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Glass-working evidences at Dürres, Albania: An archaeological and archaeometric study
Available online at
www.sciencedirect.com Journal of Cultural Heritage 9 (2008) e33ee36
Original article
Glass-working evidences at Du¨rres, Albania: An archaeological and archaeometric study Cristina Boschetti a,b,*, Cristina Leonelli b, Anna Corradi b, Paola Iacumin c, Marco Martini d, Emanuela Sibilia d, Sara Santoro e, Barbara Sassi e a
Padova University, PhD School in Science and Technologies for the Conservation of the Archaeological and Architectonic Heritage, Earth Sciences Department, via Giotto 4, 35137 Padova, Italy b Modena and Reggio Emilia University, Department of Materials and Environmental Engineering, via Vignolese 905, 41100 Modena, Italy c Parma University, Department of Earth Sciences, viale Usberti 157A, 43100 Parma, Italy d Milano Bicocca University, Department of Materials Sciences, via Cozzi 53, 20125 Milano, Italy e Parma University, Department of History, via D’Azeglio 85, 43100 Parma, Italy Received 30 March 2008; accepted 9 June 2008
Abstract For the first time an archaeological and archaeometric work presents the discovery of glass-working evidences in the area of Du¨rres Roman Amphitheatre in Albania. Glasses, coming from a layer dating back to the 11th century A.D., have been object of an archaeometric characterization to determinate the chemical composition. Moreover the oxygen isotope ratio has been calculated to hypothesize the provenance of the sands used to melt the glass. Bricks and charcoals, elements linked to the kiln structure, were analyzed by thermoluminescence and radiocarbon respectively. Ó 2008 Elsevier Masson SAS. All rights reserved. Keywords: Albania; Glass-working; Glass lump; Raw glass trade; Archaeometric characterization; SEMeEDS; Oxygen isotope ratio; Thermoluminescence dating
1. Introduction and research aims Albania, a small Balkan country facing the Adriatic Sea, has a recent history of political unstability: this event determinated a delay in the advancement of the local scientific research with a consequent lack in the knowledge of the ancient history of the region. Recently, starting from the last decade, the country has been living a period of social and political renovation and this change originated a real improved
* Corresponding author. Padova University, PhD School in Science and Technologies for the Conservation of the Archaeological and Architectonic Heritage, Earth Sciences Department, via Giotto 4, 35137 Padova, Italy. E-mail addresses: [email protected] (C. Boschetti), leonelli@ unimo.it (C. Leonelli), [email protected] (A. Corradi), paola.iacumin@ unipr.it (P. Iacumin), [email protected] (M. Martini), emanuela. [email protected] (E. Sibilia), [email protected] (S. Santoro), ba. [email protected] (B. Sassi). 1296-2074/$ - see front matter Ó 2008 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.culher.2008.06.004
interest for the cultural heritage conservation and the birth of cooperation projects aimed to enhance the local scientific research [1e3]. This paper presents a study on Middle Ages glass-working evidences found in the ancient Du¨rres town and it is part of a complex archaeological project concerning the study of the urban Roman Amphitheatre. The investigation on glass samples was planned in the perspective to contribute to reach a complete site knowledge and the analytical procedures were chosen in order to obtain data relevant to draw up a social and economical site reconstruction model. The area of the Roman Amphitheatre of Du¨rres town, Albania, is object of research in the Pilot Project (UNIPR-MAE DGPCC uff. V 2004-07) ‘‘Planning and building of the Du¨rres Urban Archaeological Park’’, currently in course. Because of its strategic position, on the Egnatia road, at the crossroad between maritime and overland routes linking the western and the eastern Mediterranean, Du¨rres was an important harbor firstly during the Greek Age and, after, during the Roman and Byzantine Empires.
e34
C. Boschetti et al. / Journal of Cultural Heritage 9 (2008) e33ee36
Later, in the Middle Ages (10the12th century), the strategic position of Du¨rres caused power struggles for its possession between the Byzantines, the Normans, the Angio` Dynasty and Venice Republic. The amphitheatre, built in the southern part of the Roman town, is dated back at the beginning of the 2nd century A.D. Starting from the 5th century, after the defection of the original use, the area was reorganised as site of a living and religious quarter with two chapels and a cemetery. In this context it is reliable to hypothesize also the presence of productive activities located in the galleries and in the cavea area. During the excavation campaign which took place during the summer of 2006 (Fig. 1a), it was found a number of materials linked to the presence of a glass-working activity: vitrified bricks (Fig. 1c) and blocks of fired clay and straw mixture, glass lumps and drops, crucibles shards (Fig. 2aec). The archaeological context suggests to date these materials to the 11the12th century. It was not possible to propose a reconstructed shape of the crucibles, but the presence of the wheel lines suggested to propose the re-use of cooking ware, a practice well attested during the Late Antiquity and the Middle Ages [4,5]. The kiln structure was probably set in an area deeply transformed by successive building operations (during the 12th century it was built a palace and in 1273 an earthquake stroke the region). Moreover, in the proximity of the glass-working waste products finding place, it was located a small structure, with circular layout, built in partially vitrified bricks and presenting clear evidences of firing on the bottom, such as charcoals and fired clay (Fig. 1b). This element was interpreted as a structure linked to the glass-working workshop: it could be an annealing oven or
Fig. 1. A panoramic view of the amphitheatre area in course of excavation (a) with the structure identified as an annealing oven or a furnace firing chamber (STR VII) and the layer containing the glass waste products (US 222) indicated in yellow. The rectangular structure visible on the left side is part of the palace built during the 12th century. Below (b) an image of the structure interpreted as an annealing oven and (c) molten bricks re-used in a wall.
Fig. 2. A choice of the materials evidence of glass-working: a crucible shard externally covered by residues of clay and straw mixture and dripped glass (a), a crucible shard with a glass layer in its inner part (b) and two aqua colour glass masses (c).
the firing chamber of a secondary glass furnace. Unfortunately the evidences are too scarce to propose a convincing interpretation and in literature there are few data suitable to be compared [5,6].
C. Boschetti et al. / Journal of Cultural Heritage 9 (2008) e33ee36
This discovery is extremely important because it testifies for the first time the presence of a glass-working activity in Albania during the Middle Ages and gives the chance to advance the first hypotheses of a local glass trade. In fact, during this period, the activity of tank furnaces in the Levantine coastal region is documented [7,8] and earliest evidences of this practice, dating back to the HellenisticRoman Age have been recently located also in Egypt [9]. These workshops produced a high amount of raw glass traded in the whole Mediterranean region, where it was shaped to produce objects. Otherwise, starting from the Early Imperial Roman Age, it is also documented the practice to recycle broken glasses [10e13]: the chemical composition of glasses obtained by fusing waste shards usually presents an enrichment in trace elements, deriving from small amounts of coloured glasses introduced into the melt [10]. One of the main aim of this research was to investigate the glass used by the Du¨rres workshop and to propose a model of production: the working of base glass, index of a high quality production, or the recycling of broken glasses, a lower profile activity.
e35
The isotope composition is expressed conventionally as ‘‘d’’ value in per thousand by comparison with an international standard of known isotope value, in this case V-SMOW (oceanic water), as follows: 18 Rsample O 1 1000 where R ¼ 16 Rstandard O
d¼
Bricks and charcoal from the kiln structure were analyzed by absolute dating techniques of widespread use in archaeology: thermoluminescence [14] and radiocarbon [15]. They are specific for ceramics and organic remains respectively. By measuring the accumulated radiation dose, thermoluminescence (TL) is able to date the time elapsed since the last firing. As the material is heated during measurements, a weak light signal, the thermoluminescence, proportional to the radiation dose is produced. Radiocarbon is a radiometric dating method that uses the naturally occurring isotope carbon-14 to determine the age of organic remains. By radioactive decay, carbon-14 is changed into stable, non-radioactive nitrogen. This decay can be used to measure how long ago once-living material died.
2. Analytical techniques 3. Experimental data and results To answer to the questions correlated to such a complex association of materials, a selection of glasses (glass lump and drops) and a partially molten brick, part of the annealing oven structure, were sampled to be characterized. Glasses were prepared in freshly fractured specimens, coated with carbon and characterized as it concerns the microstructure and the chemical composition by ESEMeEDS (ESEM Quanta-200). The batch raw materials provenance was investigated characterizing the oxygen isotope ratio: about 15 mg of fine-grained glass sample were reacted overnight (15 h) at about 600 C with BrF5. The oxygen obtained from this reaction was converted to CO2 by cycling over hot graphite in the presence of a platinum catalyst, and the CO2 measured by means of a Finnigan Delta S mass spectrometer. The standard deviation of these measurements was close to 0.2&.
3.1. The glasses The analyzed glasses were all covered by a surface iridescent layer, due to the leaching effect but, observing the unaltered glass in fresh fracture, it appears to be transparent, homogeneous and lightly coloured in green. At the electron microscope, the microstructure characterizes the samples as high quality products, made in a homogeneous glass, without any kind of blisters or stones. The results of the EDS analysis (Table 1) show that all the glasses are silicaesodaelime glasses, with other minor components (below 1.0 wt%) as sulphur and phosphorous, which were not always detected, as well as some colouring oxides: FeO and MnO. These chemical compositions are compatible with the edited data about the coastal plant ashes glasses produced in the Levant workshops
Table 1 Chemical composition (% by weight) of the samples analyzed (nd ¼ not detected) Comp. Na2O MgO Al2O3 SiO2 K2O CaO MnO FeO Traces Cl P2O5 SO3 TiO2
Albania 1 (wt%)
Albania 2 (wt%)
Albania 4 (wt%)
Albania 6 (wt%)
Albania 10 (wt%)
Albania 11 (wt%)
Albania 12 (wt%)
12.7 2.8 2.4 68.2 2.1 9.5 0.9 0.8
14.9 2.9 2.4 67.7 1.9 8.1 0.7 0.8
13.9 2.4 2.1 68.4 2.2 7.8 0.6 0.9
14.9 2.7 2.1 67.6 1.9 7.5 0.8 0.8
14.4 2.5 2.5 68.6 1.9 7.4 0.9 0.6
17.4 1.6 2.4 68.7 1.2 7.2 0.3 0.4
10.2 2.6 2.8 69.1 2.9 8.7 0.3 1.4
10.9 2.6 2.8 69.8 2.5 8.1 0.2 1.1
14 2.5 3.4 69.1 2 5.5 0.2 1.3
14.3 3.1 3.6 68.7 1.9 5.4 0.2 1.3
8.9 2.5 2.8 65 3.5 12.7 1.7 1.4
9 2.3 3.6 66.3 2.8 12 1.6 1.2
11.2 1.6 2.9 66 3 10.3 0.8 1.6
10.4 2 2.5 68.2 2.9 9.7 1.3 1.5
0.6 0 0 0
0.6 0 0 0
0.7 0.7 0.3 0
0.8 0.6 0.2 0.1
0.7 0.2 0 0.3
0.7 0 0.1 0
0.9 0.5 0.2 0.4
0.8 0.7 0.1 0.4
1 0.6 0 0.4
0.9 0.2 0.1 0.3
0.6 0.3 0.4 0.2
0.9 0.1 0 0.2
1 0.7 0.6 0.3
0.8 0.1 0.4 0.2
100
100
100
100
100
100
100
100
100
100
100
100
100
100
C. Boschetti et al. / Journal of Cultural Heritage 9 (2008) e33ee36
e36 Table 2 The d18O value of the four samples analyzed
d18O
Sample ALBANIA ALBANIA ALBANIA ALBANIA
a useful element to operate a reconstruction of the life in the town during the Middle Ages.
6 10 11 12
13.4 15.6 14.0 13.7
[16]. Observing in the detail the chemical compositions, it is possible to detect a group of samples (no. 1, 2, 4 and 10) with higher values in soda (w14% or more) and lower heavy metals content, while the others (no. 6, 11 and 12) have 10e 11% Na2O. The contents of calcium and heavy metals are very variable, but it is not possible to individuate homogeneous groups. This result makes to hypothesize the use of glasses from two different sources, hypothesis confirmed by the oxygen isotope characterization. In fact, d18O values measured on four glass samples range from 13.4& to 15.6& (Table 2) and samples 6, 11 and 12 show very similar values (mean value 13.7&) while sample 10 differs for a higher isotope value. For the moment there are few data about oxygen isotopic signature in the Middle Ages glasses but samples 6, 11 and 12 are comparable with the literature data about the Raqqa glassmaking site, in Syria [16], possible site of provenance of this base glass. 3.2. The kiln structure During the 2007 excavation campaign a few bricks from the wall structure and a charcoal sample from the bottom of the structure, interpreted as an annealing oven, could be sampled. Thermoluminescence dating, performed at CUDaM laboratory (http://cudam.mater.unimib.it), showed a weak and scarcely reproducible signal of the ceramic samples. As a consequence, only a rough estimation of the age could be performed, giving for the firing of the bricks the period 9the11th century A.D. The radiocarbon dating of the charcoal, performed at CUDaM for sample preparation and at LABEC (http://labec.fi.infn.it) for AMS, accelerator mass spectrometry, gave the period 995e1150 A.D. (þ1s cal). 4. Conclusion The analyses performed on the glasses identify them as base glasses coming from the South-eastern Mediterranean and in the future, with the advancement of the archaeometric studies aimed to determinate the ancient glass provenance, it is auspicated to go deeper in the interpretation of the analytical data. For the moment it was possible to acquire a new element indicating the economic vitality of Du¨rres harbor and the Adriatic east coast during the 11th and the 12th century and to testify exchanges with the Levantine coast. Considering the state of war in that period, with the town object of struggle between the Byzantines and the Normans, this result is quite surprising. Otherwise, the attested presence in Du¨rres of important members of the Norman and Byzantine court could explain the flourishing of a high quality crafts. To sum up, this evidence has proved to be
References [1] S. Santoro, M. Buora (Eds.), L’indagine sui Beni Culturali albanesi dell’antichita` e del medioevo: tradizioni di studio a confronto, Antichita` Alto-Adriatiche, vol. 53, Editreg, Trieste, 2003. [2] Strumenti per la salvaguardia del patrimonio archeologico: carte del rischio e catalogazione informatizzata, in: S. Santoro, M. Buora (Eds.), Proceedings of the 3rd Scientific Meeting of the Durres Project, Villa Manin di Passariano(UD)-Parma, 28e30 March, 2003, Editreg, Trieste, 2003. [3] Alte tecnologie applicate all’archeologia di Durres, in: S. Santoro, M. Buora (Eds.), Proceedings of the 4th Scientific Meeting of the Durres Project, Durres, 24 June, 2004, Editreg, Trieste, 2004. [4] D. Foy, J.B. Fe´raud, L.F. Gante`s, M. Molinier, M. Picon, Creusets de verrier de l’Antiquite´ tardive et du haut Moyen-Age de´couverts dans le sud-est de la France, in: A. von Saldern (Ed.), Proceedings of AIHV, 11th Meeting, Baˆle, August 29eSeptember 3, 1988, AIHV, Amsterdam, 1990, pp. 199e217. [5] M.D. Nenna (Ed.), La route du verre, ateliers de verriers primaires et secondaires du second mille´naire av. J.-C. au Moyen Age, Colloque international, Lyon, October 1997, Travaux de la Maison de l’Orient me´diterrane´en, 33 (2000). [6] Echanges et commerce du verre dans le monde antique, in: D. Foy, M.D. Nenna (Eds.), Proceedings of the AFAV (Association Franc¸aise pour l’Arche´ologie du Verre) Conference, Aix-en-Provence and Marseille, 7e9 June, 2001, Monique Mergoil, Montagnac, 2003. [7] Y. Gorin-Rosen, The ancient glass industry in Israel. Summar of the finds and new discoveries, in: M.D. Nenna (Ed.), La route du verre, ateliers de verriers primaires et secondaires du second mille´naire av. J.-C. au Moyen Age, Colloque international, Lyon, October 1997, Travaux de la Maison de l’Orient me´diterrane´en, 33 (2000), 49e63. [8] O. Dussart, Quelques indices d’ateliers de verriers en Jordanie et en Syrie du sud de la fin de l’e´poque Helle´nistique a` l’e´poque Islamique, in: M.D. Nenna (Ed.), La route du verre, ateliers de verriers primaires et secondaires du second mille´naire av. J.-C. au Moyen Age, Colloque international, Lyon, October 1997, Travaux de la Maison de l’Orient me´diterrane´en, 33 (2000), 91e96. [9] M.-D. Nenna, M. Picon, V. Thirion-Merle, M. Vichy, Un nouvel atelier primaire dans le Wadi Natrun (E´gypte), et les compositions des verres produits dans cette re´gion, Bulletin de l’Association franc¸aise pour l’Arche´ologie du verre (2003) 21e24. [10] M. Uboldi, M. Verita`, Scientific analysis of glasses from late antique and early medieval archaeological sites in Northern Italy, Journal of Glass Studies 45 (2003) 115e137. [11] P. Degryse, J. Schneider, U. Haack, V. Lauwers, J. Poblome, M. Waelkens, Ph. Muchez, Evidence for glass recycling using Pb and Sr isotopic ratios and Sr-mixing lines: the case of early Byzantine Sagalassos, Journal of Archaeological Science 33 (4) (2006) 494e501. [12] M. Vichy, V. Thirion-Merle, M. Picon, Note sur le recyclage de verre dans l’Antiquite´ et sur les groupes de recyclage, Bulletin de l’Association Franc¸aise pour l’Arche´ologie du Verre (2007) 55e57. [13] D. Foy, Recyclage et re´emplois dans l’artisanat du verre. Quelques exemples antiques et me´die´vaux, in: P. Ballet, P. Cordier, N. Dieudonne´Glad (Eds.), Proceeedings, La ville et ses de´chets dans le monde romain, Rebuts et recyclage, Poitiers, 19e20 September, 2002, Monique Mergoil, Montagnac, 2003, pp. 271e276. [14] M.J. Aitken, Thermoluminescence Dating, Academic Press, London, 1985. [15] S. Bowman, Interpreting the Past: Radiocarbon Dating, University of California Press, 1990. [16] J. Henderson, J.A. Evans, H.J. Sloane, M.J. Leng, C. Doherty, The use of oxygen, strontium and lead isotopes to provenance ancient glasses in the Middle East, Journal of Archaeological Science 32 (5) (2005) 665e673.
www.sciencedirect.com Journal of Cultural Heritage 9 (2008) e33ee36
Original article
Glass-working evidences at Du¨rres, Albania: An archaeological and archaeometric study Cristina Boschetti a,b,*, Cristina Leonelli b, Anna Corradi b, Paola Iacumin c, Marco Martini d, Emanuela Sibilia d, Sara Santoro e, Barbara Sassi e a
Padova University, PhD School in Science and Technologies for the Conservation of the Archaeological and Architectonic Heritage, Earth Sciences Department, via Giotto 4, 35137 Padova, Italy b Modena and Reggio Emilia University, Department of Materials and Environmental Engineering, via Vignolese 905, 41100 Modena, Italy c Parma University, Department of Earth Sciences, viale Usberti 157A, 43100 Parma, Italy d Milano Bicocca University, Department of Materials Sciences, via Cozzi 53, 20125 Milano, Italy e Parma University, Department of History, via D’Azeglio 85, 43100 Parma, Italy Received 30 March 2008; accepted 9 June 2008
Abstract For the first time an archaeological and archaeometric work presents the discovery of glass-working evidences in the area of Du¨rres Roman Amphitheatre in Albania. Glasses, coming from a layer dating back to the 11th century A.D., have been object of an archaeometric characterization to determinate the chemical composition. Moreover the oxygen isotope ratio has been calculated to hypothesize the provenance of the sands used to melt the glass. Bricks and charcoals, elements linked to the kiln structure, were analyzed by thermoluminescence and radiocarbon respectively. Ó 2008 Elsevier Masson SAS. All rights reserved. Keywords: Albania; Glass-working; Glass lump; Raw glass trade; Archaeometric characterization; SEMeEDS; Oxygen isotope ratio; Thermoluminescence dating
1. Introduction and research aims Albania, a small Balkan country facing the Adriatic Sea, has a recent history of political unstability: this event determinated a delay in the advancement of the local scientific research with a consequent lack in the knowledge of the ancient history of the region. Recently, starting from the last decade, the country has been living a period of social and political renovation and this change originated a real improved
* Corresponding author. Padova University, PhD School in Science and Technologies for the Conservation of the Archaeological and Architectonic Heritage, Earth Sciences Department, via Giotto 4, 35137 Padova, Italy. E-mail addresses: [email protected] (C. Boschetti), leonelli@ unimo.it (C. Leonelli), [email protected] (A. Corradi), paola.iacumin@ unipr.it (P. Iacumin), [email protected] (M. Martini), emanuela. [email protected] (E. Sibilia), [email protected] (S. Santoro), ba. [email protected] (B. Sassi). 1296-2074/$ - see front matter Ó 2008 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.culher.2008.06.004
interest for the cultural heritage conservation and the birth of cooperation projects aimed to enhance the local scientific research [1e3]. This paper presents a study on Middle Ages glass-working evidences found in the ancient Du¨rres town and it is part of a complex archaeological project concerning the study of the urban Roman Amphitheatre. The investigation on glass samples was planned in the perspective to contribute to reach a complete site knowledge and the analytical procedures were chosen in order to obtain data relevant to draw up a social and economical site reconstruction model. The area of the Roman Amphitheatre of Du¨rres town, Albania, is object of research in the Pilot Project (UNIPR-MAE DGPCC uff. V 2004-07) ‘‘Planning and building of the Du¨rres Urban Archaeological Park’’, currently in course. Because of its strategic position, on the Egnatia road, at the crossroad between maritime and overland routes linking the western and the eastern Mediterranean, Du¨rres was an important harbor firstly during the Greek Age and, after, during the Roman and Byzantine Empires.
e34
C. Boschetti et al. / Journal of Cultural Heritage 9 (2008) e33ee36
Later, in the Middle Ages (10the12th century), the strategic position of Du¨rres caused power struggles for its possession between the Byzantines, the Normans, the Angio` Dynasty and Venice Republic. The amphitheatre, built in the southern part of the Roman town, is dated back at the beginning of the 2nd century A.D. Starting from the 5th century, after the defection of the original use, the area was reorganised as site of a living and religious quarter with two chapels and a cemetery. In this context it is reliable to hypothesize also the presence of productive activities located in the galleries and in the cavea area. During the excavation campaign which took place during the summer of 2006 (Fig. 1a), it was found a number of materials linked to the presence of a glass-working activity: vitrified bricks (Fig. 1c) and blocks of fired clay and straw mixture, glass lumps and drops, crucibles shards (Fig. 2aec). The archaeological context suggests to date these materials to the 11the12th century. It was not possible to propose a reconstructed shape of the crucibles, but the presence of the wheel lines suggested to propose the re-use of cooking ware, a practice well attested during the Late Antiquity and the Middle Ages [4,5]. The kiln structure was probably set in an area deeply transformed by successive building operations (during the 12th century it was built a palace and in 1273 an earthquake stroke the region). Moreover, in the proximity of the glass-working waste products finding place, it was located a small structure, with circular layout, built in partially vitrified bricks and presenting clear evidences of firing on the bottom, such as charcoals and fired clay (Fig. 1b). This element was interpreted as a structure linked to the glass-working workshop: it could be an annealing oven or
Fig. 1. A panoramic view of the amphitheatre area in course of excavation (a) with the structure identified as an annealing oven or a furnace firing chamber (STR VII) and the layer containing the glass waste products (US 222) indicated in yellow. The rectangular structure visible on the left side is part of the palace built during the 12th century. Below (b) an image of the structure interpreted as an annealing oven and (c) molten bricks re-used in a wall.
Fig. 2. A choice of the materials evidence of glass-working: a crucible shard externally covered by residues of clay and straw mixture and dripped glass (a), a crucible shard with a glass layer in its inner part (b) and two aqua colour glass masses (c).
the firing chamber of a secondary glass furnace. Unfortunately the evidences are too scarce to propose a convincing interpretation and in literature there are few data suitable to be compared [5,6].
C. Boschetti et al. / Journal of Cultural Heritage 9 (2008) e33ee36
This discovery is extremely important because it testifies for the first time the presence of a glass-working activity in Albania during the Middle Ages and gives the chance to advance the first hypotheses of a local glass trade. In fact, during this period, the activity of tank furnaces in the Levantine coastal region is documented [7,8] and earliest evidences of this practice, dating back to the HellenisticRoman Age have been recently located also in Egypt [9]. These workshops produced a high amount of raw glass traded in the whole Mediterranean region, where it was shaped to produce objects. Otherwise, starting from the Early Imperial Roman Age, it is also documented the practice to recycle broken glasses [10e13]: the chemical composition of glasses obtained by fusing waste shards usually presents an enrichment in trace elements, deriving from small amounts of coloured glasses introduced into the melt [10]. One of the main aim of this research was to investigate the glass used by the Du¨rres workshop and to propose a model of production: the working of base glass, index of a high quality production, or the recycling of broken glasses, a lower profile activity.
e35
The isotope composition is expressed conventionally as ‘‘d’’ value in per thousand by comparison with an international standard of known isotope value, in this case V-SMOW (oceanic water), as follows: 18 Rsample O 1 1000 where R ¼ 16 Rstandard O
d¼
Bricks and charcoal from the kiln structure were analyzed by absolute dating techniques of widespread use in archaeology: thermoluminescence [14] and radiocarbon [15]. They are specific for ceramics and organic remains respectively. By measuring the accumulated radiation dose, thermoluminescence (TL) is able to date the time elapsed since the last firing. As the material is heated during measurements, a weak light signal, the thermoluminescence, proportional to the radiation dose is produced. Radiocarbon is a radiometric dating method that uses the naturally occurring isotope carbon-14 to determine the age of organic remains. By radioactive decay, carbon-14 is changed into stable, non-radioactive nitrogen. This decay can be used to measure how long ago once-living material died.
2. Analytical techniques 3. Experimental data and results To answer to the questions correlated to such a complex association of materials, a selection of glasses (glass lump and drops) and a partially molten brick, part of the annealing oven structure, were sampled to be characterized. Glasses were prepared in freshly fractured specimens, coated with carbon and characterized as it concerns the microstructure and the chemical composition by ESEMeEDS (ESEM Quanta-200). The batch raw materials provenance was investigated characterizing the oxygen isotope ratio: about 15 mg of fine-grained glass sample were reacted overnight (15 h) at about 600 C with BrF5. The oxygen obtained from this reaction was converted to CO2 by cycling over hot graphite in the presence of a platinum catalyst, and the CO2 measured by means of a Finnigan Delta S mass spectrometer. The standard deviation of these measurements was close to 0.2&.
3.1. The glasses The analyzed glasses were all covered by a surface iridescent layer, due to the leaching effect but, observing the unaltered glass in fresh fracture, it appears to be transparent, homogeneous and lightly coloured in green. At the electron microscope, the microstructure characterizes the samples as high quality products, made in a homogeneous glass, without any kind of blisters or stones. The results of the EDS analysis (Table 1) show that all the glasses are silicaesodaelime glasses, with other minor components (below 1.0 wt%) as sulphur and phosphorous, which were not always detected, as well as some colouring oxides: FeO and MnO. These chemical compositions are compatible with the edited data about the coastal plant ashes glasses produced in the Levant workshops
Table 1 Chemical composition (% by weight) of the samples analyzed (nd ¼ not detected) Comp. Na2O MgO Al2O3 SiO2 K2O CaO MnO FeO Traces Cl P2O5 SO3 TiO2
Albania 1 (wt%)
Albania 2 (wt%)
Albania 4 (wt%)
Albania 6 (wt%)
Albania 10 (wt%)
Albania 11 (wt%)
Albania 12 (wt%)
12.7 2.8 2.4 68.2 2.1 9.5 0.9 0.8
14.9 2.9 2.4 67.7 1.9 8.1 0.7 0.8
13.9 2.4 2.1 68.4 2.2 7.8 0.6 0.9
14.9 2.7 2.1 67.6 1.9 7.5 0.8 0.8
14.4 2.5 2.5 68.6 1.9 7.4 0.9 0.6
17.4 1.6 2.4 68.7 1.2 7.2 0.3 0.4
10.2 2.6 2.8 69.1 2.9 8.7 0.3 1.4
10.9 2.6 2.8 69.8 2.5 8.1 0.2 1.1
14 2.5 3.4 69.1 2 5.5 0.2 1.3
14.3 3.1 3.6 68.7 1.9 5.4 0.2 1.3
8.9 2.5 2.8 65 3.5 12.7 1.7 1.4
9 2.3 3.6 66.3 2.8 12 1.6 1.2
11.2 1.6 2.9 66 3 10.3 0.8 1.6
10.4 2 2.5 68.2 2.9 9.7 1.3 1.5
0.6 0 0 0
0.6 0 0 0
0.7 0.7 0.3 0
0.8 0.6 0.2 0.1
0.7 0.2 0 0.3
0.7 0 0.1 0
0.9 0.5 0.2 0.4
0.8 0.7 0.1 0.4
1 0.6 0 0.4
0.9 0.2 0.1 0.3
0.6 0.3 0.4 0.2
0.9 0.1 0 0.2
1 0.7 0.6 0.3
0.8 0.1 0.4 0.2
100
100
100
100
100
100
100
100
100
100
100
100
100
100
C. Boschetti et al. / Journal of Cultural Heritage 9 (2008) e33ee36
e36 Table 2 The d18O value of the four samples analyzed
d18O
Sample ALBANIA ALBANIA ALBANIA ALBANIA
a useful element to operate a reconstruction of the life in the town during the Middle Ages.
6 10 11 12
13.4 15.6 14.0 13.7
[16]. Observing in the detail the chemical compositions, it is possible to detect a group of samples (no. 1, 2, 4 and 10) with higher values in soda (w14% or more) and lower heavy metals content, while the others (no. 6, 11 and 12) have 10e 11% Na2O. The contents of calcium and heavy metals are very variable, but it is not possible to individuate homogeneous groups. This result makes to hypothesize the use of glasses from two different sources, hypothesis confirmed by the oxygen isotope characterization. In fact, d18O values measured on four glass samples range from 13.4& to 15.6& (Table 2) and samples 6, 11 and 12 show very similar values (mean value 13.7&) while sample 10 differs for a higher isotope value. For the moment there are few data about oxygen isotopic signature in the Middle Ages glasses but samples 6, 11 and 12 are comparable with the literature data about the Raqqa glassmaking site, in Syria [16], possible site of provenance of this base glass. 3.2. The kiln structure During the 2007 excavation campaign a few bricks from the wall structure and a charcoal sample from the bottom of the structure, interpreted as an annealing oven, could be sampled. Thermoluminescence dating, performed at CUDaM laboratory (http://cudam.mater.unimib.it), showed a weak and scarcely reproducible signal of the ceramic samples. As a consequence, only a rough estimation of the age could be performed, giving for the firing of the bricks the period 9the11th century A.D. The radiocarbon dating of the charcoal, performed at CUDaM for sample preparation and at LABEC (http://labec.fi.infn.it) for AMS, accelerator mass spectrometry, gave the period 995e1150 A.D. (þ1s cal). 4. Conclusion The analyses performed on the glasses identify them as base glasses coming from the South-eastern Mediterranean and in the future, with the advancement of the archaeometric studies aimed to determinate the ancient glass provenance, it is auspicated to go deeper in the interpretation of the analytical data. For the moment it was possible to acquire a new element indicating the economic vitality of Du¨rres harbor and the Adriatic east coast during the 11th and the 12th century and to testify exchanges with the Levantine coast. Considering the state of war in that period, with the town object of struggle between the Byzantines and the Normans, this result is quite surprising. Otherwise, the attested presence in Du¨rres of important members of the Norman and Byzantine court could explain the flourishing of a high quality crafts. To sum up, this evidence has proved to be
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