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

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.