STATISTICAL EVALUATION OF THE PRESENTLY ACCUMULATED LEAD ISOTOPE DATA FROM ANATOLIA AND SURROUNDING REGIONS

Several hundred new stable lead isotope ratio determinations of ore and slag specimens from ancient mining sites throughout Anatolia and of samples of artefacts of the Chalcolithic, Bronze Age and Early Iron Age from museum collections in Turkey and the United States have been combined with the accumulated published isotope determinations of such specimens from throughout the eastern Mediterranean and Aegean regions to form a data base of nearly 1000 analyses. It is the purpose of this paper to evaluate the practical effectiveness of using this now extensive data base to discriminate between the many sources of metals throughout this region and to propose methods to enhance this discrimination. By using the full three-dimensional isotopic data in multivariate statistical treatments and by separating isotopically resolvable source groups within some of the source areas and isolating statistically outlying specimens from them, it has been possible to characterize some ore sources more precisely and compactly and thereby achieve better resolution between ore sources. It has also been possible to isolate isotopically compatible artefact groups which possibly relate to ore sources that, as yet, have not been well defined by isotopic analysis.     

LEAD ISOTOPE CHARACTERISTICS OF THE CYPRUS COPPER ORE DEPOSITS APPLIED TO PROVENANCE STUDIES OF COPPER OXHIDE INGOTS

Nearly 200 new lead isotope analyses of sulphidic and oxidized ores from 26 copper mines on Cyprus show that the mines from different geological regions group in five distinctive isotopic groups, each with a substructure, related to the geological history of the ore formation. Comparison of lead isotope compositions of Bronze Age artefacts with these data can in many cases reveal the actual mines from which the copper for particular artefacts was obtained. The particular case of the provenance of the copper for 78 Late Bronze Age copper ‘oxhide ingots’found in Cyprus, Crete, Greece, Sardinia, Turkey and Bulgaria is discussed. The data show that all oxhide ingots so far analysed, dating to the fourteenth century BC and later, were made of copper consistent isotopically with only one mining region in the geographical north of Cyprus, and especially the Apliki mine. The study provides further evidence which supports the validity of the conventional approach to the use of lead isotope analysis for provenancing metals; this evidence is antithetical to recent suggestions of a model for the production of copper oxhide ingots which involved widespread mixing of copper from a number of ore sources throughout the Mediterranean.     

IN VITRO DECOMPOSITION OF BONE COLLAGEN BY SOIL BACTERIA: THE IMPLICATIONS FOR STABLE ISOTOPE ANALYSIS IN ARCHAEOMETRY*

To understand biogenic collagen type I decomposition and to establish how diagenesis may bias archaeometric data, modern mammalian bone was inoculated with a selection of ubiquitous soil bacteria. The presence of exogenous microbial biomass in the inoculated specimens was then checked microscopically prior to collagen extraction. The experimentally degraded bone collagen showed altered amino acid compositions, attributable to the selective breakdown of certain amino acids by the bacteria. While both the bulk collagen extract and the single amino acids exhibited shifts to more negative δ¹³ C-values, enrichment was recorded for general δ¹³ N, and a depletion trend relative to unaltered collagen was observed for individual amino acid δ¹³ N. One explanation for the enrichment of the global δ¹⁵N-values is cleavage of peptide bonds, which leaves ¹⁵ N within the substrate, while the change of ¹³C is mostly due to the altered amino acid composition. On the other hand, possible repolymerization of cleavage products under experimental conditions may also be responsible for the depletion trend of individual amino acid δ¹³C- and δ¹⁵ N-values. This paper discusses the results as a basis for the development of a method for the reconstruction of the isotopic abundance of the original collagen, using the amino acid composition of the degraded product, the contribution of individual amino acids to its global δ-values and of isotope discriminations implied in the microbial decomposition.     

OXYGEN AND CARBON ISOTOPE ANALYSIS OF HUMAN TOOTH ENAMEL FROM THE NEW KINGDOM SITE OF TOMBOS IN NUBIA

This study examines the feasibility of using oxygen isotope analysis of tooth carbonate to identify immigrants from the New Kingdom site of Tombos in Nubia (n = 30). In comparison with published data, the results (δ¹⁸O_ca,VSMOW = 31.4‰) imply a substantial presence of immigrants. However, further analysis of these data strongly suggests the need to consider hydrological and cultural factors such as the contribution of aquifer waters to the Nile, use of groundwater sources, and differences in handling and storage of water. The carbon isotope analysis, in conjunction with published ⁸⁷Sr/⁸⁶Sr data, provides additional support for the presence of immigrants at Tombos.     

PRODUCTION TECHNOLOGY OF ROMAN LEAD‐GLAZED POTTERY AND ITS CONTINUANCE INTO LATE ANTIQUITY

A broad selection of Roman lead‐glazed pottery dating from the first century ad through the fifth century ad was studied to establish locations of workshops and to address their technology of production. The ceramic bodies were analysed by ICP–AES. In addition, lead isotope analysis was undertaken on a selection of glazes. These findings suggested that there were several regions responsible for the production of lead‐glazed ceramics in the western Roman world, including central Gaul, Italy and, probably, Serbia and Romania. Using the body compositions as a starting point, the glazing techniques employed by each of the potential workshops were examined using electron probe microanalysis. It was determined that there were two primary methods of glazing. The first method used lead oxide by itself applied to non‐calcareous clay bodies, and the second method used a lead oxide‐plus‐quartz mixture applied to calcareous clay bodies. Based on these data for clay composition and glazing method, transfer of technology from the Hellenistic east to the western Roman world was proposed. Likewise, the inheritance of lead‐glazing technology into late antiquity was established by making comparisons to lead‐glazed ceramics dating to the seventh to ninth centuries from Italy, the Byzantine world and Tang Dynasty China.     

THE EFFICIENT COMPUTATION OF UNBIASED MAHALANOBIS DISTANCES AND THEIR INTERPRETATION IN ARCHAEOMETRY*

This paper argues for cross-validation to reduce bias in estimating Mahalanobis distances of individuals to groups, a particular problem with small sample sizes. Formulae for the efficient computation of cross-validated distances, which avoid excessive matrix inversion, are given. The use of Mahalanobis distances as measures of consistency, or as indications of outlying values, is described. The little-known technique of gamma plotting is outlined and discussed as an aid to interpreting distances in these terms. Both cross-validation and gamma plotting are illustrated in an example on marble composition.     

LEAD ISOTOPIC EVIDENCE FOR A MIXED PROVENANCE FOR ROMAN WATER PIPES FROM POMPEII*

Lead isotope analysis has been applied to the investigation of some Roman objects found in the town of Pompeii, consisting mostly of fistulae from the Augustan water supply system. The results of the analyses have produced ratios between 18.10 and 18.66 for ²⁰⁶Pb/²⁰⁴Pb, between 15.63 and 15.72 for ²⁰⁷Pb/²⁰⁴Pb and between 38.21 and 38.98 for ²⁰⁸Pb/²⁰⁴Pb. These data point to a fairly complex origin for the lead artefacts, probably involving several successive meltings and recyclings of a rather heterogeneous lead supply. The spread of lead isotope ratios can only be reconciled with a multiplicity of end‐members, at least three, but very probably more. There is one certain Sardinian ore, other indistinguishable Hercynian ores of Sardinia and/or Spain, and several different Alpine Mesozoic‐Tertiary mineralizations of the Mediterranean basin (Spain, Greece, Tuscany).     

MULTI‐METHOD MARBLE PROVENANCE DETERMINATIONS: THE CARRARA MARBLES AS A CASE STUDY FOR THE COMBINED USE OF ISOTOPIC,ELECTRON SPIN RESONANCE AND PETROGRAPHIC DATA*

A multi‐method approach, based on petrography, stable isotope data and electron spin resonance spectroscopy for assigning the provenance of white marbles, is presented. A total of 11 experimental variables has been used, including the quantitative measurement of the sample colour and its homogeneity. On this basis we attempt to distinguish the three main quarrying basins of the Carrara district, that is, Torano, Miseglia and Colonnata. Such discrimination, extremely uncertain on the basis of the single techniques, may be performed with acceptable confidence’ using a properly selected subset of six petrographic, isotopic and spectroscopic variables. The final resubstitution and jackknifed re‐assignment rates are, respectively, 85% and 81%. Inclusion of the remaining five variables into the classification rule does not improve the results, but simply increases data overinterpretation. The practical possibility of using such an approach for more general provenancing problems is considered.     

AN EXPERIMENTAL INVESTIGATION ON LEAD ISOTOPIC FRACTIONATION DURING METALLURGICAL PROCESSES

In this paper, experiments are designed to imitate the non‐equilibrium evaporation metallurgical process of lead. The lead isotope ratios of the remaining lead liquid with different percentage losses were then determined using high‐solution MC–ICP–MS. The results show that this process does alter lead isotopic ratios of the remaining liquid. However, the variations are so much smaller than the speculated values using the theoretical formula that in most ancient metallurgical processes, the lead isotopic fractionation can be neglected.     

THE TECHNOLOGY OF GLAZED ISLAMIC CERAMICS USING DATA COLLECTED BY THE LATE ALEXANDER KACZMARCZYK

During the 1980s, the late Alexander Kaczmarczyk undertook the analysis of some 1200 glazed Islamic ceramics from Egypt, Iran, Iraq and Syria spanning the period from the eighth to the 14th centuries ad , using a combination of XRF for the glazes, and AAS or PIXE for the bodies. The aim of the present paper is, first, to bring to the attention of researchers into Islamic ceramics the fact that these analytical data are available on the Research Laboratory for Archaeology and the History of Art website, and also that some 400 of the analysed sherds are held in the Research Laboratory. Second, the paper provides a preliminary interpretation of the analytical data in terms of the choice of glaze type (i.e., alkali–lime, lead–alkali and high‐lead), tin‐opacification, body type (i.e., quartz or stonepaste, calcareous clay, and non‐calcareous clay), and colorants.