Dye analysis of archaeological Peruvian textiles using surface enhanced Raman spectroscopy (SERS)

Surface-enhanced Raman spectroscopy (SERS) is an emerging technique for the identification of colorants at low concentrations, making it ideal for degraded and irreplaceable archaeological materials. Using silver nanoparticles (AgNPs) as the SERS platform, this research on the identification of textile dyes compares direct on-the-fiber extractionless analyses with micro-extraction methods employing hydrofluoric acid vapor, formic acid, and hydrochloric acid solutions. Seven red samples from Wari and Malena textiles from the site Huaca Malena in Peru and reference yarns dyed with Relbunium and cochineal were analyzed using individual fiber samples. Complementary analysis of archaeological samples was conducted with fiber optics reflectance spectroscopy (FORS). Carminic acid, the primary colorant of cochineal, and pseudopurpurin and purpurin, the main coloring compounds of Relbunium were detected in the reference samples. Three archeological samples provided potential matches for carminic acid and two may contain purpurin and pseudopurpurin. FORS, data indicate that all the archaeological samples contained cochineal