Assessing near infrared and terahertz spectroscopy for the characterisation of organic heritage artefacts

Our objective is to define the most appropriate non-contact spectroscopic protocol with which to interrogate the identity, moisture content and chemical character of organic heritage artefacts, as exemplified by textiles, for informed conservation and long-term preservation. Here we report initial work on the application of near infrared (NIR) and terahertz (THz) spectroscopy to the analyses of natural fibre textiles. NIR wavelengths are sufficiently short for efficient transmission of the radiation through fibre optics, so that remote sampling is possible. THz spectroscopy has been developed much more recently as an analytical tool, and also offers a truly non-destructive approach. We have recorded non-contact NIR (7800 - 4000 cm?1) and THz (10GHz - 2THz) spectra of linen and other textile fabrics. While the terahertz spectra are not immediately distinct, the near infrared spectra allow differentiation of the broad categories of textiles. THz absorption increases with moisture sorption; besides microstructural and chemical information, NIR spectra may also reveal the moisture content of fabrics. A preliminary analysis of linen suggests that by providing this information non-invasively, NIR spectroscopy has the potential for on-site monitoring of the deterioration state of fabrics.