Assessment of the Effect of Various Bleaching Agents on Papers with Foxing Stains

Abstract

The study evaluated the effect of various chemical bleaching agents on the long-term colour stability of paper and on the discoloration caused by foxing stains. Five different historical paper samples, covered with foxing stains, were characterized. Several spots were tested for the presence of transitional metal ions using laser-ablation-ICP-MS; the fibre composition and pH of the paper were also determined. Colour changes, experienced by the discoloured areas and the paper after washing and deacidification and subsequent to the application of one of the five different bleaching solutions investigated, were followed using scanned images. CIELAB values were determined with Photoshop 7.0 software. The effect of different bleaching solution applications on the colour stability of the treated paper during thermal ageing was evaluated as well. Results indicate that when higher concentration of iron ions are present in the paper, treatment with the complexing agent EDTA and sodium dithionite efficiently brightens the foxing stains and the paper and improves their colour stability. In this study, it was shown that for papers with low transitional metal content, washing and deacidification, as well as the application of sodium borohydride, gave superior results when compared to hydrogen peroxide or calcium hypochlorite treatments.