An evaluation of the effectiveness of SERS in the identification of textile dyes in real archaeological and historical samples

In the last few years the application of surface-enhanced Raman spectroscopy to the identification of historical dyes has significantly developed from the point of view of analytical protocols, aiming to reduce the need for sample pre-treatment, the required amount of sample [Brosseau et al. 2011] or even to completely avoid sampling [Leona et al. 2011]. These aspects of the evolution of the technique were extensively reported and reviewed in the literature. Whenever an analytical chemist is involved in the solution of a problem concerning the cultural heritage, he has to deal with two different issues: the development of suitable methods and the need to give precise answers to the questions of archaeologists and art historians. At the present stage of improvement of the SERS techique for the identification of dyes, it is therefore useful to evaluate its capability in recognising such substances, especially those used for textile dyeing, in a field where other analytical methods, i.e. those based on high-performance liquid chromatography (HPLC), are still most commonly and routinously used by specialised laboratories. Examples concerning the possibility of recognising by SERS dyes used in archaeological and historical samples from particular geographical areas or in the decoration of unusual textile artefacts will be discussed, with special attention to those cases where identification is made more difficult by the need of a widened database or by the use of dyes in mixtures or even by degradation effects.