Towards an early warning system for oxidative degradation of protein fibres in historical tapestries by means of calibrated amino acid analysis

Abstract

Flemish 15–17th century tapestries are among the most precious testimonies of European cultural heritage. Even in their deteriorated condition, they are still highly valued and exhibited in many museums all over the world. The present state of degradation evidenced by visual assessment in conservation practice, and confirmed with macro-scaled tensile strength tests, reveals the vulnerability of the wool and silk fibres to light exposure.The focus of this study is in the development of a micro-destructive tool that can be applied to provide information about protein breakdown at an early stage, long before fibre deterioration becomes visible. High performance liquid chromatography with fluorescence detection is a very efficient technique to determine the amino acid composition of proteins at sub-microgram level. In the first part of the study, the technique is evaluated for its efficiency in the detection of oxidative fibre damage at molecular level. The pathway for initial oxidative degradation of textile proteins is studied using a set of new and accelerated aged wool and silk reference samples. Characteristic alterations in amino acid composition of both proteins are detected and sensitive markers for the monitoring of oxidative deterioration of keratin and fibroin determined and validated on a large set of dyed reference samples. Correlation between the developed early warning markers and the physical degradation of the fibres is demonstrated.In the second part of the study, the developed early warning markers are applied to monitor the state of oxidative degradation of a large dataset of historical wool and silk samples from 15–17th century Flemish tapestries in Belgian, Spanish and British collections, allowing condition evaluation of the prestigious historical collections. The developed early warning system is found to be a powerful, micro-destructive tool for conservators and restorers to evaluate the condition of the tapestry or textile collection and to prioritise the conservation or restoration treatment of the most fragile pieces of the collection.