The combined use of SEM-EDX, Raman, ATR-FTIR and visible reflectance techniques for the characterisation of Roman wall painting pigments from Monte d’Oro area (Rome): an insight into red, yellow and pink shades

Abstract

The aim of this work has been the identification of the painter’s materials employed in the wall decoration of some destroyed buildings dating approximately between the first century B.C. and the first century A.D. This research originates from a previously started joined archaeological and analytical investigation concerning a varied group of findings that resulted from a rescue excavation performed by Soprintendenza Archeologica in the area of Monte d’Oro in Rome. The focus of this study progression has been directed to a numerous selection of monochrome red, pink and yellow-pigmented fragments. The analyses were performed by means of scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDX) combined with Raman and Fourier transform infrared (FTIR) spectroscopies; visible reflectance measurements have also been carried out and the relevance of this technique in such a kind of archaeological studies has been highlighted. Most attention has been given to the assessment of the performances of non-destructive techniques achieved by portable Raman, and visible reflectance instrumentation to test their diagnostic capabilities. In addition to the expected and well-known pigments such as cinnabar, red ochre, hematite for the reds and yellow ochre for the yellows, the study highlighted a diffuse use of mixed colours and in some cases the possible presence of overlapped painted layers and confirmed the presence of gildings. Among the mixtures of pigments, the most singular outcome concerns the pink fragments revealing the possible application of bone white, which seems to be rather uncommon as a pigment in Roman wall decorations.

Study of a surface coating present on a Renaissance Piety from the Museum of Ancient Art (Castello Sforzesco, Milan)

“…The more plausible hypothesis is that a kind of drying oil was used as a binder and mixed with pigments in order to apply the colour to the stone surfaces (Aguado-Guardiola and Fuster-López, 2017). However, it is known that FT-IR spectroscopy is only indicative of the kind of binder (Bonizzoni et al 2018, Guglielmi et al 2021. Nevertheless, the highlighted signals are consistent with the use of an oil, as confirmed by the comparison with some references (https://spectra.chem.ut.…”

“…In samples P3a and P4a, stain peaks due to organic substances (at about 1730 cm −1 as well as at about 2900 cm −1 ) are still present probably indicating the use of a compound such as oil or wax that was applied to the surface and was not removed with the cleaning (Bonizzoni et al 2011, Guglielmi et al 2021. The more plausible hypothesis is that a kind of drying oil was used as a binder and mixed with pigments in order to apply the colour to the stone surfaces (Aguado-Guardiola and Fuster-López, 2017).…”

Hyperspectral Imaging and Raman Analyses of the Red Decoration of the St. Mauro Altar in St. Salvatore's Church (Pavia)

“…Raman measurements allowed recognition of cinnabar (HgS) on some of the red decorative plant motifs and on the birds' wings (red squares in figure 1) by the bands at 253, 284 (sh) and 343 cm -1 [16]. Conversely, on the red area surrounding the restored part on the left side of the altar, the resultant decoration was made of red ochre (red circle in figure 1), characterised by the bands at 290 and 409 cm -1 [17].…”

Investigation of red substances applied to chank shell beads from prehistoric site of Qulong in Ngari Prefecture, Tibet, China

“…To further confirm the composition of the pigment, samples QSM2-12 and QSM1-16a were analyzed by Raman spectroscopy, and the external surface of QSM1-11a was analyzed by XRD and FTIR. The Raman spectrum of QSM2-12 and QSM1-16a (Figure 2) shows bands at 222 cm −1 , 289 cm −1 , 406 cm −1 , and 606 cm −1 , which are entirely characteristic of hematite (Guglielmi et al, 2022). The infrared spectrum of QSM1-11a (Figure 3; Table 1) shows bands at 467 cm −1 and 529 cm −1 which may be assigned to hematite (Bikiaris, et al, 2000), while there are also obvious diffraction peaks of hematite in the XRD spectrum (Figure 4).…”