Introduction
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.
Project partners
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.
Scientific achievements
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.
