Chemical analysis of Europe's treasured tapestries
Europe has a rich cultural heritage in tapestries. Preserving them for future generations is a challenge as the fabrics degrade over time. In response, the EESD Programme brought together museums curators, conservation experts and scientists to address this problem. Chemists with the University of Edinburgh in Scotland evaluated the effectiveness of a number of different microscopic analysis techniques. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) proved best able to identify metals (Al, Fe, Cu, Cr, Pb, etc.) contained in the tapestries. Determination of the metal content provides clues as to what kind of dye mordants were used by the tapestries' ancient creators. For instance, the presence of a special iron ion indicates whether or not alum was used as a dye. Some obstacles have yet to be overcome, such as arsenic interference with ICP-MS, which precludes accurate measurement of iron. Iron can be determined with ICP-OES, but it requires large sample sizes and hence is often not appropriate for use with historic tapestries. Care must also be taken to avoid false results caused by dust and dirt. Additional work performed by the team at the University of Edinburgh focused on the application of Liquid Chromatography-fed Mass Spectrometry (LC-MS) to measure organic constituents. The results were conclusive for some organic dye sources, such as fustic, but indeterminate for others (e.g. sawwort). The analysis was improved by introducing negative ion electrospray ionisation and trapping and fragmentation techniques. As with ICP-MS and ICP-OES, individual species were identified as markers for specific dyestuffs. These techniques will be exploited to make important decisions regarding the way in which historic tapestries are managed, addressing issues of storage, restoration and transportation.
