Micro‐Raman spectroscopic study of artificially aged natural and dyed wool

Abstract

The objective of this study was to evaluate the use of micro-Raman spectroscopy as a non-invasive vibrational spectroscopic technique applied to the examination of wool samples, which may be applied to textile materials of cultural heritage interest. In this work, a selection of wool materials were primarily investigated in their unaged states through the utility of a natural wool reference together with selected samples dyed with different natural colorants, namely woad, weld and madder. The identification of the main modes of vibration of the wool fibre keratin was assessed in all the samples, which aided the determination of the changes within the protein structure, in particular, through the cysteine and peptide cross-linkages brought about by the addition of the dyes that can produce effects similar to degradation. The dye too was assessed importantly to enable its identification through its characteristic scattering or fluorescence emissions on a woollen matrix, as well as to ascertain whether a uniform covering across the surface of the wool was achieved or not. Regarding the artificial degradation of the samples it was possible to observe numerous modifications within the molecular structure of the wool, in particular, within the amide I, C-H bending, amide III and S-S stretchings along with the physical photo-yellowing of fibres given by the presence of lipids dispersed across the surface of the wool. The effects of ageing on the dyed samples were also investigated, indicating that many of the bands relative to the colorants were still present, yet so too were numerous vibrations from the wool that also indicated a certain level of stress and degradation to the underlying wool.

Applications of Raman spectroscopy in archaeometry: An investigation of pre-Columbian Peruvian textiles

“…1650 cm −1 , indicating that changes in both band position and intensity is occurring as a consequence of degradation (Wojciechowska et al, 1999). Other degradation marks are the bands at 3060, 1656 and 1004 cm −1 assigned to ν (_C-H) and ν (CC) from aromatic moieties that in aged samples show up with significantly lower intensity (Doherty et al, 2008). These changes are due to …”

“…In the (C-H) region (not shown) bands at 2916, 3060 and 3270 cm −1 are also observed. The main Raman and infrared bands of contemporary wool were assigned in Table 1 and they are in full agreement with the literature data (Carter et al, 1994;Doherty et al, 2008).…”

Developing a non-invasive tool to assess the impact of oxidation on the structural integrity of historic wool in Tudor tapestries

“…Other peaks relevant to the oxidation process such as the peaks relating to the disulfide (450-550 cm ) can appear as very weak bands that may be masked by background noise [13,14]. Rather such groups are often identified through Raman spectroscopy [15][16][17][18], where such bands are typically stronger than in FTIR and NIR. Though useful in following chemical changes that occur in wool proteins [19][20][21][22], FTIR-ATR is ultimately destructive, requiring sacrificial samples that are not always accessible in historic collections.…”

“…To investigate the possible link between fibre strength loss and oxidation a combination of both FTIR and FT-Raman spectroscopy (FTR) could be used. FTR is often used to assess the loss of disulfide functionality in studies of hair and wool [12,15,16,20] since sulfur itself is not NIR active [59]. In combination with the oxidation products measured through FTIR, it may be possible to understand the effects of oxidation on fibre strength more closely.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part III

“…A study by Doherty et al [111] has demonstrated the utility of microRaman spectroscopy for the examination of wool fibres. Many differences have been noted between the Raman spectra of natural and artificially aged wool in the amide I, C-H bending, amide III and S-S stretching regions.…”