The Inherent Acidic Characteristics of Aged Silk

Silks are frequently a cause of concern for conservatorsand curators. Amongst other critical challenges, textileacidity is considered to pose a risk. Consequently, it iscommon practice to carry out pH measurements whenassessing condition. Enhanced acidity is usually ascribedto previous processing treatments, adsorbed pollutants,and oxidative deterioration. However, the results of thedetailed study reported in this paper suggest thatincreased acidity of silk is an expected consequence ofageing, irrespective of the effector of deterioration.Degummed Bombyx mori silk fabric was subjected to artificialageing by light, heat and heat plus high humidity, in air.The tensile strength of the fabric gradually decreasedunder each of the ageing regimes, seeming to follow firstorder decay. The pH values of saline extracts of the silkssimilarly decreased. There was a correlation between thetensile strength and the apparent acidity of the aged silks,which was independent of the ageing factor, at least to a50% drop in performance. While the tensile strength of silkwas compromised to a similar degree by high temperatureplus high humidity ageing in nitrogen, anoxic conditionsgenerated a five-fold lower increase in apparent acidity.