Towards in-situ monitoring of tapestry degradation using strain-based engineering techniques

Tapestries are large and heavy and damage may be caused while they are on continuous display, not only because of their sensitivity to the environment but also through the stress imposed by their own weight. This load becomes more significant as the tapestry ages and its component materials degrade. The effects of deformation under a constant load are well understood within engineering and procedures exist for monitoring deformation. Applying engineering techniques to the monitoring of damage caused by hanging tapestries would enable areas of degradation to be identified before it is apparent that damage is occurring. Such monitoring would allow the optimum time for conservation treatment to be predicted and different methods of treatment to be quantitatively evaluated. It would help to ensure that funding available for conservation is used most effectively. The work would have wider applications for the treatment of other textiles. Although such techniques have recently been applied in the cultural heritage sector, this remains a small and pioneering field and these techniques have not been applied to tapestry conservation.

The interdisciplinary research team at the University of Southampton, consisting of researchers from the Textile Conservation Centre (TCC) and the School of Engineering Sciences, has completed a pilot study investigating a number of possible techniques for monitoring tapestries. The work examined contact and non-contact techniques, including optical fibre strain gauges, electronic speckle pattern shearing interferometry (ESPSI), thermography and photoelasticity.

The results of the pilot study indicated that optical fibres can be attached directly to a tapestry-like material and that the strain is transferred to the sensors. Optical fibres are the most suitable permanent monitoring device for monitoring the strain locally. The study also showed that 3-D photogrammetry using digital image correlation is the most suitable technique for whole-field monitoring, allowing the entire tapestry to be monitored quickly and without direct contact. The two techniques would be used in tandem, the fibre-optic sensors acting as a reference to validate the data from the photogrammetry technique.

The current proposal is aimed at developing these techniques into a hybrid system which can be used to monitor tapestries in-situ. A post-doctoral researcher will take responsibility for developing the application of the optical fibres, while a PhD student will develop the photogrammetry technique. The major challenge will be to apply the two techniques together so that strain readings from the optical fibres provide calibration for the photogrammetry. The final stage of the project will be to apply the methodology to both a custom-woven tapestry incorporating optical fibres in its structure and to a historic tapestry belonging to one of the project partners, Historic Royal Palaces, English Heritage or the National Trust. The successful result will be a fully operational monitoring system that can be installed unobtrusively in a historic house environment. The optical fibre component will be hidden from view. The photogrammetry equipment will be portable so that it can be introduced for periodic testing and then removed.

The three investigators, Frances Lennard, Dr Janice Barton and Dr Alan Chambers, will manage the project with Dinah Eastop, Senior Lecturer TCC, and Associate Director of the AHRC Research Centre for Textile Conservation and Textile Studies, the fourth member of the current project team. An advisory panel made up of representatives from the heritage field and other researchers will provide additional support.