Cochineal, a precious source of red: cochineal dyes characterization by high performance liquid chromatography with diode array detection and principal component analysis

Abstract

The identification of precise cochineal species used to dye historical textiles can provide important information about the provenance and date of these objects. The most widely used method to identify cochineal species in textiles involves quantification of specific minor compounds, after High-performance Liquid Chromatography with Diode Array Detection (HPLC/DAD) analysis. However, there are several factors which are not presently taken in account when characterizing cochineal species on historical textiles. Not only all the species of cochineal are not well studied, but also the current studies, based on a limited number of species, frequently face difficulties with the identification of these on historical textiles, especially due to the analysis conditions and the results treatment. Therefore, a new approach on the study of cochineal species present in historical textiles was developed. Different parameters for the analysis conditions were undertaken to optimize the results for both insect species and textiles samples. Afterwards, with Principal Components Analysis (PCA), results from textiles samples exhibited a satisfactory correlation when compared with a cochineal reference database. Moreover, High-performance Liquid Chromatography with Diode Array Detector coupled with Mass Spectrometry (HPLC/DAD/MSn) analysis could offer accurate information on cochineal species and textiles samples. The characterization of six species of cochineal allowed, through PCA and HPLC/DAD/MSn analysis, the identification of unidentified cochineal insect samples and a group of Islamic and Italian historical dyed-cochineal textiles, dated from 15th to 17th centuries. This identification contributes to connect the textiles’ history, and the trade and dyeing technologies on possible different species of cochineal. This fact regards especially textiles produced in the main textile centres, where, after the 16th century, the traded American cochineal was swiftly adopted, as many historical publications assert. Although this study identified American cochineal in a 17th-century Indian textile for the first time, the results for the other analyzed textiles did not reveal the presence of this species. In this way, the possibility of the prompt spread of the American specie in European and Asian textiles dyeing seems to be more complex than what is emphasized by present publications.