The palaeo-Christian glass mosaic of St. Prosdocimus (Padova,Italy): archaeometric characterisation of tesserae with antimony- or phosphorus-based opacifiers

The present paper reports the results of archaeometric characterisation of the opaque tesserae, intentionally coloured with antimony- or phosphorus-based opacifiers, coming from one of the two only palaeo-Christian glass mosaics known in the Veneto region (Italy), i.e., the mosaic which decorated the votive chapel of St. Prosdocimus in Padova. In particular, 55 tesserae belonging to glass types “White”, “Blue”, “Yellow”, “Green” and “Brown” are examined here. The multi-methodological approach (SEM-EDS, EMPA, XRPD, imaging spectroscopy coupled, in some cases, with XAS) gave valuable insights into the complexities of palaeo-Christian glass mosaic production technologies. Two main groups are identified, one characterised by glassy matrixes and opacifiers (calcium or lead antimonate) typical of the Roman period and comprising all “White”, “Blue”, and “Yellow” tesserae and some “Green” ones, and the other characterised by glassy matrixes and an opacifier (calcium phosphate) typical of the 6th century AD, composed of “Green” and “Brown” tesserae. This suggests that, during that century there was a gradual change from older to “new” production technologies: although new opacifiers such as calcium phosphate started to be used, the frequent use of antimony-based ones (43/55 samples) supports the hypothesis that their systematic use was extended until the 6th century, although re-using old tesserae cannot be completely excluded. In addition, comparisons with compositional groups already identified in the “gold” tesserae of the same mosaic and tesserae from Ravenna demonstrate that both the same “base compositions” of the glass were used to produce transparent and opaque glass. This evidence, coupled with the results of the historical-artistic study, suggests technological connections between Padova and Ravenna, the capital of Byzantine mosaics in Italy. Micro-structural observations and chemical analyses of the Paduan antimony-based opacified glass demonstrate that different processes and raw materials were used in their production. Both in situ and ex situ crystallisation can be identified for calcium and lead antimonate in Paduan tesserae, whereas the production of tesserae opacified with calcium phosphate generally appears to be highly standardised. Although the opacifiers used in the Paduan tesserae support technological transitions, the colouring elements identified here, i.e., iron and manganese for white, yellow, brown and some green tesserae, cobalt for blue, and copper for blue and green, suggest continuity, because their use is widely testified in the production of both transparent and opaque glass artefacts dating from the Bronze Age until Medieval times, from whichever archaeological site the samples come. Peculiar relationships among the oxidation states of colouring elements, their contents in the glassy matrix, the types of opacifiers used, and the final colour of tesserae were identified. In addition, the correlations of cobalt and/or copper with other elements, together with identification of relics of colouring and “metallic” droplets, allow us to speculate on possible sources and production technologies. Lastly, identification of newly formed crystalline inclusions in tesserae also yields information on kiln temperatures, which ranged between 900 and 1150 °C, a range easily reached in the furnaces of the 6th century AD.     

Physical and Numerical Approaches for the Optimal Insertion of Seismic Viscous Dampers in Shear-Type Structures

This article presents the results of an exhaustive parametric analysis which compares the performances offered by various systems (which lead to both classical and non classical damping matrices) of added viscous dampers in shear-type structures. The aim of the research work here presented is the identification of the system of added viscous dampers which maximizes the dissipative properties under an equal “total size” constraint. The choice of the systems of added viscous dampers considered in the comparison is carried out both using a numerical approach (based upon the use of genetic algorithms) and a physically based approach (based upon the properties of classically damped systems). The comparison is carried out through the numerical evaluation of the dynamic response of representative shear-type structures to both stochastic and recorded earthquake inputs. The results obtained using both approaches indicate that a damping system based upon the mass proportional damping component of the Rayleigh viscous damping matrix (referred to as MPD system) is capable of optimizing simultaneously a number of different performance indexes, providing the best “overall” damping performances. The MPD system is characterised by viscous dampers (a) which connect each floor to a fixed point and (b) which are sized proportionally to the corresponding floor mass.     

The coloured glass of Iulia Felix

Research on the cargo of glass in the Roman ship Iulia Felix, wrecked off the town of Grado (province of Udine, North Italy) in the first half of the 3rd century AD and composed of recycling cullet carefully selected for colour and type, provided much information on Roman glass production technology. A combined approach, involving analytical, statistical, and archaeological evidence, included chemical analyses (X-ray fluorescence, electron microprobe), which indicated that the coloured samples were all soda-lime-silica in composition, with natron as flux, although cluster analysis identified many compositional groups. Comparisons among the compositional groups of the colourless glass, previously studied, and those of coloured glass showed that the production technologies of the colourless glass vessels constitute two well-defined technological end-members, also related to group types, into which those of the coloured glass samples fall. In particular, coloured glass samples—all bottles, low-status vessels—were produced with mainly beach siliceous-feldspar-calcareous sand. However, unlike the colourless type, strict control of raw materials and decolourising processes was not adopted, and recycling was also practised, as demonstrated by the Sb₂O₃, Cu and Pb patterns. In this context, a “recycling index” (RI)—[(Sb₂O₃)_X/(Sb₂O₃)_Ref] * 100—is proposed here for the first time, in order to quantify the extent of recycling of antimony colourless glass in the batch. RI is valid for glass containing abundant Sb from an end-member of colourless glass. In conclusion, although it cannot be stated unequivocally that the identified compositional trends are related to different production centres or different raw materials, the strong evidence of compositional variability among all the Iulia Felix glass samples, both colourless and coloured, supports the dispersed production model for Roman glassware and the common practice of recycling in Roman imperial times, especially for low-status vessels.     

Innovation and tradition in the fourth century mosaic of the <Emphasis Type="Italic">Casa delle Bestie Ferite</Emphasis> in Aquileia,Italy: archaeometric characterisation of the glass tesserae

The present paper focuses on the archaeometric characterisation of 38 glass tesserae of various colours from an in situ mosaic in Aquileia, Italy, dated to the second half of the fourth century AD. The examination of the textural, mineralogical and chemical features, conducted by means of a multi-methodological approach (optical microscopy (OM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), electron probe micro analysis (EPMA), X-ray diffraction (XRD) and Fibre Optic Reflectance Spectrophotometer (FORS)), has provided valuable insights into the changes in the production technology during the transition between the Roman and the Late Antique periods. The assemblage is heterogeneous, and each chromatic group is composed of tesserae produced with different base glasses and colouring/opacifying techniques, suggesting diverse supplies. A small group of tesserae shows strict links to the Roman tradition in terms of both base glass and colouring/opacifying techniques and was probably obtained by re-using tesserae from older mosaics. Conversely, a larger group of tesserae shows textural and chemical evidence of recycling and indicates the prompt use of “new” opacifying technologies (such as the use of tin compounds) or uncommon technological solutions (such as the use of quartz and bubbles as opacifiers or the addition of metallurgical slags in red tesserae), suggesting a specific production in the fourth century AD.     

A Five-Step Procedure for the Dimensioning of Viscous Dampers to Be Inserted in Building Structures

Viscous dampers have widely proved their effectiveness in mitigating the effects of the seismic action upon building structures. In view of the large impact that use of such dissipative devices is already having and would most likely have soon in earthquake engineering applications, this article presents a practical procedure for the seismic design of building structures equipped with viscous dampers, which aims at providing practical tools for an easy identification of the mechanical characteristics of the manufactured viscous dampers which allow to achieve target levels of performances. Selected numerical applications are developed with reference to simple, but yet relevant, cases.     

The First ‘Urnfields’ in the Plains of the Danube and the Po

Journal of World Prehistory - Archaeological research is currently redefining how large-scale changes occurred in prehistoric times. In addition to the long-standing theoretical dichotomy between...     

The glass of Nogara (Verona): a “window” on production technology of mid-Medieval times in Northern Italy

The site of Nogara (province of Verona, Italy) provides valuable insights into the complexities of the glass industry in mid-Medieval times, due to its timing, which ranges mainly between the 10th and 11th centuries AD, and to the great quantity of glass findings, mainly tableware. In the present paper, the combination of archaeological, chemical and textural data allows us to identify production technologies in a time-interval perceived to be a period of technological transition for glass. In particular, the frequent occurrence of recycled natron glass and only a few glass samples made with soda plant ash indicate that recycling of earlier glass was common in inland Northern Italy in the 10th–11th centuries AD. In addition, blue and reticello decorations were obtained by recycling earlier glass mosaic tesserae, as shown by much Co, Cu, Sn, Sb and Pb and the presence of crystallised calcium antimonates. A few glass samples with chemical compositions intermediate between natron and soda plant ash glass were also identified, suggesting a gradual change in glass composition from natron-based towards soda ash-based production technology, which prevailed in the 13th-14th centuries. In conclusion, the difficulty in describing mid-Medieval glass as a well-defined entity, due to the great propensity for recycling earlier glass samples which causes variability in chemical compositions, particularly those of trace elements, is clearly documented here. In any case, this paper contributes to a new type of chrono-typological scanning and to more detailed knowledge of glass production technology during mid-Medieval times in Northern Italy, little found in the literature until now.     

The Medieval lead-glazed pottery from Nogara (north-east Italy): a multi-methodological study

The present work focuses on the archaeometric characterisation of 10th–11th-century lead-glazed pottery from Nogara (Verona, north-east Italy), with the main aim of defining the production technology of both glaze and clay body, through a multi-methodological approach.