From logwood to brazilwood: A chemometric approach to classifying wood-derived dyes in artworks

Abstract

Wood-derived mordant dyes from Asia and America have historically been used to produce textiles in a wide range of colors, including yellow, red, blue, and black. While high-performance liquid chromatography (HPLC) coupled with spectrophotometry and tandem mass spectrometry with electrospray ionization (ESI MS/MS) is commonly used to analyze natural dyes, the accurate identification of these wood sources – especially the various red wood dyes collectively known as brazilwood due to their similar molecular compositions – continues to pose a significant challenge. In this study, we analyzed chromatographic data from a total of 108 extracts of natural fibers (wool and silk) that were first treated with five different mordants (along with unmordanted samples), and then dyed with wood-derived dyes: logwood (Haematoxylum campechianum L.), peachwood (Haematoxylum brasiletto H.Karst.), pernambuco (Paubrasilia echinata Lam.), and sappanwood (Biancaea sappan Tod.). Chemometric tools, including principal component analysis (PCA) and heat maps, were employed to develop an analytical model for distinguishing these dyes. Through MS/MS, 68 compounds were characterized in the extracts, leading to the successful identification of 21 markers, including sappanchalcone, sappanone B, hematoxylone B, protosappanin C, hematoxylol C, caesalpin J, sappanone A, protosappanin B, hematoxylol B, brazilein, hematein, hydroxybrazilein, hydroxyhematein, urolithins, protosappanin D, protosappanin E, and hematoxylol E. The impact of historical samples (threads from 16th- and 17th-century European textiles) on the chemometric results was also examined. This study provides a foundation for developing a model to detect wood-derived dyes in historical textiles, enhancing the understanding of historical dye practices and paving the way for future research into identifying species of red wood dyes.