Natural dyes in madder (Rubiaspp.) and their extraction and analysis in historical textiles

Abstract

Textiles coloration using extracts from the roots of various madder species (Rubia spp.) has been performed for centuries. To date, 68 anthraquinone colorants have been detected in Rubia spp. used to dye textiles. Many of these dyes are sensitive to hydrolysis and degradation from enzymes, extraction chemicals and processing temperatures, and are often overlooked as colorants in historical textiles. Conclusions in literature of the past 30 years concerning colorants present in planta and, particularly, in madder‐dyed artefacts are being challenged as new analysis methods are developed. The recent advent of ‘soft’ extraction techniques has demonstrated that anthraquinone glycosides and other sensitive molecules, such as carboxylated compounds, need to be preserved; this valuable chemical information embedded in the dye structure may be lost if extraction and analysis is too harsh. Some compounds thought to be present in madder and madder‐dyed artefacts are in fact degradation products resultant from the extraction process, and degradation pathways have been developed to better understand the reactivity and stability of these compounds. Detailed analysis of dyes in textile artefacts can reveal important cultural and heritage information concerning historical textiles relative to the specific dye species, the area of the world where this may have grown, how and where it was dyed, and, perhaps, where it was traded. Understanding the precise molecular structure of these dyes and their chemical reactivity is important to provide knowledge of their interactions with physical substrates, such as textile fibres, which could be used to develop superior techniques for analysis of artefacts.

Comparison of madder (Rubia tinctorum L.) and weld (Reseda luteola L.) total extracts and their individual dye compounds with regard to their dyeing behaviour, colour, and stability towards light

“…Knowledge of the main compounds and their degradation products is particularly useful in the field of historical textiles and their preservation [8][9][10][11][12]. Knowledge of the main compounds and their degradation products is particularly useful in the field of historical textiles and their preservation [8][9][10][11][12].…”

“…In fact, madder roots contain several dozen different anthraquinones, of which the 30 most prominent [11,13] all contribute to the final colour hue. In a natural dye source such as madder root, alizarin and purpurin are believed to account for the red colour.…”

Approaches for Detecting Madder Lake in Multi-Layered Coating Systems of Historical Bowed String Instruments

“…These plants were economically important sources of red anthraquinone compounds among which alizarin and purpurin-which originates from pseudo-purpurin by decarboxylation-are considered key-compounds for madder identification in a variety of artifacts [20]. The use of madder declined after the commercial introduction of the synthetic alizarin in 1871, which rapidly replaced the natural product in the textile industry, whereas natural madder continued to be used-in parallel to the synthetic product-for the production of artists' pigments [21].…”

Comparative sorption isotherms for colorants present in Dyers’ madder (Rubia tinctorum L.) provide new insights into historical dyeing

“…14: R 1 = OH; R 2 = R 3 = R 4 = H. Although many compounds are observed in planta, there are few studies dedicated to understanding which dyes in R. tinctorum are actually adsorbed onto mordanted wool during dyeing processes and there has been no known study on the sorption of individual dye compounds in the (19) 402 + [24,25] extracts [29]. Due to the vastly differing functional groups on the dyes, it would be expected that the dyes would perform differently when applied to wool.…”