Unveiling the colour palette of Arraiolos carpets: Material study of carpets fromthe 17th to 19th century period by HPLC-DAD-MS and ICP-MS

Abstract

Wool samples collected from thirteen Arraiolos carpets from the 17th–19th century belonging to theNational Museum of Ancient Art (NMAA, Lisboa, Portugal) collection were analysed to identify the naturaldyes and mordants employed in the traditional dyeing process, in a way to complement and improveactual knowledge on this rugs. Natural dyes were extracted from Arraiolos historical wool fibres using amild extraction method, followed by high-performance liquid chromatography with diode array and massspectrometry detection (HPLC-DAD-MS) for compound identification. Colourimetry was used to measurecolour parameters in all historical samples. Quantification of mordants in the historical fibres was carriedout by inductively coupled plasma-mass spectrometry (ICP-MS). Weld, indigo, spurge flax, brazilwood,madder and cochineal were identified as dye sources in the fibres. Alum was the most commonly usedmordant, but the presence of iron and zinc was also detected in some darker samples. The use of madderand cochineal is not referred in the available historical dyeing recipes. This study also proved that theactual visual perception of these carpets is strongly affected by the natural dyes photodegradation, whichwas mostly unaccounted for before.