Ph. Walter

Kinetics of oil saponification by lead salts in ancient preparations of pharmaceutical lead plasters and painting lead mediums.

Lead soaps can be found in archaeological cosmetics as well as in oil paintings, as product of interactions of lead salts with oil. In this context, a better understanding of the formation of lead soaps allows a follow-up of the historical evolution of preparation recipes and provides new insights into conservation conditions. First, ancient recipes of both pharmaceutical lead plasters and painting lead mediums, mixtures of oil and lead salts, were reconstructed. The ester saponification by lead salts is determined by the preparation parameters which were quantified by FT-IR spectrometry. In particular, ATR/FT-IR spectrometer was calibrated by the standard addition method to quantitatively follow the kinetics of this reaction. The influence of different parameters such as temperature, presence of water and choice of lead salts was assessed: the saponification is clearly accelerated by water and heating. This analysis provides chemical explanations to the historical evolution of cosmetic and painting preparation recipes.

Revealing the powdering methods of black makeup in Ancient Egypt by fitting microstructure based Fourier coefficients to the whole x-ray diffraction profiles of galena

Galena (PbS) is a major ingredient in ancient Egyptian eye makeup. The microstructure of PbS in Egyptian cosmetic powders is used as a fingerprint and is matched with the microstructures produced artificially in geological galena minerals. The microstructure of PbS is determined by x-ray diffraction peak profile analysis in terms of dislocation density, crystallite size, and size distribution. High-resolution powder diffractograms were measured at the ESRF Grenoble synchrotron source with high resolution and high peak-to-background ratios. The Fourier coefficients of the first nine measured reflections of galena are fitted using physically based Fourier coefficients of strain and size functions. Strain anisotropy is accounted for by the dislocation model of the mean square strain. The x-ray data are supplemented by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) micrographs, and are compared with archaeological documents. It enables us to describe the procedures of eye makeup ...

Ion beam analysis with external beams: Recent set-up improvements

Accelerator-based analytical techniques using external beams are ideally fitted to the study of works of art because of their fully non-destructive character. However, accurate quantitative analysis is not straightforward, due in particular to difficult beam monitoring. Significant improvements have been progressively made on the external beam line of the IBA facility of the Louvre museum in order to increase the accuracy and to conduct combined analyses with different IBA techniques.

Synchrotron X-ray micro-beam studies of ancient Egyptian make-up

Abstract Vases full of make-up are most often present in the burial furniture of Egyptian tombs dated from the pharaonic period. The powdered cosmetics made of isolated grains are analysed to identify their trace element signature. From this signature we identify the provenance of the mineral ingredients in the make-up and we observe different impurities in products, which have been demonstrated as synthetic substances by previous works. Focused X-ray micro-beam ( 2×5 μm 2 ) is successively tuned at 11 keV, below the LIII absorption edge of Pb, and 31.8 keV for global characterisation of the metal impurities. The fluorescence signal integrated over each single grain is detected against the X-ray micro-diffraction pattern collected in transmission with a bi-dimensional detector. Furthermore, for galena grains rich in Zn, the XANES signal at the K-absorption edge of Zn shows its immediate nearest-neighbour environment.

Usewear characterisation of prehistoric flints with IBA

Abstract Archaeology has great interest in understanding the use of prehistoric stone tools. The observation of usewear on flint artefacts may allow one to determine the matter which was worked with them: clues for this identification are given by optical microscopy on “experimental” tools. Blind tests on modern replicas used to work known materials, such as bones, meat, plants, wood, etc., have had significant success. This classic method is still widely used by specialised archaeologists in the study of usewear. We have observed, with SEM coupled with a Si(Li) detector, that the composition of usewear is related to the composition of the worked material. Simultaneously, we have initiated a systematic study of different kinds of polishes (meat, bone, plants, wood) with the techniques of RBS, NRA and PIXE. This approach provides a new model of polish formation: the mineral components of the worked matter smoothen the roughness of the flint tools. Archaeological conclusions on Predynastic Egyptian flint knives (around 4000 b.c. ) and Magdalenian burins from Etiolles, near Paris, France, (10000 b.c. ) are presented.

Insight into the usewear mechanism of archaeological flints by implantation of a marker ion and PIXE analysis of experimental tools

Abstract Archaeological flint tools exhibit, after their use, a modification of the orginal surface as a result of contact with foreign materials. The polish which appears, displays morphological and textural features characteristic of the worked material. These changes at the flint surface are mainly due to residues of the worked matter and therefore contain potential information on the tool use. However it is not clear whether the altered surface stems from a simple coating of soft matter which has filled the original roughness of the cutting edge or whether in addition to that process an erosion of the flint surface by loss of quartz spherules also occurs. An experimental study has been performed to address this issue, which is based on the implantation of Cu ions (energy 100 keV and a dose of 5 × 10 16 cm −2 ) on chipped geological flint samples, mechanical tests simulating the tool use and subsequent PIXE analysis of the edge surface with a 3 MeV proton micro-beam with a rectangular shape (15 × 20 μ m 2 ). A beam current of about 1 nA is sufficient to obtain a count rate of 800/min on the Cu Kα X-ray line. The persistence of the Cu X-ray signal all over the tool edge confirms that the polish is only due to the deposit of external matter. Archaeological implications of usewear are discussed in the light of these new data.

ANALYTICAL USE OF THE MULTIPLE GAMMA-RAYS FROM THE 12C(D,P)13C* NUCLEAR REACTION

Abstract We report the results of the measured cross section for the 12C(d,pγ)13C reaction with Eγ1 = 3089 keV, Eγ2 = 3684 keV, Eγ3 = 3854 keV, at 170° for deuteron energies between 0.5 and 4.0 MeV. A method to compute theoretically the counting rate from 12C(d,p)13C∗ reactions is described; the numerical simulation makes use of the production cross sections of the three γ-radiations which have been determined with a thin carbon target. The efficiency of the method is evaluated in a few cases, simulated and compared with experiment. The first γ-ray yield is high and leads to a sensitive and quick method (typically 10 min) for the analysis of surface layers and concentrations of carbon as low as a few ppm. With a judicious choice of the beam energy, it is possible to determine simultaneously the surface and the bulk concentrations of C using detection of γ1 and γ3.

Dating of archaeological flints by fluorine depth profiling: new insights into the mechanism of fluorine uptake

Abstract To understand the mechanism underlying fluorination of buried archaeological flints, samples of amorphous silica have been subjected to fluorine incorporation either by aqueous treatment or by ion implantation. The nuclear reaction analysis technique using the resonant 19F(p, αγ)16O reaction at 872 keV has been used to obtain profiles of fluorine with an automated electrostatic energy scanning system. Our results emphasize the role of defects for F uptake and allow us to propose a tentative mechanism for F diffusion. The use of synthetic hydrated silica appears promising to simulate the geochemical weathering of chalcedony.

In situ RBS study of the kinetics of galena thermal oxidation by means of 4He external micro-beam

Abstract In situ RBS measurements with an external He ion micro-beam have been performed on galena heated at temperatures varying from 400°C to 600°C, to study dynamically its oxidation kinetics. At each temperature, a millimetre-sized crystal is placed in a specially built oven directly facing the exit window of the beam. The thickness of the oxidised layer is measured every 2 min by means of the lead signal in the RBS spectrum, using a 3 MeV 4 He 2+ external focused beam (about 100 μm). We infer the diffusion mechanism from the growth of a phase, which is more or less stable when increasing temperature. This probing beam allows one to characterise layers of thickness extending from about 100–2000 nm.

RBS study of galena thermal oxidation in air with a 6-MeV 16O3+ ion beam

Abstract Experiments performed on cleaved cm-sized single crystals of galena (PbS) show that heating in air during a few hours at temperatures varying from 400°C to 600°C induces an irridescence. This feature seems to be sought in North Africa to produce coloured eye make-up. Qualitative observation by X-ray diffraction shows the occurrence of anglesite (PbSO 4 ) and lanarkite (PbO.PbSO 4 ). The thickness of the oxidised layer is measured by means of the lead signal in the RBS spectrum, using 6-MeV 16 O 3+ ions. This probing beam allows one to characterise layers of thickness extending from a few tens to a few hundreds nm. For larger values, a beam of 3-MeV 4 He 2+ is used instead. This technique was used to investigate the kinetics of oxidation which involves a complex diffusion phenomenon associated with the formation of reactive phases at the interface between the altered layer and the pristine material. From the thickness of the altered layer and its refractive index we infer that the irridescence is due to an interference phenomenon.