Mild extraction methods using aqueous glucose solution for the analysis of natural dyes in textile artefacts dyed with Dyer’s madder ( Rubia tinctorum L.)

Abstract

8Madder (Rubia tinctorum L.) has been widely used as a red dye throughout history. Acid-sensitive colorants present in 9 madder, such as glycosides (lucidin primeveroside, ruberythric acid, galiosin) and sensitive aglycons (lucidin), are 10 degraded in the textile back extraction process; in previous literature these sensitive molecules are either absent or present 11 in only low concentrations due to the use of acid in typical textile back extraction processes. Anthraquinone aglycons 12 alizarin and purpurin are usually identified in analysis following harsh back extraction methods, such those using solvent 13 mixtures with concentrated hydrochloric acid at high temperatures. Use of softer extraction techniques potentially allows 14 for dye components present in madder to be extracted without degradation, which can potentially provide more 15 information about the original dye profile, which varies significantly between madder varieties, species and dyeing 16 technique. Herein, a softer extraction method involving aqueous glucose solution was developed and compared to other 17 back extraction techniques on wool dyed with root extract from different varieties of Rubia tinctorum. Efficiencies of the 18 extraction methods were analysed by HPLC coupled with diode array detection. Acidic literature methods were evaluated 19 and they generally caused hydrolysis and degradation of the dye components, with alizarin, lucidin, and purpurin being 20 the main compounds extracted. In contrast, extraction in aqueous glucose solution provides a highly effective method for 21 extraction of madder dyed wool and is shown to efficiently extract lucidin primeveroside and ruberythric acid without 22 causing hydrolysis and also extract aglycons that are present due to hydrolysis during processing of the plant material. 23Glucose solution is a favourable extraction medium due to its ability to form extensive hydrogen bonding with glycosides 24 present in madder, and displace them from the fibre. This new glucose method offers an efficient process that preserves 25 these sensitive molecules and is a step-change in analysis of madder dyed textiles as it can provide further information 26 about historical dye preparation and dyeing processes that current methods cannot. The method also efficiently extracts 27 glycosides in artificially aged samples, making it applicable for museum textile artefacts. 28 29

Analytical methods for determination of anthraquinone dyes in historical textiles: A review

“…Although the coloring components and tinctorial properties of these species of Rubia differ significantly, the term 'madder' has been used historically to indicate colorants extracted from them all [38,39]. Out of 68 anthraquinoid compounds detected in madder roots of the various species [40], only a few have been identified in madder-dyed historical textiles [32,38,41,42]. Alizarin [50,51,54].…”

Degradation of lucidin: New insights into the fate of this natural pigment present in Dyer's madder ( Rubia tinctorum L.) during the extraction of textile artefacts

“…Lucidin is the only commonly reported anthraquinone detected in the roots of Rubia tinctorum to contain a primary alcohol, which could make its degradation unique. As described in our previous research [15], use of the 37% hydrochloric acid: methanol: water (2: Herein it is suggested that when such acidic methods of extraction are used to solvate the dye compounds, degradation of the aglycon lucidin may also occur. The purpose of the research described is to study the degradation of lucidin under the conditions of extraction involved with the common 37% hydrochloric acid: methanol: water (2:…”

“…xanthopur purin (7) munjistin (6) no rdamnacanthal (5 ) luci din 4 Only relatively recently has there been significant evidence confirming the primary anthraquinone components in Rubia tinctorum roots as the glycosides ruberythric acid (1) and lucidin primeveroside (3) [10][11][12][13][14]; the majority of literature has pointed to alizarin (2) as the major anthraquinone present, and whilst it does occur in the plant, it is in much lower concentrations than its glycoside [11,12,14]. We have previously suggested [15] that acidic conditions used in extraction and analysis of dyes in previous studies may have led to observations that alizarin was the primary component, it being the product of ruberythric acid hydrolysis (12). However, despite high concentrations of lucidin primeveroside (3) in Rubia tinctorum roots [11,12,14], the aglycon lucidin (4) is rarely detected (and then only in low and trace concentrations in planta and in textile artefacts [10][11][12]16]) even when acidic conditions are used that would promote hydrolysis (34); it is suspected that the reactive nature of lucidin means that it is readily converted to other compounds.…”

“…We have previously suggested [15] that xanthopurpurin may also be formed directly from lucidin (4) through an acid (or base)-catalysed loss of formaldehyde through a retro-aldol type process ( Figure 1), but there is no literature to support this proposal. The absence of lucidin in the analysis of artefacts dyed with madder is rarely acknowledged, or it is stated that lucidin is degraded into unknown products [9].…”

A New Method for Conservation of Ancient Colored Drawing on Hemp Textiles

“…To solve these problems, the optimal conservation measures should be taken to rid the inappropriate fragment sand improve the properties of textile objects for the long-term stability [2],thereby to slow down the rate of the further deterioration of hemp artifacts as much as possible [3].There is no universal protective measure for all textiles, normal conservation measures include cleaning dust and stains, pre-reinforcement of colored painting, xing separate parts, supporting weak and damaged areas with new fabrics using stitching techniques, and so on. Previous reports mainly focus on the degradation of historical textiles [4][5][6][7], the preservation environment of archaeological textiles [8,9], identi cation of dyestuffs in historical textiles [10][11][12][13], examination of cellulose textile bers [14], fungal contamination of textile objects [15], and textile cleaning [16].…”