**4. Conclusions**

In this work, the spectral features of the brazilwood marker component urolithin C have been characterized by conventional and surface-enhanced Raman spectroscopy, and compared to those of the main brazilwood chromophores in the pure reference material and in a brazilwood lake pigment sample. The results obtained suggested that the SERS

approach was suitable for use on historical textile samples and it was subsequently successfully applied to minute samples from four historical linen, silk and wool textiles dyed with brazilwood and showing varying degrees of fading. The SERS findings were correlated with HPLC-DAD and HPLC-ESI-Q-ToF-MS analyses which offered a full description of the major and minor components in each sample. The combined use of the direct colloidal approach followed by a HF pre-treatment was demonstrated to provide a fuller characterization protocol than using either approach alone. Using direct colloidal SERS methods, it was possible to observe the presence of the marker component, urolithin C, in each textile sample even when no brazilwood colorant survived and in the co-presence of other dyestuffs and textile degradation products such as 4-hydroxybenzoic acid. The additional acidic hydrolysis pre-treatment has been shown to promote the release of any remaining colorants from the mordant/textile fiber which allowed characterization of minor tannin (ellagic acid) and flavonoid dyestuff components (luteolin, fisetin) also present in the samples, although this treatment could make it harder to detect the brazilwood marker component. The results presented here confirmed the original use of brazilwood in each textile even when a further neoflavonoid-based dye, logwood, is hypothesized. This SERS methodology has the potential to be used as an in situ method for the examination of textiles where brazilwood colorant is potentially present at the fiber surface. Other artefacts where a brazilwood-based colorant is suspected in exposed surface layers could be examined using a similar approach.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/heritage4030078/s1. Figure S1: The HPLC-DAD chromatograms featured in Figure 4.

**Author Contributions:** Conceptualization, B.D., A.R., C.H., D.P. and C.M.; data curation, B.D. and I.D.; formal analysis, B.D. and I.D.; methodology, A.R., M.P.C. and C.M.; supervision, M.P.C. and C.M.; writing—original draft, B.D., I.D., A.R., C.H. and D.P.; writing—review and editing, B.D., I.D., A.R., C.H., D.P., M.P.C. and C.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the research activities in the IPERION HS project, funded by the European Commission, H2020-INFRAIA-2019-1 (Grant Agreement n. 871034).

**Data Availability Statement:** All raw and processed data are in the process of being made available to accompany this paper, please contact the corresponding author for updates.

**Conflicts of Interest:** The authors declare no conflict of interest.
