Byzantine glass has been the preserve of specialists, little understood even by the art historians who study mosaic wall decoration or mosaic icons. The reflective and translucent qualities of glass were appreciated by Byzantine authors, and it is indicative of the concerns of modern Byzantine studies that their writings have generated more comment than the actual glass itself. The essays collected in New light on old glass, edited by Chris Entwistle and Liz James, present a first attempt to introduce Byzantine glass into the mainstream of material cultural studies. This foray is not tentative: the book is large, lavishly illustrated, and includes 30 chapters devoted to aspects of Byzantine glass technology, production and use, with particular emphasis on the use of glass in wall mosaics. The papers are a record of a conference sponsored as part of a large Leverhulme research grant awarded to Liz James (University of Sussex) on the composition of Byzantine glass mosaic tesserae, and one of the longest chapters in the book presents an overview of her findings. Additional individual chapters range in content from site studies (glass mosaic tesserae from Amorium, Classe, Damascus, Daphni, Milan, Petra, Phokis [Hosios Loukas], Poreč, Ravenna, Rome, Thessaloniki, Thessaly and Torcello); to specific objects (the Lycurgus cup, the Genoa mandylion) or types of objects (gold glass, glass medallions, window glass); to techniques (silver stain); to contemporary documentation concerning glassworkers; to aesthetics (the Euphrasian basilica in Poreč and Hagia Sophia in Constantinople, the mosaic decoration of which, as suggested long ago by Robin Cormack and demonstrated fairly conclusively here – whether or not one accepts her aesthetic interpretation – in Nadine Schibille's ‘A quest for wisdom. The 6^th-century mosaics of Hagia Sophia and late antique aesthetics’, pp. 53–59, was originally composed entirely of geometric and floral decoration and crosses); to fakes; to modern recording of Byzantine mosaics (Dimitra Kotoula, ‘Recording Byzantine mosaics in 19^th-century Greece. The case of the Byzantine Research Fund (BRF) archive’, pp 260–70) and the production of new mosaic interiors (Paul Bentley, ‘Victorian or Justinianic? Painter practitioner? In situ or reverse? The mosaicing of Westminster Cathedral’, pp 338–49). The amount of material covered is extraordinary and, inevitably, the chapters vary considerably in quality (and they might have been a little more forcefully edited, to reduce inconsistencies and errors in English usage), but the wealth of detail, and information made accessible to a broad readership for the first time, is truly wonderful. It is therefore particularly unfortunate that the glossary ignores a great number of technical terms that the non-specialist will puzzle over (for example: crown glass, cullet, fluxing agents, frit, high iron manganese titanium [HIMT] glass, Levantine I, litharge, natron, opacifier, skimming products, slag); and users of the volume will regret that there is no index, particularly since discussions of, for example, the mosaics at Daphni are dispersed across several chapters, not all of which are contiguous. An introductory chapter summarising Byzantine glass production techniques would have been useful, as would a conclusion that signalled the new and significant points made across the volume. This review extracts some of this information from the various chapters in the volume, from a distinctly non-specialist standpoint.

Late Antique and Byzantine glass was apparently made in bulk in only a few locations, largely in Syria-Palestine and Egypt. (The presence of natron is an indication of a particular area of primary production.) It was then broken into large pieces of ‘raw glass’, which were sold across the Mediterranean, on which see the clear discussion in Marianne Stern, ‘Glass producers in late antique and Byzantine texts and papyri’, pp. 82–88, a wonderful discussion of the organisation of the glass industry, as reconstructed from texts and archaeology, that also manages to establish – for, I think, the first time – the presence of women in the glass production workforce. Pieces of unworked raw glass have been found at, for example, the Neonian baptistery in Ravenna (on which see Cetty Muscolino, ‘The observation and conservation of mosaics in Ravenna in the 5^th and 6^th centuries’, pp 42–52, at p. 44). At ‘secondary sites’ of production, the glass was re-melted, at which point colour was added, and the glass was used locally (this process is outlined in Elisabetta Neri, Marco Verità and Alberto Conventi, ‘Glass mosaic tesserae from the 5^th to the 6^th century baptistery of San Giovanni alle Fonti, Milan, Italy’, pp 1–10). These secondary, local sites of production are elusive, but according to Cesare Fiori (‘Mosaic tesserae from the basilica of San Severo and glass production in Classe, Ravenna, Italy’, pp 33–41), a secondary source for glass production may have been excavated in Classe, though there is no evidence that mosaic tesserae were produced here; Fiori also, at pp 36–37, provides a quick overview of HIMT and Levantine I glass sources; and, at p. 40, notes that the tesserae at Classe correspond to those in other Ravennate churches, suggesting a single source of supply. Old glass was re-used, at which point glass from different places of origin was melted together; chemical analysis cannot always, therefore, determine the ultimate source of the glass, which makes tracking trading patterns difficult (for a discussion of this issue, see Fatma Marii, ‘Glass tesserae from the Petra church’, pp 11–24 and Rossella Arletti, ‘A study of glass tesserae from mosaics in the monasteries of Daphni and Hosios Loukas’, pp. 70–75). Some colours – notably red and black – were particularly difficult to produce, and glass in these colours may have been imported separately (Marii, p. 20). Gold and silver glass tesserae require special techniques, and different base colours were used effectively to create different effects, as discussed by several authors, including all those just cited, plus Claudia Tedeschi, ‘Mosaics and materials. Mosaics from the 5^th and 6^th centuries in Ravenna and Poreč’, pp. 60–69; Polytimi Loukopoulou and Antonia Moropoulou, ‘Notes on the morphology of the gold glass tesserae from Daphni monastery’, pp. 76–81; and Hannah Witte, ‘Studies in Middle Byzantine glass mosaics from Amorium’, pp 25–32. Witte also provides a serious revision, based on new testing of the mosaic and fresco fragments, of earlier reports on the Lower City Church excavated at Amorium, which dates roughly to the tenth century.

There is a great deal of technical discussion, much of it focussing on the analysis of the chemical composition of glass; these discussions are always accompanied by tables setting details out clearly and concisely. Of more immediate interest to non-specialists, however, are discussions of how and where glass tesserae were cut for mosaic production (on which see Muscolino, esp. p. 43, who suggests that some, at least, were actually cut to fit by mosaicists on the scaffolding) and of changes in fluxing agents. Though we are not told what, exactly, fluxing agents actually do, Arletti notes that they gradually changed from natron to halophytic plant ash across the ninth to eleventh century, which is of particular interest to her because the mosaic tesserae at Daphni were created by mixing new plant ash glass with recycled natron glass while those at Hosios Loukas apparently were imported from a different production site, and show much less re-use of natron glass (pp. 73–74). This observation differentiates Hosios Loukas and Daphni from the Ravennate churches, with their single supply source (Fiori, as above), and will need to be reconciled with arguments that the same mosaic team moved from Hosios Loukas to Daphni, and then perhaps to Torcello, outlined by Robin Cormack in ‘Viewing the mosaics of the monasteries of Hosios Loukas, Daphni and the Church of Santa Maria Assunta, Torcello’, pp. 242–53. If Arletti and Cormack are both correct, we need to ask why the team changed glass supplier (or, alternatively, whether the glass supplier's stock changed, and, if so, what the significance of this change is) or, as yet another option, whether the Daphni team had access to earlier natron glass, presumably from a fairly large cache of older glass (from an earlier church?), with which it augmented its new supply of plant ash glass, either out of necessity (because the supply ran dry) or by choice (to conserve resources or because natron glass was considered to be higher quality than plant ash glass?). Bringing together the archaeology and the art historical raises new and important questions, and that is one of the great contributions of this volume.

In this vein, several authors note the hierarchy of materials, with glass tesserae increasingly replaced by stone as one moves away from the apse (in Rome: Claudia Bolgia, ‘New light on the 'bright ages'’. Experiments with mosaics and light in medieval Rome’, pp. 217–28 at p. 217) or further toward the ground (at San Vitale, Ravenna: Muscolino, p. 47; Tedeschi, p. 61) and/or as shortages occurred during the course of the decorative campaign (at Poreč: Ann Terry, ‘'To beautify small things'’, pp. 199–206, p. 201). Finally, and perhaps most importantly, two authors demonstrate that the technical details of mosaic making were often manipulated to create meaning. Terry (as above) notes that amber glass and gold tesserae were both used in ways that intentionally emphasised the luminosity of the mosaics at Poreč; while Bolgia (as above) argues that even very small shifts in the setting of the cubes in the Cosmati work on the confessio at Sta Maria in Aracoeli, Rome (1250s) were precisely calibrated to convey particular meanings.

One chapter is devoted to forgeries. Irina Andreescu-Treadgold's ‘The Christ head at the Metropolitan Museum of Art, the apse in the Bode Museum, Berlin, and other fake mosaics’ (pp. 271–90) argues that both are fakes, and expands her earlier points on this subject. Andreescu-Treadgold is one of our foremost experts on Byzantine mosaics, and she is almost certainly correct in her assessment here, but the methodology is problematic. She refuses to explain all of the details that prove the mosaics to be modern forgeries – although she explores some of them, clearly and precisely – because this would teach potential forgers lessons (see p. 277). This may be true, but it forces the reader to rely on some unsupported assertions. Andreescu-Treadgold would be the first to decry this practice in other contexts, so, however justified her reticence may be, it is unfortunate to see it here.

Beyond the realm of mosaics, there are a number of chapters that focus on other uses of glass. Two focus on cage cups, or diatreta, with a special emphasis on the Lycurgus cup in the British Museum. This is made of dichroic glass, which changes colour in different types of light, as explained in a much later chapter (p. 329). Here, Rosemarie Lierke's ‘On the manufacture of diatreta and cage cups from the Pharos Beaker to the Lycurgus Cup’ (pp. 89–102) provides an exceptionally clear and convincing explanation of the process that overturns a number of earlier suggestions; Jaś Elsner (‘The Lycurgus Cup’, pp. 103–11) supplies literary references that hint at the significance of the technique in the Late Antique world. They disagree about the original use of the cup, Lierke opting for its use as a light and Elsner arguing that it was a drinking cup; and Elsner also suggests that glass here imitates gems (p. 110), a theory taken further in the discussions of glass pendants: Chris Entwistle's ‘Late antique glass pendants in the British Museum’, pp. 131–77 (with iconographic entries in the catalogue by Paul Corby Finney) and Stefan Röhrs, Andrew Meek and Chris Entwistle, ‘A scientific study of late antique glass pendants in the British Museum’, pp. 178–88. Together, these two chapters provide an extremely useful catalogue of the 90 pendants in the British Museum (many of which have never been published before) along with a scientific study of the glass. The pendants seem to have filled a gap in the market for amulets as ‘magic gems’ declined, between roughly 350 and 550 (after which they, in turn, were replaced by metal amulets), while retaining the same core iconography as that found on gems. Most were apotropaic. The most unusual feature of the glass pendants is their colour, which is normally a rather unusual amber. According to Entwistle, amber has no known prophylactic value as a colour (pp. 135–36) and he wonders why it was used so extensively and unusually for the pendants. As is clear from a display of a selection of these pendants as part of the British Museum exhibition ‘Egypt, faith after the pharaohs’ (29.10.15-07.02.16), however, in bright light the amber glitters like gold, which was, surely, part of the colour's attraction.

Gold glass is considered in two chapters. The first, by Daniel Howells (‘Making late antique gold glass’, pp. 112–20), provides a clear and concise overview of the making and use of gold glass that supersedes all previous discussions of the medium, and concludes that gold glass fulfilled the role of silver plate for ‘the middle classes’. Howells wrote his doctoral thesis on gold glass as part of James’ Leverhulme project; his death shortly before this book appeared has deprived the scholarly world of a sharp and focussed intelligence. Howells’ chapter is followed by Andrew Meek's ‘Gold glass in late antiquity: scientific analysis of the British Museum collection’, pp. 121–30, which is a fine pendant to it, and makes the additional point that gold glass shifts from a small scale production base of high quality objects to a large scale production base of lower quality objects, thus suggesting a shift in the patronage base.

Window glass is noted in passing by Anastassios Antonaras (‘The production and uses of glass in Byzantine Thessaloniki’, pp. 189–98) but treated in detail in Claire Nesbitt's ‘Experiencing the light. Byzantine church window glass and the aesthetics of worship’, pp. 207–16, which presents a helpful overview of what we know about Byzantine windows augmented by her own new research on glass and the aesthetics of light. Francesca Dell'Acqua (‘Borders of experimentalism. Glass in the frame of the Genoa mandylion’, pp. 234–41) provides an excellent study of the unique use of glass in the ten enamels of the frame, which picture the history of the mandylion prior to its arrival in Constantiniple in 944. Dell'Acqua also argues that the frame was made in Thessaloniki, and probably dates to the 1330s or 1340s (pp. 239–40). Finally, Lisa Pilosi and David Whitehouse consider ‘Early Islamic and Byzantine silver stain’ (pp. 329–37). Silver stain has long been identified in fourteenth-century French and English glassware, and in Arab glassware from the eighth century onward, but the connection between these two has been unclear. This important chapter tracks the origin and diffusion of silver stain and, for the first time, collects a sequence of examples in Byzantine glassware, including the very well known ‘mythological bowl’ in Venice, that may provide the missing link – although, as the authors note, the precise relationship between Byzantine and Arabic silver stain remains unclear. This is nonetheless a potentially very significant contribution both to studies of international cultural exchange in the medieval period and, more prosaically, to our understanding of Middle Byzantine decorated glass.

The only other chapter to deal with glass in the Islamic world is Judith McKenzie's ‘Alexandria on the Barada. The mosaics of the Great Mosque of Damascus’ (pp. 291–309). She sees the famous mosaics of the Dome of the Rock in Jerusalem (690s) and the Great Mosque in Damascus (ca 715) as related through ‘details of workmanship’ (p. 291), and perhaps linked to mosaic wall decoration in Egypt, for which she cites three extant examples (unfortunately naming only two of them, and referencing only one of these). Her overview of the Dome of the Rock is a bit odd: McKenzie rather bizarrely perpetuates the myth that the building was constructed on the site of Mohammad's night journey, a story that appeared far later than the building, and seems to believe that scholars have ‘often assumed’ a western origin for the architecture, an argument that no credible scholar would now make. But her more important points concern the Damascus mosaics. She argues that those at the east end of the north arcade are later (she opts for 1089–1090) and, most controversially, reiterates her earlier arguments that the influence of all of the architectural mosaics was Alexandrian, and Nilotic (although, of course, Alexandria is not on the Nile). I am not convinced by this, but the chapter is otherwise extremely stimulating, and will no doubt spur further debate.

Last but not least is the chapter by Liz James, Emöke Soproni and Bente Bjørnholt, ‘Mosaics by numbers. Some preliminary evidence from the Leverhulme database’, pp. 310–28, which presents the preliminary results to be gleaned from the Leverhulme database. The key points here are that mosaics were not, perhaps, quite the élite medium scholars have long assumed, and there are considerably more of them preserved (292, when the volume went to press) than usually recognised, particularly in Italy. The diffusion and spread of mosaic wall decoration, as represented by extant examples, is visualised in a wonderful set of maps, one for each century between the fourth and the fifteenth. Clearly, we will need to rethink the old paradigms about mosaic decoration, both beliefs about is exclusivity and about its predominantly Byzantine focus. James has already begun to present further thoughts on this at conferences, and a major book in currently in press. New light on old glass is only the beginning.

A quick note on the graphics. Like the maps in James’ chapter, those in Entwistle's article are excellent, and the tables throughout the book are wonderful. Of particular note are the tables illustrating the different colour tesserae found at Petra (Marii, table 2), the colours and materials and weight of the cubes at Amorium (Witte, tables 1–3), the character, context and date of glass fragments from Hagios Polyeuktos (Nesbitt, figs 1–4), and that showing new mosaics by century and region (James, fig. 13). Lierke's diagrams are also extremely helpful. The plates are almost universally excellent (though sometimes a bit small), making the one exception – the clearly distorted image of the Virgin at Porta Panagia in Thessaly (p. 231 pl. 8, which is also mislabelled as Christ) – stand out in contrast. This illustrates a chapter devoted to a glass-less mosaic, Maria Vassilaki's aptly titled ‘The absence of glass. Talking about the mosaics at Porta Panagia in Thessaly, Greece’, pp. 229–33, which I have not considered here. Nor have I considered Nano Chatzidakis, ‘The abbot Philotheos, founder of the katholikon of Hosios Loukas. Old and new observations’ (pp. 254–59) because it is, as the author says, a summary of a longer article that appeared in Cahiers archéologiques 54 (2011/2) and says little about glass.

Many issues, of course, still remain to be resolved. For example, there is a persistent query, beginning already in the first chapter and running through the volume, about the role and nature of glass produced in northern Europe; and it will be clear from the foregoing that questions of glass supply remain open. The ordering of the chapters – which, among other oddities, separates the various contributions on Poreč and on Daphni – remains, to me anyway, enigmatic. But New light on old glass is, to mix metaphors, a goldmine of information and its editors and authors are to be congratulated for raising as many questions as they answer and for presenting hitherto obscure material in an accessible and stimulating format.