelengths emitted by ancient papers with those of modern papers that had been artificially aged. In this way they were able to locate the chromophore, which is the part of a molecule responsible for its color. In the case of cellulose, the scientists discovered that the chromophore is aldehyde, a group formed by a carbon atom that joins one of oxygen through a double bond, and another of hydrogen through a single bond.
Although this discovery could help restorers remove yellowing from paper, scientists advise caution, as chemicals intended to reverse chromophore oxidation could also damage objects.
