Investigating Organic Colorants Across Time: Interdisciplinary Insights into the use of Madder, Indigo/Woad, and Weld in Historical Written Sources, Archaeological Textiles, and Ancient Polychromy

Abstract

Organic dyes have been used from the earliest times to provide color primarily to textiles, but also as a colorant in painting. Such organic dyes could create a wealth of colors, depending on the availability and know-how of resources. These dyes are usually organic in nature, and primarily obtained from different plant sources. Unfortunately, the characterization of natural organic colorants in textiles and artworks is still a challenge. The difficulty of analyzing these materials is sometimes allied to the frequent impossibility of micro-sampling, and the frailty of the objects. Many techniques, such as HPLC (High-Performance Liquid Chromatography) and SERS (Surface-Enhanced Raman Spectroscopy), require the use of a micro-sample, which cannot be recovered after analysis. Moreover, the portable technique Fibre Optic Reflectance Spectroscopy (FORS) can present some challenges in distinguishing between different dye sources belonging to the same molecular family, such as anthraquinone reds. Although no one technique alone can unravel the world of natural dyes, a multi-analytical approach has proven to be far more effective for their identification and characterization. In the present article, we intend to share insights into three different perspectives and types of source material for the study of the use of organic colorants in ancient and historical times: The first case study presents an 18th-century historical recipe for dyeing textiles, the second case study presents a study of preserved archaeological textiles from Nubia, while the third case study presents the use of organic colorants for the polychromy of ancient Greco-Roman iconography.