Contribution to the characterization of foxing stains on printed books using infrared spectroscopy and scanning electron microscopy energy dispersive spectrometry

• ATR-FTIR and SEM/EDS analyses on paper (19th–mid-20th centuries) damaged by biological foxing.
• Typical FTIR profiles for mold grown on paper significantly different from Paper profile.
• In foxing spots, intensity of IR absorption increases slightly within the 1700–1500 cm−1 region and IR absorption at 1570 cm−1 may be considered as a marker of biological foxing.
• No difference in elemental composition between foxed spots and unfoxed areas for a given book and consistency in FTIR profiles of foxed spots for a given book.
• Advantages and disadvantages of each technique are discussed.

This study is part of research on the biological foxing formation affecting some old documents and explores the potential of ATR-FTIR spectroscopy to characterize foxing spots on paper from nine printed books, dating from early 19th century to mid-20th century. Preliminary assays allowed to highlight clear differences in FTIR spectral profiles between molds and the paper substrate on which they grew. However, spectra of foxed paper spots showed solely the absorption bands of cellulose due to very low amount of fungal elements inside the spots. Foxing spots were successfully differentiated from unstained areas of the paper by a slight intensity increase in the 1500–1700 cm−1 region and the appearance of small representative band near 1520 cm−1 which could be used as a marker for biological foxing. Comparative elemental analysis by SEM-EDS was also carried out with the intention of revealing other significant differences between the inside and the outside of spots. At this stage of the study, the findings are not totally conclusive. However, the overall results achieved by these two techniques encourage further research to gain a better understanding of biological foxing.