REPRODUCIBILITY OF ELEMENTAL ANALYSES OF BASALTIC STONE ARTEFACTS BY QUADRUPLE ICP–MS USING DIFFERENT SAMPLE SIZES AND DIGESTION METHODS,WITH IMPLICATIONS FOR ARCHAEOLOGICAL RESEARCH

Using high‐precision inductively coupled plasma mass spectrometry (ICP–MS), we measured >40 elements in basalts sampled by diamond micro‐drills to evaluate the effectiveness of different digestion methods and the reproducibility of elemental analysis for different sample sizes from 5 mg to 100 mg. The results indicate that those elements that are most suitable for geochemical characterization, such as rare earth elements (REE), high‐field strength elements (HFSE) and certain mobile elements (Rb, Sr, Th, U), show excellent reproducibility with an average relative standard deviation (RSD) of 3% between open‐beaker and pressured ‘bomb’ digestion methods. This observation rules out the presence of refractory phases such as zircon, which can only dissolve in pressured ‘bombs’, and suggests that the results from open‐beaker digestion are reliable. The ICP–MS data for powders of different weights ranging from 10 to 100 mg collected from two fine‐grained basalt artefacts display excellent reproducibility, with a RSD of <5% for the most important elements. The reproducibility is reduced when including the 5 mg weight fraction (RSD of ～2–9%), which is still sufficient for archaeological applications. Our results demonstrate the usefulness of 10 mg samples for elemental measurement, which is valuable for geochemical characterization and sourcing of fine‐grained basalt artefacts from museum collections that require minimal destructive sampling.     

LA–ICP–MS,SEM–EDS AND EPMA ANALYSIS OF EASTERN NORTH AMERICAN COPPER‐BASED ARTEFACTS: IMPACT OF CORROSION AND HETEROGENEITY ON THE RELIABILITY OF THE LA–ICP–MS COMPOSITIONAL RESULTS*

This study discusses the relevance of compositions obtained using laser ablation – inductively coupled plasma – mass spectrometry (LA–ICP–MS) for the purpose of identifying the provenance of copper‐based artefacts found in Virginia at Native American sites dated from the 16th to the 18th centuries. Ten artefacts were investigated by scanning electron microscopy – energy dispersive spectrometry (SEM–EDS) to visualize the corrosion and characterize the heterogeneities in the metal and electron probe micro‐analysis (EPMA) to determine separately the compositions of the intact metal and of the corrosion product. It is shown that the corroded surfaces are highly depleted in zinc but that representative concentrations can be determined by sampling the deeper, uncorroded metal. In contrast, lead values are highly variable because of the heterogeneous distribution of this metal within the bulk copper. Despite these problems, brass is easily identifiable and American native copper and European smelted copper can be unambiguously distinguished with LA–ICP–MS on unprepared artefacts using As, Ag, Ni and Sb trace elements.     

NO STONE UNBURNED: A COMPOSITIONAL ANALYSIS OF OBSIDIAN MICRODEBITAGE BY LASER ABLATION TOF–ICP–MS

Obsidian is an effective material for the study of prehistoric raw material use and exchange, due to the high degree of homogeneity and redundancy of obsidian materials and manufactured objects in the archaeological record. The destructive nature of many analytical techniques often impedes compositional research because of the damage that may occur to priceless archaeological artefacts. The combination of time‐of‐flight (TOF) ICP–MS with a laser ablation sample introduction system provides a highly efficient means of chemically characterizing obsidian. This study shows that sample size limit capabilities of TOF–ICP–MS analysis of obsidian can reach less than 100 μm. Sampling and analysis of microartefacts enables researchers to overcome problems of sampling bias with very little damage to the valuable existing materials within the archaeological record and expands the potential for chemical compositional analyses in archaeology.     

CHALLENGES IN THE ANALYSIS OF HETEROGENEOUS POTTERY BY LA–ICP–MS: A COMPARISON WITH INAA*

Tempers added to pottery have the potential to obscure geographical variation in the chemistry of exploited clay resources when analysed using bulk methods. A pilot study was conducted to assess the possibility of using LA–ICP–MS to analyse clay matrix in pottery with extremely subtle partitions between INAA chemical groups. LA–ICP–MS was used to analyse the clay matrix of 32 pottery samples from seven Middle and Late Woodland period (c. ad 200–800) sites in north‐east Florida and results were compared to data from INAA of the same samples. The results reveal many of the challenges in analysing highly heterogeneous materials with LA–ICP–MS. However, the study also generated data that are potentially useful in the determination of pottery provenance. In some respects, LA–ICP–MS of clay matrix replicated the chemical variation recorded by INAA, and in other respects the results are divergent. The similarities and differences between these results are explained by specific differences between the methods and the materials analysed (matrix versus bulk analysis). Suggestions for improving the method are discussed.     

THE PROVENANCE OF OBSIDIAN ARTEFACTS FROM THE WĀDĪ ATH‐THAYYILAH 3 NEOLITHIC SITE (EASTERN YEMEN PLATEAU) BY LA–ICP–MS

The geological sources of obsidian in the Red Sea region provide the raw material used for the production of obsidian artefacts found in prehistoric sites on both sides of the Red Sea, as far afield as Egypt, the Persian Gulf and Mesopotamia. This paper presents the chemical characterization of five obsidian geological samples and 20 prehistoric artefacts from a systematically excavated Neolithic settlement in highland Yemen. The major element concentrations were determined by SEM–EDS analysis and the trace element concentrations were analysed by the LA–ICP–MS method, an almost non‐destructive technique capable of chemically characterizing the volcanic glass. A comparison of archaeological and geological determinations allows the provenance of the obsidian used for the Neolithic artefacts to be traced to definite sources in the volcanic district of the central Yemen Plateau.     

THE PROVENANCE OF IRON ARTEFACTS FROM MANCHING: A MULTI‐TECHNIQUE APPROACH*

Iron finds from the Celtic oppidum of Manching in southern Bavaria (Germany) are analysed in view of their possible provenance. The exceptional size and the location of Manching are usually attributed to the presence of abundant iron ores in its vicinity. After a review of previous approaches for source determination of iron artefacts, we introduce lead isotope analysis as a new approach. However, only by combining the trace element patterns of slag inclusions and iron metal with lead isotope ratios in the metal is it possible to distinguish various iron ore formations near Manching. As a result, it turns out that, indeed, the most obvious ones—namely, bog ores near the Danube—constituted the main resources for iron production at Manching. It was even possible to select one occurrence as the most likely ore source.     

IDENTIFICATION OF POST‐DEPOSITIONAL CHEMICAL ALTERATION OF CERAMICS FROM THE NORTH COAST OF PAPUA NEW GUINEA (SANDUAN PROVINCE) BY TIME‐OF‐FLIGHT–LASER ABLATION–INDUCTIVELY COUPLED PLASMA–MASS SPECTROMETRY (TOF–LA–ICP–MS)*

The measured chemical composition of archaeological ceramics can result from a variety of geological, cultural and taphonomic factors. In the present study, we evaluate the likelihood that elevated barium concentrations in ceramics from the archaeological site of Wom/Aiser, located on the northern coast of Papua New Guinea, result from post‐depositional enrichment. Using time‐of‐flight–laser ablation–inductively coupled plasma–mass spectrometry, we mapped chemical compositional profiles across cut sections of ceramic sherds from four archaeological sites, all previously chemically characterized. We identify the formation of pronounced concentration gradients in samples from Wom/Aiser relative to sherds with low barium concentrations, consistent with post‐burial uptake.     

A STUDY OF GLASS BEADS FROM THE HALLSTATT C–D FROM SOUTHWESTERN POLAND: IMPLICATIONS FOR GLASS TECHNOLOGY AND PROVENANCE*

Eighty‐one samples taken from 68 glass beads found in southwestern Poland on sites of the Lusatian culture from the Hallstatt C and Hallstatt D subphases were analysed by EPMA. A subsample of 18 of these were additionally subjected to analysis by means of LA–ICP–MS in order to validate the results obtained by EPMA. Some glass was made using mineral soda and some using plant ash rich in sodium. Both high‐magnesium soda–lime glass (HMG) and low‐magnesium soda–lime glass (LMG) were identified. A large number of samples are characterized by low MgO content and medium K₂O content (LMMK glass), combined with low concentrations of CaO and high Fe₂O₃ and Al₂O₃. All the LMMK glass contains numerous silica crystals and inclusions composed of a number of elements (most frequently Cu, Co, Sb, As, Ag, Ni and Fe). The LMMK glass was presumably made in Europe during the Hallstatt C.     

THE USE OF TRACE ELEMENT ANALYSIS OF ENTRAPPED SLAG INCLUSIONS TO ESTABLISH ORE – BAR IRON LINKS: EXAMPLES FROM TWO GALLO‐ROMAN IRON‐MAKING SITES IN FRANCE (LES MARTYS,MONTAGNE NOIRE,AND LES FERRYS,LOIRET)*

Knowledge of the iron trade in ancient times rests on determining the source of the objects recovered during archaeological excavations. Unfortunately, attributing the origin is not always possible using archaeological tools alone. Trace element data of the ore and the archaeological material (reduction and reheating slags, entrapped slag inclusions from the bloom, bar iron and iron blades) from two Gallo‐Roman iron‐making centres, Les Martys (Montagne Noire) and Les Ferrys (Loiret), were determined using ICP–AES/MS and LA–ICP–MS. The results highlight a continuity of composition that makes it possible to establish a link between the initial ore and the semi‐finished iron products.