Identification of Historical Textiles via Non-destructive Spectroscopic Analysis and Multivariate Cluster Analysis

Abstract

One of the foremost challenges facing dye analysis of historical textiles is that the gold standard technique – high performance liquid chromatography (HPLC) – is inherently destructive, costly, and relatively few institutions have the necessary equipment and expertise. This is especially problematic considering historical samples are unique, sampling is undesirable, and historical textiles can be exceptionally fragile. One proposed solution to this is the implementation of non-destructive, spectroscopic, techniques, such as Fiber Optic Reflectance Spectroscopy (FORS). In this work, 204 well-provenanced red Norwich textiles were measured with FORS and analyzed, aiming to test if the technique would be able to discern the chromophore combinations / recipes used to dye historical textiles. Cluster analysis algorithms and spectroscopic domain knowledge were coupled with selective HPLC validation to assess overall ability of FORS to identify chromophore combinations. The UV/VIS region, particularly 380-469 nm, showed a narrow visible region that was primarily responsible for clustering behavior that correlates with HPLC-validated samples. In contrast, the near infrared (NIR) region of the spectrum contained little meaningful information in multivariate space. This indicates that FORS shows promise for identifying chromophores in textile samples. Suspecting the observed spectral inflection point shift around 600 nm was correlated to the presence of mordants, complementary X-ray fluorescence (XRF) analysis was used, with the corresponding statistical treatment, which showed no correlation. From this work, three main conclusions can be drawn: 1) FORS adequately identifies visual information, which shows reasonable correlation to HPLC-validated dye recipes, warranting further investigation, and indicating utility for confirmatory analysis, and strongly suggesting this is a good tool for persons with visual impairments; 2) XRF analysis confirms that ~600 nm inflection point shift and mordant are not correlated when measuring dyed textiles; 3) many documented structural-to-spectral relationships established in the conservation literature are too weak in dyed textiles for statistical analysis and, by extension, expert spectral identification.