The Influence of Atmospheric Oxygen on the Color Change of Selected Historic Pigments and Dyes Caused by Narrow Band Optical Radiation

Abstract

ABSTRACT Photo-oxidation has been identified as a main cause of the light-induced color and brightness changes to which historical objects in exhibitions may be subject. Therefore, a possible approach to reduce the risk of light damage is the reduction of the oxygen content in the atmosphere surrounding these objects. In order to estimate the efficiency of this approach, this work presents a comparison of the light induced changes in the reflectance spectra of a series of 30 historical colorants kept in normal ambient air with those observed in a second series stored in nitrogen. Several of them have not been studied in anoxia yet. Chemically inert binder and substrate were used for sample preparation in order to minimize their influence on photochemical processes. In contrast to previous studies on radiative damage in anoxia, the samples were irradiated by various narrow band LED light sources covering the visible part of the electromagnetic spectrum. It becomes obvious that while a few colorants exhibit no or only minor effects due to the reduced oxygen concentration the majority benefitted significantly from this measure. Only four metal-containing pigments suffered increased damage in the nitrogen atmosphere, while three showed a complex behavior and could not be assigned to one of these groups.