Insights into the secondary glass production in Roman Aquileia: A preliminary study

A set of 29 glass shards, selected from numerous ones recovered in 2017 in Aquileia (NE Italy), was studied to provide evidence of local glass production for that specific area in antiquity. These shards can be dated between the 1st and the 4th century AD. The chemical composition of glass samples was obtained using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) that enables to quantify the concentration of major, minor, and trace elements needed to investigate provenance and compositional groups and sometimes to suggest a chronological frame of the samples. To ensure that the samples are homogeneous enough to perform accurate quantification, some of them were also analysed by instrumental neutron activation analysis (INAA). Most of the chunks, working wastes, and artefact shards considered in this work exhibited similarities among them in terms of composition, which likely indicates that glass working activities were practised at the site of recovery. The analyses demonstrated the presence of both recycled glass and primary glass. Interestingly, the compositional data of raw primary glass point to both Syro-Palestinian and Egyptian regions as sourcing areas, confirming the role of the Roman city of Aquileia as a network node for the trade of goods. In addition, some particularly coloured glass fragments showed a composition typical of glass produced starting from the 1st or 2nd century AD, requiring specific types of furnaces and procedures for its manufacture, and suggesting the possibility of local highly-specialised production. The preliminary results of this work strengthen the hypothesis that Aquileia was a thriving centre, either for working primary glass or for glass recycling and production of objects with particular colours

Laser ablation-ICP-MS depth profiling to study ancient glass surface degradation

In general the analysis of archeological glass represents a challenge for a wide variety of objects because of the presence of physical and/or chemical damage on the surface of the artifact, also known as weathering or corrosion. To retrieve accurate bulk elemental information by laser ablationinductively coupled plasma-mass spectrometry (ICP-MS), the original, pristine glass needs to be Breached^, thereby penetrating the alteration layer which is often more than 10 μm thick. To study this alteration layer the laser was operated in the drilling mode, either with a low (1 Hz) or a high (10 Hz) pulse repetition rate for a period of 50 s yielding detailed spatial information for ca. 20 elements over a shallow depth (ca. 5 μm) or less-detailed spatial information for 50–60 elements over a greater depth (ca. 50 μm). Quantitative elemental depth profiles (in wt%) were obtained with the so-called sum normalization calibration protocol, based on summation of the elements as their oxides to 100 wt%.We were able to associate the increase of SiO2 (in wt%) in the alteration layer to the volumetric mass density change in the glass as a result of depletion of Na2O and K2O. Also the interaction of the number of laser shots with the alteration layer is shown experimentally via depth measurements using profilometry. Chemical and physical changes in four ancient glass artifacts, directly and indirectly measureable by laser drilling, were studied as a function of internal and external factors such as age, composition, and exposure conditions

Laser ablation-ICP-MS depth profiling to study ancient glass surface degradation

In general the analysis of archeological glass represents a challenge for a wide variety of objects because of the presence of physical and/or chemical damage on the surface of the artifact, also known as weathering or corrosion. To retrieve accurate bulk elemental information by laser ablationinductively coupled plasma-mass spectrometry (ICP-MS), the original, pristine glass needs to be Breached^, thereby penetrating the alteration layer which is often more than 10 μm thick. To study this alteration layer the laser was operated in the drilling mode, either with a low (1 Hz) or a high (10 Hz) pulse repetition rate for a period of 50 s yielding detailed spatial information for ca. 20 elements over a shallow depth (ca. 5 μm) or less-detailed spatial information for 50–60 elements over a greater depth (ca. 50 μm). Quantitative elemental depth profiles (in wt%) were obtained with the so-called sum normalization calibration protocol, based on summation of the elements as their oxides to 100 wt%.We were able to associate the increase of SiO2 (in wt%) in the alteration layer to the volumetric mass density change in the glass as a result of depletion of Na2O and K2O. Also the interaction of the number of laser shots with the alteration layer is shown experimentally via depth measurements using profilometry. Chemical and physical changes in four ancient glass artifacts, directly and indirectly measureable by laser drilling, were studied as a function of internal and external factors such as age, composition, and exposure conditions

Laser ablation-ICP-MS depth profiling to study ancient glass surface degradation

In general the analysis of archeological glass represents a challenge for a wide variety of objects because of the presence of physical and/or chemical damage on the surface of the artifact, also known as weathering or corrosion. To retrieve accurate bulk elemental information by laser ablationinductively coupled plasma-mass spectrometry (ICP-MS), the original, pristine glass needs to be Breached^, thereby penetrating the alteration layer which is often more than 10 μm thick. To study this alteration layer the laser was operated in the drilling mode, either with a low (1 Hz) or a high (10 Hz) pulse repetition rate for a period of 50 s yielding detailed spatial information for ca. 20 elements over a shallow depth (ca. 5 μm) or less-detailed spatial information for 50–60 elements over a greater depth (ca. 50 μm). Quantitative elemental depth profiles (in wt%) were obtained with the so-called sum normalization calibration protocol, based on summation of the elements as their oxides to 100 wt%.We were able to associate the increase of SiO2 (in wt%) in the alteration layer to the volumetric mass density change in the glass as a result of depletion of Na2O and K2O. Also the interaction of the number of laser shots with the alteration layer is shown experimentally via depth measurements using profilometry. Chemical and physical changes in four ancient glass artifacts, directly and indirectly measureable by laser drilling, were studied as a function of internal and external factors such as age, composition, and exposure conditions

Elemental mapping of polychrome ancient glasses by Laser Ablation ICP-MS and EPMA-WDS: a new approach to the study of elemental distribution and correlation

In this work a new approach to the physicochemical characterization of polychrome archaeological glasses through elemental maps is presented. It is the first time that elemental mapping both by Laser Ablation-ICP-MS and EPMAWDS was performed on ancient glass. The glass elemental mappings are here proposed as useful tools for a preliminary study of the overall pattern of a glass surface concerning each analyzed element. The visual inspection of the maps gives the distribution of the elements and their degree of homogeneity; this allows the identification of the correlations between elements, in order to get information about chromophores, opacifiers and their associated ores, as well as about the glass deterioration. The LA-ICP-MS quantitative elemental maps of 54 elements were performed on a glass sample area. The concentrations of the element oxides were visualized in pseudo-colors, both in 2D and 3D. EPMA-WDS elemental maps were performed on areas of surface and break-section of the samples, at the interface between bulk and decorations. LAICP- MS elemental mapping can be functional to the determination of the glass chemical composition patterns and of associations between elements, while WDS elemental mapping is mainly aimed to identify the distribution of crystalline phases or to visualize concentration gradients of elements at the interfaces of different areas, such as bulk and decorations. Both the techniques can be functional to the study of glass superficial weathering

PICKING UP THE HINT: RAW GLASS CHUNKS AND GLASS WASTES FROM PLOUGHSOIL COLLECTION IN AQUILEIA (ITALY)

Despite many well-known indications suggesting the presence of a flourishing glass production in Aquileia during the Roman age, to date no furnace has ever been identified. In November 2017, during field-walking survey activities part of the EC funded landscape archaeology project Visualising Engineered Landscape (VEiL), an extraordinary concentration of hundreds of raw glass chunks and shards of glass was identified on the surface of a ploughed field in the Northern fringes of the Roman city, just outside the ancient city walls. Fragments collected included several chunks encrusted on refractory material (the majority being natural bluegreen, with smaller quantities in blue and olive green), droplets and trails together with other glass working wastes and fragments of vessels. This remarkable in situ plough soil assemblage, clustered in a relatively small spatial dispersion, may reflect the existence of a secondary glass workshop. This paper expands on the satellite imagery analysis and the field prospections that led to the identification of the archaeological context and the preliminary outcomes provided by morphological and archaeometric analysis including Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and UVVis Reflectance Spectroscopy carried out on some of the most relevant samples of glass recovered. This new discovery could represent a unique opportunity to expand our current understanding of use and consumption of glass in Roman period in the area and the broader northern Adriatic context

Zanzibar and Indian Ocean trade in the first millennium CE: the glass bead evidence

Recent archaeological excavations at the seventh-to tenth-century CE sites of Unguja Ukuu and Fukuchani on Zanzibar Island have produced large numbers of glass beads that shed new light on the island's early interactions with the wider Indian Ocean world. A selected sample of the beads recovered was analyzed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to determine the origins of the glass used to make the beads and potential trade relationships are considered. The data show that two major glass types can be identified: mineral-soda glass, m-Na-Al, produced in Sri Lanka (and possibly South India) and plant ash soda glass. The latter comprises three subtypes: two with low alumina concentrations and different quantities of lime (here designated v-Na-Ca subtypes A and B) and one with high alumina (designated v-Na-Al). The v-Na-Ca subtype A beads are chemically similar to Sasanian type 1 glass as well as Zhizo beads found in southern Africa, while v-Na-Ca subtype B compares reasonably well with glasses from Syria and the Levant. While the mineral-soda beads were made in South Asia, it appears likely that at least some of the plant ash beads were made in South or Southeast Asia from imported raw and/or scrap Middle Eastern glass. In contrast, during this period, all beads imported into southern Africa were made of Middle Eastern glass from east of the Euphrates (v-Na-Ca subtype A) and appear to have arrived on ships from Oman and the Persian Gulf. These data suggest that the two sections of the African coast were engaged in different Indian Ocean trade circuits