Preserving Europe's cultural heritage through corrosion prevention
The survival of tapestries, woven in renowned European centres during the 15th to the 18th centuries, is jeopardized by degradation processes operating at molecular level in their components such as coloured fibres and metal threads. Their preservation relies on a better understanding of the materials and techniques used in their construction. MODHT - Monitoring of Damage to Historic Tapestries - is an interdisciplinary project involving the collaboration of experts from a number of disciplines seeking a new understanding of degradation though a chemical/materials science approach. In this direction model tapestries, prepared using traditional materials and then artificially aged, together with samples for historic tapestries were studied relating their construction materials and techniques to degradation mechanisms. X-ray Photoelectron Spectroscopy (XPS) and X-ray Diffraction (XRD) were utilized to analyse the corrosion products on historic metal threads. Sulphur compounds were found to comprise the main corrosion products with only relatively few and patchy chlorine containing products. Artificial tarnishing tests on copper and silver foils, indicated that the main corrosion products, derived from the degradation of silk and wool, were sulfide with some sulfate observed on copper coupons. Furthermore, degradation of wool was found to cause higher levels of visible corrosion than silk. Rare examples of double and triple wrapped silver gilt threads were identified with the use of Energy Dispersive X-ray microanalysis (EDX). Moreover Field Emission Gun Secondary Electron Microscopy (FEG-SEM) of single sided gilt metal filaments in longitudinal- and cross-section, produced evidence of the metal being cut but rolled rather than hammered. This suggests a combination of manufacturing techniques. Conservators, restorers, curators, conservation scientists and collection care professionals may benefit from the knowledge produced in decision-making for improved conditions of display, storage and conservation treatment of historical tapestries.
