Study of the Degradation and Conservation of Historical Leather Book Covers with Macro Attenuated Total Reflection–Fourier Transform Infrared Spectroscopic Imaging

Abstract

The analytical study of historical collagen-based materials such as leather book covers is a complex task for conservation scientists. Historical leather presents a heterogeneous composition of both organic and inorganic materials that show an evident reactivity, particularly when exposed to specific environments. Its correct preservation in archival documents remains challenging as some aspects of its chemical composition, degradation, and effectiveness of conservation treatments are still not fully understood. Here, we describe a novel application of attenuated total reflection (ATR)–Fourier transform infrared spectroscopic imaging coupled with a macro ATR accessory to study historical leather book covers. This nondestructive and high spatial resolution approach has allowed the visualization of degradation phenomena affecting this fragile material, particularly the gelatinization of collagen and, for the first time, the detection of the formation of calcium stearate (metal carboxylates or soaps). In addition, the distribution of modified soybean oil used as a treatment to maintain properties such as elasticity and hydrophobicity of the leather was studied. The effect of anomalous dispersion on the strong IR bands obtained in the ATR mode and the resulting changes to the band positions are also discussed. This research addresses issues that are relevant to the conservation of archival materials of cultural heritage for future generations.

The effect of halloysite nanotubes dispersions on vegetable-tanned leather thermal stability

“…The band at 1736 cm −1 visible only in the spectrum taken on leather grain side ( Fig. 7b) could be ascribed to the presence of waxy or fatty materials, which could have been used to finish or preserve the leather [7,62]. In addition, the high intensity band at 1025 cm −1 indicates the presence of silicates from dirt adhering to the surface of leather.…”

13C solid‐state NMR complemented by ATR‐FTIR and micro‐DSC to study modern collagen‐based material and historical leather

“…As a consequence, the fat saponification in the presence of Ca 2+ from carbonates can be triggered off and justifies the presence of specific infrared absorption bands due to the fatty acids' soaps. [2,34,41] Due to the importance of the lipid content in skin, we performed an NMR data processing for obtaining a semiquantitative ratio of the intensity of the peaks at 33 and 43 ppm related to the lipids and collagen signal, respectively (Table 4). For calf and goat parchment, the I 33.1 /I 43 ratio value is in the range 0.2-0.3, whereas its value T A B L E 3 13 C chemical shift with assignment from Aliev 14 for the parchment samples P-1, P-2 and P-3 14 ; see Table 3 reaches 1.7 for the sheep parchment characterised by the highest lipid content.…”

“…Several studies have been published in the last decade reporting the application of FTIR technique to analyse tannins in historical leather. [11,[31][32][33][34] Among them, 13 C solid-state NMR spectroscopy has proven its usefulness in characterising tanning fingerprinting in vegetable tanned leather. [23] The advantage of solid-state NMR over the widely used FTIR spectroscopy lies in the fact that the signals of collagen and aromatic molecules of tannins do not overlap in the 13 C CP-MAS spectrum.…”

“…In fact, the application of FTIR spectroscopy to characterise vegetable tannins is widely documented, [10,[26][27][28][29][30] and several researchers have also exploited its use in characterising also historical vegetable tanned leather. [11,[31][32][33][34] In addition, micro-DSC analysis provides quantitative results on the bulk material and unambiguously describes the deterioration state of historical leather identifying the key steps of deterioration process (i.e., thermal destabilisation of chemically modified and unmodified collagen, de-tanning, gelatinisation and irreversible denaturation). [35][36][37] The obtained results show that solid-state NMR spectroscopy is perfectly suitable for characterising the collagen-tannin complex in historical and archaeological vegetable tanned leathers.…”

Combined Use of Scanning Electron Microscopy–Energy-Dispersive X-ray Spectroscopy and Fourier Transform Infrared Imaging Coupled with Principal Component Analysis in the Study of Ancient Egyptian Papyri

“…3 In particular, spectroscopy has offered the opportunity for nondestructive characterization of these materials. 4,5 Thus, Raman and attenuated total reflection Fourier transform infrared (ATR–FTIR) spectroscopies have been extensively used to identify the chemical composition of selected pigments 6−8 on manuscripts, including ancient Egyptian papyri, through determination of the characteristic vibrational frequencies of specific molecular entities. In the specific case of ancient papyri and parchments, several studies demonstrated that black inks were mainly composed of carbon black and arabic gum, egg tempera, or beeswax as binders, 9 without any kind of added heavy metal (the introduction of these latter is normally traced to the advent of iron gall).…”