The Behavior of Sheep Leather Parchment to Artificial Ageing

Parchment used for restoration, book binding and art requires special performance on physical-chemical, organoleptic and aesthetic characteristics, but also good long-term stability. In this sense, the parchment is ecologically processed, with features that ensure firmness, fullness, light resistance, dimensional stability, thermal stability, malleability, flexural/pressure bending resistance. For a good behaviour in time and to artificial ageing, it is found that in the case of parchments made/obtained from sheepskin, the fat or volatile matter content must be as low as possible. The parchment with these qualities allows for the creation of new covers or historical replicas, complements for the integration of old covers, hot and/or cold stamping modelling, incision, entrainment, deposition of gold and silver foil, colouring and decoration with pigments and dyes. Some niche areas such as book bindings and art require a dedicated craftsmanship that promotes the survival of artisanal forms of production and the perpetuation of local creativity and identity. The parchments have undergone artificial ageing treatments based on the concomitant action of temperature and relative humidity for up to 16 days. Chemical (volatile matter, extractable substances, total ash, total nitrogen, dermal) and physical-chemical (measurement of colour variation and shrinkage temperature) analyses were performed to evaluate colour parameters and collagen hydrostability. The fat content of the parchment leads to oxidation reactions that cause the bathochromic effect, closing the colour, but also the deterioration over time of the fibrillar structure by depreciating the contraction temperature.