Monitoring at Intech & Institute of Physics Report

Institute of Physics Public Engagement Grant Scheme 2008, Round 2

Sensing tapestry deterioration - final report

Professor Janice Dulieu-Barton
University of Southampton, School of Engineering Sciences

Background

A multidisciplinary project is being carried out by art conservators, physicists and engineers; there are two PhD students and one RA working on the project. It is funded by the Arts and Humanities Research Council and supported by the National Trust, Historic Royal Houses and English Heritage. The aim of the project is to use a range of optical sensors to monitor the strain in historic tapestries to inform conservation decisions and make timely repairs. The project is now approaching completion; there has been considerable success in applying the sensors to tapestries. A tapestry has been designed by textile students at Winchester School of Art. The tapestry design is shown in Figure 1 and conveys the connection between art and science. The colours reference historic tapestries, with the red and blue colours being specifically drawn from two tapestries, the 14th Century Apocalypse Tapestries (Chateau D’Angers, France), referred to as "the most famous medieval tapestry” (1), and the 15th Century Devonshire Hunting Tapestry “The Boar and Bear Hunt” (Victoria and Albert Museum, London) - “the only great fifteenth century hunting tapestries to have come down to us” (2). The use of text can be seen in historic tapestries, and aids the communication of the meaning of the tapestry, and in particular, the project. The formula expresses how stress is calculated, “the measure of the average amount of force exerted per unit area”. The words Diffuses and Reflects refer to the two light-based monitoring techniques being used (digital image correlation and optical fibre sensors).

The purpose of the tapestry is to provide an opportunity to fully integrate sensors in a new tapestry; this is more difficult with a historic tapestry. The idea is to assess deformation in the early stages and compare these readings to those taken from older textiles. Along side the integrated sensors a novel non contact optical technique is also used to obtain the strain. In the original proposal it was intended to hang the tapestry in the conservation laboratory. However, this was considered to be inappropriate as the tapestry was costly to produce due to the traditional hand weaving process and too striking to be hidden in a laboratory. Figure 2 shows a photograph of the tapestry in the loom. It was decided that communication of science display would provide an excellent opportunity to obtain maximum value from this beautiful artefact. The funding from IOP has made this possible.

The purpose of the IOP grant was to provide funds to create a display that explains the purpose of the project and describes the concept of strain as measure that indicates condition and levels of deterioration. The display explains in terms that are understood by the non expert the science behind optical fibre sensors and using image correlation techniques to obtain 3D deformation maps. The display brings together conservation science, Physics through sensors and optics and engineering through structural assessment. The tapestry is now installed at INTECH - a hands-on interactive science and technology centre in Winchester – see Figure 3. INTECH was chosen as it is an ideal venue to communicate the project to the public, across the wide age range catered for at INTECH. The report explains how the display was designed and installed at INTECH and the launch event in May.

Display

A frame has been designed, and manufactured to allow the long term display and monitoring of the tapestry whilst it is on public display. For INTECH to accept the display it must be professional quality and the funds from IOP supported the design of the display and its manufacture by technicians from INTECH. A sketch of the frame design can be seen in Figure 4. It comprises a backing to mount the display and a Perspex screen to protect the tapestry. Another important feature is portability and a further objective was to design a portable hanging display for the tapestry, so that it can be moved to different locations and venues. The use of such a frame has allowed the project team to develop a monitoring methodology that is suitable for in-situ monitoring of tapestries. Furthermore it has permitted the impact of monitoring on the viewing public and from a scientific point of view the effect of working in a restricted space. Figure 5 shows a photograph of the tapestry mounted in the frame

Tapestry Monitoring

It is known that tapestries respond to temperature and humidity changes. A sensor has been installed adjacent to the display which continuously records temperature and humidity. The fluctuations in temperature and humidity readings over the first few months of installation can be seen in Figure 6. As can be seen the humidity fluctuations are large and it is thought these will have a serious effect on the deterioration of the tapestry.

The tapestry has Fibre Bragg Gratings integrated into the weave structure and also bonded to the surface (Figure 7). The sensors provide point readings of strain that can be correlated with the humidity and temperature changes. The strain from the sensors will be monitored periodically and the readings used to assess the deformation in the structure; Figure 8 shows some initial data. The proposed work will continue over the next year to monitor change in strain as given by the FBG sensors with change in humidity.

In addition to the point strain readings from the FBGs periodic readings will also be taken using digital image correlation which uses digital images taken simultaneously using two high resolution digital cameras at two angles. The general set-up is shown with the tapestry in a laboratory setting in Figure 9. Combining the data from the two images allows a 3D map of the surface to be generated. Comparison of the surface maps from two different points in time allows changes in the surface (displacement) to be measured. The mechanical strain can be determined from these maps. The image in Figure 10 shows part of a tapestry overlaid with strain maps. Areas of higher strain show up red, while areas of lower strain are blue. The red area is a weak section of silk between two structural joins in the tapestry.

Interpretation and Launch

To provide visitors to INTECH with an overview of the project, the importance of conservation and the physics underpinning the monitoring, two display boards were designed and installed next to the tapestry installation. The design and production of the display boards was funded by the IOP grant. The boards are shown Figure 11.

The launch event took place on the 11th May 2009 and was attended by the designers, tapestry weavers, sponsors and the research team. The team were delighted to welcome Elizabeth Jeavans from the IOP. A photograph from the launch day is shown in Figure 12. The team will also begin monitoring a tapestry in a historic house setting, at the National Trust’s Hardwick Hall, in the near future.

Further to this, the project is actively seeking to communicate the aim of the project and the importance of scientific communication and collaboration to as wide an audience as possible. One of the ways in which this is being done is via “Meet the Scientist” events. These events aim to give participants a clearer understanding of what being a scientist entails and the opportunities that exist. Via practical demonstrations, displays and presentations the importance of our work is communicated, and also it is demonstrated that science and engineering are applicable to a wide range of unusual and unexpected applications.

Acknowledgements

The tapestry was designed by Winchester School of Art students, Charlotte Agius and Rosalie Woods, under the guidance of the world-renowned tapestry weavers Caron Penney and Jo Howard at West Dean.

The interdisciplinary research is led by Frances Lennard from the Textile Conservation Centre (TCC), Professor Janice Barton and Dr Alan Chambers, both of the School of Engineering Sciences, and Dinah Eastop (TCC). The AHRC award is funding three years’ research (January 2007 - December 2009) and includes provision for a post-doctoral researcher, Dr Chen-Chun Ye, a specialist in optical fibres, and a PhD student, Helen Williams, who designed the display. The research is supported by a second PhD student Djallal Khennouf, funded by SES who is also working on the project.

The research team are grateful to the IOP for their generous support of the public engagement project.

Other collaborators include National Trust, Historic Royal Houses, English Heritage, Aston University and LA Vision UK.

(1) Chateau d’Angers, Centre des Monuments Nationaux. http://angers.monuments-nationaux.fr/en/
(2) Woolley, Linda. Medieval Life and Leisure in the Devonshire Hunting Tapestries, V&A Publications. 2002.

Tapestry woven at West Dean

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Figure 1. Tapestry Design

Weaving of the Tapestry

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Figure 2. Weaving of the Tapestry

Intech Science & Technology Centre

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Figure 3. Intech Science and Technology Centre

Tapestry Frame Design

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Figure 4. Tapestry Frame Design

Tapestry Display Installation

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Figure 5. Display Installation

Temperature and Humidity versus Time

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Figure 6. Temperature and Humidity versus time

Fibre Bragg Gratings attached to Tapestry

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Figure 7. Fibre Bragg Gratings attached to Tapestry

Strain data from BFGs

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Figure 8. Strain data from BFGs

Digital image correlation set-up

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Figure 9. Digital image correlation set-up

Image correlation strain data

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Figure 10. Image correlation strain data

Display Boards

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Figure 11. Display Boards

Tapestry display launch

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Figure 12. The launch