The Inherent Acidic Characteristics

Silks are frequently a cause of concern for conservators and curators. Amongst other critical challenges, textile acidity is considered to pose a risk. Consequently, it is common practice to carry out pH measurements when assessing condition. Enhanced acidity is usually ascribed to previous processing treatments, adsorbed pollutants, and oxidative deterioration. However, the results of the detailed study reported in this paper suggest that increased acidity of silk is an expected consequence of ageing, irrespective of the effector of deterioration. Degummed Bombyx mori silk fabric was subjected to artificial ageing by light, heat and heat plus high humidity, in air. The tensile strength of the fabric gradually decreased under each of the ageing regimes, seeming to follow first order decay. The pH values of saline extracts of the silks similarly decreased. There was a correlation between the tensile strength and the apparent acidity of the aged silks, which was independent of the ageing factor, at least to a 50% drop in performance. While the tensile strength of silk was compromised to a similar degree by high temperature plus high humidity ageing in nitrogen, anoxic conditions generated a five-fold lower increase in apparent acidity.