THE INHERENT ACIDIC CHARACTERISTICS OF SILK, PART II – WEIGHTED SILKS

Silk is found in many textiles of cultural and historic significance,but these fibres may deteriorate rapidly underadverse conditions, so are of particular concern to conservatorsand curators. Measurement of pH is common practicewhen assessing condition, as enhanced acidity is oftenascribed to previous processing and treatment, adsorbedpollutants and oxidative deterioration, but recent researchhas demonstrated that the increased acidity of silk is anexpected consequence of ageing, irrespective of the causeof deterioration. The study presented here builds on thisearlier work to assess the role that common silk processingmethods (bleaching and metal salt weighting) have onthis phenomenon. Tensile strength was used as a marker ofdeterioration, independent of mechanism, and was comparedwith pH values of saline extracts of various silk samples.These samples included surrogates, prepared usinghistorically accurate methods and subject to acceleratedageing, as well as a range of historic materials. It was seenthat most samples followed the same correlation betweenpH and strength as seen in the previous work. However,silks weighted with tin salts appeared to be buffered (in therange pH 6.75-7.05), irrespective of their mechanicalintegrity.