Stability and durability assessment of alum-tawed skin by light transmission analysis

Abstract

Alum-tawed skin has been widely used in the past for the production of bookbindings elements because of its physical–mechanical properties and production process, easier and faster than that required for leather. Nevertheless, unlike for other skin-based materials employed in books production, such as parchment and leather, for alum-tawed skin the manufacturing process appears to be less standardized and rather few data are available in the literature on its durability and sensitivity to deterioration.In this work, a number of commercial samples of alum-tawed skin, from different manufactures and belonging to different animal species, were analysed by Light Transmission Analysis (LTA) to characterize their collagen hydrothermal stability, so as to gather useful information regarding their possible use for restoration works. The samples were then subjected to an artificial ageing process to assess their possible long term stability compared with that of some historical samples coming from 14th, 15th and 16th century bindings.The obtained results show that, as expected, the treatments the investigated alum-tawed skin samples undergo during the manufacture processes does not induce a level of stability of the collagen molecules higher than that of the vegetable and chrome tanning used for the leather treatment, although such treatment, in some cases, makes the alum-tawed skin slightly more stable than parchment. Moreover, accelerated ageing analysis showed that whatever the initial stability of the analysed samples, it decreases with ageing more rapidly and markedly than for parchment and leather, revealing a general lower durability of the alum-tawed skin to hydrothermal deterioration.