In-situ spectrofluorimetric identification of natural red dyestuffs in ancient tapestries

The non-destructive identification of organic dyes in works of art is still a challenging goal for scientists devoted to the diagnostic of cultural heritage. In the present study, a non-destructive and in-situ analytical method was developed to this aim and applied to sets of ancient tapestries (XV-XVI century) compared with reference wool samples dyed in the laboratory. The target analytes are the red organic dyes of natural origin mostly used to dye textiles in ancient times, i.e. madder, kermes, cochineal, brazilwood and lac dye. In order to discriminate among them, the collected data were processed by a multivariate statistical approach, using principal component analysis (PCA) and cluster analysis. To validate the method, chromatographic analyses were performed on selected fragments from the same textiles previously analyzed by spectrofluorimetry. The consistency of the results allowed us to sustain the correctness of the non-invasive approach and to exploit it to analyze details of three tapestries of the precious “Arazzi dei Mesi” cycle (beginning of XVI century), belonging to the collection of the Castello Sforzesco in Milan (Italy).