To reduce staining, paper conservators have increasingly treated artworks on paper with enhanced washing using chelating agents, which form complexes with metallic ions, thus facilitating the removal of stains. However, questions remain regarding the efficacy of the method and its impact on the long-term preservation of paper. A treatment of enhanced washing was undertaken on a nineteenth-century mezzotint printed using the chine collé technique, by David Lucas after a painting by John Constable, which was disfigured by significant foxing stains. This intervention provided the opportunity to investigate the mechanism and efficacy of the treatment and whether an alkali reserve could successfully be reintroduced. The print was analysed before, during, and after treatment with a Bruker M6 Jetstream scanning X-ray fluorescence (XRF) spectrometer. The results provided spatially resolved information on the effects of the treatment and gave new insights into the heavily debated causes of foxing on paper, challenging the link with iron contamination. Instead, the distribution of foxing stains showed a correlation with the presence of potassium and calcium, and their reduction during washing corresponded with an improvement in appearance. Calcium replenishment proved only partially successful. Finally, scanning XRF has rarely been used for the analysis of artworks on paper; this study proves its value for research.
Duc et al. (Fri,) studied this question.