Ludovic Bellot-Gurlet

Raman identification of glassy silicates used in ceramics, glass and jewellery: a tentative differentiation guide

As an optical method, Raman microspectroscopy offers a great advantage over most other techniques in that it can be performed without any contact with the studied artefact, both at the laboratory using high-resolution, large spectral window instruments, and on site using medium resolution, portable instruments. Six years of experience on various materials has enabled us to propose a tentative guide to identify different types of glassy silicates and to classify them as a function of their composition. In previous papers, different families were recognised empirically using a limited set of samples and the relationship between the peak area ratio (A500/A1000) of the SiO bending (∼500 cm−1) and stretching (i.e. ∼1000 cm−1) envelopes, and the different components of the latter peak were established for porcelain glazes. In this paper, we extend the procedure to a larger set of samples (30 representative samples with known compositions selected from hundreds of spectra). Additional relationships between the origin of the material, the Raman parameters and the glass composition (fluxing oxide content, ionicity ratio, etc.) are discussed. Finally we propose different procedures with different degrees of complexity (from two to multivariate treatment) to identify the glass composition. The method is illustrated with an example, namely, the differentiation between Iznik and Kutahya productions. Copyright

Raman Studies of Corrosion Layers Formed on Archaeological Irons in Various Media

The description and identification of corrosion products formed on archaeological iron artefacts need various approaches at different observation scales. Among analytical techniques available to document phase structure at the microscopic range, Raman spectroscopy offers sensitivity and discrimination between iron corrosion products with an easy implementation. Results obtained for iron artefacts corrosion in soils and atmosphere are presented. Corrosion forms observed for anoxic and aerated soils on one hand and indoor atmosphere on the other are documented. Beyond the identification and organisation of corrosion products through hyperspectral imaging, Raman micro-spectroscopy could also provide quantitative phase proportions which will be needed in the proposition of reactivity diagnosis indicators.

The nature of the extraordinary finish of Stradivari's instruments.

What is Stradivaris “secret”? The composition of the mythical varnish that coats Stradivaris violins has raised controversial assumptions for the past two centuries. By using a complementary array of analytical tools, the chemical microstratigraphy of these varnishes has been established. The results provide information on the materials and techniques that were used by the Master, with a detailed characterization of the varnish.

Provenance of the Jerf el Ahmar (Middle Euphrates Valley, Syria) obsidians

A provenance study of obsidians collected in the Jerf el Ahmar village dated from 9500 to 8700 BC cal (Middle Euphrates Valley, Syria) was made from geochemical analyses. The elementary composition of 44 obsidian artefacts and of 19 samples from potential obsidian volcanic sources was determined by inductively coupled plasma-atomic emission spectrometry and -mass spectrometry (ICP-AES/-MS) or particle induced X-ray emission (PIXE) and scanning electron microscope-energy dispersion of X-rays (SEM-EDX). We show that each of these approaches gives reliable source assignment. We found that 42 of the Jerf el Ahmar obsidians came from the Cappadocia (Gollu Dag volcanic massif) and two from the Bingol area in Eastern Anatolia. This information confirms the arrival in the Levant of obsidian from the latter sources during the end of the Pre-Pottery Neolithic A period, most probably in relation with the diffusion of the Neolithic process from the Middle Euphrates Valley towards the Northeast.

Advanced discriminating criteria for natural organic substances of cultural heritage interest: spectral decomposition and multivariate analyses of FT-Raman and FT-IR signatures.

Natural organic substances are involved in many aspects of the cultural heritage field. Their presence in different forms (raw, heated, mixed), with various conservation states, constitutes a real challenge regarding their recognition and discrimination. Their characterization usually involves the use of separative techniques which imply destructive sampling and specific analytical preparations. Here we propose a non destructive approach using FT-Raman and infrared spectroscopies for the identification and differentiation of natural organic substances. Because of their related functional groups, they usually present similar vibrational signatures. Nevertheless the use of appropriate signal treatment and statistical analysis was successfully carried out to overcome this limitation, then proposing new objective discriminating methodology to identify these substances. Spectral decomposition calculations were performed on the CH stretching region of a large set of reference materials such as resins, oils, animal glues, and gums. Multivariate analyses (Principal Component Analyses) were then performed on the fitting parameters, and new discriminating criteria were established. A set of previously characterized archeological resins, with different surface aspects or alteration states, was analyzed using the same methodology. These testing samples validate the efficiency of our discriminating criteria established on the reference corpus. Moreover, we proved that some alteration or ageing of organic materials is not an issue to their recognition.

Nouvelles données sur la provenance de l'obsidienne des sites néolithiques du Sud-Est de la France

Abstract We analyzed the chemical composition of 22 artifacts considered as obsidians by PIXE in non-destructive mode. The samples were collected from 11 Neolithic stations in southeastern France, between the Rhone valley and the northern Alps. One piece appeared not to be obsidian. Among the others, 20 came from a single source in Sardinia and one from an unknown source. These data confirm the importance of the Sardinian origin of the obsidian found in France, in particular for the Middle Neolithic.

Raman Spectroscopy of cultural heritage Materials: Overview of Applications and New Frontiers in Instrumentation, Sampling Modalities, and Data Processing

Rooted in the long tradition of Raman spectroscopy of cultural heritage materials, in this work we provide a personal perspective on recent applications and new frontiers in sampling modalities, data processing, and instrumentation.

Early Evidence for the Extensive Heat Treatment of Silcrete in the Howiesons Poort at Klipdrift Shelter (Layer PBD, 65 ka), South Africa

Heating stone to enhance its flaking qualities is among the multiple innovative adaptations introduced by early modern human groups in southern Africa, in particular during the Middle Stone Age Still Bay and Howiesons Poort traditions. Comparatively little is known about the role and impact of this technology on early modern human behaviors and cultural expressions, due, in part, to the lack of comprehensive studies of archaeological assemblages documenting the heat treatment of stone. We address this issue through an analysis of the procedure used for heating and a technological analysis of a lithic assemblage recovered from one Howiesons Poort assemblage at Klipdrift Shelter (southern Cape, South Africa). The resulting data show extensive silcrete heat treatment, which adds a new dimension to our understanding of fire-related behaviors during the Howiesons Poort, highlighting the important role played by a heat treatment stage in the production of silcrete blades. These results are made possible by our new analytical procedure that relies on the analysis of all silcrete artifacts. It provides direct evidence of a controlled use of fire which took place during an early stage of core exploitation, thereby impacting on all subsequent stages of the lithic chaîne opératoire, which, to date, has no known equivalent in the Middle Stone Age or Middle Paleolithic record outside of southern Africa.

Trace and rare-earth element characteristics of acidic tuffs from southern Peru and northern Bolivia and a fission-track age for the sillar of Arequipa

Trace-element and REE data of glass and pumices of acidic tuffs and related fall deposits erupted in southern Peru and northern Bolivia between 20 and 0.36 Ma display typical characteristics of subduction related continental arc magmatism of the CVZ with strong LILE/HFSE enrichment and non enrichment of HREE and Y. Geochemical variations of these tuffs are linked to subduction processes and controlled by changes in tectonic regimes which occured with each Quechua tectonic pulse and affected the astenospheric wedge and both the dowgoing and the overriding lithospheres. During Neogene — Pleistocene times, tuffs erupted in northern Bolivia are typically enriched in Zr, Hf, Th, Ba, LREEs and other incompatible elements and incompatible /Yb ratios are much higher relative to those erupted from southern Peru, at a given SiO2 content (65–67 wt. for dacites, 72–73 wt.% for rhyolites). ZrHf ratios increase eastward from 27 to 30 and CeYbN ratios from 11 to 19 reflecting the variation of degree of wedge contribution. Fractionation of the LREE over the HREE and fractionation of incompatible elements may be due to their heterogeneous distribution in the magma source. More highly fractionated REE patterns of Bolivian tuffs than Peruvian tuffs are attributed to variable amounts of contamination of magmas by lower crust. After the Quechua compressional event at ~7 Ma, SrY ratios of tuffs of the same age, erupted at 150–250 km or 250–400 km from the Peru-Chile trench, increase from southern Peru to northern Bolivia. These differences may be attributed to the subduction of a swarm oceanic lithosphere under the Bolivian Alti-plano, leading to partial melting of the sudbucted lithosphere. New FT dating of obsidian fragments of the sillar of Arequipa at 2.42 ± 0.11 Ma. This tuff dates the last Quechua compressional upper Pliocene phase (~2.5 Ma) and confirms that the sillar is not contemporaneous with the Toba 76 tuff or the Perez ignimbrite of northern Bolivia. Geochemical characteristics of tuffs erupted before and after this last compressional phase remained the same and provide evidence that the upper Miocene (~7 Ma) compressional deformations played the most important role on the variability of the geochemical characteristics of the southern Peruvian and northern Bolivian tuffs.

Rapid Quantification of Bone Collagen Content by ATR-FTIR Spectroscopy

Expensive and time-consuming preparation procedures for radiocarbon and stable isotope analyses can be conducted on archaeological bone samples even if no collagen is preserved. Such unsuccessful preparation can lead to the partial destruction of valuable archaeological material. Establishing a rapid prescreening method for evaluating the amount of bone collagen while minimizing the impact of sampling constitutes a challenge for the preservation of archaeological collections. This study proposes and discusses a new methodology to detect and quantify collagen content in archaeological bone samples by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. A total of 42 Pleistocene to modern bone samples were selected according to their nitrogen content measured using an elemental analyzer. Comparison of collagen content estimation using ATR-FTIR and mass spectrometry reveals that some of the studied samples are contaminated by a nitrogen source coming from the burial environment. Two different FTIR calibration approaches were tested on the uncontaminated samples: peak-to-peak ratio and multivariate regression (PLS). The two approaches yield similar results with a good correlation of ATR-FTIR analyses and N wt% from 0.7 to 4wt% (R²=0.97–0.99; standard error of estimation ±0.22 to 0.25wt%). While collagen content remains difficult to detect in poorly preserved bones (less than ~3wt%), ATR-FTIR analysis can be a fast alternative for sample screening to optimize the sampling strategy and avoid partial destruction of valuable samples that do not contain enough collagen for further analysis.