Spectral Changes of Paper Exposed to Ambient Solar Radiation

Solar radiation is known to be responsible for the photodegradation of materials including works of art and artefacts in the outdoor environment. Paper is one of the most light sensitive materials, because light can cause its darkening and fading. Damage goes beyond visual alteration by attacking the physical structure of paper, causing weakening and embrittlement. Ultraviolet (UV) radiation is hazardous and its damage is cumulative. Such effect can also occur in shaded rooms, due to the combined action of artificial and natural light sources. Thus, a better knowledge of UV radiation effect on paper would help both cultural heritage and paper manufacturing techniques. The present pilot study aims to analyse spectral absorbance changes in paper sheets exposed to ambient solar radiation in Rome during a field campaign held in July 2006. Ambient solar UV doses were recorded by means of spectral and broad band instruments. Results show that the absorbance changes were significant at wavelengths below 400 nm and that photodegradation proceeded faster during the first hours of exposure. A multivariate analysis taking into account wavelengths between 290 and 325 nm, paper sheets absorbance changes and the corresponding absorbed doses is carried out and preliminary results are presented. Possible archeometric applications are also proposed