Laser ablation coupled to mass quadrupole spectrometry for analysis in the cultural heritage

A Nd:YAg laser operating at 1064 nm, 150 mJ, 3 ns pulse duration, 1-10 Hz repetition rate and 109 W/cm2 intensity is employed to irradiate ancient metallic and ceramic samples in high vacuum. A mass quadrupole spectrometer (MQS), operating between 1-300 amu with sensitivity better than 0.1 ppm, analyzes elements and compounds. Repetitive laser ablation removes in controlled manner the first surface layers of the irradiated samples so that the irradiation time can be correlated to the layer depth. MQS can be fixed to peculiar masses so that during the laser irradiation the mass yields can be plotted as a function of the sample depth. The technique permits to give the depth profiles of elements, chemical compounds and isotopes characterizing the composition of the analyzed samples. The analysis of ancient coins based on bronze and silver alloys and of old vitrified colored ceramics has been investigated to identify peculiar elements of the colored layers. Particularly, the lead isotopic ratios 208Pb/207Pb and 206Pb/207Pb were measured in bronze coins. Measurements were compared with the database of lead isotopic ratios in lead minerals extracted from old mines in the Mediterranean basin. In some cases, of special interest for Archeologists, the comparison has indicated that the lead employed for the coin production could have been extracted from mines of particular geographic sites. © Published under licence by IOP Publishing Ltd

LAMQS analysis applied to ancient Egyptian bronze coins

Some Egyptian bronze coins, dated VI-VII sec A.D. are analyzed through different physical techniques in order to compare their composition and morphology and to identify their origin and the type of manufacture. The investigations have been performed by using micro-invasive analysis, such as Laser Ablation and Mass Quadrupole Spectrometry (LAMQS), X-ray Fluorescence (XRF), Laser Induced Breakdown Spectroscopy (LIBS), Electronic (SEM) and Optical Microscopy, Surface Profile Analysis (SPA) and density measurements. Results indicate that the coins have a similar bulk composition but significant differences have been evidenced due to different constituents of the patina, bulk alloy composition, isotopic ratios, density and surface morphology. The results are in agreement with the archaeological expectations, indicating that the coins have been produced in two different Egypt sites: Alexandria and Antinoupolis. A group of fake coins produced in Alexandria in the same historical period is also identified. © 2010 Elsevier B.V. All rights reserved

LAMQS and XRF analyses of ancient Egyptian bronze coins

A set of Egyptian bronze coins, dating back to the sixth or seventh century AD, has been studied by different experimental techniques in order to compare their composition and surface morphology, the process of coinage and, possibly, to also identify the place of production. The measurements have been performed by laser ablation with mass quadrupole spectrometry and energy dispersed X-ray fluorescence. Both analyses are non-invasive and can be safely used according to the integrity requirements of the analyzed pieces. Owing to the poor number of available samples, this work, more than to solve a numismatic question, has been carried out in order to test the validity of the above experimental techniques in view of further analyses on the same coins, based on better quality statistics. The preliminary results, presented in this paper, indicate significant differences in the chemistry of the coins' patina, i.e. composition and isotopic species content. This seems to support, in agreement with the archaeological expectations, the hypothesis of the existence of a local mint in Antinoopolis, never before considered in Egyptian numismatics. © 2010 Taylor & Francis