This study presents the results of an archaeometrical investigation performed on 75 black glass beads dated to the 9th-5th century BC coming from Bologna, Cumae and Pozzuoli (Italy), and Chotin (Slovakia). The analyses of the major, minor and trace elements -as well as that of Sr and Nd isotopes performed on a selection of samples coming from Bologna -provided evidence for two different production technologies in Iron Age black glass found in Italy (natron glass, probably produced in Egypt) and Slovakia (wood ash glass, probably produced in Europe). In both cases, the glasses derive their black colouration from the high presence of iron (around 12% FeO), introduced into the glass batches through the intentional choice of dark sands. The production model appears to be small-scale and experimental, characterised by the use of non-sorted raw materials and poorly defined formulae, producing glass with a high chemical variability. The wood ash technology appears to have dropped out of use in Europe until the Medieval period, while natron production spread quickly, becoming predominant throughout the Mediterranean. Response to Reviewers:Answers to referees' comments and list of revisionsReviewer #1: The authors took in consideration most of the comments raised by this reviewer. Few points remain to be clarified.-The experimental section has been improved. The authors added a comment regarding the experimental protocol used for EPMA being equal to the condition reported in Henderson 1988b. However, the LA-ICPMS section becomes more unclear than before. In the original version we read that NIST 612 and 614 were used for external calibration, and that two glass standards (not specified) were used as secondary standards to check for accuracy and precision. The new version states instead that NIST 610 and 614 were used for external calibration, and NIST 612 was used as secondary standard to check for accuracy and precision. What happened to

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Several technological inventions (silica melting, high temperature processes, use of opacifiers and colorants such as Sb, Cu, Pb and Co) were united in making ancient glass, but we do not yet understand how these new techniques, materials and pigments were adopted. Links with the earliest metal industries, dating to five millennia ago, have been suggested. In this paper, we present Sb isotopic analysis as a technique to examine the earliest glass, recovered from excavation contexts almost a century old, and compare it to the first use of antimony as a metal. The antimony used as opacifier in the earliest glass appears to be native Sb, rather than stibnite, and is isotopically identical to the first antimony used in metallic form. Its origin seems to lie in the Caucasus, confirming the relation between the origin of glass and the development of metallurgy.

In large parts of the Mediterranean recipes for the earliest man-made glass changed from melting mixtures of crushed quartz pebbles and halophytic plant ashes in the Late Bronze Age to the use of quartz sands and mineral soda during the Early Iron Age. Not much is known about this transition and the experimental materials which would inevitably have been connected to such technological change. In this paper we present a unique snapshot of developments in glass technology in Anatolia during the Middle Iron Age, when glass is still a relatively rare commodity. The present work focusses on black glass beads decorated with yellow trails from eighth to seventh century BCE Sardis, glass beads that are very rare for this period, and on this site. A full elemental analysis of the beads was made, and Sr, Pb and B isotope ratios were determined. This study reveals the use of a combination of a previously unknown source of silica and of mineral soda, giving rise to elevated (granite-like) Sr isotope signatures, as well as high alumina and B concentrations. The yellow trails of glass on the beads consist of leadtin yellow type II, lead stannate, showing the earliest occurrence of this type of opacifier/colourant so far, predating any other findings by at least four centuries. The production of these glass beads may be local to Sardis and experimental in nature. It is therefore suggested that Sardis may have played its role in the technological development of the glass craft during the Iron Age.

During the production of natron glass most features of the raw materials are lost and only some bulk geochemical characteristics have potential as provenance indicators. To determine the primary origin of archaeological glass artefacts, suitable sand raw materials have to be accurately characterised. In this respect, information about the possible variation in geochemical properties within a silica source is also vital to account for potential (partial) overlap of different sources. In this study, it is shown that the variation in major and minor elemental composition of beach sand on a local scale is smaller than the variation in Roman natron glass. Therefore, a single sand deposit can be seen as a relatively homogeneous source of silica for glass production. Nd isotopic signatures are identical for all samples analysed. The isotopic composition of Sr however varies considerably due to local variations in the relative proportions of carbonates and silicates (mostly feldspar).