Monitoring of damage to historic tapestries
Tapestries woven during the 15th to 18th centuries are among the most valuable testimonies of European cultural heritage. Extensive collections exist in historic palaces, houses, museums and cathedrals in varying degrees of preservation and conditions of display. Condition assessment of historic tapestries by conservators is an integral part of the collections care process, enabling prioritisation for interventive treatment, and monitoring of condition over time. It is an expertly skilled process. Tapestry is a complex weave structure, which can often appear sturdier than its true condition. Until a tapestry is moved or handled, which in itself may cause damage, it is difficult to appreciate the full extent of degradation. Conservators have expressed a need for an objective, scientific, numerical tool to aid in this process. Many scientific analytical techniques can be applied to tapestry wool, silk and metal threads. The project has aimed to evaluate which techniques would provide the most useful information for conservators, and can be optimised to provide simple “markers” of damage. It was important to relate the markers of damage to physical properties – and thus to context of use, whether hanging on display or rolling in storage.
Methods of measuring physical properties directly (such as tensile strength) require large sample sizes and/or many repeated measurements to produce reproducible results. This is not possible with historic tapestries where any removed sample size must be minimal (i.e. micro-samples or non-destructive). Loss of physical properties is preceded by chemical changes. Analytical techniques for detecting chemical change are sensitive to small differences occurring during and after degradation. Therefore, the project looked for methods which would detect the signature chemical change of a tapestry on degradation, and which could then be directly correlated to physical properties. This information can be used to prioritise and design the appropriate conservation treatment or collections care conditions required for the long term preservation of these priceless artefacts.
Historic Royal Palaces was proud to collaborate with six partner institutions on this project:
Patrimonio Nacional (Spain), Institut Royal du Patrimoine Artistique (Belgium), University of Manchester, National Museums of Scotland, University of Edinburgh, and Birkbeck College (University of London)
Scientific objectives and approach
The project has aimed to correlate visual assessment of damage by conservators with:
1. Measured markers of chemical damage
2. Expected patterns of damage based on acquired knowledge of effect of dyeing on fibres
3. History of use and display of case study tapestries, based on archival research.
The scientific objectives required to achieve these aims were:
- Comprehensive analysis of artificially aged model tapestry material to improve and develop appropriate analytical techniques
- Utilisation of the refined techniques on historic samples
- To identify and develop the correlation of the results from different techniques to identify suitable markers for degradation
- Dissemination of results to end-users.
The project involved the preparation of model tapestries based on traditional techniques. The intensive research and documentation for preparation of these models has enhanced knowledge of such practices, and these model tapestries now serve as rigorous scientific standards. The model tapestries were used as a tool to develop methods and identify novel markers for the characterisation of fibres, dyes and metal threads. The scientific data collected has led to new correlations between chemical alteration at the molecular level and changes in tensile strength of the fibre and fabric. The use of sophisticated analytical instrumentation for micro-scale quantitative analysis now makes it possible to characterise minute historic samples. Links between chemical composition and actual mechanical strength have been identified.
The information obtained from amino acid compositions, surface chemical compositions, molecular weight distributions, infrared spectra and mechanical properties of fibres has been correlated with the historic tapestry conditions as recorded by conservators. Analysis of dye degradation products and mordants, also at the micro level, has led to further information on the dyes and mordants originally used.
- The model tapestries have proven to be an invaluable resource for the advancement of the scientific analysis techniques, some of which have been applied to historic tapestry materials for the first time during this project. The ageing of selected model samples has allowed the photochemical reactions of the fibres and different natural dyes to be assessed as candidates for “markers of damage”
- The collation of documentation and data resulting from the field campaigns with historic tapestries has enabled much of the associative work to relate the trends and conclusions reported for the scientific study to the visually assessed condition, display history and context of the historic tapestries
- The characterisation of metal threads in this project has contributed new information to the field of study of construction and manufacturing techniques of these precious and intricate materials
- Sensitive damage micro-markers have been identified and provide a basis to analyse wider tapestry collections. A range of surface & bulk, thermal and chemical analytical techniques have been applied and evaluated in terms of their effectiveness to assessing damage in accelerated aged model tapestry materials and historic tapestries. The structural and chemical modifications to wool and silk fibres have been related to the macro properties of the tapestry strength and integrity
- Dyeing methods appear to influence the strength properties of unaged fibres. Since the dyeing method is dependent on the natural source, accurate identification of the original dye source and/or mordant is thus an important factor in damage predictions. The development of new methods for characterising dye sources in historic samples has provided vital support in the attainment of this goal.
The project has produced an objective testing scheme for damage assessment with which conservators will be able to assess and track the condition of the tapestries within their care. This is especially important because of the invisibility of fibre damage: changes at the molecular level have consequences for the physical strength of the tapestry. A new understanding of degradation has been obtained and changes in overall strength and colour can be described for the first time in chemical terms. The state of the fibre is of vital importance for the overall mechanical integrity of the tapestries and will determine how they will withstand being transferred to other locations for display. The proven correlations between amino acid analysis, molecular weight (silk) and tensile strength (among other markers) of silk and wool confirms the value of applying these analytical results to future conservation strategy. Useful correlations and inter-relationships have been established which will benefit conservators. For example, the analytical techniques could be used to prioritise tapestries for interventive conservation treatment, and also to justify the level of intervention or support required in order to stabilise and display a tapestry.
This research has been published in a wide variety of forums to disseminate information internationally, from peer-reviewed academic journals and conferences, to informal talks and tours for visitors and students. In addition to presentations at external international conferences, a final “MODHT” Workshop, at Hampton Court Palace, was undertaken in June 2005 to effectively disseminate the objectives, results and conclusions to potential end-users. Over 70 delegates attended with representation from heritage organisations around the world. The results and discussion of the meeting and project will be published for wider dissemination.
Contact: Kathryn Hallett Kathryn.firstname.lastname@example.org
For our publications list, please download the PDF below.
This research project was supported by the European Commission under the Fifth Framework Programme and contributing to the implementation of Key Action 4: 'The City of Tomorrow and Cultural Heritage, subsection 4.2.1 Improved damage assessment of cultural heritage,' within the Energy, Environment and Sustainable Development. Contract No. EV4K-CT-2001-00048
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