Raman spectroscopy in experimental rock art: Improving the study of ancient paintings

Abstract

The present work analyzes Raman spectra of red, white, and black experimental paintings manufactured according to archeological and ethnographical data from Patagonia (South America), in order to provide reference patterns to better understand ancient signatures of rock art. Methodological insights are also presented, evaluating pitfalls and advantages of Raman spectroscopy. For this purpose, different pigments (hematite, gypsum, charcoal) mixed with binders and additives (Lama guanicoe fat, blood, urine, saliva, gypsum) were combined. Results show that, despite its high‐spatial resolution, Raman analysis shows painting spectra often reflecting multicomponent signals at micrometer‐scale. Results also indicate that fat and blood show well‐defined spectra in paintings, whereas saliva and urine have negligible signatures, so a relatively high and low archeological preservation is expected, respectively. On the other hand, laser‐related thermoalteration processes of fat and blood binders are triggered by the presence of hematite. This thermoalteration promotes conspicuous signatures in fat and blood binders related to disordered CC bonds (ca. 1,330 and 1,566 cm−1), which are also found in charcoal. Therefore, disordered carbon in the Raman spectra of rock art may not necessarily imply the presence of charcoal‐bearing pigments but may also result from thermoalteration of organic materials. Evidence of blood migration through rock porosity is registered as well, with significant implications for rock art preservation, composition, and dating.

Los Motivos Rojos en El Campo Volcánico Pali Aike (Santa Cruz, Argentina): Distribución De Pinturas Rupestres, Composición De Pigmentos Y Fuentes De Procedencia

“…3.800 años AP. Se trata de un entierro primario de cinco individuos que fueron depositados sobre una superficie vegetal de manufactura antrópica con abundantes restos de ocre y huesos de fauna asociados (L'Heureux y Barberena, 2008;Ozán et al 2020).…”

“…La μXRF permite caracterizar la composición química de una gran cantidad de materiales, tales como artefactos líticos, vidrios, metales y pastas cerámicas (Cremonte et al 2015;Durán et al 2012;Respaldiza Galisteo et al 2017;entre otros). Por su parte, la espectroscopía Raman ha sido aplicada en Patagonia, principalmente en pinturas rupestres (Brook et al 2018;Gurin et al 2021;Romero Villanueva y Barberena, 2017;Rousaki et al 2018;Wainwright et al 2002), aunque también ha sido utilizada para estudiar residuos de pigmentos en estratigrafía (Fiore et al 2008), tiestos cerámicos (Rousaki et al 2015), minerales asociados a restos humanos (Franco et al 2012;Ozán et al 2020;Tomasini et al 2015), artefactos óseos pintados (Romero Villanueva y Barberena, 2017) y objetos arqueológicos subacuáticos (Elkin et al 2012), entre otros materiales.…”

Dynamic repulsive interaction enables an asymmetric electron–phonon coupling for improving Raman scattering

“…Surface-enhanced Raman spectroscopy (SERS), which depends on the electromagnetic mechanism (EM) and chemical mechanism (CM), is an indispensable candidate method for detecting molecules with extremely high sensitivity, and intensively applied in cross-disciplinary fields including chemistry, biology, agriculture and archaeology. [1][2][3][4][5] The EM is attributed to the local electromagnetic fields augmented by local surface plasmon resonance (LSPR) with superior SERS performance, while the CM is mainly induced by the charge transfer associated with complementary effects, say, molecule resonance, exciton resonance, Mie resonance, 6 etc., between the substrate and the molecule. [7][8][9][10][11] Nevertheless, the practical application of EMbased noble metal SERS substrates is hindered by poor surface uniformity, stability and biocompatibility.…”