Raman and ATR-FTIR analyses of medieval wall paintings from al-Qarawiyyin in Fez (Morocco)

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A multi-analytical study has been undertaken to characterise wall paintings from the al-Qarawiyyin university in Fez, dating back to the 9th century and still in activity, with the aim of identifying the pigments used and going back to the painting techniques adopted by the Moroccan craftsmen of the time. The investigation crossed Raman and ATR-FTIR structural analyses along with XRF elemental ones, as well as colorimetric measurements. The colours and shades of six representative fragments collected during a recent excavation have been examined. Hence, red ochre (mainly hematite) was used to obtain brown-red colour, calcite for white, bistre for carbon-based black, while blue shades were achieved using azurite. Mixtures of pigments were created to widen the colour palette: cinnabar, minium and hematite were identified in orange hues while lapis lazuli and azurite were observed in grey-blue areas. The exploration of mortar layers revealed gypsum, gypsum/calcite and calcite type plasters. Furthermore, the observation of the morphological aspect of the interface between the plaster and the painting layer seems indicating that the lime-secco-painting skill had been the adopted painting technique.