Historic tapestries bridge chemistry and art
Historic tapestries are a valuable source of authentic evidence on cultural heritage. Conservation scientists and curators have directed their efforts towards identifying the origin of tapestries' deterioration with the aim to inhibit degradation and ensure future preservation. Research studies focused on developing reliable markers to be exploited as diagnostic tools to monitor physicochemical changes and assess the extent of the damage. Models of tapestries were prepared employing an integrated approach involving chemistry and science. Materials and dyes were chosen with great consideration for the model samples which were then subjected to artificial ageing using various conditions. Degree of damage, past documentation, environmental conditions, etc., were some of the criteria used for selecting the individual fibres under investigation. In the case of wool fibres, these were subjected to accelerated and natural ageing and surface analysis was performed employing a combination of analytical techniques. Alterations in atomic ratio and chemical states of elements present were detected by X-Ray Photoelectron Spectroscopy (XPS). Results showed that decrease in carbon quantity is associated with increase in oxygen suggesting that oxidative loss of surface lipids occurs during the ageing process. Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS), a method widely used for polymer surface characterisation, was also employed to verify the results obtained by XPS. It was observed that cleavage of covalent cysteine disulphide bonds induced cysteic acid formation resulting in surface oxidative ageing. The aforementioned methods indicate that the textile strength depends on the surface chemical modifications that occur with ageing. Hence, both the atomic ratio of C/O along with the percentage of oxidative sulphur at the fibre surface could be exploited as textile strength markers. It is evident that detailed understanding of the mechanisms underlying tapestry deterioration at the molecular level enhances conservator-restorers knowledge, promoting optimum future preservation.
