Non-invasive analysis of natural textile dyes using fluorescence excitation-emission matrices.

Multidimensional fluorescence spectroscopy was assessed as a non-invasive and non-destructive method for the analysis of components in natural textile dyes. Results demonstrate that components in the natural dyes fluoresce and wool's intrinsic fluorescence is, in many cases, not a considerable analytical interferent. In the case of some self-dyed reference yarns, like those dyed with northern and lady's bedstraws, wood horsetail, safflower, salted shield lichen, dyer's madder and cochineal, the fluorescence excitation-emission matrices (EEMs) are sufficiently characteristic for using them as a primary means of identification (or assignment to a family of dyes). With most of the studied yellow and green dyes (heather, silver birch, some bloodred webcap treatments, alkanet), however, the spectra can be used as additional information for identification. This study reports multidimensional fluorescence data for a collection of wools dyed with natural dyes (31 dyed wool yarn samples that were self-dyed with 18 different natural dyes) that were used as references in a case study of two historical textiles for which liquid chromatography-mass spectrometry was used as a confirmatory technique. Given its utility as a rapid and non-destructive/non-invasive method with information-rich multidimensional EEM output, the front-face fluorescence spectroscopy of surfaces using a fiber optic probe is a promising technique for the analysis of dyes on cultural heritage textiles.