The influence of soil environment on the degradation of archaeological leather

Abstract

Leather objects, found in archaeological excavations, survive in a specific environment. This leather material is very delicate and only little is known about the mechanism of its (bio)degradation in a soil environment. The main goal of this study was to clarify how leather is affected by a soil environment and why archaeological leathers have their typical properties. We tested the influence of the soil (bio)degradation processes on the mechanical properties, colour difference, morphological changes, possible absorption of additional inorganic components from soil and changes of the leather composition. The microbial activity of the soil was also analysed.

Rapid deterioration in buried leather: archaeological implications

“…Peak ratio ranges in unburied samples were dependent on tannage and dye, showcasing that the ability of amide ratios to assess degradation in archaeological vegetable-tanned leather are likely to be dependent on past manufacturing. The results presented in this paper support previous results on leather degradation, 22,40,41 where specific ratio values have been used to assess protein health in vegetable-tanned leather FTIR. For example, the amide I/amide II ratio in new leather lies between 1.25 and 1.3, whereas values above 1.8 indicate acid hydrolysis but below 1.0 demonstrate alkaline hydrolysis.…”

“…3 ). 22 Yet, leather is routinely recovered in good preservation states from Vindolanda. Thus, these results challenge claims that the leather tannins are the most important component for long term survival of vegetable-tanned leather, and that other mechanisms must be in place.…”

“…The role of post-burial perimineralisation on long term survival of non-mineral organic material like plant remains and coprolites have been researched in detail 22,23,[45][46][47][48] and shown that elemental cementation can carry an important role for the preservation of vegetable-tanned leather. Possibly, a role for post-burial elemental accumulation in leather samples, impacted by the charge of the vegetable-tannin species present in the leather, could be important for long-term stability.…”

“…2). Vyskočilová et al, 22 also noted rapid changes in buried leather samples following burial and immediate soil reaction with vegetable tannins as well as absorption of mineral salts from the soil environment. The most likely cause of the difference to WL buried leather, which appears to maintain a structure more similar to pre-burial, is early microbe and fungal activity.…”

“…16 FTIR has been applied to historical and archaeological leather samples to identify bond structures associated with tanning compounds and organic dyes, 8,[17][18][19][20][21] and in damage assessments with focus on the integrity of the collagen backbone. 22,23 Furthermore, FTIR-ATR spectra have been used on buried leather samples to detect collagen preservation and destabilisation. 7 The FTIR spectra of vegetable-tanned leather are complex, making peak assignments highly complicated, but the key components that may be reected are collagen (vegetable) tannins and lipids (specic peaks summarised in ESI, Table 1 †).…”