Colette Vignaud

Analysis of rock art painting and technology of Palaeolithic painters

Archaeologists have attempted the interpretation of rock art, but have often disregarded the technical aspects of paints. Analysing paint samples for preparation techniques and studying the various compounds used, allows us to determine the technology of early painters. Palaeolithic artists used two main colours: red (iron oxide: natural hematite or heated goethite) and black (charcoal or manganese oxides). These pigments could be prepared in different ways (grinding, mixing with extender and/or binder or by heating) in order to enhance the properties of the paints. Analyses attempt to determine the physicochemical nature of the matter and its preparation mode, and to get an idea of its geographic origin. This paper presents techniques and methods used in the C2RMF laboratory for manganese oxide pigments. Distinction between manganese oxides with or without other cations is made and heat treatment of manganese oxide minerals is described. Results obtained for black pigment in Lascaux and Ekain caves are presented and discussed. From paint analyses, several conclusions are drawn concerning the technical level of Palaeolithic artists.

A multi-analytical study of bone diagenesis: the Neolithic site of Bercy (Paris, France)

Bone remains play an important role in archaeology as a source of information about the past. However, they alter over time. Alteration occurs at all scales from the macroscopic to nanoscopic level. The evaluation of information extracted on palaeodiets, ages and palaeoclimates from their chemical and isotopic composition requires the study of diagenetic modifications by means of different complementary analytical methods. Diagenetic parameters that quantify the post-mortem alteration of bone are bone histology, porosity, protein content, crystallinity of bone apatite, carbonate content, enrichment and leaching of chemical species in general. The investigation of these features can be performed by a combination of complementary elemental and structural analyses (particle-induced x-ray emission, particle-induced γ-ray emission, scanning electron microscopy (SEM) coupled with energy dispersive x-ray (EDX), electron microprobe, x-ray diffraction, infrared spectroscopy, transmission electron microscopy (TEM) with EDX), microscopic observations (optical, SEM, TEM) and porosity measurements.The study of animal bones from the Neolithic site of Bercy, France (4000 BC) from the same archaeological layer within different local depositional, hydrological and redox environments illustrates the possible information that can be extracted from the diagenetic study on the processes affecting the state of bone preservation. The main characteristic of the bone buried in the waterlogged zone is a high level of preservation of the organic matter and a low level of porosity inhibiting major structural or chemical modifications. The bone sample from the zone with a fluctuating hydrological regime shows a low level of organic matter and high porosity. Knowledge of the diagenetic patterns enables an estimation of the reliability of information obtained from bone analyses.

The crystallinity of ancient bone and dentine: new insights by transmission electron microscopy

We studied various archaeological and palaeontological bones and dentines from different burial environments by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and transmission electron microscopy (TEM), in the framework of a general study of diagenesis. FT-IR and XRD were used to evaluate the global preservation state of the bone and dentine mineral phase by determining a splitting factor (SF) or a crystallinity index (Cl), respectively. These data can be combined with studies on the nanometer scale made with TEM. This latter technique, coupled with electron microdiffraction, provides determination of dimensions and shapes of individual bone and dentine apatite nanocrystals as well as of secondary minerals formed during diagenesis. It enables us to distinguish between heat-induced recrystallization processes and crystal growth in solution occurring during diagenesis.

XRD study of the goethite-hematite transformation: Application to the identification of heated prehistoric pigments

Abstract When heated, yellow goethite dehydrates and transforms to red hematite. Both iron oxides were used by the Palaeolithic artists as pigments, one question being whether those people took advantage of the phase transformation. To answer this question, the dehydration of synthetic goethite was studied by XRD coupled to Rietveld refinement. It was shown that no hydroxylated hematite is formed during the early stages of dehydration, the presence of hydroxyl ions in materials treated at high temperatures being explained by trapped water inside porous microstructure (TEM). Archaeological samples from the south of France were investigated. Some of them exhibit distinctive features of heating which, supports the idea that Palaeolithic people used both natural and ex-goethite hematite.

Tem observations of goethite dehydration: application to archaeological samples

Abstract Red and black were the two colours around which Palaeolithic art was organised. Manganese oxides and charcoal were the black pigments and hematite (α-Fe 2 O 3 ) the red one. The latter mineral is naturally abundant, but archaeological observations nevertheless suggest that the well-known colour change accompanying the dehydration of yellow goethite (α-FeOOH) to red hematite may have been employed by Prehistoric artists to obtain red pigment. In order to confirm this assumption, a study was carried out on synthetic goethite samples using XRD and TEM. In particular, the goethite-to-hematite transformation was observed in situ and provided useful information about both dehydration and recrystallisation processes. The existence of water up to high heating temperatures was found to be coherent with the typical porous microstructure accompanying the phase transformation. Similar studies were carried out on archaeological hematites coming from Troubat, a French Pyrenean Palaeolithic site. Characteristic features of previous heating were identified, such as pores or small amounts of maghemite (α-Fe 2 O 3 ), which confirms that Prehistorics had acquired this technical know-how.

From mastodon ivory to gemstone: The origin of turquoise color in odontolite

Abstract Heat-induced color changes of fossilized Miocene mastodon ivory (13-16 Ma) have been known at least since the Middle Ages. Cistercian monks are believed to have created odontolite, a turquoise- blue “gemstone,” by heating mastodon ivory found in Miocene geological layers next to the Pyrrenean chain, France, to use it for the decoration of medieval art objects. This material has been the object of investigations of famous European naturalists and gemmologists, among them Réaumur (1683-1757). Although vivianite [Fe3(PO4)2·8H2O] is the commonly accepted coloring phase supposed to appear when heating fossilized mastodon ivory, our previous spectroscopic studies using PIXE/PIGE and TEM-EDX demonstrated that the chemical composition of collection odontolite and heated mastodon ivory corresponds to well-crystallized fluorapatite [Ca5(PO4)3F] containing trace amounts of Fe (230-890 ppm), Mn (220-650 ppm), Ba (160-620 ppm), Pb (40-140 ppm), and U (80-210 ppm). No vivianite has been detected. To provide new insights into the physico-chemical mechanism of the color transformation of fossilized ivory, we used the combination of UV/visible/near-IR reflectance spectroscopy, time-resolved laser-induced luminescence spectroscopy (TRLIF), and X-ray absorption near-edge structure (XANES). Contrary to what had formerly been described as the color origin in odontolite, our study has conclusively identified traces of Mn5+ by UV/visible/near-IR reflectance spectroscopy, TRLIF, and XANES inside the fluorapatite. Thus, odontolite owes its turquoise-blue color to Mn5+ ions in a distorted tetrahedral environment of four O2- ions. XANES also demonstrated oxidation of disordered octahedral Mn2+ ions to tetrahedral Mn5+ species in apatite during the heat process. So we give the first evidence of the real color origin in odontolite.

Heat induced transformation of fossil mastodon ivory into turquoise 'odontolite'. Structural and elemental characterisation

Abstract The present work deals with the structural and elemental analysis of turquoise mineral imitations as ‘odontolite’ or bone turquoise by transmission electron microscopy (TEM), scanning electron microscopy (SEM–EDX) and particle induced X-ray and γ-ray emission (PIXE–PIGE). The aim of the work is to evidence the former deliberate transformation of fossilised ivory by man in order to transform them into semi-precious stones. We show that the crystal structure of ‘odontolite’ artefacts consisting of fluorapatite (Ca5(PO4)3F) corresponds to that of heated fossil mastodon ivory (12–15 million years old). Metallic traces detected by PIXE–PIGE in these ‘odontolites’ are discussed in order to explain their role for coloration. Other more greenish turquoise imitations have a bone-like structure and composition, and carbonate–hydroxylapatite. The presence of copper salts at the surface is responsible for their green coloration.

Color origin and heat evidence of paleontological bones: Case study of blue and gray bones from San Josecito Cave, Mexico

Abstracts Results of the investigation of paleontological blue and gray bone fragments of small vertebrates coming from stratigraphic layer 770 at San Josecito Cave (Nuevo Leon, Mexico, dating between 28 000 and 19 000 years BP), are presented. Structural and elemental analyses combining X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and particle-induced X-ray and γ-ray emission (micro-PIXE/PIGE), as well as spectroscopic investigations [i.e., UV/visible/near-IR reflectance spectroscopy and X-ray absorption near-edge structure (XANES) spectroscopy] were performed to identify precisely the origin of the blue stain. Prior research has shown that Mn5+ in tetrahedral coordination could be responsible for the turquoise blue color in mastodon ivory some tens of million years old that was modified by a heat process. Manganese is present in the anionic form of (MnO4)3- and partially substitute for (PO4)3- in the hydroxyapatite matrix. The spectroscopic data of the present study have revealed a heat-induced modification, revealed traces of Mn among the typical bone constituents (Ca, P, Sr, Zn), and provided insights into the color origin of the blue paleontological bones from San Josecito Cave. Cations of Mn5+ in a tetrahedral environment of four O2- ions in the apatite structure are found in these bones, the same color origin as in the blue mastodon ivory. As indicated by XANES, Mn4+ ions in octahedral coordination as in pyrolusite are found in gray bones. The presence of submicroscopic Mn oxide inclusions might explain the color of the San Josecito gray bones. The formation of Mn5+ very likely is induced by heat treatment of the bones under oxidizing conditions. The heat-induced modification of both types of paleontological bones also is indicated by the direct observation of apatite crystals using TEM. The question remains, however, how the heat originated inside the cave.

Heating effect on manganese oxides used as black Paleolithic pigment

Manganese oxihydroxide behaviour has been studied under heat treatment to understand the transformation mechanisms and subsequently to gain insights into the preparation procedures of black painting materials during the Palaeolithic period. These manganese oxihydroxides have been studied as a function of heat treatment by TEM, XRD, DTA and FTIR and XANES (Mn K-edge) spectroscopies. These materials have been used as black pigments during the Palaeolithic period to realise rock art paintings such as in Lascaux (Dordogne, France) and Gargas (Midi-Pyrénées, France). Specific morphological, chemical and structural criteria were determined to distinguish between natural and heat-treated pigments.

Non-Destructive Portable Analytical Techniques for Carbon In-Situ Screening Before Sampling for Dating Prehistoric Rock Paintings

Direct dating of prehistoric paintings is playing a major role in Paleolithic art studies. Very few figures can be directly dated since the necessary condition is that they contain organic carbon-based material. Thus, it is very important to check the presence of organic carbon-based material in situ before sampling in order to protect the visual integrity of the paintings or drawings. We have tested and compared 3 different portable analytical systems that can be used in cave environments for detecting carbon in prehistoric paintings: (1) a very compact X-ray fluorescence (XRF) system in Villars Cave (Dordogne, France); (2) a portable micro-Raman spectrometer in Rouffignac Cave (Dordogne, France); and (3) an infrared reflectography camera in both caves. These techniques have been chosen for their non-destructiveness: no sample has to be taken from the rock surface and no contact is made between the probes and the paintings or drawings. The analyses have shown that all the animal figures have been drawn with manganese oxides and cannot be directly dated by radiocarbon. However, carbon has been detected in several spots such as black dots and lines and torch marks. 14C results were obtained from 5 torch marks selected in Villars Cave, with ages between 17.1–18.0 ka cal BP. Three methods were used to identify carbon in black pigments or to confirm the presence of torch marks by carbon detection. Thanks to these new analytical developments, it will be now possible to select more accurately the samples to be taken for 14C dating prehistoric paintings and drawings.