Manufacture, Analysis and Conservation Strategies for Historic Tapestries

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Abstract

This project aimed to address the lack of research into the mechanical properties and degradation mechanisms for historical tapestries at the fabric level and understand how effective conservation support strategies can be in the preservation of these artifacts. The research incorporated a large range of techniques from diverse disciplines including weaving, ageing, computer modeling, biochemistry and conservation science. The successful manufacture and ageing of relevant samples provided an excellent opportunity to include testing of historical samples for comparison. Tensile testing of all samples provided a valuable insight into the characteristics of degraded historical samples compared to artificially aged samples. Although individual ageing processes – including UV ageing, Relative Humidity (RH) – thermal cycling and mechanical strain ageing produced a reduction in strength, the historical samples showed a far greater loss of strength due to the combination of all types of ageing in addition to handling and pollution damage.A proteomic analysis of the wool fibres resulted in a greater understanding of the degradative “dark” wool ageing process which suggests that wool yellowing and tendering can be produced not just through photo-chemical reaction. Additionally, the chemical analysis laid an important foundation for future research into linking chemical mechanisms of damage with mechanical loss of strength. Analysis using electron paramagnetic resonance spectroscopy (EPR) provided an insight into the free radical chemistry of a range of wool/wool samples. It was observed that the light aged samples produced thiyl radicals whereas thioperoxy radicals were seen in the heat-humidity aged samples. This implies separate chemical reactions occur to produce degradation in the different ageing regimes. EPR analysis of some historical samples produced a carbon-based radical peak linked to a soot calibration signal. Further research on historical samples found phenolic radicals, possibly linked to the complex dye chemistry. Further research needs to be undertaken to fully clarify these findings.A world-wide questionnaire to textile conservators has provided a useful resource in terms of a survey of methods and materials used across the world – including technical data as well as more “ethical” motivations for conservation. The results of this survey were used along with the physical data collated in the mechanical testing as information inputted into a finite element model (FEA) to undertake the digital modeling of a tapestry hanging under its own weight. Although more research is needed to fully develop this model, a preliminary investigation has been established which can be used in future research as a tool for textile conservators across the world.

Keyword(s)

Accelerated ageing; Degradation ; EPR; Finite element analysis; Silk; Tapestry; Tensile testing; Wool

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