# First discovery of charcoal-based prehistoric cave art in Dordogne

Ina Reiche, Yvan Coquinot, Antoine Trosseau, Anne Maigret

► To cite this version:

Ina Reiche, Yvan Coquinot, Antoine Trosseau, Anne Maigret. First discovery of charcoal-based pre-historic cave art in Dordogne. Scientific Reports, 2023, 13, pp.22235. 10.1038/s41598-023-47652-1. hal-05371378

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# First discovery of charcoal-based prehistoric cave art in Dordogne

Ina Reiche¹*, Yvan Coquinot², Antoine Trosseau¹,³, Anne Maigret²

1 PSL University, ENSCP, CNRS, Paris, France

2 C2RMF, Louvre Museum, Paris, France

3 present address: University of Caen, France

Archaeologists have long been puzzled by the exact age of Paleolithic cave art in Europe especially in the Franco-Cantabrian region with hundreds of decorated caves because the creation of this parietal art (paintings, drawings and engravings) is closely tied to the appearance of first modern humans in Europe and their ways of life. The Dordogne region, one of the richest regions in terms of Paleolithic cave art in the world with more than 200 cave sites, is currently known to provide figures of cave art solely made with mineral coloring matters that cannot be dated directly. Using in-situ non-invasive Raman spectroscopy combined with portable X-ray fluorescence analysis as well as visible and infrared imaging of the decor of the Font-de-Gaume cave, we show the presence of a large number of charcoal-based Paleolithic figures besides others made of iron and manganese oxides in the main galleries for the first time. The creation periods of the cave art at Font-de-Gaume are mainly attributed to the Magdalenian period and probably more complicated constituted of at least two creation phases than commonly established as shown by the direct or partial superimposition of carbon-based and iron- and/or manganese-based figures. Our new results contribute to a better understanding of the organisation of the ornamentation and thus of the imaginary language of our Prehistoric ancestors. The discovery opens new research possibilities for re-reading of the complex panels and absolute radiocarbon dating.
## Key words

Paleolithic cave art, coloring matter, charcoal, manganese and iron oxide, animal representations, Font-de-Gaume cave

## Main text

A large number of Carbon (charcoal)-based black graphical entities was discovered by our team between the 27th and the 29th of February 2020 in the décor of the main galleries of the Font-de-Gaume cave, Dordogne, Southern France. The Dordogne is one of the world's richest regions in terms of decorated Paleolithic caves such as the famous Lascaux cave ¹,². The decoration recognised in 1901 by Capitan, Peyrony and Breuil was known to be created using different iron (Fe) and manganese (Mn) oxide-based coloring matters, thus preventing direct radiocarbon dating ³. The discovery of C-based cave art is therefore not only crucial for the Font-de-Gaume cave but for the whole Dordogne region.

The décor of the Font-de-Gaume cave shows naturalist mono-, bi- and polychrome paintings as well as engravings of different animals and signs in their main galleries. A little over two hundred figurative depictions were counted and can be divided in approximately two thirds to animal art and one third to signs (tectiforms)⁴,⁵. Mainly bison (N 80), mammoths, deer, horses and two negative hands are represented, which is why Font-de-Gaume is also called "Bison Cave"³.

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"
⁶ 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. (1910) hypothesized at least two different styles of representations right after the discovery of the cave art in Font-de-Gaume³. Leroi-Gourhan (1979) also stated that at least two creation steps are noticeable from the outset in the Font de Gaume cave⁷. 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 ⁸⁻¹⁰.

Henri Moissan, a French Nobel prize winner, identified in 1902 Fe and Mn oxides in the coloring matter samples from the Font-de-Gaume décor ¹¹. 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-situ¹²⁻¹⁷.

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 (p-XRF) and micro-Raman spectroscopy. In-situ micro-Raman spectroscopy allows a precise identification of mineralogical phases of the Fe- and Mn-oxides and the detection of carbon (C)-based compounds ¹⁶,¹⁸,¹⁹. In-situ pXRF enabled the determination of different types of Mn-oxide compounds in the black prehistoric figures¹³,¹⁶,²⁰, even if this method presents intrinsic analytical difficulties linked to the strong penetration of X-rays²¹. Charcoal-black-based graphical entities could be identified and differentiated from other carbon (C)-based materials thanks to its characteristic broad scattering bands using Raman spectroscopy and deduced from the absence of a Mn signal in the in-situ pXRF spectra¹⁸. Moreover, false color processed infrared light (FCIR) imaging shows a different contrast for C-based figures, which provides an extrapolation of the identified presence of C in small areas to parts or the whole figure.
However, the observed systematic reddish contrast of C-based lines in the graphical entities is
not fully understood.

The two types of naturalistic and schematic representations of animals are superimposed at the
central crossing of the main and the lateral galleries of the Font-de-Gaume cave, the so-called
“Carrefour”. This series of figure comprises the naturalistic facing reindeers no. 11 and 12 (Fig.
1a), the naturalistic panel no. 13 with a reindeer likely superimposed with a horse that it difficult
to read, the naturalistic panel no. 14 with a bison superimposed with a deer and the schematic
bison 15 in addition to some unidentified schematic marks (Fig. 2a). Above the reindeer no. 11,
there is a black dotted line, which crosses the animal representation below the black contour
line. FCIR imaging revealed the presence of another animal below the reindeer no. 12 that was
not recognized until now, likely a black horse (Fig. 1b). Superimposed with the reindeer no. 13,
there are also unidentified black lines that appeared reddish in the FCIR image (Fig. 2b). A
detailed description of the graphical entities, such as their artistic techniques, the in-situ
measurement points and the analytical results, is given in the supplementary information (SI,
Figure description).
<figure><img src="image_2.png" /><figcaption>Figure 1 a) Vis image of the selected panel at the “Carrefour” ranging from the facing reindeers no. 11 and 12 at Font-de-Gaume cave and b) corresponding False colour processed infrared light (FCIR) image of the facing reindeer evidencing the underlying black horse figure with the indicated analytical pXRF and micro-Raman point analyses.</figcaption></figure>
a)

<figure><img src="image_3.png" /></figure>
b)

<figure><img src="image_4.png" /><figcaption>Figure 2 a) Vis image of the selected panel at the “Carrefour” of the panels no. 13 and 14 composed of a reindeer and a horse as well as bison and a reindeer, respectively, and the schematic bison no. 15 and (b) corresponding False colour processed infrared light (FCIR) image with the indicated analytical pXRF and micro-Raman point analyses.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>Figure 3. Detail of the Carrefour: a) in-situ Raman spectra of the bison 14 (R019) and the deer 13 (R025) with the analytical spots indicating the presence of charcoal, Mn oxides and calcite. The Raman bands around 1398 cm⁻¹ and 1597 cm⁻¹ are those of charcoal. The band at 1085 cm⁻¹ is the main calcite band. Mn oxides are identified thanks to the bands between 500 and 670 cm⁻¹ b) pXRF spectra of the bison 15, of the wall support and of the superimposed figures of the panel 14 showing different intensities of the Mn peak.</figcaption></figure>
All black lines are not exhibiting the same contrast color in the FCIR image indicating the presence of different kinds of black coloring matter (Fig. 1b and 2b, SI Figure description). There are black lines that remain black in the FCIR images while others turn reddish after this imaging processing. In-situ pXRF showed that the black lines that appear black in the FCIR images correspond to Mn-based lines whereas those that appear reddish do not show a clear Mn-signal in their corresponding spectra (Fig. 3b, Table 1). These lines depict the typical C-based broad bands, especially with the shape of those of charcoal, at 1385 cm⁻¹ and 1594 cm⁻¹ in the Raman spectra (Fig. 3a), whereas the other black lines that remain black in the FCIR image show the presence of Ba bearing Mn oxide phases such as pyrolusite and romanechite (Fig. 3b). A semi-quantitative approach allowed the determination of the ratio of mineralogical phases in the Mn-oxide-based representations (Table 1, SI Table S1 and XRF data and spectra excel sheet) and thus a further discrimination between Mn-O-based figures. The chemical composition of the red areas of the reindeer 11 and 12 is corresponding to Fe-oxides, hematite, whereas the black lines of these figures correspond to the Mn oxides romanechite (0.6-0.8) and pyrolusite (0.2-0.4). The dotted line above reindeer no. 11 crossing the animal below is composed of a C-black as it shows the characteristic broad Raman scattering bands of charcoal and a reddish contrast in the IRFC image. The reindeers 13 and the bison 14 mainly show romanechite (Ba rich Mn oxide confirmed by pXRF) as coloring matter, whereas underlying marks and the underlying deer show charcoal. The bison no. 15 is entirely drawn with charcoal (Fig. 3a). This figure as well as the underlying deer 14 are stylistically more schematic in comparison to the other naturalistic bison and reindeers. Interestingly, these figures are displayed in the opposite direction as the above lying Mn-O-based reindeer and bison. A similar spectral response corresponding to charcoal is found for the unknown figure, likely the horse, below the red ventral area of the reindeer no. 12. The head of the horse in charcoal is also directed in the opposite direction to that of the red reindeer no. 12.
Thus, we observe graphical entities that are made using charcoal that exhibit a schematic style below two types of Mn-O-based figures. The different types of coloring matter can be considered as distinctive characteristic of different creation phases according to observation in other comparable decorated caves such as Lascaux ²,⁸,¹⁰ and can correspond to different imaginary languages of specific prehistoric groups. Our current knowledge indicates differences in the type of Mn-O-based coloring matter between the Lascaux (cryptomelane-based) and the Font-de-Gaume (romanechite and pyrolusite-based) cave but shows similarities between Font-de-Gaume and Rouffignac's black coloring matter ¹⁶,²⁰,²². Above all, the identification of several charcoal-based figures below the characteristic Magdalenian style Mn-O-based and Fe-O-based figures opens new research avenues to chronologically classify the cave art more precisely, improve the knowledge of creation phases, the frequentation of the cave site and, eventually, allow interregional comparison with absolute dates. The “perspective tordue” of the bison no. 15, named Picasso by our team because of its schematic style, might be even more ancient than the Magdalenian period.

**Main references**

1. Leroi-Gourhan, A. *Préhistoire de l'art Occidental*. (1965).

2. Aujoulat, N. *Lascaux: le geste, l'espace et le temps*. (Editions Seuil, 2004).

3. Capitan, L., Breuil, H. & Peyrony, D. *La Caverne de Font-de-Gaume aux Eyzies Dordogne*. vol. 1 vol (Monaco : Impr. A. Chêne, 1910).

4. Capitan, L. & Breuil, H. Les signes tectiformes sur les parois de a grotte de Font-de-Gaume. *Assoc. Fr. Pour Av. Sci.* 756-759 (1905).

5. Vialou, D. & Vilhena Vialou, A. Font-de-Gaume : le site des tectiformes. *PALEO Rev. Archéologie Préhistorique* 219-230 (2014).
6. Paillet, P. *Le bison dans les arts magdaléniens du Périgord*. vol. 33 (CNRS éditions, 1999).

7. *Lascaux inconnu*. (Editions de Centre national de la recherche scientifique, 1979).

8. Lorblanchet, M. *Les grottes ornées de la préhistoire: nouveaux regards*. (Éd. Errance, 1995).

9. Lorblanchet, M. *Art pariétal. Grottes ornées du Quercy*. (2010).

10. Reiche, I., Vignaud, C., Chalmin, É., Menu, M. & Geneste, J.-M. The ornamentation steps of the Bull Rotunda of the Lascaux cave give new insights into the temporality of the living. *Archaeometry* accepted.

11. Moissan, H. Sur les matières colorantes des figures de la Grotte de Font-de-Gaume. *Compte-rendu de l'académie des sciences* 1539–1540 (1902).

12. Beck, L. et al. First use of portable system coupling X-ray diffraction and X-ray fluorescence for in-situ analysis of prehistoric rock art. *Talanta* **129**, 459–464 (2014).

13. Beck, L. et al. In situ Analysis of Rock art in the Cave of Rouffignac by Using a Portable XRF-XRD System. *ArchéoSciences* **No 36**, 139–152 (2012).

14. Gay, M. et al. Efficient quantification procedures for data evaluation of portable X-ray fluorescence – Potential improvements for Palaeolithic cave art knowledge. *J. Archaeol. Sci. Rep.* **10**, 878–886 (2016).

15. Gay, M., Plassard, F., Müller, K. & Reiche, I. Relative chronology of Palaeolithic drawings of the Great Ceiling, Rouffignac cave, by chemical, stylistic and superimposition studies. *J. Archaeol. Sci. Rep.* **29**, 102006 (2020).

16. Trosseau, A., Maigret, A., Coquinot, Y. & Reiche, I. *In situ* XRF study of black colouring matter of the Palaeolithic figures in the Font-de-Gaume cave. *J. Anal. At. Spectrom.* **36**, 2449–2459 (2021).

17. Beck, L. et al. Non-destructive portable techniques for carbon in-situ screening before sampling for dating prehistoric rock paintings. *Radiocarbon* **55**, 436–444 (2013).
18. Pagès-Camagna, S., Duval, A. & Guicharnaud, H. Study of Gustave Moreau's black drawings: identification of the graphic materials by Raman microspectrometry and PIXE. *J. Raman Spectrosc.* **35**, 628–632 (2004).

19. Lahlil, S. *et al*. The first in situ micro-Raman spectroscopic analysis of prehistoric cave art of Rouffignac St-Cernin, France. *J. Raman Spectrosc.* **43**, 1637–1643 (2012).

20. Gay, M., Plassard, F., Müller, K. & Reiche, I. Relative chronology of Palaeolithic drawings of the Great Ceiling, Rouffignac cave, by chemical, stylistic and superimposition studies. *J. Archaeol. Sci. Rep.* **29**, 102006 (2020).

21. Calligaro, T., Castelle, M., Lebon, M. & Mauran, G. Spectrométrie de fluorescence des rayons X portable : quantification, imagerie, où en est-on ? in *Instrumentation portable. Quels enjeux pour l'archeometrie?* (CNRS Editions, 2019).

22. Reiche, I. *et al*. Analyses non invasives in situ des œuvres préhistoriques de la grotte de Font-de-Gaume pour une meilleure connaissance du décor pariétal polychrome et de son organisation. *PALEO Rev. Archéologie Préhistorique* (in press).
<table><caption>Table 1. Analytical results obtained on the different figures of the “Carrefour” at Font-de-Gaume cave.</caption><thead><tr><th>XRF Analysis</th><th>Raman Analysis</th><th>Figure</th><th>Type of coloring matter (pXRF)</th><th>Type of coloring matter (Raman)</th><th>Color contrast in FCIR</th><th>Coloring matter inferred from FCIR</th></tr></thead><tbody><tr><td>XRF_001 -<br>XRF_008</td><td>R_001-R_003</td><td>Reindeer no. 11</td><td>Fe oxide<br>mean Ba Mn oxide<br>(group II <sup>16</sup>)</td><td>mix of romanechite<br>(Ba<sub>2</sub>Mn<sub>5</sub>O<sub>10</sub>, xH<sub>2</sub>O)<br>/ pyrolusite (MnO<sub>2</sub>)</td><td>black</td><td>Mn oxide</td></tr><tr><td>XRF_012 -<br>XRF_017</td><td>-</td><td>backbone of<br>Reindeer no. 12</td><td>Fe and Mn oxide</td><td>-</td><td>black</td><td>Mn oxide</td></tr><tr><td>XRF_018 -<br>XRF_022<br>XRF_024 -<br>XRF_025</td><td>R_004 - R_009</td><td>black figure under<br>Reindeer no. 12</td><td>Mn signal as low as<br>in the wall support</td><td>charcoal</td><td>reddish</td><td>charcoal</td></tr><tr><td>XRF_026 /<br>XRF_027</td><td>R_010 - R_021</td><td>Deer no. 13</td><td>Mn oxide</td><td>charcoal</td><td>black (because<br>of super-<br>imposition of<br>charcoal with<br>Mn oxide)</td><td>Mn oxide</td></tr><tr><td>XRF_028 -<br>XRF_030</td><td>-</td><td>black dots of an<br>unidentified figure<br>under deer no. 13</td><td>Mn oxide</td><td>charcoal</td><td>reddish</td><td>charcoal</td></tr><tr><td>XRF_032 -<br>XRF_036<br>XRF_037</td><td>R_023 - R_027</td><td>Bison 14<br>(+ black dots<br>around it)</td><td>high Ba Mn oxide<br>(group I <sup>16</sup>)</td><td>charcoal<br>mix of romanechite<br>(Ba<sub>2</sub>Mn<sub>5</sub>O<sub>10</sub>, xH<sub>2</sub>O)<br>/ pyrolusite (MnO<sub>2</sub>)</td><td>black</td><td>Mn oxide</td></tr><tr><td>XRF_031<br>XRF_037<br>XRF_038 -<br>XRF_041</td><td>R_027 - R_034</td><td>Deer 14</td><td>Mn signal as low as<br>in the wall support</td><td>charcoal</td><td>reddish</td><td>charcoal</td></tr><tr><td>XRF_042 -<br>XRF_046</td><td>R_035 - R_046</td><td>Bison 15</td><td>Mn signal as low as<br>in the wall support</td><td>charcoal</td><td>reddish</td><td>charcoal</td></tr></tbody></table>
## Figure legends

Figure 1. a) Vis image of the selected panel at the “Carrefour” ranging from the facing reindeers no. 11 and 12 at Font-de-Gaume cave and b) corresponding False colour processed infrared light (FCIR) image of the facing reindeer evidencing the underlying black horse figure with the indicated analytical pXRF and micro-Raman point analyses.

Figure 2 a) Vis image of the selected panel at the “Carrefour” of the panels no. 13 and 14 composed of a reindeer and a horse as well as bison and a reindeer, respectively, and the schematic bison no. 15 and (b) corresponding False colour processed infrared light (FCIR) image with the indicated analytical pXRF and micro-Raman point analyses.

Fig. 3. Detail of the carrefour with indicated analytical points: a) in-situ Raman spectra of the bison 14 (R019) and the deer 13 (R025) indicating the presence of carbon. The bands at 1385 cm⁻¹ and 1594.2 cm⁻¹ are those of carbon black. The band at 1085 cm⁻¹ is the main calcite band. Mn oxides are also identified thanks to the bands between 500 and 670 cm⁻¹ b) pXRF spectra of the bison 15, of the wall support and of the superimposed figures of the panel 14.

Table 1. Analytical results obtained on the different figures of the “Carrefour” at Font-de-Gaume cave.
# Methods (including separate data and code availability statements)

## Photographic imaging

Photography under visible light (VIS) was performed with the use of two halogens on stand that allows to obtain images in high definition (Nikon, 24 MPixel) with well-lit figures for identification of the areas to be analyzed and the detailed study of the figures without traveling on site.

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.

## Image treatment

The false color processed infrared image (FCIR) is a composite image obtained by superimposing two images representing the same view, one in the VIS and the second in IR range.

The IR image is produced using a sensitive camera from 400 to 1000 nm associated with a filter placed in front of the lens, which cuts the visible light and only allows radiation with a wavelength above 900 nm. A more or less contrasted grayscale image is obtained. Its interpretation can be difficult because it is depending on the properties of the pigments to absorb the IR light. In the colorimetric space, the red, green and blue (RGB) parts of the IR image are combined with the red and green layers of the VIS image using Photoshop®. The gray levels of the IR are then translated into color, and we get a new image in false color (FC). This
association of both types of images makes it possible to differentiate different materials, which
can appear very similar in the VIS image.

**Experimental conditions of portable X-ray fluorescence analysis (pXRF)**

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. It also benefits of a camera. The experimental conditions were 600 s of analysis with
40 kV and 40 μA delivered by the tube.

**Data treatment procedures**

**Linear regression based on elemental ratios**

This protocol aims at bringing a first description of the black coloring matter based on Mn
oxides by discriminating several groups corresponding to different phases or mixtures from
spot measurements in pXRF directly on the prehistoric paintings. It has been previously used
by other scholars ¹⁻³ but it was checked and improved for the current case study of the decor of
the Font-de-Gaume cave ⁴.

The pXRF spectra obtained during these measurements are processed with the PyMca software
⁵. This software allows to fit the elemental peaks and to obtain an intensity in number of counts.

As stated above, we use the intensity of Ba and Mn in this protocol. The signal of Mn is several
orders of magnitude stronger in the coloring matter than in the substrate, while Ba is only found
in the coloring matter. Thus, it is possible to use the signal ratios of these elements as distinction
markers of the different types of coloring matters used. Depending on the Ba/Mn intensity ratio,
several raw materials are then differentiated. In practice, the intensities of Ba are plotted versus
those of Mn in a graph, and a linear regression is performed, allowing to assess the uncertainty.
By doing so, an offset appears in the linear regression, so the meaningful quantity to study is
actually the slope of these curves. Last but not least, this protocol allows studying coloring
matters that are not pure because only two characteristic elements are used in the process.

Experimental conditions of portable micro-Raman spectroscopy

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. The head is mounted on a stable tripod with one axial
translation (forward and backwards) and three rotation axes. Such long working distances
guarantee the safety of the paint. The measuring head is connected to an air-cooled Nd: YAG
laser (Coherent DPSS 532; λ = 532 nm; laser power on the sample lower than 5 mW) and to
the spectrometer via a 5 m long, flexible fiber optic cable. The Raman device is mounted with
the HE 532 spectrometers from Jobin-Yvon HORIBA. A Peltier-cooled CCD detector (only for
λ = 532 nm laser excitation; focal length 300 mm; fixed grating 920 lines / mm; fixed
wavenumber from 100 cm⁻¹ to 3215 cm⁻¹; spectral resolution of about 3 cm⁻¹) was used for
quick identification of the coloring matter. The integration time during the measurements was
ranging between one second and 6 s with 10 to 30 accumulations. Analogous conditions were
employed as those used at the Rouffignac cave⁶.

Data treatment procedure

The spectra are evaluated with the LabSpec software® in order to obtain the characteristic
Raman shift. Spectra are treated by Edge filter artefact and baseline corrections. The baseline
is subtracted (use of the ROI 250-800/1200 cm⁻¹). Peak fitting is performed by fitting the Raman bands with Gaussian and Lorentzian amplitudes.

Characteristic Raman bands of different mixtures of the geological references of the Mn oxides (pyrolusite and romanechite) are shown in the Figure 4. The semi-quantitative evaluation of the Mn oxides is complicated because of the superimposition of different Mn oxide bands and the variation of the Raman signals with low intensity.

<figure><img src="image_6.png" /><figcaption>Figure 4. Raman spectra of different mixtures of geological pyrolusite (P) and romanechite (R) references measured with the same equipment, with their characteristic bands indicated.</figcaption></figure>

Different C-based references were studied as well⁷. The treated Raman spectra are represented in the Figure 5.
<figure><img src="image_7.png" /><figcaption>Figure 5. Raman spectra of different C-based references measured with the same equipment.</figcaption></figure>

## Methods references

1. Beck, L. et al. First use of portable system coupling X-ray diffraction and X-ray fluorescence for in-situ analysis of prehistoric rock art. Talanta 129, 459-464 (2014).

2. Gay, M. et al. Efficient quantification procedures for data evaluation of portable X-ray fluorescence - Potential improvements for Palaeolithic cave art knowledge. J. Archaeol. Sci. Rep. 10, 878-886 (2016).

3. Gay, M., Plassard, F., Müller, K. & Reiche, I. Relative chronology of Palaeolithic drawings of the Great Ceiling, Rouffignac cave, by chemical, stylistic and superimposition studies. *J. Archaeol. Sci. Rep.* **29**, 102006 (2020).
4. Trosseau, A., Maigret, A., Coquinot, Y. & Reiche, I. In situ XRF study of black colouring matter of the Palaeolithic figures in the Font-de-Gaume cave. J. Anal. At. Spectrom. 36, 2449-2459 (2021).

5. Solé, V., Papillon, E., Cotte, M., Walter, P. & Susini, J. A Multiplatform Code for the Analysis of Energy-Dispersive X-ray Fluorescence Spectra. Spectrochimica Acta B 62(1), 63-68 (2007)

6. Lahlil, S. et al. The first in situ micro-Raman spectroscopic analysis of prehistoric cave art of Rouffignac St-Cernin, France. J. Raman Spectrosc. 43, 1637-1643 (2012).

7. Pagès-Camagna, S., Duval, A. & Guicharnaud, H. Study of Gustave Moreau's black drawings: identification of the graphic materials by Raman microspectrometry and PIXE. J. Raman Spectrosc. 35, 628-632 (2004).

## Acknowledgements

We acknowledge the authorization for performing the research and the on-site measurement campaigns by the Direction régionale des Affaires culturelles (DRAC) Nouvelle Aquitaine through the archaeological operation at LES-EYZIES-DE-TAYAC-SIREUIL Font-de-Gaume (analyses matière picturale) code no. 028046 (2020-2021). We thank the numerous members of the Font-de-Gaume team, without whose continuous and friendly support this research would have been impossible. We specially thank Jean-Jacques Cleyet-Merle and Georges Levy, administrators the site until 2021, and later their successor Marc Martinez for their trust and confidence. A particular thanks goes to all the guides that have been accompanying us in this research for ten years: Jean-Marie, Jean-Pierre, Céline, Brigitte, Thibaud, Stéphanie, and many others. We warmly thank Patrick and Elena Paillet (Muséum National d'Histoire Naturelle, MNHN, and Ministère de la Culture) as well as Catherine Cretin (Musée National de Préhistoire, les Eyzies-de-Tayac) besides all the other team members of the joint
archaeological operation "Font-de-Gaume inconnu" for the fruitful scientific discussions. The C2RMF is acknowledged for the provision of the experimental equipment necessary to performing this research (scientific imaging, Raman et pXRF). Michel Menu is thanked for his support of the program. The ANR DepthPaint program (ANR-20-CE29-0018) provided partial funding for the travel during measurement campaigns additionally to the C2RMF.

**Author contributions**

Conceptualization: IR, methodology: IR and YC, data acquisition: AT, AM, YC and IR, investigation: AT, YC and IR, data curation: AT, AM and YC, writing - original draft: IR, writing - review and editing: AT, YC, AM and IR, visualization: AT and AM, supervision: IR, project administration: IR, funding acquisition: IR, heading the archaeological operation at Font-de-Gaume: IR.

**Data and code availability statements**

All discussed data are either shown in the manuscript or in the supplementary information (SI).
The codes used are either open source (PyMCA) or are acquired licenses by the C2RMF. The
data are available through request to the corresponding author.

**Further statements**

Humans are not directly used in the study.

We confirm that all methods were carried out in accordance with relevant guidelines and
regulations.

We confirm that all experimental protocols were approved by a named institutional and/or
licensing committee.

We confirm that informed consent was obtained from all subjects and/or their legal guardian(s).
**Competing interest declaration**

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

**Additional information (containing supplementary information line**

The article contains supplementary information (SI).

**Corresponding author:**

Dr. Ina Reiche, PhD, habilitation thesis, CNRS research director

Head of FR New AGLAE 3506 CNRS-C2RMF-Chimie Paristech

Member of the PCMTH team, PSL-ChimieParistech, IRCP UMR8247 CNRS-C2RMF

Centre de recherche et de restauration des musées de France (C2RMF)

14 quai François Mitterrand, 75001 Paris, France

Phone : +33-1-40205669, ina.reiche@culture.gouv.fr / ina.reiche@chimieparistech.psl.eu

**Extended data figure/table legends**

Figure 4. Raman spectra of different mixtures of geological pyrolusite (P) and romanechite (R) references measured with the same equipment, with their characteristic bands indicated.

Figure 5. Raman spectra of different C-based references measured with the same equipment, with their characteristic bands indicated.