UNCERTIR · Analytical Uncertainty of Quantitative Methods Based on IR-spectroscopy for Heritage Material Characterisation

Non-destructive and non-invasive methods of characterisation of heritage materials are increasingly in demand. Recent applications of near- and mid-IR spectroscopy combined with chemometrics provided a step change in the quantitative determination of chemical and physical properties of many heritage materials of organic origin, including their dating. However, the uncertainty of determination could reduce the acceptance of such methods by users. Therefore, UNCERTIR focuses on the analyses of the causes of uncertainty, which could originate in (a) uncertainty of reference analytical data used for method development; (b) large inhomogeneity of material properties typically associated with heritage materials; (c) the contribution of degradation products and changes in heritage material manufacture; and (d) method of spectral data collection as deemed acceptable by the conservation community, often allowing only minimal contact between the probe and the analysed material. The project methodology will be based on numerical evaluation of the contributions to the overall method uncertainty by using separate sample sets of pure model materials and naturally degraded inhomogeneous materials; by comparing different reference analytical methods, e.g. for determination of pH or degree of polymerisation; by application of different methods of statistical evaluation of groups of samples; and by using different methods of collection of spectra. Of particular interest will be methods of dating heritage materials, where significantly different accuracies have been observed for paper, parchment or photographs, the cause of which remains unknown. The project will be of significant importance to heritage and users not only because of the variety of newly developed methods but also because, for the first time, the users will be provided with a comprehensive evaluation of analytical uncertainty.