PARTICLE‐INDUCED X‐RAY EMISSION (PIXE) ANALYSIS OF OBSIDIAN FROM TEOTIHUACAN

A collection of 50 archaeological obsidian samples studied in the framework of the Preciudadela Project (Teotihuacan, Mexico) has been analysed using particle‐induced X‐ray emission (PIXE) with the external beam line of the Accélérateur Grand Louvre d'Analyse Elémentaire facility (C2RMF, Paris) and of the Instituto de Física (UNAM, Mexico). This work addresses the provenance of these obsidian samples, with the purpose of determining if they come from the obsidian sources exploited by Teotihuacans (mainly Otumba and Sierra de Pachuca), from other sources, or arrived via commercial exchanges with other regions. For that, the elemental compositions derived from the PIXE spectra have been compared with data published in the literature on the basis of instrumental neutron activation analysis. From the concentrations of selected key elements (Na, K, Mn, Fe, Zn, Rb, Sr, Zr), it was possible to unambiguously assign the provenance of most samples. Many originate from two major sources, namely Sierra de Pachuca (Hidalgo) and Otumba (Mexico), which were the main obsidian deposits used by the Teotihuacans. However, some samples exhibit a compositional fingerprint matching other provenances, i.e., Paredón (Puebla) and Zacualtipan (Hidalgo).     

CHARACTERIZATION OF PACIFIC NORTHWEST COAST OBSIDIAN BY X-RAY FLUORESCENCE ANALYSIS

Several geological sources of obsidian in the Pacific Northwest have been characterized by means of their trace element concentrations, as measured by X-ray fluorescence analysis. The technique is fast and completely non-destructive, making it well-suited for identifying the sources of obsidian from which artifacts were fabricated.     

QUANTITATIVE RESULTS OF XRF ANALYSIS OF ANCIENT COINS BY MONOCHROMATIC X-RAY EXCITATION

The analysis by XRF applied to old coins is improved by use of monochromatic X-ray excitation of variable energy. In addition the effects of relief and irregular shape are eliminated. A method of absolute quantitative analysis without any reference standard has been set up. Results of the analysis of 52 early Greek and 4 late Roman empire gold coins are reported.     

ANALYSIS OF EUROPEAN AMBER BY CARBON-13 NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

Amber, a class of fossil resins, comprises largely terpenoid components. The structure of the major, insoluble portion has not been defined previously. We report the analysis of European amber by carbon-13 nuclear magnetic resonance spectroscopy directly on solid samples. Two major types are defined, depending on the appearance of the alkene resonances. Baltic amber (succinite), along with other northern ambers such as gedanite, has a pronounced resonance from an exomethylene group. The southerly ambers (rumanite, schraufite, walchowite, delatynite and true simetites) lack the exomethylene resonances. The succinite group gives spectra consistent with a labdane-type precursor and the rumanite-like ambers give spectra consistent with an abietane-type precursor. These results are best explained by at least two different palaeobotanical sources of the fossil resins.     

QUANTITATIVE ANALYSIS OF COPPER-TIN BRONZES BY MEANS OF GLOW DISCHARGE OPTICAL EMISSION SPECTROMETRY

Glow discharge optical emission spectrometry (GDOES) has been used for obtaining calibration curves for copper, tin, lead, silver, antimony, arsenic, zinc and iron from standards including copper-base alloys (Cu 61.33-99.95%) and from bronze Punic coins. The GDOES results were calibrated using atomic absorption spectroscopy with inductively coupled plasma atomization (ICPAAS) to analyse the standards and coins. For all these materials, the results show that via GDOES it is possible to obtain reliable and reproducible calibration curves for copper, tin, lead, zinc and iron with a linear behaviour as a function of the content. The quantitative GDOES and ICPAAS data for the coins have been also compared with those obtained via X-ray fluorescence (XRF) and it is shown that GDOES, ICPAAS and XRF agree well with one another considering that the bronze coins are inhomogeneous to some degree. As an example of GDOES analytical features, a depth concentration profile through a thin bronze patina is shown and briefly discussed.     

FINE WARE FROM LOCRI EPIZEPHIRI: A PROVENANCE STUDY BY INDUCTIVELY COUPLED PLASMA EMISSION SPECTROSCOPY

Fifty-six sherds of fine ware from Locri Epizephiri were analysed by inductively coupled plasma optical emission spectroscopy (ICPOES) and flame emission spectroscopy (FES). The sherds had been excavated on the archaeological areas of Marasà Sud, Centocamere and San Cono, and represent local and imported products from the seventh to the second century BC. The samples were dissolved by fusion with lithium metaborate and analysed for nine elements (Al, Fe, Ca, Mg, Ti, Mn, Sr, Ba and Cr) by ICPOES, while Na and K were determined by FES. The analytical data were subjected to hierarchical agglomerative clustering and principal components analysis to classify the sherds into compositional groups. The results obtained indicated that Corinthian, Attic and Ionian products or imitations may be classified in a few separate groups, while most local products are found in a unique, large group.     

X-RAY FLUORESCENT ANALYSIS OF ANGLO SAXON JEWELLERY

X-ray fluorescence analysis of 30 pieces of Anglo Saxon jewellery, from the Ashmolean Museum, Oxford, is followed by a comparison with similar results obtained from contemporary coinage. The standards of fineness for the coinage are applied to the jewellery and used to date its manufacture. An appendix describes repeatanalyses of some coins which, at first, had widely differing results from XRF and specific gravity methods.     

DETECTION OF NEAR-SURFACE SILVER ENRICHMENT ON ROMAN IMPERIAL SILVER COINS BY X-RAY SPECTRAL ANALYSIS*

A collection of 218 Roman imperial silver coins, covering three centuries, was analysed non-destructively by two variants of X-ray spectral analysis. Electron beam excitation and energy-dispersive spectrometry was used for the analysis of the uppermost thin layer (3 μm) of each coin, while X-ray tube excitation and wavelength-dispersive spectrometry was applied for the analysis of thicker layers (30 μm), Ag and Cu as major constituents and 18 minor elements were determined quantitatively. Comparing the silver content of the obverse and the reverse of a coin, inhomogeneities could be identified. By comparison of the silver content of the upper thin and the thick surface layers, near-surface silver enrichment could be detected. Inhomogeneities and enrichments increase in the second and more so in the third century. A large scatter of the silver content and silver enrichment for coins of the same emperor was attributed to varying abrasion of Ag-enriched layers of the individual coins during decades of circulation.     

RIETVELD X-RAY DIFFRACTION AND X-RAY FLUORESCENCE ANALYSIS OF AUSTRALIAN ABORIGINAL OCHRES*

Rietveld phase analysis of X-ray powder diffraction patterns and chemical analysis by X-ray fluorescence spectroscopy have been used to characterize a series of red and yellow ochre samples from Aboriginal ochre deposits in South and Western Australia. The ochres were found to have diverse mineralogy, being mixtures of up to seven minerals, and also to have complex trace element signatures. The mineralogical characteristics and geochemistry of the ochres can be used to identify the source quarries. Using this combination of analytieal techniques it may be possible to trace the source of ochres in burial sites and on objects back to the original quarries.     

AMBER FROM THE DOMINICAN REPUBLIC: ANALYSIS BY NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

The carbon-13 NMR spectra of amber from several mining sites in the Dominican Republic show considerable variation. In certain cases the differences are sufficiently distinct to serve as a reliable indicator of provenance. The gradations within the resonances of unsaturated carbons may reflect the relative ages of the samples, because fossilization and diagenesis can remove this functionality.