Understanding the ageing behaviour of nineteenth and twentieth century tin-weighted silks

In the late nineteenth and early twentieth centuries silks processed in Europe were frequently weighted with tin phosphate/silicate. There is particular concern over these silks in collections, since they appear susceptible to catastrophic deterioration. The aim of this research was to better understand the consequences of tin weighting on the ageing behaviour of silk, and so inform preventive conservation policies for these artefacts. Samples treated according to two authentic procedures, 'pink tin' and 'dynamite', were prepared and characterized. The mechanical performances of the silks were then assessed before and after artificial ageing. Environmental scanning electron microscopy energy dispersive X-ray spectroscopic (ESEM-EDS) analyses of the treated samples suggest that pink tin-weighted silks incorporate sodium tin(IV) phosphate with some tin(IV) oxohydroxide, while dynamite tin weighting provides a complex sodium tin(IV) aluminophosphosilicate inclusion. The mechanical strength tests reveal that although the weighted silk samples were weaker than untreated silk after their initial weighting treatment, there was a smaller decrease in strength than expected after ageing. This suggests that the long-term stabilities of the tin-weighted silks may be somewhat less problematic than previously considered, which may lead to a reassessment of current preventive conservation strategies.