Exploring the properties and degradation of iron gall inks and logwood ink and their mixtures on various paper supports

Abstract This study investigates the properties of iron gall inks, iron logwood ink, and their mixtures on various paper supports (Whatman filter paper, machine-made paper, and historic rag paper). Samples underwent thermal accelerated ageing, and their vibrational spectra were obtained using portable Raman and FTIR spectrometers. Raman spectroscopy revealed changes in the characteristic bands of the metal complex in both iron gall and mixed inks. Changes were also observed in the Raman bands of iron logwood ink across different paper supports. The most significant changes occurred on Whatman paper, the smallest were noted on historic rag paper. These findings were corroborated by colourimetric measurements, which showed the highest total colour change on Whatman samples. Molecular changes in degraded samples, detected by non-invasive reflection FTIR spectroscopy, were most pronounced in copper-containing samples. Size-exclusion chromatography showed that iron logwood inks, like iron gall inks, contribute to the degradation of paper support.