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

Historical and archaeological textiles are among the most crucial and vulnerable records of our social and cultural history. Analysis of organic colorants found in these materials is unquestionably one of the most powerful tools to understand historical developments, cultural exchanges, and progress in science and technology. Natural anthraquinones represent the most commonly used natural colorants for textile dyeing until the late 19th century. The identification of anthraquinones in cultural heritage objects is a challenging task due to the small size of historical samples, diversity of potential dye sources, variable extraction procedures and dyeing methods, complex chemical constitution, structurally analogous chromophores, and possible presence of degradation products and contaminants. Developments in dye analysis of historical interest have originated and expanded along with the general advances in analytical science. In the last few decades, a close cooperation between science and cultural heritage disciplines contributed enormously to this field. The topic of historical dyes and their analysis in textiles, artworks, archaeological objects and cultural heritage materials has been reviewed several times in the last fifteen years. However, no review has been published to-date exclusively on the analysis of anthraquinone colorants in historical and archaeological textiles. Overall, liquid chromatography (LC)-based techniques have been the most widely used method for anthraquinone dye analysis. Owing to increasing demand of minimally invasive/non-invasive techniques, recent developments of novel techniques have resulted in the availability of many alternative/complementary methods to LC-based analysis. This review begins with a short overview of sources, chemistry and importance of natural anthraquinone dyes found in historical textiles before turning to a detailed discussion on developments involving established and emerging analytical techniques of anthraquinone dye analysis for textile cultural heritage materials. To illustrate the state-of-the-art, representative examples of analytical techniques highlighting their advantages, limitations and applicability are also presented.