Composition, production and procurement of glass at San Vincenzo: an early medieval monastic complex in southern Italy

136 glasses from the ninth-century monastery of San Vincenzo and its workshops have been analysed by electron microprobe in order to situate the assemblage within the first millennium CE glass making tradition. The majority of the glass compositions can be paralleled by Roman glass from the first to third centuries, with very few samples consistent with later compositional groups. Colours for trailed decoration on vessels, for vessel bodies and for sheet glass for windows were largely produced by melting the glass tesserae from old Roman mosaics. Some weakly-coloured transparent glass was obtained by re-melting Roman window glass, while some was produced by melting and mixing of tesserae, excluding the strongly coloured cobalt blues. Our data suggest that to feed the needs of the glass workshop, the bulk of the glass was removed as tesserae and windows from a large Roman building. This is consistent with a historical account according to which the granite columns of the monastic church were spolia from a Roman temple in the region. The purported shortage of natron from Egypt does not appear to explain the dependency of San Vincenzo on old Roman glass. Rather, the absence of contemporary primary glass may reflect the downturn in long-distance trade in the later first millennium C.E., and the role of patronage in the “ritual economy” founded upon donations and gift-giving of the time

Composition of Late Hellenistic to Early Roman glass vessels from the Souk Excavations, Beirut

Sixty-six glass vessels from excavations in Beirut and dated first century B.C.E. to the first century C.E. have been analysed by electron microprobe. The majority are relatively high in Al2O3, CaO and P2O5, are weakly coloured, manganese-colourless, or yellow–brown-amber and on compositional grounds the glass material is considered to have originated in the Levant. Manganese oxide was added as a decolouriser and MnO contents are continuous between 0.02 and 2.0%. Limpid, weakly-coloured glass occurs over the whole MnO range, while most colourless glass has MnO above 0.7%, and all amber and olive glasses have MnO below 0.3%. There is a strong correlation between sulphur and soda concentrations in all the Levantine glass, but total sulphur is lowest in amber and olive, reflecting the reducing conditions required to form the ferri-sulphide chromophore and the lower solubility of the S2− ion as opposed to SO42−. Iron is also low in the amber glass relative to other colours, as some Fe was added with the manganese that they contain. Hence, amber glasses were produced at the primary stage from mixtures of natron and sand with no other additives apart from any organic reducing agents. In the second half of the first century C.E. slumped bowls in antimony-decolourised Egyptian glass become apparent, along with colourless cast vessels with mixed antimony-manganese compositions. Antimony is known to have been used as a decolouriser in earlier Hellenistic glass, but it does not appear in the present assemblage until this later introduction of Egyptian glass. The introduction of glass-blowing technology does not seem to have coincided with any significant change in composition

Seventeenth-Century Façon de Venise Glass from De Twee Rozen Glasshouse, Amsterdam: Technology out of Step with Fashion?

De Twee Rozen glasshouse was one of the best-known glasshouses in seventeenth-century Amsterdam and an important producer of glass in the Venetian style. It occupied two sites: initially at Keizersgracht, from 1621, it then moved in 1657 to Rozengracht, further from the center of the city. Production debris recovered from a deposit close to the Keizersgracht site were originally attributed to an earlier glasshouse, but a reinterpretation in light of more recent excavations firmly attributes these glasses to the first location of De Twee Rozen. We present 50 new SEM-EDS analyses of vessel glass, moils, trim-offs, unfinished objects, and production waste from the later site at Rozengracht and compare these with previously published analyses from both sites. Several changes in glass technology appear to have been introduced following the change of location. First, a cristallo-type technology, involving the purification of ashes to produce a glass with lower Fe2O3 appears to have been used exclusively at Rozengracht. Thus, the introduction of glass production in the Venetian style was not accompanied by the signature Venetian glassmaking technology, which seems to have followed later. Second, the relatively new method of opacification using antimony was introduced, along with other changes, such as the introduction of lead into the cobalt-blue glass used in polychrome decorative canes. The origins of these new technologies are discussed in particular in view of the presence of the chemist Johann Rudolf Glauber at De Twee Rozen and its direction by a Venetian master, Nicalao Stua, from 1667

The blues of Romuliana

The paper presents a set of glass fragments excavated at several different locations within and outside the late Roman fortified imperial residence Felix Romuliana (Gamzigrad, Serbia). This small group of eighteen fragments and mosaic glass tesserae are distinguished by their cobalt blue colour. The majority of the finds are mosaic tesserae (six pcs) and sheets of glass (five pcs), which could be related to architectural decoration (sectilia panels). Others are pieces left behind from secondary glass working (four pcs). There are also two fragments tentatively identified as window pane pieces, and only one find is a vessel sherd. The materials are dated to the 4th century. Significantly, some of the production debris and the two “window pane” fragments were found inside the destruction of a glass furnace. The analyses of the chemical glass composition of the finds confirmed that the blue colourant in all samples is cobalt, and antimony is also present at notable levels (except for one sample), likely to produce opacification of the glass. Regarding the origin of the raw glass, the data on almost all pieces suggests a Syro-Palestinian provenance, and a single sample could be related to Egyptian primary glass production. Importantly, the concentrations of the oxides added to the base glasses in order to modify the colour are positively correlated in certain samples, hinting at the makeup of the cobalt bearing ingredient and at a likely existence of particular production practices of the late Roman period

Glass groups, glass supply and recycling in late Roman Carthage

Carthage played an important role in maritime exchange networks during the Roman and late antique periods. One hundred ten glass fragments dating to the third to sixth centuries CE from a secondary deposit at the Yasmina Necropolis in Carthage have been analysed by electron microprobe analysis (EPMA) to characterise the supply of glass to the city. Detailed bivariate and multivariate data analysis identified different primary glass groups and revealed evidence of extensive recycling. Roman mixed antimony and manganese glasses with MnO contents in excess of 250 ppm were clearly the product of recycling, while iron, potassium and phosphorus oxides were frequent contaminants. Primary glass sources were discriminated using TiO2 as a proxy for heavy minerals (ilmenite/spinel), Al2O3 for feldspar and SiO2 for quartz in the glassmaking sands. It was thus possible to draw conclusions about the chronological and geographical attributions of the primary glass types. Throughout much of the period covered in this study, glassworkers in Carthage utilised glass from both Egyptian and Levantine sources. Based on their geochemical characteristics, we conclude that Roman antimony and Roman manganese glasses originated from Egypt and the Levant, respectively, and were more or less simultaneously worked at Carthage in the fourth century as attested by their mixed recycling (Roman Sb-Mn). In the later fourth and early fifth centuries, glasses from Egypt (HIMT) and the Levant (two Levantine I groups) continued to be imported to Carthage, although the Egyptian HIMT is less well represented at Yasmina than in many other late antique glass assemblages. In contrast, in the later fifth and sixth centuries, glass seems to have been almost exclusively sourced from Egypt in the form of a manganese-decolourised glass originally described and characterised by Foy and colleagues (2003). Hence, the Yasmina assemblage testifies to significant fluctuations in the supply of glass to Carthage that require further attention

Exotic glass types and the intensity of recycling in the northwest Quarter of Gerasa (Jerash, Jordan)

Major and trace elements are presented for 149 glass fragments ranging in date from the Roman to Early Islamic periods (1st – mid-8th centuries CE), excavated during the Danish-German Jerash Northwest Quarter Project's fieldwork between 2011 and 2016. The results confirm a clear dominance of Levantine glass types, but also reveal 12 glasses of Egyptian and Mesopotamian compositions recovered from two houses destroyed by the major earthquake which hit parts of the Levant in January 749 CE. These closed and undisturbed contexts from the final phase of occupation reveal the presence of relatively more pristine Levantine as well as imported material that is less visible in earlier contexts in the Gerasa assemblage, where the recycling indexes are high and chemical signatures of any exotic glass were largely lost due to remelting and their dilution by the overwhelming quantities of glass produced in the Levantine region. This emphasizes that imported glass may frequently be underestimated or even invisible in glass compositional studies, depending on the archaeological context sampled and the approach taken to artifact quantification. Levantine glass was attributed to Roman, Late Roman (Jalame) and Byzantine/Early Islamic (Apollonia) productions based primarily on MnO, Al_{2}O_{3} and Na_{2}O concentrations, which offered an advantage over previous approaches. While colorants in weakly colored glass indicate recycled material, their concentrations are sensitive to context, with higher concentrations in the early periods when the use of intentionally colored glass was more frequent. We have therefore developed the concept of the intensity of recycling, which was estimated using components modified during prolonged melting, such as K_{2}O, P_{2}O_{5} and Cl. A pronounced enrichment in CaO, also dependent upon the intensity of recycling, may affect the assignment to compositional groups and should be taken into consideration in future. Recycling in Gerasa appears to have been more intensive than was the case for cities closer to the primary production centers on the Mediterranean coast, consistent with the view that the dependency on recycling increases further away from the source of the primary material. In contrast, the cities in the coastal plain could readily exploit the marine transportation network, which appears to have played a major role in the distribution of raw glass

The technology of polychrome glazed ceramics in Ifriqiya: new data from the site of Chimtou

Ifriqiya (roughly Tunisia and eastern Algeria) is believed to have played a significant role in the diffusion of ceramic glazed technologies into other regions of the Western Mediterranean. However, due to limited analysis on North African glazed ceramics, its role in technology transfer remains poorly understood. This paper uses SEM–EDS and petrographic analyses to understand the technology employed in the production of Tunisian ceramics through the study of 30 polychrome glazed ceramics from a medieval settlement at the site of Chimtou (ancient Simitthus), Tunisia, dated to the late ninth-twelfth century. The results show that these are lead-rich glazes with varying contents of alkalis, coloured with copper, iron and manganese oxide and applied over a calcareous body. Opaque glazes were obtained using cassiterite crystals as opacifier or by adding crushed quartz. The use of lead stannate as a colourant and opacifier in one light yellow glaze raises questions about the mechanisms of introduction of tin opacification technology in North Africa. Scrap metal seems to have been used as a source of lead for the glazes; while iron slag was probably used as a source of iron to colour the glaze in one sample, pointing to a cross-craft interaction between glazemaking and metallurgy