An important development in the potential dating of European cave art has been made by the use of portable x-ray fluorescence equipment to analyze the pigments used in the paintings. If the black paint is based on Manganese dioxide there is no possibility of radiocarbon dating it, however, if black paint is based on charcoal can be identified, then the possibility of radiocarbon dating does exist. The scientific team carried this analysis out in Font de Gaume Cave in France.
A variety of photographic techniques were used to enhance variations in black pigments in the paintings. These small variations were assumed to be perhaps related to the use of different black pigments which could then be analyzed with the portable x-ray fluorescence (pXRF), and micro-raman spectroscopy.
“From a technical and a stylistic perspective, two types of animal representations can be distinguished. On the one hand, we have lifelike painted bison treated with bi- or polychromy, where painting and engraving are associated with the relief effects of the wall for an exceptional rendering. Different shades can be observed, ranging from black to brown and from red to yellow as well as the designs being mainly done in black and red. The archetype of “hyperbison” is found in many of these individuals. There are also drawn naturalist bison with black lines. On the other hand, there are graphical entities of different animals as well (bison, horse, deer) that are drawn and exhibit a more schematic style. Capitan et al. hypothesized at least two different styles of representations right after the discovery of the cave art in Font-de-Gaume. Leroi-Gourhan also stated that at least two creation steps are noticeable from the outset in the Font de Gaume cave. Evidence of different creation steps of the ornamentations have also been provided for the Bull Rotunda in the Lascaux cave and Pech-Merle, Lot, France–Henri Moissan, a French Nobel prize winner, identified in 1902 Fe and Mn oxides in the coloring matter samples from the Font-de-Gaume decor. Today, this UNESCO world heritage site is protected and sampling is only allowed by authorities in highly exceptional cases. The awareness of the fragility of decorated cave sites has led to a transition from micro-sampling to non-invasive analyses, carried out in-situ. Scientific imaging was used to record figures and panels of the Font-de-Gaume cave. Areas of interest could be selected for in-situ point analyses by portable X-ray fluorescence analyses (pXRF) and micro-Raman spectroscopy.” (Reiche et al. 2023:1-2)
Along with the pXRS and micro-Raman spectroscopy, the rock art was photographed with a range of color filters which also helped enhance the analysis of some pigment differences. “Photographic imaging allows observing coloring matters at the scale of the panels and figures in the cave. The points for chemical analyses by pXRF and for mineralogical analyses by portable micro-Raman Spectroscopy can be judiciously chosen. This also limits the number of analyses required per figure and allows extrapolating the results of the physico-chemical analyses to the whole figure or at least the remaining visible part of it. The results of the analysis can therefore be read and discussed in the prehistoric context at the scale of a figure, a panel or even an area in the cave.” (Reiche et al. 2023)
“Portable XRF analyses were conducted in-situ in the cave with the portable ELIO device of the brand XG-Lab/Bruker® of the C2RMF fixed on a tripod with two axial translations (forward and backwards as well as left to right) and three rotation axes. This standardized device holds a 50 kV X-ray tube with a Rh anode that can deliver a power of 4 W. The detector is a 17 mm2 SDD whit an energy resolution of 140 eV at the Mn Kα line. It is also equipped with a collimator able to focus the beam into a 1 mm spot, two lasers, a positioning system and a tripod. The distance between the measuring head and the wall is 5 mm. It also benefits of a camera for the observation of the measurement spot. The experimental conditions were 600 s of acquisition time with 40 kV and 40 μA delivered by the X-ray tube.” (Reiche et al. 2023) The first known use of pXRF equipment to analyze pictographs was by Bonita Newman and Lawrence Loendorf in 2005. (Newman and Loendorf 2005)
“The mobile Raman measuring device used was developed by Jobin–Yvon HORIBA and consists of components that can be easily moved during a measurement campaign. The device is equipped with a “Superhead SH 532” measuring head with an Olympus “long working distance” objective. In-situ Raman measurements require an arrangement with high flexibility and high stability at the same time. A working distance of 10 mm between the head and the wall guarantees the safety of the painted wall.” (Reiche et al. 2023) Raman spectroscopy detects the vibrational frequency of molecules, and since the molecules of each element vibrate at different frequencies the various elements can be distinguished. Micro-raman spectroscopy is raman spectroscopy through a microscope so a very small area can be analyzed, like a painted line or dot.
These
studies determined that some black lines, dots, and areas were created using
charcoal as the black pigment meaning that these could also be dated using
radiocarbon (C14) dating. These techniques could be reasonably
expected to be reliable in other instances of painted pictographs as well.
NOTE: Some images in this posting were retrieved from the internet with a search for public domain photographs. If any of these images are not intended to be public domain, I apologize, and will happily provide the picture credits if the owner will contact me with them. For further information on these reports you should read the original reports at the sites listed below.
REFERENCES:
Baum, Stephanie, 2023, First discovery of carbon-based cave art in France's Dordogne region could pave way for precise radiocarbon dating, 18 December 2023, https://phys.org/news/2023-12-discovery-carbon-based-cave-art-france.html. Accessed online 29 December 2023.
Reiche, Ina, Yvan Coquinot, Antoine Trosseau and Anne Maigret, 2023, First discovery of charcoal based prehistoric cave art in Dordogne, 14 December 2023, Nature Portfolio, Scientific Reports, 13:22235, https://doi.org/10.1038/s41598-023-47652-1. Accessed online 29 December 2023.
SECONDARY REFERENCE:
Newman, Bonita, and Lawrence Loendorf, 2005, “Portable X-Ray Fluorescence Analysis of Rock
Art Pigments.” Plains Anthropologist, vol. 50, no. 195, pp. 277–83. JSTOR,
http://www.jstor.org/stable/25670828. Accessed 9 Sept. 2024.
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