Colour in Kaitags : a new scientific approach to detecting dyes in textiles

The project for the scientific analysis of Kaitag textiles – the results of which are reported here with special focus on the identification of the dyes – was promoted by the MATAM association (Museum of Ancient Textile Art Milan) and carried out by the Universities of Bergamo and Milan as the logical continuance and updating of the important analytical project conducted by Harald Bohmer and Recep Karadag almost two decades ago. On the one hand, our project was inspired by the need to determine, for a given artefact, the execution technique and the materials used, not only for the sake of knowledge but also for practical conservation purposes. At the same time, from a methodological point of view, the intent was to use not only the most frequently-applied analytical procedures, but also non-invasive techniques suitable for in-situ analysis, and such as to safeguard the integrity of the objects examined. The most representative tints were selected for analysis in order to obtain a wider knowledge of the dyes, and their combinations, used over the centuries in Daghestan. In addition, special attention was paid to those tints for which the identification of the dyes is notoriously more difficult (especially yellow) and to cases of suspected alteration of the dye or evident damage to the thread. A total of 23 Kaitag textiles were examined, dating from the 17th to the 18th century. A preliminary imaging campaign was performed on all of them using infra-red (IR) reflectography and ultraviolet (UV) fluorescence, in order to better understand the technique used and to highlight any later integrations of the textiles (which, however, were detected in only a few cases). In addition, the presence of a black-ink underdrawing was observed using reflectography. Thereafter, the dyes were analysed using non-invasive techniques such as visible reflectance spectroscopy (vis-RS) on 250 measurement points, and Fourier-transform infrared spectroscopy (FTIR) on 30 measurement points. Colorimetric data were acquired on each of the points studied during the vis-RS measurements. Also, energy dispersive X-ray fluorescence (ED-XRF) was performed on two of the fabrics using a portable handheld spectrometer. Extracts from 65 tiny portions of dyed thread were then examined by high-performance liquid chromatography (HPLC) and surface-enhanced Raman spectroscopy (SERS); other threads were analysed without extraction by energy-dispersive X-ray analysis coupled with scanning electron microscopy (SEM-EDS), attenuated total reflection (ATR) FTIR spectroscopy and Fourier-transform Raman (FT-Raman) spectroscopy. The dyes identified, which were all of natural origin, include: madder for red, indigo for dark and light blue, weld for yellow (the substance or substances used to obtain the more intense yellow hues, however, remains unidentified), weld (or sometimes a different yellow dye) and indigo for green, tannins mordanted with iron for dark brown, again tannins, sometimes with the addition of indigo, for black. A high content of iron is often accompanied by corrosion of the dyed thread. Finally, the ink used for the underlying drawing was carefully examined and identified as carbon ink.