Raman microscopy of prehistoric paintings in French megalithic monuments

Abstract

International audienceRemains of pictorial decorations in a series of six representative megalithic monuments of Brittany (France) and two French stelae have been studied by micro-Raman spectroscopy for the first time. Fungal colonies on the painted orthostats made it difficult to obtain in situ Raman spectra of the paint components. Nevertheless, paint micro-specimens studied in the laboratory by micro-Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electronic microscopy combined with energy dispersive X-ray spectroscopy have made possible to characterise the materials present. The minerals α-quartz, albite, microcline, muscovite, phlogopite, celadonite, beryl and anatase have been identified in the granitic rocks supporting the paintings, while dolomite and calcite are dominant in the calcareous rocky substrata. Haematite is the main component of the red pictographs, whereas amorphous carbon and manganese oxides/oxihydroxides have been used in the black ones. Calcite, gypsum and amorphous carbon have been detected as additional components of the paint in some cases. Contamination with modern tracing materials (polystyrene and ε-copper-phthalocyanine blue) has been detected in several cases. The presence of pigments as decorative elements in megalithic monuments of Western France and its possible relation with those of the Iberian Peninsula create interesting expectations for the knowledge of the European megalithic culture

Viability of Raman microscopy to identify micro‐residues related to tool‐use and modern contaminants on prehistoric stone artefacts

“…The main vibrational bands in the spectra at 1236, 1304, 1416 and 1530 cm −1 (Fig. S5A, Supporting Information) are similar to the Raman fingerprint of fungi collected in situ on Neolithic paintings . Similar spectra were also obtained on individual fungi filaments encountered on the edges of the other four artefacts (examples in Fig.…”

Uncovering the hidden content of layered documents by means of photoacoustic imaging

“…Several studies have employed similar photoacoustic imaging approaches to delineate the distribution of endogenous absorbers in turbid tissues, reaching imaging depths up to several millimetres, even in cases that higher, more attenuating acoustic frequencies (>25 MHz) were detected . Furthermore, our previous research has shown that strong photoacoustic signals can be generated by pencil underdrawings with an energy fluence as low as ~10 μJ/cm 2 , which is considerably smaller than the typical irradiation fluence values used in traditional non‐destructive CH optical characterisation techniques such as Raman and laser‐induced fluorescence spectroscopy . Therefore, the incorporation of a higher power laser source in a more sophisticated illumination scheme, involving the simultaneous irradiation of the document from many sides or from various angles in respect to the vertical axis, could provide adequate SNR for reading printed text within documents consisting of several tens of pages.…”

A vueltas con la cronologia del prótomo pintado en “El portalón de Cueva Mayor” (Ibeas de Juarros, Burgos)

“…Ahora bien, como decíamos, es necesario caracterizar con precisión la composición química de los materiales pictóricos presentes para poder descartar cualquier alteración moderna o la presencia de elementos inusuales. Para ello se recurrió a la microespectroscopía Raman, una técnica no destructiva, que se ha revelado muy eficiente para identificar la composición química y mineralógica de pinturas rupestres (Hernanz et al 2012;Hernanz et al 2014;Hernanz et al, 2015;Hernanz et al, 2016;Hernanz et al, 2017). Opcionalmente, como ha sucedido en algunos casos Ruiz et al 2012) y así ocurrió en éste, se buscó la detección de compuestos de carbono apropiados, su caracterización y cuantificación de cara a la posibilidad de intentar la datación por radiocarbono (AMS 14 C).…”