Fourier‐transform surface‐enhanced Raman spectroscopy (FT‐SERS) applied to the identification of natural dyes in textile fibers: an extractionless approach to the analysis

Abstract

In the present study, an application of a silver colloid substrate in order to obtain Fourier-transform surface-enhanced Raman (FT-SER) spectra of natural historical dyes is presented. In detail, we collected a spectral database from solutions of pure dyes and then we carried out extractionless both hydrolysis and non-hydrolysis FT-SERS analyses on wool fibers previously dyed in our laboratory and on ancient textiles. The term 'extractionless' refers to a method of SERS analysis applied directly on the fiber, thus avoiding the extraction of dyes from textile samples. The combination of a low-energy source of radiation, as in the FT-Raman technique, with SER spectroscopy can bring the important advantage of reducing the fluorescence typical of ancient samples and organic dyes. In some historical textile samples, for which SER spectra by use of visible excitation could not be obtained, the FT-SER spectrum of an iron-gall dye was recorded without hydrolysis, while, with an HF hydrolysis pre-treatment on ancient fibers, madder, lac dye and brazilwood were clearly recognized.

A diagnostic study on folium and orchil dyes with non-invasive and micro-destructive methods

“…but these compounds are actually the precursors of orchil and therefore they may not be a correct reference to compare with. A more proper comparison can be carried out with the spectrum of orcein recently published by Zaffino et al [40] which shows similar spectral features. In the case of folium, there is no reliable reference to compare with; the spectrum of a blue area, tentatively attributed to folium in a work by Edwards et al [29], largely differs from those obtained here.…”

Surface-Enhanced Raman Spectroscopy: Using Nanoparticles to Detect Trace Amounts of Colorants in Works of Art

“…Simply, a small amount of colorant is released, in situ, from the surface of the dyed object becoming available for coupling to the silver nanoparticles. This methodology has proven critical to attain highly reproducible, conclusive dye identification in many instances, and has delivered superior results for the analysis of paints and glaze layers (Pozzi et al 2012a(Pozzi et al , 2014aZaffino et al 2014). …”

“…The authors noted, though, that in this case SERS analysis allowed the detection of the diagnostic bands for the dyestuffs even without the HF hydrolysis pretreatment step, likely because the two colorants identified also display a strong normal Raman spectrum. Zaffino et al (2014) extended the SERS analysis of colorants in textiles to NIR excitation, comparing HF pretreatment and non-hydrolysis procedures on a large set of reference dyes and dyed fibers, as well as historical samples from Chinese Ningxia (18th and 19th century) and Caucasian Kaitag (17th and 18th century) textiles. This work included the first instance of FT-SERS spectrum of an iron-gall dye on a sample from the latter (Zaffino et al 2014).…”

“…Zaffino et al (2014) extended the SERS analysis of colorants in textiles to NIR excitation, comparing HF pretreatment and non-hydrolysis procedures on a large set of reference dyes and dyed fibers, as well as historical samples from Chinese Ningxia (18th and 19th century) and Caucasian Kaitag (17th and 18th century) textiles. This work included the first instance of FT-SERS spectrum of an iron-gall dye on a sample from the latter (Zaffino et al 2014). In one of the most extensive applications of the combined HF pretreatment and silver colloid SERS, Pozzi et al examined an important corpus of Navajo blankets in the collection of the Art Institute of Chicago (Pozzi et al 2014b), allowing the identification of the colorants in their various red woolen yarns in a selection of 8 19th-century blankets.…”

Raman Spectroscopy of cultural heritage Materials: Overview of Applications and New Frontiers in Instrumentation, Sampling Modalities, and Data Processing

“…By far the most amply demonstrated approach has been the non-extractive hydrolysis with hydrofluoric acid (HF) vapors. Initially proposed by Leona [181] the HF pre-treatment method is now amply validated as a fundamental step, especially to release colorants from their complexes with metal ions in lake pigments dispersed in oil binding medium [243,247,315]. Although direct identification of colorants with colloidal pastes on samples of pastels and watercolors has been achieved [35][36][37], this HF pretreatment is the most successful analytical protocol to date to identify red lakes in glazes and oil paint layers in paintings and polychrome sculptures.…”