Dyes from the Ashes: Discovering and Characterizing Natural Dyes from Mineralized Textiles

Abstract

Vesuvius eruption that destroyed Pompeii in AD 79 represents one of the most important events in history. The cataclysm left behind an abundance of archeological evidence representing a fundamental source of the knowledge we have about ancient Roman material culture and technology. A great number of textiles have been preserved, rarely maintaining traces of their original color, since they are mainly in the mineralized and carbonized state. However, one outstanding textile sample displays a brilliant purple color and traces of gold strips. Since the purple was one of the most exclusive dyes in antiquity, its presence in an important commercial site like Pompeii induces us to deepen the knowledge of such artifacts and provide further information on their history. For this reason, the characterization of the purple color was the main scope of this research, and to deepen the knowledge of such artifacts, the SERS (Surface Enhanced Raman Scattering) in solution approach was applied. Then, these data were enriched by HPLC-HRMS analyses, which confirmed SERS-based hypotheses and also allowed to hypothesize the species of the origin mollusk. In this context, a step-by-step integrated approach resulted fundamental to maximize the information content and to provide new data on textile manufacturing and trade in antiquity.

Inside the History of Italian Coloring Industries: An Investigation of ACNA Dyes through a Novel Analytical Protocol for Synthetic Dye Extraction and Characterization

“…Reference spectra databases currently only contain a small proportion of the dyes made and sold on the market, and the vast range of available dyes make it difficult to develop, navigate and update databases—making it challenging to use techniques that rely upon comparison with known compounds. Moreover, inconsistencies in nomenclature—where different manufacturers refer to the same dye molecules by their own brand names, or use similar names for chemically different dyes—make it challenging to identify dyes even when their commercial names are listed [ 2 , 9 , 10 ]. Together, these factors make the identification of these types of dyes from historical and artistic matrices a highly complex matter; for this reason, it is desirable to develop ad hoc methodologies and (re-)organize bibliographical sources.…”

“…For example, in spectroscopic analysis such as Raman spectroscopy, synthetic dyes often produce more intense spectral peaks. This can allow for spectra to be obtained without enhancements such as surface-enhanced Raman spectroscopy, which is required for natural dyes [ 2 , 9 ].…”

The 20th century and its new colours: Investigating the molecular structures of historical synthetic dyes using Raman spectroscopy

“…Interest in the identification of synthetic dyes is growing significantly as early synthetically dyed objects are recategorised from contemporary to historical, 10,11 authentication questions arise, 12 and conservation issues begin to require attention. 13 Traditionally and most commonly, textile dyes on fibres are analysed by extraction and separation of components using chromatography with either mass spectrometry [14][15][16][17][18] and/or photodiode array detection. 19,20 Whilst these techniques are still the gold-standard for confident identification, 7,9,21 they require sampling and are destructive.…”

“…Traditionally and most commonly, textile dyes on fibres are analysed by extraction and separation of components using chromatography with either mass spectrometry 14–18 and/or photodiode array detection 19,20 . Whilst these techniques are still the gold‐standard for confident identification, 7,9,21 they require sampling and are destructive.…”

Dyes of a Shadow Theatre: Investigating Tholu Bommalu Indian Puppets through a Highly Sensitive Multi-Spectroscopic Approach

“…Visible light Fiber Optic Reflectance Spectroscopy [9][10][11][12], coupled to an optical microscope (micro-FORS), was employed to obtain preliminary information about the class of dyes: reflectance spectra were acquired directly on stubbons used to sample to dyes during the conservation treatments. The same samples were then analyzed with Surface Enhanced Raman Scattering (SERS) [13][14][15][16][17][18], which is based on the great enhancement of the Raman signal of an analyte in close proximity of a metal nanostructured substrate, allowing it to obtain vibrational spectra that, otherwise, would be affected by a dramatic fluorescence background. In the last decades, SERS spectroscopy has showed its great analytical potentiality [19], and it is nowadays increasingly used for the characterization of colorants in art objects.…”