Colourless Roman glass from the Zadar necropolis: An exploratory approach

Journal of Archaeological Science: Reports 15 (2017) 194–202

Contents lists available at ScienceDirect

Journal of Archaeological Science: Reports journal homepage: www.elsevier.com/locate/jasrep

Colourless Roman glass from the Zadar necropolis: An exploratory approach I. Coutinho a b c d

MARK

, T. Medici , L.C. Alves , Š. Perović

a,b,*

a

c

d

Research Unit VICARTE, Vidro e Cerâmica para as Artes, FCT NOVA, Lisboa, Campus de Caparica, Caparica 2829-516, Portugal Department of Conservation and Restoration, FCT NOVA, Lisboa, Campus de Caparica, Caparica 2829-516, Portugal C2TN, Instituto Superior Técnico, Universidade de Lisboa, Bobadela LRS 2695-066, Portugal Museum of Ancient Glass, Poljana Zemaljskog odbora 1, Zadar 23000, Croatia

A R T I C L E I N F O

A B S T R A C T

Keywords: Roman Glass Croatia Colourless μ-PIXE Primary glass sources Recycling

This paper presents the study of eighteen samples of colourless glass dated to the Roman period (1st to 3rd centuries C.E.) and that were unearthed in Zadar, Croatia. In this exploratory research, the chemical composition of the glass, which was determined by μ-PIXE, was divided into two main groups based on the alkali and alkaliearth contents: glass with low CaO and Al2O3, and high Na2O contents (Group 1), and glass with high CaO, Al2O3, and low Na2O contents (Group 2). The chemical composition from Group 1 is related to polygonal bottles and the composition from Group 2 to bell-shaped bottles, the latter being considered of local provenance. The analysis of MnO, Sb2O5 and Al2O3 contents and ratios suggests that only three samples from Group 1 were obtained from a primary glass source discoloured with Sb and the remaining fragments are the result of recycling activities, whereas all fragments from Group 2 were made using a different primary glass source discoloured with Mn. Finally, considering all the compositional characteristics of the analysed glass, it is proposed that the primary glass source of Group 1 was Egypt, and that glass from Group 2 came from the Levant region.

1. Introduction For the past few decades, relevant research has been carried out on several aspects of Roman glass, including its history, employed raw materials, and production processes and organization. Long since identified as a natron glass, the relative homogeneity of the recognized compositions led to a commonly accepted model concerning the organization of the production, based on the assumption that glass from raw materials was probably made in a limited number of places (primary workshops) and then it was distributed throughout the empire in the form of glass chunks to be worked in a multitude of workshops producing the objects (secondary production) (e.g. Rehren and Freestone, 2015; Jackson and Paynter, 2016). Analysis performed made possible to identify and define five major compositional types of glass, dated from the 4th to the 8th centuries: Levantine I and II, Egypt I and II, and HIMT glass; among these, only the primary production places for Byzantine groups Levantine I and Levantine II have been so far identified (e.g. Freestone et al., 2000; Freestone, 2003; Gorin-Rosen, 2000; Nenna, 2014). Trace element and isotope analysis allowed further recognition of smaller groups of glass of consistent compositions, whose origin remains however unknown (Brems and Degryse, 2014; Schibille et al., 2016; Jackson and Paynter, 2016). Roman colourless glass has been the subject of interest by a

*

Corresponding author. E-mail address: [email protected] (I. Coutinho).

http://dx.doi.org/10.1016/j.jasrep.2017.07.025 Received 26 March 2017; Received in revised form 27 July 2017; Accepted 28 July 2017 2352-409X/ © 2017 Elsevier Ltd. All rights reserved.

considerable number of scholars (e.g. Jackson, 2005; Silvestri et al., 2008; Gallo et al., 2013; Jackson and Paynter, 2016). These studies made possible to understand that this glass was made with extreme care, reflecting the mastery of Roman glassmakers in controlling and understanding the complexity of furnace conditions, selection of raw materials, and the chemistry involved in adding the correct decolourant agents, antimony and manganese, in the right proportions to obtain a bright discoloured glass (e.g. Jackson and Paynter, 2016; Jackson, 2005; Foster and Jackson, 2010). Roman colourless glass made with antimony has been attributed to high status glass, because it gives origin to a perfectly discoloured and brilliant matrix. Glass discoloured with manganese can present a slight tint and was mainly used in the less luxury items (e.g. Jackson, 2005; Silvestri et al., 2008; Foster and Jackson, 2010; Freestone, 2015a). The need of a very accurate selection of raw material, combined with the complexity of the discolouration process, implies that colourless glass could be the result of models concerning the organization of the production that can differ from those applied to the more common naturally coloured glass, thus suggesting a separate analytical approach for this group of glasses (Silvestri et al., 2008; Foster and Jackson, 2010). In this paper, we aim to contribute to the current knowledge on Roman colourless glass dated between the 1st and 3rd centuries from

Journal of Archaeological Science: Reports 15 (2017) 194–202

I. Coutinho et al.

Fig. 1. Map of Croatia with the areas of excavation identified. Examples of the types of objects found among the archaeological excavations (Isings, 1957).

deceased in the afterlife, and they reflected his or her social status, occupation, and age. These burial items were widely used in everyday life. For example, large glass urns (olla), which contained the cremated remains of the dead, were also employed in the storage of vegetables (Fadić, 2006a). Toilet bottles, which contained perfumes and balsams, were also used in cremation, and prismatic jugs served as measuring vessels for liquids and as tableware (Perović, 2013). Although in absence of archaeological evidence, the great amount of glass circulating in the Zadar area suggests the existence of local secondary workshops, suitable for glass working. Also, based on several typological groups of objects (bell-shaped bottles, polygonal bottles — pseudo-mercury, square body jugs, among others), we presume a local production that differs from the imported one. Some of these supposed local objects are made of colourless glass.

one of the most prosperous centres in the Eastern Adriatic coast of Zadar, Croatia, where a local secondary production is presumed. With this exploratory investigation, we intend to identify chemical features that allow us to discuss the models of production of the types of objects assumed to be locally produced. Relating these compositions with known coeval and selected compositions retrieved from literature will give the opportunity to discuss probable commercial routes of glass in this region of the Roman Empire. 1.1. Glass finds in Zadar A significant amount of Roman glass has been uncovered in and around Zadar, Croatia, suggesting that a secondary glass workshop existed in this area (Fadić, 1997). Most of the objects came from excavations at Roman cemeteries in Zadar (Iader), Starigrad (Argyruntum), and Ivoševci (Burnum), as shown in Fig. 1. From the excavations performed in Zadar, more than 3000 complete objects and a comparable number of pieces requiring restoration were recovered. Many glass objects were found in rescue excavations in the Relja district of Zadar (Fadić, 2006b; Perović and Fadić, 2009). About 2000 graves containing considerable quantities of glass objects were uncovered here. These finds prompted the establishment of a specialised museum (Museum of Ancient Glass) for conservation, restoration, display and study of these artefacts. While the excavations in Starigrad were conducted in the early 1900s, those at the Roman cemetery in Zadar are more recent (Gluščević, 2002). At each cemetery, evidence of both inhumation and cremation was found. Both of these burial rituals were practiced during the Roman imperial age, although the former prevailed in the later part of that period. Some inhumations in Dalmatia were accompanied by the construction of graves, while others were not, and cremated remains were found in urns made of ceramics, stone, or glass (Fadić, 2006a). Above the sepulchres stood several types of tombstones (stela, cippus, ara, and epitaph). The long-term use of the Zadar cemetery is confirmed by the discovery of Liburnian sepulchres dating from the 7th century B.C.E. and inhumation tombs from the late 5th and 6th centuries C.E. Most of these graves are dated between the 1st and 4th centuries C.E. The typology of the glass artefacts from the cemetery of Zadar is extremely broad. Among the finds are mosaic cups, game counters, bottles, jugs, plates, dishes, beakers, urns, toilet bottles, droppers, amphorae, decorative pins and other jewellery (Fadić, 1997). The tombs also yielded oil lamps, coins, ceramic artefacts, metal objects, and pins made of animal bone. These items were usually offered to assist the

1.2. Chemical composition of Roman glass Discussing the provenance of Roman glass is highly related with the discussion of the silica sources (Freestone, 2003). This glass was made employing natron as the alkali source, which was collected from evaporite lakes like the ones that existed in Wadi Natrum, in Egypt. This mixture of minerals commonly called natron and that are rich in sodium was then added to a silica source, usually an impure lime-bearing silica sand (Freestone, 2005). Depending on the region where they are collected, silica sources can be richer or poorer in impurities. Some of these impurities such as kaolinite, feldspar, zircon (ZrSiO4), monazite (REE phosphate), rutile (TiO2), and iron oxides, are minerals that can bring various amounts of trace elements very useful on the provenancing of glass, but can also bring glass a natural hue, as is the case with iron (Moretti and Hreglich, 2013; Velde, 2013; Brems and Degryse, 2014; Ceglia et al., 2014). Roman glass dated from the 1st to the 3rd centuries has an alumina variation between 2 and 3 wt%, which translates a very homogeneous composition of glass produced on a massive scale (Freestone, 2005). It was also between the 1st and 3rd centuries that colourless glass knew its apogee, becoming popular until the end of the 3rd century, where it started to decline (Silvestri et al., 2008; Jackson, 2005). Considering the almost perfectly discoloured glass that is found dated to the 1st and 3rd centuries one can infer that roman glassmakers had a strong practical knowledge and understood the influence and importance of several factors that affected the glass colour and discolouring processes. To obtain a colourless glass, in addition to a careful selection of raw materials, MnO or Sb2O5 were added to the batch, to counteract the effect of iron, oxidising Fe2 + to Fe3 +, 195

Journal of Archaeological Science: Reports 15 (2017) 194–202

I. Coutinho et al.

of colourless glass, ranging from the completely uncoloured glass to the very light hues of green and blue. With the intent of investigating the decolouration method (or methods) applied to the shapes considered of local production, glass samples from fragments identified as imported items were also analysed as a control group. This was possible to perform due to the fact that local and imported items share the same chronology (1st to 3rd centuries), were unearthed from the same archaeological contexts and present different levels of glass decolouration. Colourless glass have been related in majority with the production of high quality tableware, which was subjected to changes of taste. This change in taste resulted in the situation where certain shapes might have been produced in short and closed periods of time (Silvestri et al., 2008). Regarding the bell-shaped bottles, it seems that this situation applies, where this shape was produced during a determined period of time in a specific region, according most probably with the taste and needs of the local consumers. In Table 1, the description, hue, and date of the fragments under study are presented. The photographs of the majority of the fragments under study are presented as Supplementary material (Appendix A).

which is practically uncoloured (Brems and Degryse, 2014; Jackson, 2005). When MnO or Sb2O5 are above 0.5 wt%, the intentionality of this addition is generally assumed (Jackson, 2005; Silvestri et al., 2008). The other important factors that must be taken into account when discussing the discolouring effect are the thickness of the glass, the furnace conditions, and the composition of the glass itself (Ceglia et al., 2014). Regarding the glass chemical composition, the raw materials that are introduced in the batch will influence the redox ratio, where anthracite, carbon, pyrite, and sulphides have a reducing effect, and alkali nitrate, sulphates, and iron oxide will result in a oxidising effect. Glasses with higher concentrations of network modifiers like Na and K will most likely be more oxidised (Ceglia et al., 2014). Finally, the furnaces and its technology will also influence the ferrous and ferric ions final ratio in the glass, strongly influencing its colouring or decolouring effects. The two main factors here are the oxygen partial pressure (pO2), and the melting temperature. Concerning the furnace atmosphere, a ventilated furnace promotes the oxidation, while an atmosphere rich in CO/CO2 favours the reduced state. In terms of melting temperatures, for a soda–lime–silica glass the increment of the melting temperature will benefit the formation of iron in its ferrous state (Ceglia et al., 2014). In more recent studies, it has been possible to detect the practice of recycling based on the presence of decolouring agents, and subsequently recognize and separate the glass that was made directly from raw materials (primary glass), from the glass that was made adding recycled cullet (Freestone, 2015b; Schibille et al., 2016).

2.2. Sample preparation In order to avoid erroneous results by analysing and quantifying corrosion layers instead of the uncorroded bulk glass, it was decided to sample all selected objects. Small glass samples of 2–4 mm2 were dry cut from the selected glass fragments with a diamond wire. Samples were embedded in an epoxy resin and polished with SiC sandpapers down to 4000 mesh. This sampling procedure was performed only in broken objects and on individual fragments without possible connections.

2. Methodology 2.1. Samples under study The choice of glass samples to be analysed in this preliminary research was made according to their possible and currently attributed provenance. Among the eighteen fragments being studied here, it is possible to identify shapes that are commonly found in glass finds from the Roman period from several locations, like the lotus-bud beaker (sample A5205 type Isings 31), the amphoriscos (sample A12632 type Isings 15), the globular bottle (sample A15265, type Isings 101), the plate (sample A8353, type Isings 118) and the jug (sample A15523 type Isings 53). However, there are shapes, such as the bell-shaped vessel (Fig. 2), and the pseudo-mercury bottle (type Isings 84), that are very uncommon to find outside Croatian contexts. These shapes appeared in other Mediterranean areas, nevertheless the elevate number of findings in Dalmatian region allowed one to propose that the bell-shaped bottles and the pseudo-mercury bottles could have been a Croatian production (Fadić, 2011). In what concerns the colour of the glass, all samples are

2.3. μ-PIXE Quantitative results were achieved with μ-PIXE ion beam analytical technique using an Oxford Microbeams OM150 type scanning nuclear microprobe setup with the in-vacuum configuration. To allow efficient detection of low energy X-rays such as the ones of Na, all the glass fragments were irradiated in vacuum with a focused 1 MeV proton beam and the produced X-rays collected by a 8 μ m thick Be windowed Si(Li) detector. In order to avoid or detect possible local glass heterogeneities, X-ray imaging (2D elemental distribution) and spectra were obtained from an irradiated sample area of 750 × 750 μ m2. For trace elements quantification (typically elements with atomic number above the one of Fe), a 2 MeV proton beam was used with a 350 μ m thick Mylar foil positioned in front of the Si(Li) X-ray detector. Its use as Xray filter reduces or avoids the strong contribution to the total X-ray spectra of elements such as Si, K and Ca, thus allowing raising the beam current and accumulated beam charge in order to attain higher sensitivity (lower detection limits) for elements such as Cu, As and Sb. The samples were also coated with a thin carbon layer in order to prevent sample beam-charging and consequently X-ray spectra degradation. Operation and basic data manipulation, including elemental distribution mapping, was achieved through the OMDAQ software code (Grime and Dawson, 1995), and quantitative analysis with GUPIX program (Campbell et al., 2010). The results are expressed in weight percentage of oxides and were normalized to 100%. In order to validate the obtained concentration results, a glass reference standard, Corning B, was also analysed. Those values are presented in Table 2. 3. Results and discussion 3.1. Glass chemical composition

Fig. 2. Example of a bell-shaped vessel (inventory number A13027) from the Museum of Ancient Glass, Zadar. This form do not have an attributed Isings type.

As it can be seen in Table 2, all analysed samples are made of soda–lime–silica glass, and consistent with natron-based glass presenting 196

Journal of Archaeological Science: Reports 15 (2017) 194–202

I. Coutinho et al.

Table 1 Inventory number, typology (with the types according to Isings, 1957 ), glass hue, archaeological site, and attributed date to the Roman glass objects under study. Sample

Shape and Isings number

Glass hue

Archaeological site

Date

A4284

Polygonal bottle, form 84 (Isings, 1957) (also designated as pseudo-mercury type) Lotus-bud beaker, form 31 (Isings, 1957) Polygonal bottle, form 84 (Isings, 1957) (also designated as pseudo-mercury type) Polygonal bottle, form 84 (Isings, 1957) (also designated as pseudo-mercury type) Bell-shaped bottle Bell-shaped bottle Bell-shaped bottle Plate, form 5 (Isings, 1957) Polygonal bottle, form 84 (Isings, 1957) (also designated as pseudo-mercury type) Amphoriscos, form 15 (Isings, 1957) Polygonal bottle, form 84 (Isings, 1957) (also designated as pseudo-mercury type) Bell-shaped bottle Bell-shaped bottle Bell-shaped bottle Bell-shaped bottle Bell-shaped bottle Globular bottle, form 101 (Isings, 1957) Jug, form 53 (Isings, 1957)

Colourless

Starigrad (Argyruntum)

2nd–3rd century

Very light blue

Ivoševci (Burnum): Roman military camp

1st century

Very light blue

Starigrad (Argyruntum)

2nd–3rd century

Colourless Very light green Very light blue Very light blue Colourless

Zadar: Zadar: Zadar: Zadar: Zadar:

2nd–3rd century 2nd–3rd century 2nd–3rd century 2nd–3rd century 1st–2nd century

Colourless Colourless

Zadar: Zrinsko Frankopanska street Zadar: unknown site (probably Nin Aenona)

2nd–3rd century –

Colourless Very light blue Very light green Very light yellow Very light green Colourless Colourless Light yellow

Zadar: Zadar: Zadar: Zadar: Zadar: Zadar: Zadar: Zadar:

– 2nd–3rd century 2nd–3rd century – 2nd–3rd century 2nd–3rd century 1st–2nd century 1st–2nd century

A5205 A5459 A7784 A7795 A7797 A7798 A8353 A8758 A12632 A14318 A14432 A15140 A15253 A15258(9) A15261 A15265 A15523

Shopping Shopping Shopping Shopping Shopping

Mall Mall Mall Mall Mall

Relja Relja Relja Relja Relja

unknown site (probably Nin Aenona) Relja Garden Shopping Mall Relja Shopping Mall Relja Shopping Mall Relja Shopping Mall Relja Shopping Mall Relja Shopping Mall Relja

antimony oxide content < 0.02 wt% (see Table 2). Samples from this group are really colourless glass. From the 11 samples belonging to Group 2, 10 samples have a MnO content above 1.25 wt% and only two of them are really colourless. The first question that arises is if the presence of the decolourizing agents is due to intentional addition, thus the objects are the result of the transformation of a primary glass source, or is the consequence of recycling activities. Hypothesis on the usage of recycled cullet will be discussed below. The previous defined groups considering the alkali and alkali-earth contents of the glass will now be analysed and described in more detail.

low values of MgO, P2O5 and SO3. The contents of SiO2 range between 68 and 73 wt%, Na2O vary between 12.6 and 19.6 wt%, CaO between 4.6 and 8.0 wt%, and Al2O3 range between 1.7 and 3.0 wt%. Concerning the contents of alumina, calcium oxide, and soda (see Fig. 3), the samples appear divided into 2 groups: Group 1, composed by seven samples, is characterised by low CaO and Al2O3 contents, and high Na2O content, and Group 2, which is composed by eleven samples and is characterised by high CaO and Al2O3 contents, and lower Na2O content. Both these compositional groups have already been identified in other studies and can be considered the main types of glass circulating in the Roman period dated to the 1st and 3rd centuries (e.g., Silvestri et al., 2008; Schibille et al., 2016; Jackson, 2005). These groups were also identified in a more recent study by Jackson and Paynter (2016), and are presented in Appendix 2 of this referred paper identified as Antimony (Sb) (colourless) and as Mixed antimony and manganese (Sb–Mn) (varying from blue-green to colourless), which corresponds to Group 1 and Group 2 of this study, respectively. The glass studied by Silvestri et al. (2008) comes from a ship, Iulia Felix, that wrecked in the North of Italy, off the coast of Grado, and the finds are dated to the first half of the 3rd century. The analysed glasses split into two main compositional groups with characteristics very close to the ones reported in the current study. The glass finds reported by Schibille et al. (2016) came from Carthage and are dated between the 3rd and 6th centuries. In the glass identified as being from the Roman period, again two groups with chemical characteristics close to the groups identified in the present study where assigned, where it was also determined that one group was composed with glass discoloured by antimony and the other group was discoloured by means of a mixture of antimony and manganese. Finally, in the study of Jackson (2005), the glass from three different sites in the UK dated to the 1st and 4th centuries was analysed. The resulting data was divided into two compositional groups, where Group 1 is composed by colourless glass discoloured with antimony (composed in majority by the probable imported objects, previously designated as a control group), and Group 2, with nearly colourless glass, have a mixture of manganese and antimony in its composition (mainly composed by the objects of probable local production). The groups identified in the current study find a direct comparison with the groups reported by Jackson (2005). Concerning the discolouration of the samples under study, only six fragments, belonging to Group 1, have an antimony oxide content above the μ-PIXE detection limit and the remaining samples have an

3.1.1. Group 1: low CaO and Al2O3, high Na2O Group 1, probably discoloured by Sb2O5, is composed by six really colourless samples (four polygonal bottles, a globular bottle, and a plate), and a very light blue lotus-bud beaker (sample A5205). According to Brems and Degryse (2014), values of MnO above 0.1 wt% can be considered the result of a deliberate addition or the result of the introduction of recycled cullet into the batch. Having in mind that the MnO contents in the samples from this group vary between 0.01 and 0.40 wt%, one can propose that some of these glass fragments were discoloured by means of intentional addition of antimony (Sb2O5 varying between 0.15 wt% and 0.89 wt%, and one sample has antimony below < 0.02 wt%) or might be the result from the transformation of recycled glass. To better verify the premise of recycling one can look at the values of elements such as Co, Ni, Zn, As, and Pb. Concerning Co, Ni, Zn, and As oxides, in majority they all present values in such low amount that are below the detection limits of the μ-PIXE or in the order of dozens of μ g/g, which according to Brems and Degryse (2014) may indicate that they came with the raw materials that were used to melt the primary glass. However, looking to the amounts of PbO, in four samples of this group this oxide appears with an element concentration between 100 and 550 μ g/g. Brems and Degryse (2014) point the interval between 100 and 1000 μ g/g for elements such as Pb as an indication of concentrations related to limited recycling of carefully selected cullet. It is also pointed out that these concentrations are just indicative and more investigation is needed to better defined boundaries between elements' concentrations that come from the raw materials employed in the primary glass and from the recycling of cullet (Brems and Degryse, 2014). Having in mind what was discussed above, one can say that the objects belonging to this group can be considered luxury items, made 197

198

(+/−) Measured Certified* Relative error (%)

18.6 18.4 19.6 16.7 18.0 17.9 16.9 18.0 1.0 13.5 13.9 13.9 15.6 14.6 14.2 14.1 12.6 14.8 13.9 12.9 14.0 0.8 17.0 17.0 0

Na2O

0.2 0.3 0.4 0.3 0.3 0.4 0.4 0.3 0.1 0.3 0.4 0.5 0.5 0.4 0.4 0.4 0.5 0.5 0.4 0.5 0.4 0.1 0.9 1.03 13

MgO 1.70 1.77 1.94 1.97 1.83 2.13 2.16 1.9 0.2 2.35 2.60 2.67 2.66 2.69 2.72 2.59 2.83 2.22 2.60 2.92 2.6 0.2 4.2 4.36 4

Al2O3

* Certified values in Brill (1999) and Wagner et al. (2012).

Average Standard Dev. CMoG B

(+/−) A15140 A15523 A5459 A7795 A7797 A7798 A15261 A15258 A12632 A15253 A14432

A8758 A15265 A8353 A5205 A7784 A14318 A4284

Group 1

Average Standard Dev. Group 2

Sample

Group 71.8 71.4 69.5 71.8 70.7 70.4 71.0 70.9 0.8 73.3 70.7 70.3 68.6 70.5 70.4 71.0 70.6 70.0 70.7 70.9 70.6 1.1 63.7 62.27 2

SiO2

0.13 0.10 < 0.07 0.11 < 0.06 0.12 < 0.05 0.13 0.16 0.10 < 0.05 0.12 0.02 0.50 0.82 39

< 0.06 0.03 < 0.05 0.12 < 0.03 < 0.05 < 0.06

P2O5 0.29 0.30 0.31 0.13 0.38 0.29 0.26 0.28 0.08 0.11 0.23 0.17 0.33 0.22 0.22 0.12 0.14 0.12 0.23 0.14 0.18 0.07 0.18

SO3 1.26 1.27 1.12 1.11 1.17 1.06 1.12 1.16 0.08 1.09 0.89 1.08 0.71 0.87 0.86 1.06 0.94 0.94 0.89 0.98 0.94 0.11 0.17

Cl 0.32 0.38 0.45 0.48 0.40 0.48 0.51 0.43 0.07 0.47 0.62 0.54 0.69 0.65 0.64 0.49 0.65 0.70 0.62 0.47 0.59 0.09 1.02 1.00 2

K2O

Table 2 Chemical composition of the Roman glass samples determined by μ-PIXE, in weight percent of oxides and in μg/g.

4.65 4.90 5.04 5.44 5.57 5.62 5.79 5.29 0.43 7.31 7.79 7.58 7.48 7.45 7.52 7.33 7.89 6.96 7.79 7.99 7.55 0.30 8.40 8.56 2

CaO 0.06 0.06 0.09 0.05 0.06 0.07 0.08 0.07 0.01 0.06 0.05 0.07 0.06 0.06 0.06 0.05 0.07 0.06 0.05 0.05 0.06 0.01 0.11 0.089 24

TiO2 0.01 0.01 0.17 0.78 0.02 0.29 0.40 0.24 0.28 0.42 1.25 1.65 1.76 1.25 1.30 1.48 1.76 2.19 1.25 1.67 1.45 0.45 0.21 0.25 16

MnO 0.26 0.31 0.38 0.28 0.40 0.42 0.46 0.36 0.08 0.29 0.34 0.49 0.45 0.38 0.38 0.40 0.65 0.42 0.34 0.37 0.41 0.10 0.29 0.34 15

Fe2O3 20 μg/g 10 μg/g 20 μg/g 30 μg/g 30 μg/g 30 μg/g 30 μg/g 25 μg/g 8 μg/g 20 μg/g 20 μg/g 20 μg/g 30 μg/g 20 μg/g 20 μg/g 20 μg/g 30 μg/g 50 μg/g 20 μg/g 30 μg/g 25 μg/g 9 μg/g 0.18 0.19 5

5 μg/g < 2 μg/g 13 μg/g 22 μg/g 28 μg/g 25 μg/g 30 μg/g 20 μg/g 9 μg/g 5 μg/g 18 μg/g < 4 μg/g 18 μg/g 17 μg/g 20 μg/g 16 μg/g 14 μg/g 112 μg/g 11 μg/g < 4 μg/g

2.59 2.66 3

ZnO

CuO

0.01

< 10 μg/g < 10 μg/g < 10 μg/g < 10 μg/g < 10 μg/g 20 μg/g < 10 μg/g < 10 μg/g < 10 μg/g < 10 μg/g < 10 μg/g

20 μg/g 50 μg/g < 30 μg/g < 10 μg/g 20 μg/g 40 μg/g 20 μg/g

As2O5

0.04 0.05 0.05 0.04 0.05 0.05 0.05 0.05 0.004 0.05 0.06 0.07 0.07 0.07 0.07 0.07 0.08 0.08 0.07 0.08 0.07 0.01 0.02 0.019 5

SrO

0.46 0.46 0

0.52 0.72 0.67 < 0.02 0.89 0.50 0.57 0.64 0.15 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02

Sb2O5

0.01 0.01 0.02 0.02 0.01 0.02 0.02 0.02 0.01 0.02 0.03 0.05 0.06 0.04 0.04 0.05 0.05 0.04 0.04 0.04 0.04 0.01 0.06 0.12 50

BaO

0.51 0.61 16

40 μg/g 90 μg/g 550 μg/g < 10 μg/g 100 μg/g 120 μg/g 160 μg/g 175 μg/g 180 μg/g 20 μg/g < 10 μg/g < 10 μg/g < 10 μg/g < 10 μg/g < 10 μg/g < 10 μg/g < 10 μg/g 120 μg/g < 10 μg/g < 10 μg/g

PbO

I. Coutinho et al.

Journal of Archaeological Science: Reports 15 (2017) 194–202

Journal of Archaeological Science: Reports 15 (2017) 194–202

I. Coutinho et al.

Fig. 3. Binary plots of (a) alumina versus calcium oxide, and (b) calcium oxide versus sodium oxide, both in weight percent of oxides and measured by μ-PIXE.

(2005) and Silvestri et al. (2008). It is interesting to note that all analysed bell-shaped bottles belong to this compositional group. From this, one can infer several situations: bell-shaped bottles were made from this specific glass type (the high lime and alumina, low soda was a much cheaper glass, its utilisation being consistent with the making of utilitarian vessels); these vessels were made in a specific workshop, during a limited period of time when only this glass type was being received in Zadar; or only this type of glass was brought to Zadar and the low lime and alumina, high soda glass vessels (Group 1) were imported items. This last hypothesis conflicts with the idea that the polygonal bottles are also considered a locally produced shape and the ones analysed in this study proved to belong to Group 1. These hypotheses will be developed below.

from high quality glass discoloured by intentional addition of Sb. This group was possibly made from a primary glass source melted together with a carefully selected amount of cullet. This explains the pure and homogeneous composition presented by this group, and also the very well discoloured glass. Recycling issues will be addressed later. 3.1.2. Group 2: high CaO, Al2O3, low Na2O This group is composed by all the bell-shaped vessels, one polygonal vessel, one jug, and one amphoriscos. According to the archaeological contexts (see Table 1), these objects can be dated mainly to the 2nd and 3rd centuries. Excluding one bell-shaped bottle (A15261), and the amphoriscos (A12632), all show a light yellow, green or blue tint. Concerning the chemical composition of these fragments, in their majority they have MnO contents above 1 wt%, and Sb2O5 below the detection limit of 0.02 wt%. According to what is known so far about Roman glass from this period, the deliberate addition of manganese instead of antimony to discolour the batch, although known before, became prevalent during the 4th century (Maltoni et al., 2016; Silvestri et al., 2008; Foster and Jackson, 2010). Comparing the composition of this group mainly discoloured with MnO with the previous one mainly discoloured by Sb2O5, the current group is richer in alumina which implies the use of a less pure source of silica. This situation was already noted by Gallo et al. (2013) in their study of Roman glasses dated to the 1st and 2nd centuries, from the North Adriatic Italy. From these results, it is suggested that the change in the employed discolouring agent is associated with a change in the primary glass supply. The same results were also found by Jackson

3.2. Primary glass sources The composition of the samples under study were compared with coeval glass compositions found in the literature (archaeological glass from the Museum of Adria (Gallo et al., 2013), glass recovered from the shipwreck Iulia Felix (Silvestri et al., 2008), glass from Serbia (Stojanović et al., 2015), glass from Pergamon (Rehren et al., 2015), and the glass chunk from ’En Ya’al (Freestone, 2015a)). The compositions from literature were selected according to their chronological period, where only compositions from fragments dated between the 1st and 4th centuries were used, and also according to the glass colour, where only the compositions reported for colourless glass fragments were selected. Fig. 4. Binary plot of weight ratios of Al2O3/SiO2 vs. the weight ratio of TiO2/Al2O3. The dashed line serves to divide the proposed primary glass production centres between Egyptian and Levantine origins (Schibille et al., 2016). Representative literature values for coeval Roman glass from other locations are also represented in the plot (Gallo et al., 2013; Silvestri et al., 2008; Stojanović et al., 2015; Rehren et al., 2015; Freestone, 2015a).

199

Journal of Archaeological Science: Reports 15 (2017) 194–202

I. Coutinho et al.

with a mean equal to DL/2. Having this in mind, the calculated value of the DL/2 was used in Fig. 5 plots (Silvestri et al., 2008). To the data of the glasses found in Croatia, the results from the analysis performed to the Iulia Felix shipwreck colourless glasses (dated to the first half of the 3rd century) were added as the representative of Roman glass compositions from this period (Schibille et al., 2016; Silvestri et al., 2008; Freestone, 2015a). Analysing Fig. 5, one can assume that the two endmember types of glasses from Iulia Felix study (primary glass discoloured with Mn and primary glass discoloured with Sb) are the ones made directly from the raw materials with no addition of recycled cullet — primary glass sources. All samples that appear in the middle are the result of glass made with the mixture of recycled cullet. With this in mind, one can propose that in the samples from Croatia, only three fragments (A4284, A14318, and A8353) were made with recycled cullet, where the resulting glass was discoloured by the simultaneous presence of antimony and manganese. These three fragments all belong to Group 1 and have the higher Pb contents of all measured samples (see Table 2). Still in Group 1, two polygonal bottles and a globular bottle are the three fragments compatible with the Iulia Felix endmember glasses identified as being discoloured with antimony and made directly from the raw materials. It is yet curious to identify one fragment from Group 1 (A5205) that is consistent with glass made directly from the raw materials and discoloured with Mn. All samples belonging to Group 2 are consistent with the Iulia Felix end-member glasses identified as being discoloured with manganese and melted directly from the raw materials. Considering Fig. 5a, and taking into consideration that the position of the samples between the two end-members reflects the proportion of the two colourless glass types in the glass mixture, two of these samples of recycled glass (A4284 and A14318, both polygonal bottles) are more or less placed in the middle, and for one recycled glass sample (A8353, a plate) it is observed that it is closer to the end-member discoloured with antimony. Looking at Fig. 5b, when the glass shows a major displacement to the right (higher amounts of iron), it is proposed that this is due to remelting contaminations, and the higher iron contents are probably due to the incorporation of iron scales from the pontil and blow pipe that have fallen into the batch (Schibille et al., 2016; Jackson and Paynter, 2016). In Fig. 5b, the behaviour of iron was inspected, and it is noticed that small or inexistent deviations are observed comparing with the glass from the Iulia Felix end-members, pointing again for glass melted directly from the raw materials. In the case of the recycled glass, it shows that this glass was being recycled for the first time and was also the result of carefully selected cullet. The three fragments identified as being made from recycled glass show a lower iron content comparing

In Fig. 4, the ratios of TiO2/Al2O3 versus Al2O3/SiO2 are plotted. In recent papers (e.g., Schibille et al., 2016), this plot is being used to compare data instead of the more common plot of Al2O3 versus CaO, because it allows for the comparison of the mineralogy of the glassmaking sands. With this combination of oxides, it is possible to create a chart where the mineralogical characteristics of the glass are represented, namely the quartz content (SiO2), the feldspar content (Al2O3), and the heavy minerals content (TiO2) (Schibille et al., 2016). Analysing Fig. 4, it is observed that the glass from Croatia perfectly fits the coeval samples analysed from different places. With regard to Group 1, all samples can be compared with coeval glass sets discoloured with antimony. Samples from Group 2 are comparable with literature values for glass discoloured with manganese. Glass from Group 1 is characterised by low levels of trace elements like Sr and Ba (see Table 2). Consulting Fig. 4, it is also perceptible a slightly higher content of titania in relation to samples from Group 2. Considering all the compositional characteristics of this group (high content of soda and low contents of lime), it is possible to propose that the source of raw glass for Group 1 was in the Egypt area (Nenna et al., 2000; Nenna, 2014; Freestone, 2003; Schibille et al., 2016; Jackson, 2005). Concerning Group 2, the analysed samples within this set were in their majority dated between the 2nd and 3rd centuries. Schibille et al. (2016) propose that with the change of the silica sources, the alumina content in the glass increases with chronological time. With this in mind and observing Fig. 4, its is proposed that the samples within this group were produced later in the 3rd century. Glass from this group have higher levels of Sr and Ba (see Table 2), which can be related to shell-bearing sands. Combining all the information collected from the chemical composition it is possible to propose that the primary glass that compose this group had its origin in the Syria–Palestine region (e.g., Schibille et al., 2016; Freestone, 2015a; Jackson, 2005).

3.3. What about recycled glass? In order to study the decolouration processes of the samples under study, the approach presented by Freestone (2015b) and Schibille et al. (2016) was adopted. In Fig. 5a, one can see a binary chart with alumina versus the ratio of manganese to the sum of manganese plus antimony oxides, which gives the indication of the relative proportions of the two colourless glass types in the glass mixture (Freestone, 2015b). Whenever it was necessary to use oxides such as antimony oxide, whose concentration values, if present in the glass, are below the μ -PIXE detection limit (DL), it is reasonable to assume that its concentration is a distribution between zero and the DL, with an equal probability, and

Fig. 5. Binary plots of (a) alumina vs. the fraction of manganese oxide divided by the total concentration of discolourants, and (b) iron oxide vs. the fraction of manganese oxide divided by the total concentration of discolourants (Freestone, 2015b; Schibille et al., 2016), measured by μ-PIXE. Values from the Iulia Felix glass were also plotted as the representative of Roman glass compositions from the 2nd and 3rd centuries (Silvestri et al., 2008).

200

Journal of Archaeological Science: Reports 15 (2017) 194–202

I. Coutinho et al.

the majority of compositional characteristics of both glass groups, it is proposed that Group 1 was made with glass from Egypt, and Group 2 can be assign to a Levantine region. Having in mind that the samples under study are of colourless glass, it was a priority to understand if it was discoloured by antimony, by manganese, or by the presence of both due to cullet recycling. Relying on the contents of Pb one can propose the presence of recycled glass in some samples from Group 1. Recycling activities were evidenced when resorting to plotting the data in binary chart with alumina versus the ratio of manganese to the sum of manganese plus antimony oxides. This plot gave the indication of the relative proportions of the two colourless glass types (Roman glass decoloured with Mn and Roman glass decoloured with Sb) in the glass mixture. This chart revealed to be very useful, allowing to propose that four fragments from Group 1 were made directly from primary glass sources (three fragments from a primary glass source decoloured with Sb, and one fragment from a primary glass source decoloured with Mn), and three fragment are the result of glass recycling activities. Regarding the bell-shaped vessels, these were made employing only primary glass probably from the Levantine region, which represents a more cheaper glass comparing with the Sb decoloured one. From this study, one can propose that this shape, considered of local production, was most probably a common and utilitarian vessel, that was still important enough to be made with colourless glass from a primary glass source showing no signs of recycling. One fragment from Group 1, supposedly imported from Egypt and showing no signs of recycling, was identified as being decolourized with Mn. One fragment is not enough to propose a possible change in the production technology of glass decolouring but it shows the need for further investigation. Concerning the alleged local production of the two appointed types of bottles, the actual possibility of detecting a correlation among typology, composition, and the production of single workshops in a limited time span is currently debated (Freestone, 2009; Jackson and Foster, 2015). The bell-shaped bottles seem to have consistent compositions, but further analysis are needed in order to verify if they can be considered as a group of objects made in the same workshop, or even in a group of workshops using the same base raw-material. On the other side, the polygonal bottles don’t appear as an equally homogeneous group. Their compositions fall mostly in Group 1 (two were identified as recycled glass and two were made directly from a primary glass source), but one of them is comprised in Group 2. Despite the fact that for the past few years the number and quality of the studies concerning Roman colourless glass have increased significantly bringing an enormous amount of new information, there are still interesting new facts to be discovered about the production, used trading routes, recycling activities, and glass decolouring technologies.

with the Iulia Felix recycled glass, implying that the glass found in Croatia suffered a smaller number of re-melting activities. Having in attention that all glass fragments from Group 1 under study are perfectly discoloured (including the sample with Mn and with Sb below the detection limit), one can assume that the choice of cullet was made extremely carefully, in order not to contaminate the uncoloured glass with coloured one. This fact was already verified by others (Jackson and Paynter, 2016). Glass fragments from Group 2 are also attempts to have discoloured glass but present more natural hues than the glass from Group 1. Considering now the hypotheses proposed above for the bell-shaped bottles all belonging to the same compositional group (Group 2 — high CaO, Al2O3, low Na2O), from the analysis of Fig. 5 it was determined that they were made adding manganese to the batch. In the compositions reported by Tantrakarn et al. (2009) from glass fragments also recovered from Zadar, it is observed that from a total of 48 analysed bell-shaped vessels, they have identified 40 fragments discoloured with manganese, which is consistent with the discolouring technology found in the bell-shaped bottles analysed in the present study. This comes to reinforce the idea that the bell-shaped vessels were a more utilitarian and common shape, made with a cheaper glass, when the glass discoloured with antimony was no longer used or saved for more luxury shapes. However, one fragment – A5205 – presents the characteristics of glass from an Egyptian origin in terms of alkali, alumina, and titania contents, but was discoloured with Mn instead of Sb and shows no traces of recycling. Can this indicate a change in the producing technology of primary glass from Egypt? One sample is not enough to achieve any conclusions and the study of more fragments from this chronology is needed. This new data shows that for the bell-shaped vessels (all in Group 2) considered probable local productions, primary glass from Levantine regions and discoloured with Mn was the one being imported by Croatian secondary workshops. The antimony discoloured glass, probably imported from Egypt, was identified in the imported items and in the majority of polygonal bottles, also considered of local production. An hypothesis can be formulated: glass from both primary production locations (Levantine region and Egypt) was imported and the Mn discoloured glass was used for more common and utilitarian shapes. This glass shows yet no signs of recycling probably because the fragments under study and belonging to Group 2 are dated to the beginning of usage of this Mn discoloured glass. Regarding the Sb discoloured glass, already some recycling activity is identified, where half of the fragments belonging to Group 1 were considered the result of recycled glass with the simultaneous presence of Mn and Sb. 4. Conclusions

Acknowledgments Eighteen samples of colourless glass were analysed and chemically characterised by μ -PIXE. This analytical technique allowed for the quantification of major, minor, and some trace elements of the glass. Glass composition was divided into two major groups based on the alkali and alkali-earth contents. Group 1 comprises the samples with high contents of soda and low contents of alumina and lime. Group 2 is composed by the samples with a composition low in soda and high in lime and alumina. Moreover, it is suggested that Group 1 was decoloured by Sb, and Group 2 by Mn. It was possible to assign certain objects' shapes to the defined compositional groups, where polygonal bottles are the mostly present in Group 1, and bell-shaped bottles are exclusive of Group 2. The objects considered of imported origin and designated as a control group are mainly present in Group 1 (A15265, A8353 and A5205), and only one object (A15523) falls into Group 2. Within each group, comparing the composition of these samples with the composition of the objects identified as probable products of local origin, no significant differences are observed. Regarding the origin of the primary glass sources, after considering

The authors would like to acknowledge the support of the Portuguese Science and Technology Foundation (FCT-MCTES), under the projects UID/ EAT00729/2013 and UID/Multi/04349/2013. The authors also thank Professor Ian Freestone for his advise and for helping to clarify some points, thus improving the quality of the article. References Brems, D.D., Degryse, P.P., 2014. Trace element analysis in provenancing Roman glassmaking. Archaeometry 56 (SUPPLS1), 116–136. Brill, R.H.R.H., 1999. Chemical Analyses of Early Glasses, v.2, The Tables. The Corning Museum of Glass, Corning, New York. Campbell, J.L.J.L., Boyd, N.I.N.I., Grassi, N.N., Bonnick, P.P., Maxwell, J.A.J.A., 2010. The Guelph PIXE software package IV. Nucl. Instrum. Methods B 268, 3356–3363. Ceglia, A.A., Nuyts, G.G., Cagno, S.S., Meulebroeck, W.W., Baert, K.K., Cosyns, P.P., Nys, K.K., Thienpont, H.H., Janssens, K.K., Terryn, H.H., 2014. A XANES study of chromophores: the case of black glass. Anal. Methods 6 (8), 2662. http://xlink.rsc.org/? DOI=c3ay42029a. Fadić, I.I., 1997. Trasparenze imperiali: Vetri romani dalla Croazia. Skira, Milan.

201

Journal of Archaeological Science: Reports 15 (2017) 194–202

I. Coutinho et al.

(4), 763–780. Jackson, C.M.C.M., Paynter, S.S., 2016. A great big melting pot: exploring patterns of glass supply, consumption and recycling in Roman Coppergate, York. Archaeometry 58 (1), 68–95. Maltoni, S.S., Silvestri, A.A., Marcante, A.A., Molin, G.G., 2016. The transition from Roman to Late Antique glass: new insights from the Domus of Tito Macro in Aquileia (Italy). J. Archaeol. Sci. 73, 1–16. http://dx.doi.org/10.1016/j.jas.2016.07.002. Moretti, C.C., Hreglich, S.S., 2013. Raw materials, recipes and procedures used for glass making. In: Janssens, K.K. (Ed.), Modern Methods for Analysing Archaeological and Historical Glass. vol. I Wiley, Chichester. Nenna, M.D.M.D., 2014. Egyptian glass abroad. HIMT glass and its markets. In: Keller, D.D., Price, J.J., Jackson, C.C. (Eds.), Neighbours and Successors of Rome: Traditions of Glass Production and use in Europe and the Middle East in the Later First Millennium AD. Oxbow Books, Oxford & Philadelphia, pp. 177–193 Ch. 18. Nenna, M.-D.M.-D., Picon, M.M., Vichy, M.M., 2000. Ateliers primaires et secondaires en Egypte à l’époque gréco-romaine. La Route du verre. Ateliers primaires et secondaires du second millénaire av. J.-C. au Moyen Âge. pp. 97–112. http://cat.inist.fr/? aModele=afficheN&cpsidt=1158844. Perović, Š.Š., 2013. Bottiglie a sezione quadrata come strumenti di misurazione. In: Per un corpus dei bolli su vetro in Italia. Atti delle XIV Giornate Nazionali di Studio sul vetro del Comitato Italiano AIHV (Trento, 16-17 ottobre 2010), Cremona, pp. 123–131. Perović, Š.Š., Fadić, I.I., 2009. Zaštitno arheološko istraživanje dijela antičke nekropole Zadra na Zrinsko- Frankopanskoj ulici. Diadora 23 (Zadar), 23. Rehren, T.T., Connolly, P.P., Schibille, N.N., Schwarzer, H.H., 2015. Changes in glass consumption in Pergamon (Turkey) from Hellenistic to late Byzantine and Islamic times. J. Archaeol. Sci. 55, 266–279. http://dx.doi.org/10.1016/j.jas.2014.12.025. Rehren, T.T., Freestone, I.I., 2015. Ancient glass: from kaleidoscope to crystal ball. J. Archaeol. Sci. 56, 233–241. http://dx.doi.org/10.1016/j.jas.2015.02.021. Schibille, N.N., Sterrett-Krause, A.A., Freestone, I.I., 2016. Glass groups, glass supply and recycling in late Roman Carthage. Archaeol. Anthropol. Sci. 1–19. http://link. springer.com/10.1007/s12520-016-0316-1. Silvestri, A.A., Molin, G.G., Salviulo, G.G., 2008. The colourless glass of Iulia Felix. J. Archaeol. Sci. 35 (6), 331–341. Stojanović, M.M.M.M., Šmit, ž.ž., Glumac, M.M., Mutić, J.J., 2015. PIXE-PIGE investigation of Roman imperial vessels and window glass from Mt. Kosmaj, Serbia (Moesia Superior). J. Archaeol. Sci. Rep. 1 (1), 53–63. Tantrakarn, K.K., Kato, N.N., Hokura, A.A., Nakai, I.I., Fujii, Y.Y., Gluščević, S.S., 2009. Archaeological analysis of Roman glass excavated from Zadar, Croatia, by a newly developed portable XRF spectrometer for glass. X-Ray Spectrom. 38 (2), 121–127. Velde, B.B., 2013. Glass Compositions over Several Millennia in the Western World. In: Janssens, K.K. (Ed.), Modern Methods for Analysing Archaeological and Historical Glass. vol. I. Wiley, Chichester, pp. 67–78. Wagner, B.B., Nowak, A.A., Bulska, E.E., Hametner, K.K., Günther, D.D., 2012. Critical assessment of the elemental composition of Corning archeological reference glasses by LA-ICP-MS. Anal. Bioanal. Chem. 402 (4), 1667–1677.

Fadić, I.I., 2006a. Argyruntum u odsjaju antičkog stakla. Arheoloski Muzej, Zadar. Fadić, I.I., 2006b. Lokalitet: Zadar-Relja (Relja vrt). Hrvatski Arheološki Godišnjak (Zagreb) 3, 350–351. Fadić, I.I., 2011. Pseudomerkur bočice s područja Liburnije — proizvodi lokalne staklarske radionice (Pseudo Mercury bottles — products of local glass workshop), Zbornik I. međunarodnog arheološkog kolokvija. In: Međunarodnog arheološkog kolokvija Rimske keramičarske i staklarske radionice. Proizvodnja i trgovina jadranskim prostorom, Crikvenica / Proceedings of the 1st Colloquium, Roman Ceramic and Glass Manufactures; Production and Trade in the Adriatic region, Crikvenica, pp. 333–354. Foster, H.E.H.E., Jackson, C.M.C.M., 2010. The composition of late Romano-British colourless vessel glass: glass production and consumption. J. Archaeol. Sci. 37 (12), 3068–3080. http://dx.doi.org/10.1016/j.jas.2010.07.007. Freestone, I.I., 2003. Primary glass sources in the mid-first millennium AD. In: Annales of the 15th Congress de l’Association Internationale pour l’Histoire du Verre. AIHV Association Internationale pour l’Histoire du Verre International Association for the History of Glass, Nottingham, pp. 111–115. Freestone, I.I., 2009. The batch: its recognition and significance. In: Janssens, K.K., Degryse, P.P., Cosyns, P.P., Caen, J.J., Van’t dack, L.L. (Eds.), Annales of the 17th Congress de l’Association Internationale pour l’Histoire du Verre. University Press Antwerp, pp. 130–135. Freestone, I.C.I.C., 2005. The provenance of ancient glass through compositional analysis. Mater. Res. Soc. Symp. Proc. 852, 1–14. http://discovery.ucl.ac.uk/1329052/. Freestone, I.C.I.C., 2015a. The Composition of a Glass Chunk from ’En Ya’al (Nahal Refa’im). Hadashot Arkeologiyot-Excavations and Surveys in Israel. 127. pp. 1–3. Freestone, I.C.I.C., 2015b. The recycling and reuse of Roman glass: analytical approaches. J. Glass Stud. 57, 29–40. Freestone, I.C.I.C., Gorin-Rosen, Y.Y., Hughes, M.J.M.J., 2000. Primary glass from Israel and the production of glass in late Antiquity and the early Islamic period. In: Nenna, M.D.M.D. (Ed.), La Route du verre. Maison de l’Orient Méditerraneéan - Jean Pouilloux, Lyon, pp. 65–83. Gallo, F.F., Silvestri, A.A., Molin, G.G., 2013. Glass from the Archaeological Museum of Adria (North-East Italy): new insights into Early Roman production technologies. J. Archaeol. Sci. 40 (6), 2589–2605. http://dx.doi.org/10.1016/j.jas.2013.01.017. Gluščević, SmiljanSmiljan, 2002. Rasprostiranje zadarskih nekropola. Hist. Antiqua (Pula) 8, 381–384. Gorin-Rosen, Y.Y., 2000. The ancient glass industry in Israel: summary of new finds and new discoveries. In: Nenna, M.D.M.D. (Ed.), La Route du verre. Maison de l’Orient Méditerraneéan - Jean Pouilloux, Lyon, pp. 49–64. Grime, G.W.G.W., Dawson, M.M., 1995. Recent developments in data acquisition and processing on the Oxford scanning proton microprobe. Nucl. Instrum. Methods B 104, 107–113. Isings, C.C., 1957. Roman Glass from Dated Finds. J.B. Wolters, Groningen. Jackson, C.C., Foster, H.H., 2015. Provenance studies and Roman glass. In: Bayley, J.J., Freestone, I.I., Jackson, C.C. (Eds.), Glass of the Roman World. Oxbow Books and The Association for the History of Glass, Oxford, pp. 44–56. Jackson, C.M.C.M., 2005. Making colourless glass in the Roman period. Archaeometry 47

202