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The materials uncovered in excavations in several provinces of the Roman empire provide important evidence to the frequent use of glass in most precious opera sectilia. Glass pieces imitating a dozen of ancient marbles and exotic stones have been identified in the collection belonged to Evangelista Gorga, samples of which were selected for analysis in order to obtain valuable information on the Roman glassmaking technology of the 2nd century AD, especially on coloration techniques. The monochrome and polychrome glass tesserae replicating precious marbles and rare stones were: porfido verde antico, litomarga verde, turquoise, pavonazzetto, gabbro eufotide, diaspro nero e giallo, semesanto, alabastro tartarugato, rosso antico, cipollino rosso, giallo antico, and onyx. XRF quantitative chemical composition was determined allowing the types of glass used and the colouring techniques to be identified. Results have been compared with similar data obtained by studies on coloured Roman glass and mosaic tesserae. Similarities and discrepancies are discussed and hypotheses are suggested on the technology of this extraordinary Roman production.

The Villa del Casale at Piazza Armerina (Sicily) is world famous for its beautiful and extensive mosaic floors dating to the fourth-century A.D. Before a recent restoration of the Villa, it was possible to take a representative sampling of coloured glass and stone tesserae from the baths’ floors that were examined by chemical and minero-petrographic analysis, respectively, with the goal of determining the production-centre/s of the glass, and the provenance of the stones. The laboratory techniques used were SEM-EDS on polished sections, powder XRD and polarised OM on thin sections, extended to reference stones found in a Villa’s ancient storehouse. The obtained results had shown that the white and pinkish tesserae were exclusively made of local (from the Caltanissetta province) limestones, while the black ones were cut from an obsidian, likely of a Liparote origin; the turquoise and gold-leaf tesserae were exclusively made of glass manufactured according to the Roman and Byzantine tradition while both stone and glass were used for the dark and yellow hues (giallo antico was identified among stone yellow hues). As for the glass tesserae, the results of the chemical analysis of a few samples (mostly erratic) have allowed to date them to the fifth- to sixth-century and to the eighth- to ninth-century A.D. and thus to testify to a hitherto unknown ancient restoration of the Villa mosaics.

The so-called Venetian enamelled coppers are a group of objects produced in Italy during the 15th century. Up to now, about 300 objects have been recognized in private collections and in European and US museums. At the end of 19th century, a Venetian origin was suggested, but their provenance is still debated. In this study, the enamel compositions from 22 enamelled copper products from Italian and French collections have been analysed by invasive and non-invasive techniques. A comparison of the results with Tuscan and Venetian glass databases reinforces the suggestion of a Tuscan (most probably Florentine) origin for these works of art.

This study focuses on the Byzantine glass tesserae from Hierapolis (Phrygia, central Turkey). Fifty-seven samples of loose tesserae from two sites in the town (the theatre and the church of St. Philip) are analysed by particule-induced X-ray emission and particule-induced gamma ray emission and electron probe X-ray microanalysis to obtain the chemical composition and identify the colourants and opacifiers. The aims are to add new information to the scant knowledge of the Byzantine glassmaking technology, to constrain the chronology of the mosaics and to trace the supply routes of the tesserae. In the destruction layers of the theatre, tesserae produced following the Roman glassmaking technology (natron glass opacified by calcium and lead antimonate) were found. They were made using a Levantine 1 raw glass, generally attributed to the early Byzantine period (fifth to sixth c.). In the church, the samples attest a technological change from Roman tradition, and a complex pattern according to building history (two phases are attested, probably in the sixth and eighth to ninth c.), and a multiplicity of supply. Three glass types and some recipes not attested before in this chronological range for the production of tesserae are documented, such as the use of a local low-chlorine natron glass for the production of black and red tesserae, the blue colouring by a source of cobalt with zinc in a natron glass tessera and the opacification with tin oxide (both in a lead-free and in a high-lead natron glass), as well as with quartz.

The Basilica di Santa Croce (Basilica of the Holy Cross) is the major Franciscan church in Florence (Italy). Among the prominent masterpieces preserved in this church, there are 22 medieval stained glass windows. Between 2000 and 2013, the Opera di Santa Croce started a restoration campaign of six of the most important ones, dated 14th c. In this paper, the archaeometric data collected during the restoration campaign are reported. Two major base glass compositions (potash-lime-silica and soda-lime-silica) were identified by quantitative chemical analysis. Results are compared with similar investigations on Italian stained glass windows of the 14th-15th centuries and many similarities are highlighted. Some interesting "secrets" of the coloring techniques based also on multilayer glass pieces were revealed. Finally, SEM-EDS analyses allowed the main weathering glass phenomena to be investigated.

The results of an archaeometric trial study performed on an important finding of Renaissance maiolica (mid-15th to early 16th century) from the Ducal Palace of Urbino are presented. Mineralogical–petrographic data (XRD, OP, SEM–EDS) and chemical characterization (ICP/AES–MS: major and trace elements) of both ceramic bodies and glazes were compared with similar data provided on coeval maiolica found in archaeological excavations in Pesaro, now stored in the city's Municipal Museum, in order to verify an origin of the potteries from common (Pesaro) or different (Pesaro and Urbino) production centres. The results indicate that ceramic bodies were produced with quite similar illitic–calcareous clays, most probably taken from the same local Pliocene Formation. Similarities were also found concerning the glaze's glass (silica–lead), colourants (cobalt, copper and manganese) and pigments (lead antimonate and cassiterite).

Fifty-eight gold leaf tesserae from eight archaeological sites situated in the Byzantine Empire and two Early Islamic (one in medieval Palestine), covering the period that goes from the 4th c. to the 12th c., were analysed by EPMA, SEM-EDS and PIXE-PIGE to determine the composition of both the glass and the gold leaves. The good match until the 6th c. between circulating monetary alloys and the gold leaf compositions together with the type of glass used, provided criteria that can be used to date the tesserae fabrication. The data obtained allow newly produced tesserae to be distinguished from re-used ones. Because after the 7th c. the circulation of gold in the Byzantine Empire was less controlled, the same relationship is harder to establish. The results suggest the existence of workshops in the Eastern and Western part of the Mediterranean and a more advanced technology to manufacture a palette of glass colours for gold leaf tesserae in the Eastern region.

The enamels of the Altar of San Giovanni, from the Baptistery of Florence, were investigated using both non-invasive and micro-invasive analysis in order to elucidate the glass melting and colouring techniques. A few fragments detached from the altar and recovered by the restorers were analysed in cross-section by electron probe microanalysis. Moreover, non-invasive investigations by portable XRF allowed a large number of enamelled plaques to be investigated. The results showed a good agreement between the two techniques and made it possible to identify similarities or differences in the enamels of the three manufacturing periods of the altar.

Venetian enamelled glass is one of the most significant subjects of the art and technology of Renaissance glassmaking. These items were made in Venice from the second half of the 15th through the 17th centuries and were imitated in other European glassmaking centers during this period and again in Murano during the 19th century. Only a limited number of analyses of these masterpieces have been published up to now. In this paper the non-invasive PIXE–PIGE technique was applied to analyse the glass and enamels of eleven objects from the Louvre collection. The results disclose interesting details on the glassmaking technology and the raw materials and colourants used. The comparison between these data and the recipes in Venetian glassmaking treatises allowed identifying a group of objects corresponding to the genuine Venetian Renaissance production, while some discrepancies were found for other objects, probably being ascribable to a contemporary production outside Venice (facon de Venise) or to a 19th century Muranese manufacture.

The glass jewellery collection of Archduke Ferdinand II, today part of the Collection of Sculpture and Decorative Arts, Kunsthistorisches Museum, Vienna, Austria, is a rare example of early modern lampwork. The small glass items, made by shaping fine glass rods and tubes in front of the flame of an oil lamp, date from before 1596. Although lampworked glass objects must have been popular collectibles, only a few pieces have survived. Therefore, the examination of this collection is a unique opportunity for the study of sixteenth-century lampworking technology. The rarity of the glass objects limited the examination to non-destructive methods. Optical microscopy provided an overview of the glass colours and surfaces. Subsequently, non-invasive portable energy dispersive X-ray fluorescence analysis (XRF) was carried out to classify the glass types. Further invasive investigations were carried out with micro-invasive electron probe microanalysis (EPMA) and energy dispersive X-ray microanalysis in a scanning e...

The study concerns the chromatic alteration of mosaic glass tesserae in the Sao Joao Chapel, Sao Roque Church in Lisbon. This precious chapel was commissioned by the King of Portugal, Joao V, in 1742. The polychrome marbles, stucco bas-reliefs, precious silver sculptures and three mosaic altarpieces were sent by ship to Lisbon. Alessio Mattioli, the glassmaker who produced the glass tesserae for the mosaics, was the famous inventor of new compositions for difficult colours in opaque glass such as red, orange, and the variety of flesh colours. In fact Mattioli succeeded in imitating the technique of painting to produce altarpieces that were “eternal”, or, at least, more durable in appearance than paintings. Our research is based on archive documents discovered in St. Peter's Fabrica in Rome concerning the decoration of the Sao Joao Chapel in the Sao Roque Church in Lisbon and the compositions of Mattioli's glass. The chromatic alterations producing conspicuous spots and shades of grey, brown, and white are similar to the alterations in many mosaic altarpieces in the Basilica di San Pietro in Rome, dating from the same period. The findings of the chemical analyses on glass and weathering products, are the first attempts to understand the weathering mechanism and to prepare a restoration and conservation plan.

The durability of glass depends both on its chemical composition and on the environment in which it is conserved. The glassy particles of smalt in samples from two sixteenth-century wall paintings in Rome were investigated to study the technology of glass melting and colouration, and the origin of the pigment discolouration. A potash–lime silica and an unusual soda–potash–lime silica were identified through analysis. These compositions were compared with recipes recorded in Italian medieval and Renaissance treatises that help understand the technology used in the preparation of smalt. The mechanisms of weathering are discussed in terms of glass durability in relation to its chemical composition and to aggressive environmental conditions. In the case of the two wall paintings studied here, smalt discolouration was found to be due to several factors: leaching of alkali, leaching of cobalt, formation of micro-cracks and glass corrosion.

Although Venice is regarded as being one of the most important centres of glass manufacture and trade in Western Europe, little is known about the origins of the Venetian glassmaking. Some archaeologists suggest there is a continuity in the history of glass making, in its transplantation from the Roman centres of the mainland (Altino and Aquileia), first to some islands of the lagoon, and later to the town. Some others, instead, think that there was no continuity at all and that the art of glassmaking was imported in Venice from the Islamic glass factories of the Middle East. Of great help in answering this and other technological questions is the information about the composition of ancient glass from well-dated excavations that allows to conclude on the early technology, sources of raw materials and long-distance trade. Some significant glass findings, including fragments of pots used for glass melting, were found on the island of Torcello and, more recently, in two emergency excavations in the historic centre of Venice. In this paper, the chemical composition of a large set of glass findings (and related materials) from the Venetian lagoon dating from the 7th to the 13th centuries is determined by X-ray microanalysis in order to throw new light on the glassmaking technology in the early centuries of the Venetian tradition. The results show that in this period there occurred a gradual transition from the Roman technique (a two-ingredient formulation with silica-lime sand and natron as a fluxer), towards the use of silica sand and soda plant ash. There is evidence, therefore, for a production continuity with the Roman period (melting pots and glass scraps with a natron-based composition), yet restricted to transparent blown items. No evidence was found for a local production of glass tesserae for the mosaics of the church of St. Maria Assunta in Torcello.

The original version of this article, unfortunately, contained error. Modifications have been made to the Introduction, Results and discussion, Conclusions and figure caption. The original article has been corrected.

Glass tesserae have been produced for use in mosaic decoration for more than 2000 years and constitute an important part of cultural heritage. They were applied to the architecture of pagan and religious monuments initially in the Mediterranean area, and later spread throughout the world. The paper examines the properties of vitreous mosaic tesserae, with particular reference to the techniques of glass melting, the colouring and opacification of glass pastes and smalti and the preparation of metal-leaf tesserae. Brief general information on the nature of glass, including its optical and mechanical properties and chemical durability are discussed and the manufacturing techniques and their development are described on the basis of historical sources and scientific analysis of finds. Particular reference is made to the different mixtures of raw materials used to make, opacify and colour glass in different centres of production in past centuries. The weathering mechanism of the tesserae is discussed, ...