Coupling of electron and vibrational spectroscopy with false colour imaging for the investigation of natural dyes in historical fabrics (15th-18th centuries)

A series of historical textile fragments belonging to the Guggenheim collection had been previously studied by FORS and IRR imaging. The need for further analysis emerged in order to get a better understanding of the applied dyes. Under this perspective, SERS measurements and false colour images (UVFC and IRFC) were acquired on selected samples dated back between the fifteenth and the eighteenth centuries and constituted by velvets, embossed velvets, brocades, brocatelles, damasks, lampasses, satins, gros and taffetas of Italian manufacture. The cross-checking of spectroscopic data allowed for confirming some of the results previously obtained, but in the majority of cases much more complex situations were found. On many occasions, SERS and FORS demonstrated their complementarity allowing for discovering the use of mixtures instead of single dye as previously assumed. In addition to indigotin, cochineal and tannins, already identified in the previous investigation, new data allowed for determining the presence of orcein, annatto, luteolin, quercetin and saffron. The FC images supported the obtained results but evidenced the need for the generation of a complete database of historical dyes employed with different dyeing procedures, substrates, mordants and as mixtures with different proportions. The multi-technique approach, involving both non-invasive and micro-invasive methods, also allowed for checking the compatibility of compounds with both the declared historical period and the origin of the investigated textile fragments.