Amorphous glass fragments from archaeological surface surveys: Potential chronological use of ion beam and isotopic analytical characterization

Analytical techniques have been used to implement the archaeological information from surface surveys. We have shown that the compositional comparison of amorphous samples, e.g. glass, can provide important chronological information when compared with findings from other sites. A group of 61 glass fragments, recovered from an archaeological surface survey at the site of the Roman city of Duratón (1st to 3rd century AD), near Segovia, Spain, have been analysed by combined Particle Induced X-ray/Gamma-ray Emission (PIXE-PIGE) techniques and by isotope dilution mass spectrometry. Four groups of objects were identified. The largest group by far, corresponds to the typical sodium-rich natron-made Roman glass. Compared with data reported in previous studies, including a few on the Iberian Peninsula, the composition of Duratón natron glass is similar to that of the widespread Roman 1st-3rd century AD glasses. The glasses of the nearby Patones, six of which have been analysed in this study, belong, on the contrary, to the so-called HIMT glass. This is compatible with the soda-lime-silica glass pattern observed in the Western Mediterranean. HIMT glass is dominant in this area from the 4th century onward. HIMT glass products are much easier to make and less expensive. Strontium and neodimium isotope analysis confirms the compositional proximity of the Duratón glasses to three groups of 1st-3rd century samples from Barcino, Lyon and the Iulia Felix wreck and point to a production of the glass in the Eastern Mediterranean. Pliny the Elder in his Naturalis Historia had specifically mentioned the glass production of Hispania and Gallia, which should hopefully be confirmed by the findings in the corresponding regional sites. This is the case for Gallia but not yet for the Iberian Peninsula, where few Roman glass analyses have been completed.