Deterioration Characteristics of Various Simulated Samples of Ancient Tanned Leathers: A Comparative Study by Shuli Yao, Hailiang Yang, Haoyue Li, Yue Yu, Ya-nan Wang, Yang Zhou, Bi Shi and Yunhang Zeng

Abstract

Archaeological leathers were tanned using different methods. 
However, the influence of tanning methods on the long-term stability of these leathers remains unclear. In this study, artificially aged leather samples with varying degrees of deterioration were prepared using antique smoke, vegetable, and aluminum tanning techniques, along with accelerated aging via composting. The samples were analyzed, and results indicated that the smoke-, vegetable-, and aluminum-tanned leathers exhibited surface roughness; color change; disruption of the collagen fiber network; reduced porosity; and decreased thermal stability, mechanical strength, and softness as the degree of deterioration increased. Furthermore, different trends in moisture and collagen (assessed via hydroxyproline) contents were observed in all the artificially aged samples compared with their unaged counterparts. Smoke-tanned leather exhibited reductions of 40.61% in moisture and 75.49% in hydroxyproline after five days of ageing, and aluminum-tanned leather showed reductions of 34.4% in moisture and 76.30% in hydroxyproline after 10 days of ageing. Conversely, vegetable-tanned leather showed increments of 54.69% in moisture and 35.66% in hydroxyproline after 30 days of ageing. This phenomenon occurred because the hygroscopicity of the vegetable tanning agent was higher than that of the two other agents, and the degradation of vegetable tannins was more rapid than that of collagen during deterioration. These findings demonstrate the important effects of tanning methods on the deterioration of archaeological leathers and suggest that accurate identification of the tanning method is vital for predicting deterioration trends and designing effective preservation strategies for these artifacts.