Abstract
In this study we used an analytical approach based on complementary techniques that targets all structural levels of collagen in leather to investigate how vegetable-tanned leather deteriorates during soil burial tests. For the first time, a group of deterioration markers specific to molecular, fibrillar and fibrous structure of collagen in leather was associated with the deterioration of buried leather. The application of the second order derivative of FTIR-ATR spectra analysis allowed us to detect loosening of collagen–tannin matrix, de-tanning and gelatin formation based on the behaviour of collagen and tannin spectral components (intensity variation and shifts). Collagen denaturation observed by DSC analysis and its thermo-oxidative behaviour measured by TG/DTG analysis, as well as the altered morphology of collagen (namely melt-like fibres and distorted fibrillar ultrastructure) imaged by SEM confirmed the FTIR-ATR analyis results. These analytical outcomes enabled us to understand the effect of leather hardening/cementing through soil mineral penetration into its fibrous structure and thus correctly interprete the higher-than-expected shrinkage temperatures and intervals determinatd by MHT method. Thus, MHT method proved to be suitable for a quick evaluation method that can direcly support the first conservation decision after excavation. The combination of FTIR-ATR, DSC, TG/DTG and SEM can be particularly useful to provide insights on the deterioration mechanism of archaeological leather and support best decision on its long-term preservation.
Highlights
Materials, whether natural or created by humans, sooner or later undergoes alterations as a consequence of the interaction between their structure and environment
Effects of leather burial on collagen shrinkage activity by Micro Hot Table (MHT) method It was shown that the hydrothermal stability of new, undamaged leather depends on the tannin type, animal species and processing method, and influences leather resistance against deterioration [24,25,26,27]
The analytical approach based on Fourier transform infrared spectroscopy (FTIR)-Attenuated total reflection (ATR), differential scanning calorimetry (DSC), Thermal gravimetry (TG)/Differential thermal gravimetry (DTG), MHT and Scanning electron microscopy (SEM) provided clear evidences that could help understanding deterioration of archaeological leather
Summary
Whether natural or created by humans, sooner or later undergoes alterations as a consequence of the interaction between their structure and environment. Leather can be considered as the first biomaterial ever produced. It was one of the major materials in the past, and its use continues into the present. Its wide usability is the reason why leather artefacts are frequently found during archaeological excavations. The varied properties of leather that provide such a wide use are due to the intrinsic chemical, morphological and physical properties of collagen, to the species from which it originates, and to the method with which hide was processed.
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