Colour and chemical composition in ancient glass: An examination of some roman and wealden glass by means of ultraviolet-visible-infra-red spectrometry and electron microprobe analysis

Glass sherds from the Roman town at Colchester and from the post-mediaeval glasshouse site at Knightons near Dunsfold in Surrey have been investigated by ultraviolet-visible-infra-red spectrometry and by electron microprobe analysis. The glass is coloured by visible absorption bands of iron, cobalt and manganese, whose origins are discussed.     

Chemical composition characterization of ancient glass finds from <Emphasis Type="Italic">Troesmis</Emphasis>—Turcoaia,Romania

This paper reports and discusses the chemical composition of 20 glass fragments discovered during the 2012 archeological survey at Troesmis (Turcoaia, Tulcea county, Romania) and dated to the Roman and the Byzantine/Early Medieval periods. The data were obtained by two external Ion beam analysis (IBA) methods—namely Particle-induced X-ray emission (PIXE) and Particle-induced gamma-ray emission (PIGE)—and they were compared to the recognized compositional glass groups from the Mediterranean region during the first millennium AD. The Troesmis assemblage turned out to contain samples belonging to several distinct categories of ancient glass, obtained from different raw materials and manufacturing procedures. Some of the analyzed vitreous finds from Troesmis were the result of glass recycling, while others were identified as deriving from Roman glass vessels imported from the Levantine or Egyptian shores of the Mediterranean. This archeometric study brings additional arguments for the long-range commercial exchanges during the Roman period.     

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.     

WASTE GLASS,VESSELS AND WINDOW‐PANES FROM THAMUSIDA (MOROCCO): GROUPING NATRON‐BASED BLUE–GREEN AND COLOURLESS ROMAN GLASSES

A collection of window‐panes, vessels and alleged waste from Thamusida has been investigated by OM, SEM–EDS, ICP–MS, ICP–OES and XAS at the Fe–K and Mn–K edges. Glass samples have been characterized as natron‐based soda–lime–silica glasses, with low magnesium and low potassium. The results have been compared with 43 reference groups available for ‘naturally coloured’ and colourless glasses of both Roman and later ages. Two main types were distinguished: RBGY 1 (R oman B lue–G reen and Y ellow 1) and RBGY 2 (R oman B lue–G reen and Y ellow 2). Given their compositional similarity to the Levantine I or, to a lesser extent, HIMT glasses, the Syrian–Palestinian coast for RBGY 2 and Egypt for the RBGY 1 have been suggested for their provenance. Most Thamusida samples have been assigned to the RBGY 2 type. A small group of Thamusida colourless vessels was included into the RC (R oman‐C olourless) compositional field; the latter still being defined. The alleged waste pieces may define a local production that should have been of secondary type. The investigations performed on local raw materials seem to discount the possibility of a primary glass‐making site. XAS measurements determined that Fe²⁺ contents ranging between 30 and 52% are able to assure an aqua blue colour; below 30%, the glasses turn light green or light yellow.     

Supply routes and the consumption of glass in first millennium CE Butrint (Albania)

Archaeological, historical and analytical evidence can identify trade patterns and the movement of people and products and thus reveal the cultural and economic connections that existed at a given time. In the case of first millennium CE glass, the manufacture of raw glass in a limited number of glass making installations with unique compositional characteristics makes it possible to trace the likely origin of the raw materials at consumption sites. In this way the analytical characterisation of a large corpus of glass finds can identify changes in the supply routes of high-end industrial products from the Roman to the middle Byzantine period.     

Pliny the Elder and Sr–Nd isotopes: tracing the provenance of raw materials for Roman glass production

In Roman and Byzantine times, natron glass was traded throughout the known world in the form of chunks. Production centers of such raw glass, active from the 4th to 8th century AD, were identified in Egypt and Syro-Palestine. However, early Roman primary glass units remain unknown from excavation or scientific analysis. The ancient author Pliny described in 70 AD that besides Egyptian and Levantine resources, also raw materials from Italy and the Gallic and Spanish provinces were used in glass making. In this study, the primary provenance of 1st–3rd century AD natron vessel glass is investigated. The use of combined Sr and Nd isotopic analysis allows the distinguishing and characterizing of different sand raw materials used for primary glass production. The isotope data obtained from the glass samples are compared to the signatures of primary glass from known production centers in the eastern Mediterranean and a number of sand samples from the regions described by Pliny the Elder as possible sources of primary glass. Eastern Mediterranean primary glass has a Nile dominated Mediterranean Nd signature (higher than −6.0 ? Nd), while glass with a primary production location in the western Mediterranean or north-western Europe should have a different Nd signature (lower than −7.0 ? Nd). Most Roman glass has a homogeneous ⁸⁷Sr/⁸⁶Sr signature close to the modern sea water composition, likely caused by the (intentional) use of shell as glass raw material. In this way, strontium and neodymium isotopes now prove that Pliny's writings were correct: primary glass production was not exclusive to the Levant or Egypt in early Roman days, and factories of raw glass in the Western Roman Empire will have been at play.     

STONES FROM MEDIEVAL GLASSMAKING: A SUITABLE WASTE PRODUCT FOR RECONSTRUCTING AN EARLY STAGE OF THE MELTING PROCESS IN THE MT LECCO GLASS FACTORY*

The Mt Lecco glass factory was one of the most important production centres in Liguria (Italy) during the 14th and 15th centuries. Archaeological evidence indicates that the whole production cycle took place here. During the glassworking process, production defects such as ‘stones’ were identified and discarded. Stones are partially melted, glass‐coated relics of raw materials or fragments of crucible. The study of the microtexture of stones together with microprobe analyses of phases provides a key for understanding the glassmaking procedure carried out in the Mt Lecco glass factory. The melting rate can be inferred from the compositional variability of glass, which suggests fractional melting of the batch. Glass composition indicates that the Mt Lecco production was a mixed‐alkali one, probably made of quartz‐bearing material as vitrifying agents, plant ashes as fluxing agents and dolomitic limestones as stabilizing agents.     

The Production and Circulation of Carthaginian Glass Under the Rule of the Romans and the Vandals (Fourth to Sixth Century ad): A Chemical Investigation

Fifty‐seven glass samples from Carthage dating to the fourth to sixth century ad were analysed using the electron microprobe. The results show that these samples are all soda–lime–silica glass. Their MgO and K₂O values, which are below 1.5%, suggest that they were made from natron, a flux that was widely used during the Roman period. The major and minor elements show that these samples can be divided into four groups, three of which correspond to the late Roman period glass groups that were found throughout the Roman Empire: Levantine I, and ‘weak’ and ‘strong’ HIMT. Of particular interest is our Group 2, which is technologically and compositionally similar to HIMT glass and the CaO and Al₂O₃ values of which are similar to those of Levantine I. Glass of similar composition has been reported by several authors and is predominantly found dating from the late fifth to seventh century. This could represent a ‘new’ glass group; therefore further study is needed to determine its origin. Also, this study suggests that the Vandal invasion in North Africa did not disrupt the glass trade between Carthage and the Levantine coast.     

DEEPLY COLOURED AND BLACK GLASS IN THE NORTHERN PROVINCES OF THE ROMAN EMPIRE: DIFFERENCES AND SIMILARITIES IN CHEMICAL COMPOSITION BEFORE AND AFTER ad 150*

In this work we attempt to elucidate the chronological and geographical origin of deeply coloured and black glass dating between 100 bc and ad 300 on the basis of their major and trace element compositions. Samples from the western and eastern parts of the Roman Empire were analysed. Analytical data were obtained by means of a scanning electron microscope – energy‐dispersive system (SEM–EDS, 63 samples analysed) and laser ablation – inductively coupled plasma – mass spectrometry (LA–ICP–MS, 41 samples analysed). Among the glass fragments analysed, dark brown, dark purple and dark green hues could be distinguished. Only among the dark green fragments could a clear compositional distinction be observed between fragments dated to the periods before and after ad 150. In the early samples (first century bc to first century ad ), iron, responsible for the green hue, was introduced by using impure sand containing relatively high amounts of Ti. In contrast, a Ti‐poor source of iron was employed, containing Sb, Co and Pb in trace quantities, in order to obtain the dark green colour in the later glass samples. The analytical results obtained by combining SEM–EDS and LA–ICP–MS are therefore consistent with a differentiation of glassmaking recipes, detectable in glass composition, occurring in the period around ad 150.     

The composition of late Romano-British colourless vessel glass: glass production and consumption

One hundred and twenty-eight colourless glass tablewares from settlement contexts throughout the British Isles, dating from the mid-3rd to 4th century AD, were analysed by ICP-AES spectrometry. Three distinct compositional groups were identified based upon the use of different decolourisers and primary raw materials, with possible sub-groups within these. These compositions have distinct, but overlapping chronological ranges, suggesting colourless glass production in at least three, possibly more, centres in the late Roman period. The compositional analysis highlights the high degree to which recycling of glass was taking place during this late period. The chronological distribution of some of these compositions is more restricted within the British assemblages than is observed in other published assemblages from Western Europe. This distinction may indicate different supply patterns of glass to the Western provinces.     

MEDIEVAL GLASS FROM ROCCA DI ASOLO (NORTHERN ITALY): AN ARCHAEOMETRIC STUDY

An archaeometric study was performed on 33 medieval glass samples from Rocca di Asolo (northern Italy), in order to study the raw materials employed in their production, identify analogies with medieval glass from the Mediterranean area and possible relationships between chemical composition and type and/or production technique, contextualize the various phases of the site and extend data on Italian medieval glass. The samples are soda–lime–silica in composition, with natron as flux for early medieval glasses and soda ash for the high and late medieval ones. Compositional groups were identified, consistent with the major compositional groups identified in the western Mediterranean during the first millennium AD . In particular, Asolo natron glass is consistent with the HIMT group and recycled Roman glass; soda ash glass was produced with the same type of flux (Levantine ash) but a different silica source (siliceous pebbles, and more or less pure sand). Cobalt was the colouring agent used to obtain blue glass; analytical data indicate that at least two different sources of Co were exploited during the late medieval period. Some data, analytical and historical, suggest a Venetian provenance for the high/late medieval glass and a relationship between type of object (beaker or bottle) and chemical composition.     

Reviews

Book reviewed in this article:
Review article: The Spanish shipwrecks of 1554: The Nautical Archaeology of Padre Island (Studies in Archaeology). J. BARTO ARNOLD III and ROBERT S. WEDDLE
Ships and Sea Power Before the Great Persian War, The Ancestry of The Ancient Trireme. H. T. WALLINGA
The Trireme Project. Operational Experience 1987–90, Lessons Learnt. TIMOTHY SHAW (Ed.)
Die Kogge von Bremen, Band I, bauteile und baublauf. WERNER LAHN
A Cog-like Vessel from the Netherlands. ALEYOIS VAN DE MOORTEL
Ancient Shipwrecks of the Mediterranean and the Roman Provinces (BAR International Series 580). A. J. PARKER
Visione del Drachio. BALDISSERA QUINTO DRACHIO. PIETER VAN DER MERWE
Bronze Age, Greek & Roman Technology—Selected Annotated Bibliography. JOHN PETER OLESON
Practices of Archaeological Stratigraphy. EDWARD C. HARRIS, MARLEY R. BROWN III and GREGORY J. BROWN (Eds)
Det nordiska skeppet. Teknik och samhällstrategi i vikingatid och medeltid. bjÖrnvarenius
The Shipbuilder's Repository, 1788. DAVID H. ROBERTS (Ed.)
Predicaments, Pragmatics, and Professionalism: Ethical Conduct in Archaeology (Special Publication No. 1). J. NED WOODALL (Ed.)     

Sanitas per Aquas. Spas,Lifestyles and Foodways

Excavations in Bokerly and Wansdyke, Dorset And Wilts, 1888-91. By Lieutenant-General Pitt - Rivers, D.C.L., F.R.S., F.S.A., Inspector of Ancient Monuments in Great Britain, etc. With Observations on the Human Remains, by J. G. Garson, M.D. Vol. III. Printed privately. 1892. By E. Sidney Hartland.     

MAKING COLOURLESS GLASS IN THE ROMAN PERIOD*

This paper discusses the compositional analysis of Roman colourless glass from three sites in Britain. The findings suggest that two broad compositional groups can be identified on the basis of the choice of the initial raw materials selected for glass production, in particular the sand. The largest of these groups is inherently different from the naturally coloured, blue–green glasses of the same period, while the other group is compositionally similar. Further subgroups are apparent on the basis of the decolorizers used. These glass groups are explored in the light of the current theories concerning the organization of glass production in the Roman world.     

THE COMPOSITION AND MANUFACTURE OF EARLY MEDIEVAL COLOURED WINDOW GLASS FROM SION (VALAIS,SWITZERLAND)—A ROMAN GLASS‐MAKING TRADITION OR INNOVATIVE CRAFTSMANSHIP?*

Archaeological excavations between 1984 and 2001 at the early Christian cemetery church in Sion, Sous‐le‐Scex (Rhône Valley, Switzerland), brought to light more than 400 pieces of coloured window glass dating from the fifth or sixth centuries ad . The aims of this paper are threefold: first, to characterize the shape, colour and chemical composition of the glass; secondly, to understand whether the production of the coloured window panes followed traditional Roman glazing techniques or was of a more innovative nature; and, thirdly, to provide some indications as to the overall design of these early ornamental glass windows. Forty samples of coloured glass have been analysed by wavelength‐dispersive X‐ray fluorescence. The results of the chemical and the technological studies showed that most of the glass was produced using recycled glass, particularly as a colouring agent. Some of the glass was made of essentially unmodified glass of the Levantine I type. The results taken together seem to confirm that raw glass from this region was widely traded and used between the fourth and seventh centuries ad . The artisans at Sion were apparently still making use of the highly developed techniques of Roman glass production. The colour spectrum, manufacture and design of the windows, however, suggest that they represent early examples of ornamental coloured glass windows.     

Glass from the Archaeological Museum of Adria (North-East Italy): new insights into Early Roman production technologies

In the present study, the first archaeometric data on an ample selection of intentionally coloured (or decoloured) Early Roman glass (1st–2nd centuries AD) from the Archaeological Museum of Adria (Rovigo, Italy) are reported. The analysed samples are 61 in total, both transparent and opaque, and were characterised from the textural (SEM-EDS), mineralogical (XRPD) and chemical (XRF, EPMA, LA-ICP-MS) points of view. This combined approach allowed us to identify the raw materials and production technologies employed in the manufacture of glassware. Results for the transparent samples show that they are all silica-soda-lime glasses. Most of them, independently of colour, have compositions close to those of typical Roman glass, produced with natron as flux. No relationships were identified among chemical compositions, types or production techniques, but a dependence on bulk composition was identified for some particular colours, revealing the careful and intentional selection of raw materials. This is the case of Sb-colourless glass, produced with sand of high purity, a group of intensely coloured objects, mainly emerald green and black, produced with soda ash as flux, and some blue examples produced with various sources of sand or soda ash as flux. Two main types of opacifiers were identified for the opaque samples: calcium antimonate for white, mauve and blue glasses, and lead antimonate for the yellow ones; in one case, a yellow lead-tin antimonate was also identified. As regards the opaque glasses, most of the samples opacified with calcium antimonate are silica-soda-lime in composition, similar to the typical Roman glass. Instead, samples opacified with lead and/or lead-tin antimonates are lead glasses, suggesting different production technologies.     

MULTIVARIATE ANALYSIS OF COMPOSITIONAL DATA: APPLIED COMPARISONS FAVOUR STANDARD PRINCIPAL COMPONENTS ANALYSIS OVER AITCHISON'S LOGLINEAR CONTRAST METHOD

There has been debate about whether standard principal components analysis is appropriate for the multivariate analysis of compositional data (e.g. oxide composition of glass), Loglinear transformation has been recommended by Aitchison as a prerequisite. This paper argues that previous comparisons of methodological merits have tended to circularity of argument by making assumptions about the form of a good multivariate result. To break the circularity of argument the authors have introduced randomized variables into five data sets. A good result must recognize these randomized variables as noise and place them near the centroid of the principal components scattergram of variable loadings. Standard principal components analysis is found to perform better than loglinear transformation in its ability to recognize the randomized variables. It is concluded that loglinear transformation tends to introduce spurious structure into a table of compositional data. This paper is followed by a comment by M. J. Baxter.