Spectral sensitivity of the discoloration of Historical rag paper

Abstract

This paper discusses the spectral sensitivity of the discoloration of historical rag paper simultaneously affected by Relative Humidity (RH) and Oxygen concentration [O2] in the ambient environment. Sacrificial samples were degraded using narrowband radiation sources centred at 450 nm, 525 nm, and 625 nm in combinations of RH and [O2] at two levels: 0% [O2] and 70% RH, 21% [O2] and 70% RH, 0% [O2] and 20% RH, and 21% [O2] and 20% RH. Diffuse reflectance was measured before and during the degradation experimental runs. Consistent qualitative results were obtained for the change in reflectance and the change in tristimulus total color change in CIELAB color space. In both cases, the increase of discoloration was modelled logarithmically over time. Among the three factors investigated in this research, wavelength of the radiation (Λ) was found to have the strongest effect. The radiation at 450 nm induced the most and fastest discoloration whereas the radiation at 625 nm induced the least and slowest discoloration. This spectral dependence was likely to be related to the photo energies at different wavelengths, but other factors were found to have played a role. Further analyses revealed that the main effects and the effects of the interactions between [O2] and Λ and between RH and Λ on the discoloration of historical rag paper were statistically significant. It suggests that managing the spectral power distribution of the radiation source can be crucial in the collection management.