Ina Reiche

A new 3D micro X-ray fluorescence analysis set-up: First archaeometric applications

A new 3D micro X-ray fluorescence (micro-XRF) analysis method based on a confocal X-ray set-up is presented. The capabilities of this new method are evaluated and illustrated with depth sensitive investigations of paint layers in ancient Indian Mughal miniatures. Successive paint layers could be distinguished non-destructively with a depth resolution of about 10 μm. Major and minor elements are detectable and can be discriminated in different layers. New light could be shed on ancient painting techniques and materials with this new 3D micro-XRF set-up.

Emerging Approaches in Synchrotron Studies of Materials from Cultural and Natural History Collections

Synchrotrons have provided significant methods and instruments to study ancient materials from cultural and natural heritages. New ways to visualise (surfacic or volumic) morphologies are developed on the basis of elemental, density and refraction contrasts. They now apply to a wide range of materials, from historic artefacts to paleontological specimens. The tunability of synchrotron beams owing to the high flux and high spectral resolution of photon sources is at the origin of the main chemical speciation capabilities of synchrotron-based techniques. Although, until recently, photon-based speciation was mainly applicable to inorganic materials, novel developments based, for instance, on STXM and deep UV photoluminescence bring new opportunities to study speciation in organic and hybrid materials, such as soaps and organometallics, at a submicrometric spatial resolution over large fields of view. Structural methods are also continuously improved and increasingly applied to hierarchically structured materials for which organisation results either from biological or manufacturing processes. High-definition (spectral) imaging appears as the main driving force of the current trend for new synchrotron techniques for research on cultural and natural heritage materials.

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.

TRACE ELEMENT COMPOSITION OF ARCHAEOLOGICAL BONES AND POST-MORTEM ALTERATION IN THE BURIAL ENVIRONMENT

Abstract We have performed Particle Induced X-ray Emission (PIXE) and Particle Induced Gamma-ray Emission (PIGE) analyses with an external proton millibeam on archaeological bones in order to determine possible alteration processes in their burial environment (dissolution, uptake and diffusion of foreign ions). The PIXE method enables us to quantify the post-mortem alteration by determining the concentration profile of several trace elements like Al, Si, S, Mn, Fe, Cu, Zn and Sr in transverse bone sections, while that of fluorine is inferred from PIGE analysis. Examples of concentration profiles of archaeological bone cross sections from the Seine river site in Paris, Bercy (4000 B.C.), are shown.

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.

Imaging fossil bone alterations at the microscale by SR-FTIR microspectroscopy

Diagenetic alterations modifying fossil bones over geological time can limit their use as archaeological and paleontological proxies. The understanding of fossilization processes and the evaluation of the extent of diagenetic alterations of bones therefore constitute major issues in current research. The complex hierarchical structure of bone tissue and the spatial heterogeneity of the diagenetic alterations induce significant chemical variations in fossil bones at the microscale. We adapted a sample preparation procedure based on PMMA impregnation that allowed us to obtain bone thin sections independent of their level of degradation. As a first step to investigate the variations in bone composition at the histological scale, synchrotron radiation FTIR micro-spectroscopy (FTIRM) was applied on two fossil bone samples displaying distinct preservation states: (a) a bone from Magdalenian layers dated to 15 ka of the Bize-Tournal cave (Aude, France) and (b) another from Song Terus site (Java island, Indonesia, 60 ka). The first one is partially recrystallized but still contains zones with locally preserved collagen and biogenic carbonates, whereas the other consists of a recrystallized mineral fraction without any remaining collagen fraction. These data obtained on the microscale were compared to bulk measurement data and the relationships between different IR diagenetic parameters explored. This analytical approach allowed the characterization of diagenetic alterations such as collagen loss, carbonate uptake and mineral recrystallization in heavily altered fossil bone tissue at the histological scale. Using the presented procedure, the histological bone structures could be studied, even for brittle samples altered by an extensive loss of their collagen matrix during diagenesis.

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.

Microscale imaging of the preservation state of 5,000-year-old archaeological bones by synchrotron infrared microspectroscopy.

AbstractArchaeological bone materials record characteristic markers of life in prehistoric times (dating, climate, environment, diet, human migration) in their isotopic and chemical composition in addition to palaeontological, archaeozoological, anthropological and palaeogenetic information. Thus, the discovery and conservation of archaeological bone materials is of great importance to get access to this information. However, archaeological materials are altered by different postmortem processes and it appears necessary to estimate if the archaeological information is still reliable or if it has been modified during burial. As archaeological bone materials present a high structural hierarchy at the micro- and nanoscale, changes induced by diagenetic phenomena have to be observed at these scales. One method for revealing post mortem changes of the bone structure and composition at the microscale is synchrotron radiation micro-FTIR imaging (SR micro-FTIR). Thus, thin sections of about 5,000-year-old archaeological bones have been analysed in transmission mode at the IRIS beamline (BESSY II, HZB Berlin) to determine markers of the state of bone preservation at the microscale. The archaeological bone material comes from station 19 of the Neolithic site of the Chalain Lake. By using SR micro-FTIR it was possible to image characteristic bone structures, e.g. osteons (the constitutive histological unit of cortical bone), using the absorption band ratios corresponding to different chemical bone constituents (collagen content and quality, phosphate crystallinity, carbonate content). These data allow us to precisely evaluate the state of preservation of a 5,000-year-old bone at the histological level. FigureChemical mapping of a thin section of the archaeological bone AB_CH19nb1 from the Neolithic station 19 at Chalain Lake

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.

Depth profiling reveals multiple paint layers of Louvre Renaissance paintings using non-invasive compact confocal micro-X-ray fluorescence

The High Renaissance marks one of the most significant and prolific periods of artistic production in painting. Artists of this epoch advanced many aspects of pictorial art that continue to be debated and researched today. The typical painting technique during this time period consisted of superimposing multiple layers of thinly applied paint to achieve realistic optical impressions and desired visual effects. The presence of multiple thin layers in Renaissance paintings presents a challenging case study. In the work presented here, a laboratory-based confocal micro-X-ray fluorescence analysis (CXRF) spectrometer called LouX3D is applied to the non-destructive study of the Renaissance paintings series Famous Men, from the Louvre collection. Elemental depth profiles measured directly on the paintings are compared to lateral scans and results of conventional analyses on cross-sections removed from the paintings in the same locations. This comparison enables a better evaluation of the feasibilities of CXRF depth profiling using the LouX3D set-up for the investigation of paint layers. The limit of depth profiling is reached due to absorption effects, which depend on the chemical composition of the paint layers, on their order and on the performance of the set-up. Care must be taken if the same element is present in adjacent layers, if the layers are thin (<10 μm), or if the composition within a layer is highly heterogeneous. Paint sequences on the original paintings, including later retouchings, were successfully detected using CXRF measurements. This study highlights the great potential of this laboratory-based method when used in combination with other techniques for completely non-invasive painting analyses.