Gelatine sizing and discoloration: a comparative study of optical spectra obtained from ancient and artificially aged modern papers

The role of gelatine sizing in ancient paper discoloration is still subject to debate. In this report we have addressed this issue by comparingthe optical reflectance of sized and non-sized artificially aged modern papers with reflectance data obtained from a set of ancientspecimens. We have used different ageing procedures and prepared the gelatine following methods set down in ancient recipes. Gelatinesizedaged papers showed an optical response comparable with that of ancient paper specimens, while very small reflectance modificationswere observed in pure cellulose unsized samples under the same ageing conditions. In addition, measurements carried out on puregelatine films confirmed that gelatine plays a major role in paper discoloration. Some differences in discoloration effects induced by arti-ficial and natural ageing on sized paper are discussed and a possible explanation is proposed.