Chemical and Physico-Mechanical Characterizations of Leather for Restoration

Leather is a complex material mostly consisting of a matrix of collagen, chemically stabilized by various tannins. This matrix, sooner or later undergoes alterations as a consequence of interactions between their structure and environment. A comprehensive study based on multiple chemical and physico-mechanical standard tests regarding leather samples which were artificially aged from 7 to 112 days has been made at 70°C. The behavior in artificial aging of calf leather samples tanned at pilot level with two different vegetal tannins, mimosa and quebracho, were investigated due to its's similarity to the natural degradation of historical leather samples. Physico-mechanical characteristics of historical leather can be corelated with the high impact of degree of deterioration even though there are no standard regulations. To be able to choose the proper way to achieve compatibility with an appropriate material in the restoration-conservation process, multiple sample characteristic must be known. The condition of historical leather can be assessed by a series of simple visual and physical examinations which determine the flexibility, strength and coherency of the fibers and then correlate these assessments with the condition of leather as determined by various chemical and physical-chemical analyses. Therefore, the following chemical standard tests were made: volatile substances, shrinkage temperature, extractable substances, total soluble substances and the following physico-mechanical tests: tensile strength, elongation at breaking and tear resistance.