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Le forme del vetro: tecnologie a confronto. Produzioni vitree e invetriate in Sicilia, Italia peninsulare, Ifrīqiya e al-Andalus tra IX e XI secolo

A new perspective: the “WINDOWGLASSMED” project

Camilla Bertini
p. 379-390

Résumé

Despite an apparent contraction of long-distant trade suggested by Pirenne,1 recent analytical studies suggest that glass was still traded to Europe from Egypt and the Levant where it was originally produced during the Early Medieval period.2 The overall picture that emerges from these data though is far from clear. In addition, there is no doubt that Early Medieval glass chemical composition has been heavily influenced by recycling and mixing recycling practices over the years,3 but at the same time, “contemporary” produced compositions (such as Levantine – Apollonia type, Foy 2, or plant ash) were also circulating at the time together with this highly recycled glass.4 There is no doubt therefore that our understanding of glass production is still partial to this day and that more works needs to be done, especially that e a broader range. The idea for the WINDOGLASSMED project stems from these premises. By analysing glass samples from different part of Western Europe for LA-ICP-MS and isotopic analysis (Sr and Nd), this project will be the first detailed multidisciplinary study focused on well-dated 7th–10th century to create a detailed, chronologically-resolved map of Early Medieval glass in Western Europe, reflecting both trade patterns and practices such as recycling.

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Introduction

1In the past twenty years, many studies have contributed to expand our knowledge on 1st millennium CE glass and its production, and the contribution of archaeometry to this progress is undeniable. Despite this positive evolution, there are still some biases that need to be addressed in our research. One of the main gaps in our vision as glass researchers is that there has been no systematic and geographically widespread analytical study on composition and recycling practices focused specifically on Early medieval Western glass artefacts.

  • 5 To learn more about the project: https://cordis.europa.eu/project/id/895153.

2The WINDOWGLASSMED project will be the first to focus specifically on the chemical ‘fingerprinting’ of western European glass from several countries to reconstruct Early Medieval trade and economy in the crucial period of change spanning the 7th to 10th centuries. In this paper, I will explore the importance of my new WINDOGLASSMED project5 and why it is crucial for glass studies not only to broaden their horizon by explore multidisciplinarity, but also why it is fundamental to find new way at looking at our data.

Central production model and other current key topics in glass research

  • 6 Nenna et al. 2005; Nenna 2015.
  • 7 Gorin-Rosen 1995; 2000; Tal – Jackson-Tal – Freestone 2004; Phelps 2018.
  • 8 Gorin-Rosen 2000; Phelps 2018, p. 268.
  • 9 Freestone – Gorin-Rosen – Hughes 2000; Phelps 2018, p. 268.
  • 10 Freestone 2015; Phelps 2018, p. 268.
  • 11 Freestone – Pointing – Hughes 2002.

3The use of scientific techniques in glass studies helped advance considerably not only what we know about the material itself and its technology, but it allowed to make better hypothesis concerning the overall glass production context during the whole 1st millennium, and especially for the Late Roman – Early Medieval period: with the right scientific technique, we can now assign a chemical “fingerprint” for each sample by identifying what raw materials have used to make the glass in the first place. This chemical fingerprint not only mirrors the technological choice made by the glassmakers, but it creates a direct link with the primary production areas. The 1st millennium CE was dominated by natron-based glass, for which production sites have been recognised in Egypt6 and Israel7 together with several secondary (glass-working) workshops dated to the late Byzantine-Umayyad periods - Bet Shean,8 Apollonia,9 and Tel Aviv.10 The existence of few primary production centres for natron-based glass and the overall dominance of the same natron-based recipes suggests a centralised production model, where glass was made from raw materials in very few production centres and then distributed in forms of chunks across the Mediterranean and beyond.11

  • 12 Henderson et al. 2016, p. 142.
  • 13 Phelps 2018, p. 270.
  • 14 Phelps 2018.

4For plant ash-based glass, which began to be reintroduced ad the dominant formula from the 8th century CE onwards, contrasting models are still debated. By analysing plant ash glass from different sites dated from the 8th to the 14th century CE, Henderson suggests that production was occurring in “sub-zones associated with the large cosmopolitan urban hubs with thriving economies supporting the manufacture of a range of materials” suggesting therefore that production was localised rather than centralised.12 On the other hand, other scholars suggest instead that both centralised and localised production could have been possible for plant ash glasses. Work from Phelps and colleagues strongly suggests that “the supply of the majority of glass within Ramla followed a centralised production model in which chunk glass was traded from Tyre and shaped into vessels at Ramla”.13 Moreover, the scale of production for Tyre furnaces “is too high for local use” and implies that surplus glass was produced to be traded. At the same time thought, evidence for trade of vessels rather glass chunks in group of Mesopotamian/Iranian origin (P-3 and P-4) implies a more localised production model made possible by the fiscal unification and increased centralisation provided by the Abbasid Caliphate.14

5Concerning natron-based glass, it easily understandable why this suggested model is a simplified version of what was going on in reality: glass trade was way more complex that just a simple unidirectional exchange of raw glass from primary production centre “A” to a hypothetical secondary production centre “B”. One glass fragment does not represent necessarily one single production stage/production episode, but it could be the result of several different remelting processes of the same glass or two or more glasses together of the same or even different chemical composition. To complicate things further, the remelting could have happened in several different secondary workshops, which makes it nearly impossible to reconstruct of its melting history back to the original raw glass formula.

  • 15 These markers can be used only in weakly coloured (what is commonly called “blue-green” in the lit (...)
  • 16 The incorporation of elements from the fuel ash (e.g., potassium, magnesium, and phosphorus) or th (...)
  • 17 The loss of alkali (e.g., Na) is due to the reheating of the glass. To know more about this topic, (...)
  • 18 The presence of both Mn and Sb, typical decolourants for the 1st millennium CE, at the same time i (...)

6Glass recycling in particular has been a key topic of research for many years. Several studies showed how certain markers can be used to assess with a certain degree of confidence that a glass sample went through extensive recycling: either the glass falls between two know compositional groups (and therefore it would be the result of mixing of these two), or the glass shows some “recycling makers” in its composition that indicates an increase in specific trace elements,15 the incorporation of certain contaminants,16 the loss of alkali,17 or the occurrence of two different types of decolourants agents in colourless or weakly-coloured glasses.18

  • 19 E.g. Freestone et al. 2003; Henderson – Evans – Barkoudah 2009; Brems et al. 2013a; 2013b; Degryse (...)

7Despite not being able to reconstruct its entire “recycling” history, it is possible to retrieve other information concerning the nature of the sample itself, such as discussing its origin: 87Sr/86Sr and 143Nd/144Nd isotopic ratios proved to be successful in assessing glass provenance.19

8By determining both Sr and Nd isotopic signatures of a glass artefacts and its raw materials (sand and halophytic plants for natron and plant ash-based glasses respectively) we can link the geological origin of the lime and the sand used to make the glass in the first place. Bear in mind that each isotopic ratio provides a fingerprint will be typical not of the primary workshop is associated with, but of the raw materials used to produce the raw glass in the first place, which complicates things further.

  • 20 Barfod et al. 2020.

9It is also useful to remember how that area of sourcing of these raw materials and the one of primary production might not necessarily match, though ideally the raw materials were sourced from an area where they were easily accessible and economically advantageous to transfer them to the primary workshop. You can understand therefore why caution is always to be expected when consider glass provenance. The potential of Hf has also tested recently as provenance marker has also been recently explored in glass from the ancient city of Gerasa (Jordan).20

10I have tried to summarise in this brief introduction the different directions taken in glass studies through the last years twenty years. What really transpires is that the use of scientific techniques opened a completely new perspective on glass technology and its trade during the 1st millennium CE. But are scientific techniques the solution to all our research questions? Have we, as glass researchers, subconsciously focused our research by on the relatively biased pool of data? Should we try to explore other possibilities maybe with an eye towards other areas of research.

The “Mediterranean-centric” vision and other gaps in glass current research on Western European glass

  • 21 Brill – Wosinski 1965; Gorin-Rosen 1995; 2000; Henderson 1999; Nenna et al. 2005; Tal – Jackson-Ta (...)
  • 22 Freestone – Gorin-Rosen – Hughes 2000; Foy – Nenna 2003; Henderson – McLoughlin – McPhail 2004; Ph (...)
  • 23 Hodges – Whitehouse 1983; McCormick 2001; Wickham 2005; Hodges 2012; Pirenne 2014.
  • 24 Whitehouse 2003.

11As I have already explained, both archaeological21 and scientific22 evidence therefore support the centralised production model and glass was reaching the West in spite of the economic contraction described by historians.23 Therefore, glass was indeed “a thing that travelled” across Europe,24 but for the West, it remains unclear whether this was direct, long-distance trade, a system in which glass circulated locally between various secondary workshops, or its re-circulation due to recycling.

Figure 1. A diagram representing the relation between raw materials, workshops, and final raw glass composition, originally suggested by Freestone and colleagues years ago. From the original model, a connection between raw glasses and the workshops has been added to describe the reintroduction of glass within the production context through recycling. In addition, another section has also added to represent repetitive recycling of glass (2D glass in the figure); each different grey shade represents the overall increasing in recycling markers in that specific glass composition.

Figure 1. A diagram representing the relation between raw materials, workshops, and final raw glass composition, originally suggested by Freestone and colleagues years ago. From the original model, a connection between raw glasses and the workshops has been added to describe the reintroduction of glass within the production context through recycling. In addition, another section has also added to represent repetitive recycling of glass (2D glass in the figure); each different grey shade represents the overall increasing in recycling markers in that specific glass composition.

Freestone – Pointing, – Hughes 2002, fig. 2, p. 259)

  • 25 Paynter 2008; Duckworth et al. 2016.

12This trend can be explained if we look at the nature of glass research of the past twenty years. Traditionally, the primary aim of the chemical analysis of glass has been to link the final product with the raw ingredients and location of its primary production. The immediate consequence of this is that most of the chemical and isotopic data available are focused on the Mediterranean, Levant, and the Middle East. Another less evident consequence is that when new data becomes available, independently from where they are acquired, they are immediately tied into a picture of glass compositional groups derived from East Mediterranean and Italian materials, with the aim of determining by which long-distance trade route they had arrived. Again, this can be partly justified again because of the nature of the model itself. Yet the picture is far from this simple, because recent research demonstrates that these primary products were often extensively modified in local, small-scale glass workshops, via practices such as recycling, mixing, and addition of raw ingredients or even the re-heating of glass could significantly modify its composition.25 If this complexity is clear, why do we keep focusing on certain areas and selectively avoid others?

  • 26 Schibille et al. 2020; De Juan Ares et al. 2021.
  • 27 Pactat 2021; Pactat – Constant – Schibille 2021.
  • 28 Neri et al. 2019; Bertini – Henderson – Chenery 2020; Occari – Freestone – Fenwick 2021.

13Both North and Western Europe have been bypassed in glass analysis and the reason cannot be always looked into to our desire to connect everything with the central production area. Even if very recent papers continue to bring new data from Spain26 and France27 and Italy,28 data for Northern and Western European glass were still in my opinion scarce when compared to other geographical areas. It thus relegates North and West Europe to the periphery, ignoring local trade routes, technologies, and paths of knowledge exchange, compounded by a lack of analysis on well-dated samples for the period.

14Should we still base our considerations on production model based on the model envisioned for the Roman period and, most importantly, just the Mediterranean area? This is a good start, but if we want things to progress, we need to look at other production landscapes too rather than to continuously rely on Mediterranean-centric solutions.

Composition, typological parallels and provenance of Early Medieval Western European glass

  • 29 E.g. Shortland – Rogers – Eremin 2007; Wedepohl – Simon – Kronz 2011; Brems – Degryse 2014; Hender (...)
  • 30 Jackson 2005; Schibille – Freestone 2013; Duckworth et al. 2016; Jackson – Paynter 2016; Schibille (...)

15Trace element and isotope analysis have revolutionised our picture of glass composition, trade, and technology. Laser ablated plasma mass spectrometry (LA-ICP-MS) provides a picture of the geological origins of the glassmaking ingredients,29 along with – crucially – evidence for technological practices such as recycling, mixing and the addition of colorants30 or other ingredients to pre-formed glass batches, all of which may have been more extensive outside the Mediterranean trade routes, but its full potential has not yet been realised.

  • 31 Gaut 2011.
  • 32 Callmer – Henderson 1991; Henderson – Holand 1992.
  • 33 E.g. Harden 1971; 1978; Price 2000; Feveile 2006; Campbell 2007.
  • 34 E.g. Henderson et al. 2016; Phelps et al. 2016; Sode 2017; Schibille et al. 2019.

16Scandinavia in this case is emblematic: Scandinavian archaeometric studies either do not go beyond basic compositional classification31 or are limited to studies dated to almost thirty years ago.32 In direct contrast, typological study of western European glass vessels – which seeks to define the location of secondary production (glass working) – has been extremely localised to date33 and has rarely been integrally linked with the bigger picture or with chemical data, with a few good exceptions.34

  • 35 Hunter – Heyworth 1998; Evison 2000; Feveile 2006; Evison et al. 2008; Broadley 2019.
  • 36 Nasman 1986; Evison 2000, fig. 7, p. 57; Feveile 2006, fig. 34–35, p. 236–37; Evison et al. 2008, (...)
  • 37 Nasman 1986; Feveile 2006, fig. 20, p. 217.

17Moreover, it has been heavily discussed how there are intriguing hints of typological parallels between Early Medieval Western European vessels, but such parallels uncover crucial questions that remain unanswered to this day. The consensus is that some Anglo-Saxon glass vessel types from England bear typological similarities to some of the types produced in the Rhineland, northern France, and Belgium:35 distribution maps for some common Early Medieval Northern European types such as claw beakers or funnel beakers36 and vessels with reticella rods37 clearly shows how these types were diffused on both the English east Coast and Scandinavian between the 7th and the 9th century CE. These typological parallels clearly suggest long-distant trade between around the English Channel with the estuaries of the major European rivers, the eastern North Sea and the western part of the Baltic. A crucial question remains though: where these vessels have been made originally?

  • 38 Feveile 2006, p. 253.
  • 39 Feveile 2006, p. 253.
  • 40 Evison et al. 2008, p. 7.

18Glass from Ribe (Denmark) supposedly came from the Frankish/Rhine area via Dorestad and the Frisian coast;38 Ribe’s glass types, albeit with some minor differences, have been closely compared to the Hamwic assemblages,39 which again suggests a common area of production: vessels could have been made in sEngland has instead suggested as production area for reticella rods to be used as decoration for 8th to 10th century CE glass vessel.40

19There is no denying that such connections are intriguing, but they need to be verified by more than just typological similarities: what about the raw glass that has been used to make such artefacts?

20Do these typological findings mirror the compositional ones, suggesting they were made from the same composition of glass in the same workshops, or do they imply movement of technical knowledge, craftspeople, or some other, complex economic relationship?

  • 41 See for example Cramp 2006, p. 56 about Jarrow and Wearmouth window glass.

21A multidisciplinary approach is the key to progress on this front. Typology alone cannot be considered a proxy for provenance and trade. Despite glass being a highly specialised craft (and therefore only limited available), we can only suggest that two glass vessels with the same type and decoration have been made in the same workshop or maybe being the product of itinerant craftsmen,41 but it cannot be presented as a certainty as we often do.

  • 42 And therefore, artefacts made from glass produced most likely in the same primary production works (...)
  • 43 E.g. the reasons behind the shortage of natron that could have caused the reintroduction of plant (...)

22On the other hand, when chemical composition is involved, we can say with certain degree of confidence that two artefacts with the same geological fingerprint might have been produced with raw materials sourced from the same area.42 When we make these associations based on chemical data, the picture is still incomplete if the archaeological context or their social and economic are not considered: production does not happen in a social vacuum. What are the reasons behind the artisans’ technological choices?43 Can we trace in the chemical composition remnants of these choices made in the past?

Recycling of glass and its influence

  • 44 Freestone 2015, p. 15.

23Recycling has only quite recently become the subject of research, yet it has significant potential to alter previous interpretations. If we look at the current published data, it is evident that after the 8th century CE there is an increase in recycling practices,44 which has been generally explained by a decrease in supply of glass from the primary production areas”. This seems sometimes just a very straightforward explanation, but can we look at it from different point of views, and maybe reflect more about the significance of the phenomenon itself?

  • 45 Duckworth 2020.
  • 46 Lucas, personal communication.

24For example, could it be that recycling was even more widespread than what we thought originally? Duckworth seems to think so:45 she has recently shown that Roman to Early Medieval glass recycling seems to have been practiced on a large scale, revising upwards our estimates of the quantity of glass in circulation, and throwing doubt upon simplistic compositional groupings. Lucas, has obtained evidence – through chemical analysis coupled with experimental glassmaking – for the intensive recycling and compositional transformation of Anglo-Saxon glass at several sites in England, probably due to a limited supply of fresh glass.46

  • 47 Bertini 2018.
  • 48 Bertini – Henderson – Chenery 2020, p. 120.

25My own PhD research demonstrated the influence of secondary production centres, which drastically altered the original raw glass composition through recycling and mixing practices.47 The case of glass from Comacchio (Italy) is a perfect example of this. Despite the variety of recipes worked overall in the workshop, it appears clear in Comacchio glass how mixing processes had a big influence on the final chemical composition. When the overall glass recipes are taken into account, the largest group of samples in Comacchio glass (n =63) dated to the entire chronological span of glass samples (first half of seventh–eleventh century CE) is characterised by a “mixed origin” composition48 with relatively high recycling markers values (>100 ppm) and in-between compositional values (fig. 2A -B, and fig 3 respectively). Comacchio’s case is exceptional because of its intrinsic nature as secondary glass-workshop and its glass waste still left in the assemblage: in normal circumstances, glass waste was not left in the workshop (archaeological record) but it would be reintroduced in the production cycle. Comacchio therefore represents a unicum, an exception than nonetheless allows us to spot a quite substantial portion of the glass was recycled.

Figure 2. Comacchio glass EMPA and LA-ICP-MS data after Bertini, Henderson, and Chenery 2020:(A) Zr/SiO2 vs. Ce/La representative of the sand source (B) Zr/SiO2 vs. Sr/CaO ratios representative of the lime component. Both ratios reveal the mixed nature of the intermediate compositions since almost all samples fall between the range of Foy-2 and Levantine A and B group.

Figure 2. Comacchio glass EMPA and LA-ICP-MS data after Bertini, Henderson, and Chenery 2020:(A) Zr/SiO2 vs. Ce/La representative of the sand source (B) Zr/SiO2 vs. Sr/CaO ratios representative of the lime component. Both ratios reveal the mixed nature of the intermediate compositions since almost all samples fall between the range of Foy-2 and Levantine A and B group.

Figure 3. Group means of recycling markers and decolourisers data in Comacchio glass by assigned compositional group, all non-recycled samples except for the intermediate group (Log scale). The latter shows relatively high recycling markers compared to the non-recycled groups.

Figure 3. Group means of recycling markers and decolourisers data in Comacchio glass by assigned compositional group, all non-recycled samples except for the intermediate group (Log scale). The latter shows relatively high recycling markers compared to the non-recycled groups.
  • 49 Freestone 2015; Jackson – Paynter 2016.
  • 50 Duckworth et al. 2016; Jackson – Paynter 2016; Schibille – Sterrett-Krause – Freestone 2016.

26Until now, however, there has been no systematic and geographically widespread analytical study on composition and recycling practices focused specifically on Early medieval glass materials. Previous works are either too broadly centred,49 or mostly focused on Roman materials.50 In no way this wants to be a critique to the previous approaches, but the same technological process must be looked from a different perspective to advance our knowledge and also to better integrate previous research. To get a better idea of the problem, we need to move on from considering the singular occurrence: one archaeological site is not enough to observe any meaningful trend over time, but instead we need to look at the matter from a much broader perspective than before.

  • 51 Duckworth 2020, p. 305.

27To quote again Duckworth,51recycling is most visible when it is outside of normal practice”. What other phenomenon or trends are we missing because are out of our traditional perspective?

28It is clear from these three research themes (production model, glass trade, and recycling processes) that the processes that describe glass production are extremely complex and dynamic and should not be limited only to the result of either aesthetic or technological choices. The way to approach this issue is definitely an integrated approach, considering glass as a material from multiple “point of research”: chemical composition, typology, and archaeological context need to go hand in hand to produce a “close to reality” model of production (or at least point us in the right direction and suggests new research trends and questions).

The WINDOGLASSMED project

29The idea for the WINDOGLASSMED project stems the research gaps I have exposed in the previous chapter. This project will be the first detailed multidisciplinary study focused on well-dated 7th–10th century to create a detailed, chronologically-resolved map of Early Medieval glass in western Europe, reflecting both trade patterns and practices such as recycling. The project is also innovative in combining state of the art chemical analysis (LA-ICP-MS) and isotope analysis at two world-leading laboratories (Fields Museum and British Geological Survey), with mapping and historical research conducted in collaboration with the DARMC at Harvard and the McCord Centre for Landscape at Newcastle. The combination of archaeological science with deep historical research makes this project fundamentally interdisciplinary. The inclusion of GIS and mapping in the project adds a further interdisciplinary dimension, as well as an accessible output that will benefit scholars interested in the history of trade, technology, the economy, and Europe in the medieval period.

  • 52 Bertini – Henderson – Chenery 2020.
  • 53 Pactat – Munier 2020; Pactat – Constant – Schibille 2021.
  • 54 De Juan Ares et al. 2019; Schibille et al. 2020.
  • 55 Neri et al. 2019; Occari – Freestone – Fenwick 2021.
  • 56 Brill – Stapleton 2012.
  • 57 Comacchio and Barking Abbey isotopic data are in preparation.

30The first objective is to focus specifically on the chemical and isotopic ‘fingerprinting’ of Western European glass from several countries to reconstruct Early Medieval trade and economy in the crucial period of change spanning the 7th to 10th centuries. We have already discussed how, although the results of glass analysis are increasingly used as a proxy for trade, this has been over-simplified to date, for example, by taking little account of practices such as recycling, which are increasingly shown to have altered the chemistry of the glasses in question. My work on Comacchio52 and Barking Abbey glass also showed me how few comparative LA-ICP-MS we had for European glass the 7th century CE onwards. Even if new LA-ICP-MS data has been made available in recent years from France,53 Spain,54 and Italy,55 the areas investigated are unequivocally Mediterranean-centred (Spain and Italy high in this list), skewing our picture of what was happening in the West. Similar consideration can be said about glass provenance studies: aside from Brill and Stapleton data,56 to my knowledge there is still no Sr and Nd signatures available for Western European glass dated to the Early Medieval period.57 How can we try to reconstruct a realistic model for glass trade, if we missing important markers for provenance from areas we are interested in?

31First, trace element analysis of well-dated samples of vessel glass from Denmark, Norway, Italy, and Spain will be conducted at the Field Museum (Chicago). To complement the results of trace element analysis and to create a more robust picture of trade and recycling practices, neodymium and strontium isotope analysis will be conducted on a subset of the sampled material (<50 samples). The results of scientific analysis will be interpreted through the use of statistical software packages, including “R”.

  • 58 For an example, see the discussion of lead in 10th and 11th century glasses, in Duckworth – Cuénod (...)

32Duckworth’s large database of >10,000 compositional data points from peer-reviewed articles focused on first millennium glass (in collaboration with Andreas Kronz, Georg-August-Universität, Göttingen), will provide a broader context for the results. The long-distance movement of ‘raw’ glass will be identified based upon affinity with known compositional groupings. Evidence for practices such as recycling can be gleaned in numerous ways from the chemical and isotope data, for example where high quantities of colorant elements are identified within a colourless glass, or where mixing lines are apparent. Chemical evidence for shared technological practices across different regions and glass compositions may imply the movement of craftspeople, or knowledge exchange.58

33The second objective is to create a database of scientific results plotted against archaeological data and geographical coordinates for the samples and assemblages in question. To achieve this, archaeological and analytical results will be integrated in one database, along with other relevant published material. This will constitute the basis for data interpretation and the creation of geographical information system (GIS) distribution maps of glass vessels, which take into account chronology, type, and chemical ‘signature’ and are linked with my research into trading hubs and other relevant archaeological and historical evidence for the period.

  • 59 Formerly DARMC or Digital Atlas of Roman and Medieval Civilizations (https://darmc.harvard.edu/).
  • 60 https://www.ncl.ac.uk/mccordcentre/.

34Another fundamental goal is to link the chemical and archaeological data with major Early Medieval trading sites, glass imports, trade routes and exchange networks in the selected Western European areas to historically contextualise the results of scientific analysis. The main trade routes and commercial hubs through which glass was imported and circulated in the selected regions, and the social phenomena connected with such exchange, will be identified through historical texts and archaeological reports. This will be done in collaboration with MAPS (“Mapping Past Societies”, Harvard University)59 and with the McCord Centre for Landscape (Newcastle university)60 Lastly, GIS distribution maps will be created and later included in the MAPS online dataset. This point is crucial because not only these maps will help finally show some distribution patterns and trends what might have not been considered so far, but also because they will be made available to scholars around the world via the MAPS online resources, even to the non-glass specialists.

Conclusion and further work

35My main goal when I approached the writing of this paper was not only to present the WINDOWGLASSMED project, but also to clarify the reasons why we need to change our approach to glass study, including the gaps that I think are particularly affecting our perception of Early Medieval glass production. Glass is not produced in a vacuum, but it a highly specialised craft where both glassmakers and glassworkers choices had a profound impact on the final product; their choices also were deeply affected by the social and economic changes. The potential for glass to become a maker for trade has been ignored so far, but glass was indeed a “thing that travelled”: how did glass reached its destination is a long and fascinating journey, but we are still missing the intermediate stops along the way.

36To trace a more comprehensive and realistic production model, it becomes therefore essential to create an improved and multi-faceted research framework while keep pushing our metaphorical theoretical boundaries. This project wants to produce more data and to reflect mostly on our methodology, on how we observe and study glass and how to look at data in a new, but exciting (and hopefully promising!) way, but it is far from comprehensive. I am painfully aware that, even when I will be finished, not nearly enough data will be available for some of the areas that I am examining with my research (e.g., Scandinavia). If nothing else, this result will produce new data and new questions, and I hope that its results will be a start in the right direction.

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Notes

1 Pirenne 2014.

2 Gorin-Rosen 2000; Tal – Jackson-Tal – Freestone 2004; Nenna 2015.

3 E.g. Mirti – Lepora – Saguì 2000; Mirti et al. 2001; Freestone – Hughes 2006; 2008; Silvestri – Marcante 2011; Schibille – Freestone 2013; Bertini – Henderson – Chenery 2020.

4 Verità – Renier – Zecchin 2002; Uboldi – Verità 2003; Freestone – Hughes 2006, Sode – Gratuze – Lankton 2017; Neri et al. 2019; Bertini – Henderson – Chenery 2020.

5 To learn more about the project: https://cordis.europa.eu/project/id/895153.

6 Nenna et al. 2005; Nenna 2015.

7 Gorin-Rosen 1995; 2000; Tal – Jackson-Tal – Freestone 2004; Phelps 2018.

8 Gorin-Rosen 2000; Phelps 2018, p. 268.

9 Freestone – Gorin-Rosen – Hughes 2000; Phelps 2018, p. 268.

10 Freestone 2015; Phelps 2018, p. 268.

11 Freestone – Pointing – Hughes 2002.

12 Henderson et al. 2016, p. 142.

13 Phelps 2018, p. 270.

14 Phelps 2018.

15 These markers can be used only in weakly coloured (what is commonly called “blue-green” in the literature) or colourless glass when their level is present over a certain threshold: over their “usual” levels, but not sufficiently high to suggest intentional addition to the melt (>100 ppm). The increase of such elements is the result of repetitive recycling over time.

16 The incorporation of elements from the fuel ash (e.g., potassium, magnesium, and phosphorus) or the glass-working instruments and melting pots (e.g., iron) over time. To deepen the topic, refer to Paynter 2008.

17 The loss of alkali (e.g., Na) is due to the reheating of the glass. To know more about this topic, please refer to Paynter 2008.

18 The presence of both Mn and Sb, typical decolourants for the 1st millennium CE, at the same time in a specific glass composition. More about the use of Sb and Mn as decolourisers and their mixing in recycled glasses in Jackson 2005. On the effect of extensive recycling over a long-period of time, refer to Silvestri 2008 work on Iulia Felix cargo glass.

19 E.g. Freestone et al. 2003; Henderson – Evans – Barkoudah 2009; Brems et al. 2013a; 2013b; Degryse 2014; Brems et al. 2018.

20 Barfod et al. 2020.

21 Brill – Wosinski 1965; Gorin-Rosen 1995; 2000; Henderson 1999; Nenna et al. 2005; Tal – Jackson-Tal – Freestone 2004; Nenna 2015.

22 Freestone – Gorin-Rosen – Hughes 2000; Foy – Nenna 2003; Henderson – McLoughlin – McPhail 2004; Phelps et al. 2016; Phelps 2018.

23 Hodges – Whitehouse 1983; McCormick 2001; Wickham 2005; Hodges 2012; Pirenne 2014.

24 Whitehouse 2003.

25 Paynter 2008; Duckworth et al. 2016.

26 Schibille et al. 2020; De Juan Ares et al. 2021.

27 Pactat 2021; Pactat – Constant – Schibille 2021.

28 Neri et al. 2019; Bertini – Henderson – Chenery 2020; Occari – Freestone – Fenwick 2021.

29 E.g. Shortland – Rogers – Eremin 2007; Wedepohl – Simon – Kronz 2011; Brems – Degryse 2014; Henderson et al. 2016.

30 Jackson 2005; Schibille – Freestone 2013; Duckworth et al. 2016; Jackson – Paynter 2016; Schibille et al. 2016.

31 Gaut 2011.

32 Callmer – Henderson 1991; Henderson – Holand 1992.

33 E.g. Harden 1971; 1978; Price 2000; Feveile 2006; Campbell 2007.

34 E.g. Henderson et al. 2016; Phelps et al. 2016; Sode 2017; Schibille et al. 2019.

35 Hunter – Heyworth 1998; Evison 2000; Feveile 2006; Evison et al. 2008; Broadley 2019.

36 Nasman 1986; Evison 2000, fig. 7, p. 57; Feveile 2006, fig. 34–35, p. 236–37; Evison et al. 2008, p. 88–90; Broadley 2019, p. 57.

37 Nasman 1986; Feveile 2006, fig. 20, p. 217.

38 Feveile 2006, p. 253.

39 Feveile 2006, p. 253.

40 Evison et al. 2008, p. 7.

41 See for example Cramp 2006, p. 56 about Jarrow and Wearmouth window glass.

42 And therefore, artefacts made from glass produced most likely in the same primary production workshop. Primary production centres are located close to the raw materials given the high volume of raw materials necessary to produce glass in the first place: a source close to the primary production centre is simply more convenient.

43 E.g. the reasons behind the shortage of natron that could have caused the reintroduction of plant ash glass has been discussed in these terms by Shortland et al. 2006 and Phelps et al. 2016.

44 Freestone 2015, p. 15.

45 Duckworth 2020.

46 Lucas, personal communication.

47 Bertini 2018.

48 Bertini – Henderson – Chenery 2020, p. 120.

49 Freestone 2015; Jackson – Paynter 2016.

50 Duckworth et al. 2016; Jackson – Paynter 2016; Schibille – Sterrett-Krause – Freestone 2016.

51 Duckworth 2020, p. 305.

52 Bertini – Henderson – Chenery 2020.

53 Pactat – Munier 2020; Pactat – Constant – Schibille 2021.

54 De Juan Ares et al. 2019; Schibille et al. 2020.

55 Neri et al. 2019; Occari – Freestone – Fenwick 2021.

56 Brill – Stapleton 2012.

57 Comacchio and Barking Abbey isotopic data are in preparation.

58 For an example, see the discussion of lead in 10th and 11th century glasses, in Duckworth – Cuénod – Mattingly 2015.

59 Formerly DARMC or Digital Atlas of Roman and Medieval Civilizations (https://darmc.harvard.edu/).

60 https://www.ncl.ac.uk/mccordcentre/.

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Table des illustrations

Titre Figure 1. A diagram representing the relation between raw materials, workshops, and final raw glass composition, originally suggested by Freestone and colleagues years ago. From the original model, a connection between raw glasses and the workshops has been added to describe the reintroduction of glass within the production context through recycling. In addition, another section has also added to represent repetitive recycling of glass (2D glass in the figure); each different grey shade represents the overall increasing in recycling markers in that specific glass composition.
Crédits Freestone – Pointing, – Hughes 2002, fig. 2, p. 259)
URL http://0-journals-openedition-org.catalogue.libraries.london.ac.uk/mefrm/docannexe/image/12694/img-1.jpg
Fichier image/jpeg, 176k
Titre Figure 2. Comacchio glass EMPA and LA-ICP-MS data after Bertini, Henderson, and Chenery 2020:(A) Zr/SiO2 vs. Ce/La representative of the sand source (B) Zr/SiO2 vs. Sr/CaO ratios representative of the lime component. Both ratios reveal the mixed nature of the intermediate compositions since almost all samples fall between the range of Foy-2 and Levantine A and B group.
URL http://0-journals-openedition-org.catalogue.libraries.london.ac.uk/mefrm/docannexe/image/12694/img-2.png
Fichier image/png, 233k
Titre Figure 3. Group means of recycling markers and decolourisers data in Comacchio glass by assigned compositional group, all non-recycled samples except for the intermediate group (Log scale). The latter shows relatively high recycling markers compared to the non-recycled groups.
URL http://0-journals-openedition-org.catalogue.libraries.london.ac.uk/mefrm/docannexe/image/12694/img-3.png
Fichier image/png, 75k
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Camilla Bertini, « A new perspective: the “WINDOWGLASSMED” project »Mélanges de l’École française de Rome - Moyen Âge, 135-2 | 2023, 379-390.

Référence électronique

Camilla Bertini, « A new perspective: the “WINDOWGLASSMED” project »Mélanges de l’École française de Rome - Moyen Âge [En ligne], 135-2 | 2023, mis en ligne le 01 mars 2024, consulté le 20 juin 2024. URL : http://0-journals-openedition-org.catalogue.libraries.london.ac.uk/mefrm/12694 ; DOI : https://0-doi-org.catalogue.libraries.london.ac.uk/10.4000/mefrm.12694

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Auteur

Camilla Bertini

School of History, Classics and Archaeology, Faculty of Humanities and Social Sciences Newcastle University, NE1 7RU, United Kingdom – History Department, Harvard University, Cambridge MA 02138, camilla.bertini@newcastle.ac.uk

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