Towards a Routine Methodology for Assessing the Condition of Historic Silk

key words: Silk, fibroin, accelerated ageing, condition, yellowness index, molecular weight, sorbed moisture To ensure continued access and long-term preservation it is essential to understand the condition of an artefact, and the behaviour of its component materials, in order to set limits on display and handling. In support of curators and conservators of collections with historic textiles, we are developing rapid and routine technology, involving near infrared spectroscopy coupled with multivariate analysis, which, when applied non-invasively on-site, will allow the estimation of the state of deterioration of silk fabrics. Pursuing this aim, we have now carried out further analytical studies on silks artificially aged under different regimes for up to 20 days: dry thermal, high heat and humidity, and sunlight equivalent irradiation. The tensile strengths, yellowness indices, apparent molecular weights of fibroin, and near infrared spectral sorbed moisture parameters for the aged silks were determined. The mechanical performance of silk diminished exponentially over each ageing time course. For the various silks, the increases in yellowness indices and decreases in fibroin molecular weights and moisture contents showed similar kinetics to the mechanical changes. While each parameter was correlated with the tensile strength, silks exposed to the different accelerated ageing factors exhibited diverse correlations. It is concluded that, when formulating a general model for characterising the condition of silk using chemometrics, the reference set should include examples of silks which have been exposed to the full variety of ageing factors.