Integrated analytical approach for the characterisation of dyed wool fibres in the earliest Moroccan carpet

This work consists of a scientific documentation of the eighteenth-century Chiadma carpet, currently on display at the Dar Si Said Museum in Marrakech. It is the earliest known carpet in Morocco, an example of Morocco’s tangible cultural heritage, commonly known as “Zarbia”. The study included scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) measurements, optical reflectance, 3D fluorescence, surface-enhanced Raman spectroscopy (SERS), and confocal µ-Raman spectroscopy. Since the few studies carried out on the Moroccan antique carpet heritage have focussed exclusively on the artistic aspects, the aim of the present work is to apply an integrated and non-destructive analytical approach to characterise the dyes used and then provide response elements on the dyeing protocol adopted. The wool fibres analysed by electron microscopy showed a certain degree of degradation/tearing and the presence of some impurities, while EDS allowed the detection of mordants in red and yellow fibres. In terms of dyes, the analyses highlighted carminic acid from cochineal extract in pinkish red shades, flavonoids from weld or Daphne gnidium in yellow shades, and natural indigo from Isatis or Indigofera tinctoria in blue shades. Mixtures of yellow dye plants with either madder or indigo were present in orange-yellow and green colours, respectively. The non-invasive techniques allowed rapid and real-time analysis, but their specificity was limited in terms of tracing the dyes to their botanical origin, i.e. the yellow-dyeing plants on aged fibres. On the other hand, the study highlighted the mastery of natural dye processing and provided relevant data to support any restoration of this prestigious carpet, which has suffered from ancient, non-controlled indoor conditions.