title: Investigation of crimson-dyed fibres for a new approach on the characterization of cochineal and kermes dyes in historical textiles.
abstract: The colorant behaviour of cochineal and kermes insect dyes in 141 experimentally-dyed and 28 artificially-aged samples of silk and wool was investigated using ultra-high performance liquid chromatography coupled to photodiode array detector (UHPLC-PDA), liquid chromatography electrospray ionisation mass spectrometry (LC-ESI-MS) and image scanning electron microscopy - energy dispersive X-ray spectroscopy (SEM-EDX). Partial-least squares discriminant analysis (PLS-DA) was then used to model the acquired UHPLC-PDA data and assess the possibility of discriminating cochineal insect species, as well as their correspondent dyed and aged reference fibres. The resulting models helped to characterize a set of 117 red samples from 95 historical textiles, in which UHPLC-PDA analyses have reported the presence of cochineal and kermes insect dyes. Analytical investigation of the experimentally-dyed and artificially-aged fibres has demonstrated that the ratio of compounds in the insects dye composition can change, depending on the dyeing conditions applied and the type of fibres used. Similarities were observed when comparing the UHPLC-MS and SEM-EDX results from the dyed and aged references with the historical samples. This was verified with PLS-DA models of the chromatographic data, facilitating the classification of the cochineal species present in the historical samples. The majority of these samples were identified to contain American cochineal, which is in agreement with historical and dye identification literature that describe the impact of this dyestuff into European and Asian dyeing practices, after the Iberian Expansion in the 16th century. The analytical results emphasize the importance of using statistical data interpretation for the discrimination of cochineal dyes, besides qualitative and quantitative evaluation of chromatograms. Hence, the combination of UHPLC-PDA with a statistical classification method, such as PLS-DA, has been demonstrated to be an advisable approach in future investigations to assess closely related species of natural dyes in historical textile samples. This is particularly important when aiming to achieve more accurate interpretations about the history of works of art, or the application of natural dyes in old textile production.
authors.affiliation: Sector Research Movable Heritage, Cultural Heritage Agency of the Netherlands (RCE), P.O. Box 1600, 3800 BP, Amersfoort, The Netherlands; CHAM (Portuguese Centre for Global History), Faculdade de Ciências Sociais e Humanas, Universidade Nova de Lisboa e Universidade dos Açores, Avenida de Berna, 1069-061 Lisboa, Portugal. Electronic address: ana.serrano@fcsh.unl.pt.
authors.forename: Ana
authors.initials: A
authors.lastname: Serrano
authors.affiliation: Sector Research Movable Heritage, Cultural Heritage Agency of the Netherlands (RCE), P.O. Box 1600, 3800 BP, Amersfoort, The Netherlands; Analytical Chemistry, IMM, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands. Electronic address: h.vandendoel@student.ru.nl.
authors.forename: Andre
authors.initials: A
authors.lastname: van den Doel
authors.affiliation: Programme Conservation and Restoration of Cultural Heritage, University of Amsterdam, Johannes Vermeerplein 1, 1071 DV, Amsterdam, The Netherlands. Electronic address: m.r.vanbommel@uva.nl.
authors.forename: Maarten
authors.initials: M
authors.lastname: van Bommel
authors.affiliation: CHAM (Portuguese Centre for Global History), Faculdade de Ciências Sociais e Humanas, Universidade Nova de Lisboa e Universidade dos Açores, Avenida de Berna, 1069-061 Lisboa, Portugal. Electronic address: hallj@fcsh.unl.pt.
authors.forename: Jessica
authors.initials: J
authors.lastname: Hallett
authors.affiliation: Sector Research Movable Heritage, Cultural Heritage Agency of the Netherlands (RCE), P.O. Box 1600, 3800 BP, Amersfoort, The Netherlands. Electronic address: i.joosten@cultureelerfgoed.nl.
authors.forename: Ineke
authors.initials: I
authors.lastname: Joosten
authors.affiliation: Sector Research Movable Heritage, Cultural Heritage Agency of the Netherlands (RCE), P.O. Box 1600, 3800 BP, Amersfoort, The Netherlands. Electronic address: k.van.den.berg@cultureelerfgoed.nl.
authors.forename: Klaas J
authors.initials: KJ
authors.lastname: van den Berg
keywords: Electrospray ionisation mass spectrometry; Historical textiles; Image scanning electron microscopy – energy dispersive X-ray spectroscopy; Insect dyes; Partial-least squares discriminant analysis; Ultra high-performance liquid chromatography