AN ASSESSMENT OF BACK-SCATTERED ELECTRON PETROGRAPHY AS A METHOD FOR DISTINGUISHING MEDITERRANEAN OBSIDIANS

The recent application by Burton and Krinsley (1987) of back-scattered electron (BSE) petrography to obsidians from sources located in the south-western United States established that this method can effectively resolve and characterize included micro-crystalline phases that have proven difficult to analyse by optical thin-section microscopy. In the first extension of their original study, we have examined, using BSE petrography, obsidians from island sources located in the Mediterranean, including sources known to have been exploited in prehistory. Because of the kinetic contrasts on their crystallization, these microcrystalline phases reflect the magmatic history of the obsidian, providing information about superheating, supercooling, sub-solidus processes, and other phenomena. This information is of significance for the chemical analysis of Mediterranean obsidians and also as the basis for a powerful alternative to existing non-destructive analytical methods for the sourcing of archaeological and art-historical obsidian.     

ELECTRON SPIN RESONANCE STUDY OF WHITE MARBLES FROM THARROS (SARDINIA): A REAPPRAISAL OF THE TECHNIQUE,POSSIBILITIES AND LIMITATIONS*

The characterization of various samples of white marble from the archaeological site of Tharros (Sardinia) is the starting point for the reexamination of the capabilities of electron spin resonance (ESR) spectroscopy as a tool for identifying the quarries of origin of ancient marble artefacts. Existing methods and data bases are employed for the assignment of our samples, but also reviewed to see if a more extensive use of the technique is feasible. It turns out that ESR spectroscopy, coupled with other available methods, may readily provide valuable information, often yielding the final answer to the problem of marble provenance. However, it is also clear that much work has still to be done to standardize the data collection and analysis procedures and to expand the available data base.     

LEAD ISOTOPE ANALYSES OF ISLAMIC POTTERY GLAZES FROM FUSTAT,EGYPT*

Lead isotope analyses have been undertaken on a group of Islamic lead‐glazed pottery artefacts from Fustat, Egypt, spanning the period from the eighth to the 14th century ad , that had previously been the subject of a comprehensive typological, chronological, petrographic and technological study. Comparison of the lead isotope ratios for the glazes with those for lead ores from Egypt, Iran, Tunisia, Anatolia, Greece, Sardinia and Spain provided information on the possible sources of the lead used in the production of the glazes. The results show that the lead used in glaze production by the Islamic potters at Fustat was most probably obtained from distant ore sources in Iran or Tunisia, Sardinia, Spain and the Taurus Mountains. Different ore sources were favoured in different periods and, to a limited extent, for different types of pottery, but at no time did the Fustat potters use the potentially more accessible Egyptian ore sources.     

OBSIDIAN IN THE MEDITERRANEAN AND THE NEAR EAST: A PROVENANCING SUCCESS STORY

Obsidian provenancing studies comprise one of the most productive and successful research programmes of archaeological science. Obsidian characterization has been successful because workable obsidian is homogeneous on a small scale, analysable by a large number of methods, and is restricted to a small number of mainly readily distinguishable geological sources. Analytical, dating, source, and trade studies within the western Mediterranean, central and eastern Europe, the Aegean, and Anatolia and the Near East during the last 30 years or so are reviewed. Research has shown that distributions are mainly separate in the four regions examined, and that obsidian was traded up to 900km in the prehistoric period. Publications on obsidian in the areas under review reached a peak of frequency in the later 1970s and 1980s, but have now decreased in number. This may reflect changing fashions in archaeometric studies, and a current lack of routine application of the provenancing methods developed.     

PROVENANCING OF LIGHTWEIGHT VOLCANIC STONES USED IN ANCIENT ROMAN CONCRETE VAULTING: EVIDENCE FROM TURKEY AND TUNISIA

The mastery of the use of lightweight rocks in concrete as a means of controlling the thrusts of large‐scale vaults was among the most important contributions of the Roman builders to the development of vaulted architecture. The string of volcanoes along the Tyrrhenian coast of Italy produced a variety of lightweight rocks, which allowed the builders in Rome to develop highly sophisticated ways of manipulating form and mass to create stable structures. The use of lighter rocks in vaults and heavier in foundations occurs from the mid‐first century bc in Rome, but the systematic use of imported lightweight rocks only began in the early second century ad under Trajan ( Lancaster 2005 , 59–64). Soon thereafter, the technique of using lightweight stones to build large vaults spread throughout the empire, usually to areas that had a local source of lightweight volcanic material. However, there was also a seaborne trade in lightweight rocks to areas that did not have local sources of such material. The intention of our analysis is to determine as precisely as possible the provenance of the lightweight stones used in vaulting of two areas of the Mediterranean, modern Turkey (ancient Cilicia) and Tunisia (ancient Africa Proconsularis), and thus to provide a better understanding of the nature of this trade.