Plant Ash Glass from First Century CE Dibba, U.A.E

Vrije Universiteit Brussel

Plant ash glass from first century CE Dibba, U.A.E Van Ham-Meert, Alicia; Claeys, Philippe; Jasim, Sabah; Overlaet, Bruno; Yousif, Eisa; Degryse, Patrick Published in: Archaeological and Anthropological Sciences

DOI: 10.1007/s12520-018-0611-0

Publication date: 2019

Link to publication

Citation for published version (APA): Van Ham-Meert, A., Claeys, P., Jasim, S., Overlaet, B., Yousif, E., & Degryse, P. (2019). Plant ash glass from first century CE Dibba, U.A.E. Archaeological and Anthropological Sciences, 11(4), 1431-1441. https://doi.org/10.1007/s12520-018-0611-0

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Download date: 04. Oct. 2021 Archaeological and Anthropological Sciences https://doi.org/10.1007/s12520-018-0611-0

ORIGINAL PAPER

Plant ash glass from first century CE Dibba, U.A.E

Alicia Van Ham-Meert 1,2 & Philippe Claeys2 & Sabah Jasim3 & Bruno Overlaet4 & Eisa Yousif3 & Patrick Degryse1,5

Received: 13 November 2017 /Accepted: 2 February 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018

Abstract This paper presents the chemical and isotopic analyses of glass from the first century CE excavated in Dibba (United Arab Emirates). The elemental composition was determined using inductively coupled plasma-optical emission spectrometry (ICP- OES) and micro-X-ray fluorescence (μXRF), as well as the isotopic composition using laser ablation-multi collector-ICP-mass spectrometry (LA-MC-ICP-MS) for Sr and solution MC-ICP-MS for Nd. This study revealed the unique elemental and isotopic composition of this material, matching the local geology and providing a strong argument for a previously unknown production site, possibly local, for this material. Two glass hues are observed in the assemblage (green and amber); both have the same chemical composition. The colour difference is due to differences in the oxidation state of the chromophores whether or not purposefully is unclear. The production of blown glass vessels shows a technology, not yet evidenced before, for this period in this region.

Keywords U.A.E. . Plant ash glass . Sr isotopes

Introduction Situated on the Golf of Oman, Dibba was already an important port in antiquity connecting the caravan trade Present-day Dibba is situated on the border between the with a seafaring route. Goods found in Dibba indicate United Arab Emirates (U.A.E.) and Oman (Fig. 1). The city trade or contact with the Roman Empire, the Indian con- consists of three parts, one located in Oman, one in the emirate tinent and the Parthian empire (Jasim 2006;Seland2014). of Sharjah and one in the emirate of Fujeirah. The glass sam- In pre-Islamic times Dibba was known as the Arab Suq of ples considered in this paper were excavated in Dibba Al Jahiliyah (Jasim 2006). Hisn, in the emirate of Sharjah. Archaeological evidence links Dibba to the inland town of Mleiha, probably the seat of a regional kingdom (Overlaet et al. 2016). Mleiha was strategically located between two Electronic supplementary material The online version of this article coastal harbour settlements, ed-Dur on the West and Dibba (https://doi.org/10.1007/s12520-018-0611-0) contains supplementary material, which is available to authorized users. on the East coast of the Oman peninsula. Southeast Arabia is an archaeologically densely studied * Alicia Van Ham-Meert region, but only limited information is available about its [email protected] glassware, especially in pre-Islamic times. Local govern- ments strongly support archaeological research, and dur- 1 Earth and Environmental Science, Division of Geology, KU Leuven, ing the last decennia, excavations at sites such as ed-Dur, Celestijnenlaan 200E, 3001 Heverlee, Belgium Kush, Mleiha and Dibba have yielded important glass 2 Analytical, Environmental and Geo-Chemistry, VUB, Pleinlaan 2, finds (Whitehouse 2000;WorrelandPrice2001). These 1050 Brussels, Belgium are generally considered to be imports from the Roman 3 Sharjah Archaeology Authority, Sheikh Rashid Bin Saqr Al Qasimi and Parthian or Sasanian empires (Whitehouse 2000; Street, Helwan, Sharjah, United Arab Emirates Worrel and Price 2001),aviewwhichmayhavetobe 4 Ancient Near East and Iran, Royal Museums of Art and History, revised in light of recent analytical results. Jubelpark 10, 1000 Brussels, Belgium Large quantities of late pre-Islamic glass have been exca- 5 Faculty of Archaeology, Archaeological Sciences, Universiteit vated in Dibba at two locations close to the coastline, in a Leiden, Einsteinweg 2, 2333 CC Leiden, Netherlands collective tomb and in a settled area (Jasim 2006). Most of Archaeol Anthropol Sci

Fig. 1 Map situating the main modern cities and archaeological sites in the U.A.E.

the glass from the tomb has familiar BRoman^ shapes and 2007) and the burials at ed-Dur (Whitehouse 1998, 2000). decorations and is clearly imported. There are, for example, Although the shape of the plain blown unguentaria from the cast ribbed bowls and patterned mould-blown flasks with two Dibba mound is not unusual, they are distinctive because they handles (Jasim 2006). However, white opaque glass are made of markedly thicker glass. Comparable unguentaria unguentaria or small flasks are of particular interest for our with thick walls are only occasionally reported from Near study. In the settled area, fragments (including bottoms, necks Eastern sites. Specimens are known from amongst others and lips) of identical unguentaria were discovered (Fig. 2) Bahrain, Seleucia and Dura Europos. This observation alongside chunks of unworked glass (Jasim and Yousif prompted Andersen to suggest a possible Mesopotamian or 2014). In fact, unguentaria are the only vessel shape found Egyptian origin for them (Andersen 2007:34–35, type 7). with this unworked glass. The opacity of the glass, as de- Most glass finds in the region are associated to burials, and scribed in the excavation reports, most probably stems from such a large quantity in a single room is unique for the region. its heavy corrosion, rather than from an intentional The excavators identified several successive occupational opacification. The finds from the settlement are related to phases of the construction in which the glass deposit was some industrial or economic activity such as storage or trade found. The glass is associated with level III, which consisted of (raw) materials but might also point to the existence of a of a raster-like group of 52 rectangular mud-brick cell-shaped local glass production or a workshop (Jasim and Yousif 2014). Brooms^, each measuring c. 2–3by1.5–3m.Thesoilof Unguentaria are small flasks that are typically found in BRoom 21^ was scattered with glass chunks, broken vessels tombs and were used to contain small quantities of valuable and waste. Other rooms contained various other materials fluids or powders for cosmetic, aromatic or medicinal use. such as shells, stones and amphorae with bitumen (Jasim They were extremely popular and mass-produced. The most and Yousif 2014). None of these rooms or cells has doors or common are plain free-blown vessels with a globular to trian- passages, which suggest that this may have been the founda- gular body and a long neck (Andersen 2007). Pattern decorat- tion of a building or storage facility. The objects may have ed mould-blown specimens in the shape of miniature ampho- fallen down when the floor, supported by this mud brick maze, rae; dates or even fish are also found. A representative selec- collapsed. Part of this construction remains to be excavated tion comparable to the finds from Dibba is known from the and final interpretations must await further research at Dibba. contemporary Tylos period burials on Bahrain (Andersen Unfortunately, the area is partly covered by modern housing Archaeol Anthropol Sci

Fig. 2 Top: drawings of flasks found in the tombs near Dibba (Jasim and Yousif 2014; Jasim 2006); bottom left: sample from room 21; bottom right unguentarium found in a tomb near Dibba

(Jasim and Yousif 2014). In the absence of specific glass All the analysed samples were heavily weathered on the workshop equipment such as kilns or crucibles, we will hence- outside. Chunks of glass were chipped from the inside of the forth tentatively refer to the location as a Bstorage facility^. samples and mounted in epoxy resin. These were then The nature of the finds at the mound, amongst which are polished up to 1 μm using diamond paste. The samples are various raw materials and Roman, Indian and Mesopotamian representative of the whole assemblage within this room. storage jars, emphasises the international connections of Dibba as a trade-port (Jasim and Yousif 2014). The aim of Table 1 List of analysed sample with colour and typology this particular study is to characterise the glass to determine Sample number Colour Typology whether the raw glass is consistent in composition with one of the known primary producers or, whether a local glass pro- 001.03 Amber Chunk duction can be evidenced (no kiln has been reported), parallel 001.06 Amber Chunk to the attested import of Roman glass (Whitehouse 2000; 05.01 Amber Flask Jasim and Yousif 2014). 05.06 Green Chunk In order to compare the glass composition with known 008.05.02 Amber Flask glass making sites and to determine the manufacturing tech- 008.05.09 Green Flask nology, the elemental and isotopic composition of the glass 008.43.07 Amber Flask was determined. 009.01.02 Green / 009.004.02.03 Green Flask 009.004.10.05 Amber Flask 009.13.16 Green Chunk Materials and methods 009.26.03 Amber Chunk 009.26.11 Green Chunk Archaeological samples 012.06.02 Amber Flask 012.07.02 Amber Flask All samples originate from the same layer and context, room 013.09.05.03 Amber Chunk 21 of the construction on the mound. A sample was taken 013.12.09 Green Chunk from an unguentarium from the tombs (SM2004_1482, illus- 13.16.03 Amber Chunk trated in Fig. 2); however, it proved too corroded for any 013.20.03 Amber Flask analysis to be meaningful. 013.20.04 Amber Chunk Two colours of glass can be distinguished: light green and 013.20.12 Green Chunk dark amber. Different types of remains were sampled: chunks 016.03 Green Chunk of unworked glass and fragments of unguentaria (flask in 017.10.03 Amber Flask Table 1). A full list of samples is provided in Table 1. Archaeol Anthropol Sci

Inductively coupled plasma-optical emission weighing 100 mg of sample and dissolving it through succes- spectrometry sive acid treatments summarised in order in Table 2. After dissolution, Nd was isolated by successive ion exchange chro- In order to be able to measure major and minor elements in the matography using the TRU and Ln resins from Eichrom®. glass, it was decided to use lithium metaborate fusion for Solutions of approximately 30 ppb Nd were analysed using sample preparation. Samples were crushed in an agate mortar a Neptune MC-ICP-MS instrument (Thermo Scientific, and slightly wetted with Milli-Q water to facilitate the Bremen, Germany) equipped with a Pfeiffer (Asslar, crushing procedure. One hundred milligrams of each sample Germany) OnTool™ Booster 150 dry interface pump 3 −1 was carefully weighted, and approximately 500 mg LiBO2 (130 m h pumping speed). The instrumental settings are was added. The samples were then fused at 1000 °C for found in Table 3. J-Ndi was used as standard; the results are

10 min and dissolved in 50 ml 0.42 M HNO3. For analysis expressed as εNd with respect to the chondritic uniform reser- by ICP-OES, samples were diluted 10× and a series of HIQU voir CHUR, using Eq. 1. single element solutions (CHEM-LAB, Belgium) was used to prepare calibration solutions. Standard reference materials 0 1 143Nd were used to control the whole procedure (NIST 620, NIST 144 BNd sample C εNd ¼ @ −1A Â 10; 000 ð1Þ 610, SGT 10, SO2, BCS 267, BCS 269, BCR-1G). ICP-OES 143Nd 144 was performed on a Varian 720-ES instrument, fitted with a Nd CHUR double-pass glass cyclonic spray chamber, a concentric glass nebuliser SeaSpray and an extended high solids torch. Solutions were introduced in the spectrometer using the ns-LA-MC-ICP-MS Varian SPS3 Sample Preparation System. The ICP-OES is fitted with a CCD detector. Sr isotopic analysis was performed using nanosecond laser ablation multicollector ICP-MS. Measurements were per- Loss on ignition formed in triplicate, using an Analyte G2 193 nm ArF* excimer-based laser ablation system (Teledyne Photon To account for any losses of (structural) water, carbonates or Machines, Bozeman, MT, USA) at a fluence of 4.05 J/cm2, volatile elements during the lithium metaborate fusion, loss on beamsize of 104 μm, frequency of 25 Hz and 13 μm/s trans- ignition (LOI) tests were performed. When possible, 500 mg lation speed. Linescans of 3 min were performed for each of sample was placed in an alumina crucible and fired at measurement. 1000 °C for 1 h. Then, the samples were weighted again, The MC-ICP-MS is the same as the one used for pn-MC- and the difference allowed to determine the LOI. Results from ICP-MS; measurements were performed in medium resolu- the ICP-OES analysis were normalised to the total of the anal- tion and using a Ni jet sampler cone and a Ni BX^ skimmer ysis + LOI, as the loss on ignition is mainly water from the cone. The plasma was operated under wet conditions by crushing procedure for the samples. pumping 100 μl/min 3% HNO3 solution to improve stability. Corning D was used as a secondary standard for this analysis; μXRF its isotopic composition and suitability as standard are discussed elsewhere (Van Ham-Meert et al. 2018). In order to obtain information on some volatile species (lost Instrumental settings are found in Table 3. during lithium metaborate fusion), such as S, micro-X-ray fluorescence measurements were performed. These were done on an M4 tornado, fitted with a Rh-tube at 40 kVand 700 μA, Results with a 25-μm spotsize. The samples were mapped at 1000 μm/s; spectra used in this paper are averages of 2 × Elemental analysis 2 cm areas on the maps. Measurements are used in an indic- ative way (presence/absence of these volatile elements), as The elemental composition of the samples, as determined quantitative data was already obtained using ICP-OES. through ICP-OES, is reported in Table 4. This table also reports results for the SGT-10 standard reference material, Pneumatic nebulisation-multicollector-inductively which was measured to check the validity of the data. The coupled plasma-mass spectrometry detection limits and relative standard deviation (in %) are also reported. For most samples the relative standard deviation is Nd isotopic analysis was performed through pneumatic below 1%, indicating a very good repeatability. Notable ex- nebulisation-multicollector inductively coupled plasma mass ceptions are P and Ni where low concentrations in the stan- spectrometry (pn-MC-ICP-MS). This was achieved by first dard resulted in poor repeatability. The difference between the Archaeol Anthropol Sci

Table 2 Dissolution procedure for Nd isotopic analysis Acid T t (h) Evaporation Evaporation (°C) T (°C) time (h)

3 ml 14 M HNO3 200 1 200 4

1mlHClO4 200 0.5 240 1 3 ml HF 90 13 180 4 3 ml aqua regia 200 1 200 4 1.5 ml 2 M HNO3 reference value for SGT-10 and the measured value is smaller Most samples have the typical composition of soda-lime than 5% for all elements except Ba and Cr. However, as the silica glass, with Na2O levels between 10 and 14.5 wt%, CaO samples considered here contain very little of these elements, levels between 3.5 and 6.5 wt% and silica concentrations > the inability to quantify them is not problematic. The average 60 wt%. Samples which contain less Na2O, most often also composition of the green and amber glasses was also deter- show depleted levels of K2OandAl2O3 coupled to elevated mined; sample 013.12.09 was excluded from this analysis, as levels of Sr and MgO levels. Lowered Na2O and K2O are its composition differs significantly from the other glasses often associated with alkali leaching during weathering, (discussed further in this paper). whereas elevated Sr can be due to ion exchange with the The elemental composition of the green and amber environment in the weathering layers. Though it was tried to glasses is indistinguishable within instrumental and proce- avoid weathered parts in the sampling process, influence of dural error. Different hues were hence not achieved through corrosion cannot be excluded and is likely important in sample the use of different colouring elements; rather, they are 013.12.09 where Na2O concentrations are below 1.5 wt%, linked to the oxidation states of the elements. The concom- hence its exclusion in further calculations. 3+ 2− itant presence of Fe and S leads to an amber colour, The presence of more than 1.5 wt% of K2OandMgOinall whereas Fe2+ (with or without sulphur) gives a green colour the samples indicates the use of plant ashes as flux, rather than (Paynter and Jackson 2017). The presence of sulphur was a mineral soda flux (Sayre and Smith 1961). The presence, in confirmed by μXRF analysis (Fig. 3), confirming the nature low concentrations, of Fe and Ti indicates the use of a rela- of the chromophore in the glasses to be Fe-S related. tively clean sand as silica source used for glass making.

Table 3 Instrumental settings of the MC-ICP-MS for the measurement of Sr and Nd isotopes

Instrumental settings Parameter Sr Nd RF Power (W) 1200 1250 Plasma gas flow rate (l/min) 15 15 Nebuliser flow rate 1.05 0.75 Sampling cone Ni Bjet^ Ni Bjet^ (1.0 mm) (1.0 mm) Skimmer cone Ni BX^ Ni BX^ (0.7 mm) (0.7 mm) Integration time (s) 5 4

Nd cup configuration Cup L4 L3 L3 L1 C H1 H2 H3 H4 Isotope 142Nd 143Nd 144Nd 145Nd 146Nd 147Sm 148Nd 149Sm 150Nd Interference 142Ce 144Sm 150Sm Amplifier 1011 1011 1011 1011 1011 1012 1011 1012 1012

Sr cup configuration Cup L4 L3 L3 L1 C H1 H2 H3 H4 Isotope 82Kr 83Kr 84Sr 85Rb 86Sr 87Sr 88Sr 89Y Interference 164Er2+ 166Er2+ 84Kr+, 168Er2+, 170Er2+, 86Kr+, 87Rb+, 176Yb2+ 168Yb2+ 170Yb2+ 172Yb2+ 174Yb2+ Amplifier 1012 1012 1011 1012 1011 1011 1011 1011 Table 4 Elemental analysis of the glass from Dibba by ICP-OES; the average composition of each colour is reported as well as the detection limit (DL) and the relative standard deviation as determined by measuring SGT-10

SiO2 Na2OCaOK2OMgOAl2O3 Fe2O3 MnO P2O5 TiO2

Amber 001.03 61.41 14.35 6.41 3.44 3.39 1.40 0.79 0.03 0.32 0.10 001.06 67.37 13.57 5.63 3.43 2.99 1.43 0.78 0.03 0.29 0.10 05.1 70.62 11.52 5.22 3.07 3.49 2.14 1.17 0.03 0.27 0.15 008.05.02 66.43 10.00 4.46 2.67 4.57 1.82 1.03 0.03 0.26 0.13 008.43.07 74.57 10.22 4.64 2.66 6.55 1.15 0.72 0.03 0.21 0.09 009.004.10.05 77.01 8.48 3.94 2.35 5.51 1.60 0.99 0.04 0.21 0.13 009.26.03 69.69 12.63 5.38 3.30 3.98 1.35 0.86 0.03 0.27 0.11 012.06.02 70.26 12.01 5.25 3.19 3.42 1.63 0.89 0.03 0.28 0.11 012.07.02 71.72 8.84 5.99 2.61 5.20 1.38 0.87 0.03 0.28 0.11 013.009.05.03 72.92 13.53 5.85 3.59 3.48 1.60 0.89 0.03 0.32 0.11 013.16.03 69.02 10.43 6.89 2.93 4.57 1.65 0.92 0.03 0.31 0.12 013.20.03 69.92 14.42 6.49 3.46 4.07 1.65 0.95 0.03 0.34 0.12 013.20.04 68.19 12.41 6.61 3.22 4.13 1.64 0.91 0.03 0.32 0.12 017.10.03 68.24 12.87 6.10 3.42 3.99 1.65 0.93 0.03 0.31 0.12 Green 05.06 65.41 11.47 5.67 2.99 5.19 0.92 0.59 0.03 0.25 0.08 008.05.09 75.73 6.40 6.99 2.11 6.74 1.10 0.69 0.03 0.25 0.09 009.1.2 65.85 12.81 5.46 3.31 3.69 1.50 0.93 0.03 0.27 0.11 009.004.02.03 74.36 9.20 6.31 2.73 6.30 1.07 0.68 0.03 0.26 0.09 009.13.16 62.61 8.58 5.51 2.33 4.51 2.17 1.25 0.04 0.20 0.15 009.26.11 64.13 10.08 4.01 2.71 3.76 1.33 0.87 0.03 0.22 0.11 013.12.09 60.77 1.03 12.52 0.31 4.21 0.79 0.53 0.03 0.33 0.07 .16.03 72.52 8.02 5.23 2.30 4.61 1.16 0.72 0.03 0.28 0.09 Amber Average ± std 69.81 ± 3.74 11.80 ± 1.94 5.63 ± 0.87 3.09 ± 0.39 4.24 ± 0.98 1.58 ± 0.24 0.91 ± 0.11 0.03 ± 0.002 0.29 ± 0.04 0.12 ± 0.01 Green Average ± std 68.66 ± 5.37 9.51 ± 2.16 5.60 ± 0.93 2.64 ± 0.42 4.97 ± 1.18 1.32 ± 0.42 0.82 ± 0.22 0.03 ± 0.004 0.25 ± 0.03 0.10 ± 0.03 SGT-10 73.00 ± 0.44 11.75 ± 0.13 10.79 ± 0.07 0.33 ± 0.00 1.81 ± 0.01 1.59 ± 0.01 0.33 ± 0.00 0.04 ± 0.00 0.1 ± 0.1 0.10 ± 0.00 Difference with 04− 15 0 2 − 2 − 5n.a− 2 reference value (%) DL 0.081 0.002 0.006 0.001 0.001 0.007 0.003 0.001 0.030 0.001 Rel standard dev. 0.60 1.13 0.64 0.72 0.70 0.73 0.82 0.70 83.07 0.53

Sr (ppm) Cu (ppm) Ni (ppm) Zn (ppm) Zr (ppm) Cr (ppm) V (ppm) Y (ppm) Ba (ppm) Sc (ppm) La (ppm)

Amber 342 9 33 36 32 46 15 3 66 2 42 284 11 29 39 19 40 18 4 73 2 36 272 12 39 46 30 63 32 4 66 2 36 258 9 31 47 24 53 3 4 44 1 16 364 11 22 39 15 51 16 2 39 1 28 249 15 37 41 30 48 29 3 37 2 26 303 14 34 33 20 43 29 2 53 2 22 295 14 27 39 24 56 40 3 65 2 37 501 14 28 36 23 45 11 3 50 2 40 297 13 33 41 25 46 10 3 74 2 37 721 11 25 43 25 50 30 5 60 2 44

388 8 41 46 26 52 35 4 66 1 46 Sci Anthropol Archaeol 451 9 33 42 21 54 26 3 64 2 40 368 14 37 41 23 68 13 3 62 2 40 Green4116 2426 163725246 1 37 680 8 28 32 18 41 18 3 41 1 45 302 10 42 102 21 50 58 58 64 2 47 532 9 21 30 13 34 2 3 47 1 41 316 10 38 36 23 56 11 4 38 3 37 215 11 25 33 17 40 7 2 39 1 28 2306 8 33 29 9 34 22 2 36 1 80 Archaeol Anthropol Sci

Isotopic analysis 34 35±9 0.001 n.a. 38 ± 7 2.66 Table 5 reports the results of the Sr and Nd isotopic analysis. Sr enters the glass with the source of Ca, in this case with plant ash. Hence, the strontium isotopic composition of glass re- flects the soil where the plants used for producing the ash grew (Freestone et al. 2003; Henderson et al. 2009). 1 2±1 n.a. 1 ± 1 0.000 Nd enters glass as a trace element present in the silica source and hence informs on the geological age and isotopic composition of the deposit used for glassmaking (Degryse and Schneider 2008). There are a few samples for which it was impossible to 0.02 ± 0.00 0.00 ± 0.00 0.01 ± 0.00 52 17 47 ± 9 58±12 0.001 0.67 determine the Sr and/or Nd isotopic composition because there was not enough sample available (sample nos. 05.01, 13.20.03, 009.004.02.03, 009.13.16, 013.12.09). The strontium isotopic composition of the samples ranges from 0.7085 to 0.7088. One sample (008.05.02) falls outside 2 n.a. 11 ± 21 3±1 6.90 this bracket (0.70903 ± 0.00013); its high standard deviation attests the unreliability of this result, which will hence be excluded from the discussion. Most Nd isotopic compositions fall between − 4.1 and − 4.9. Those few samples with different 32 22 ± 19 22±11 n.a. 0.001 values are associated with high errors and were the samples with the lowest Nd concentration (most notably sample 008.05.02 and 009.26.11). Low Nd contents likely compro- mised these results; they are hence excluded from the discussion. 38 42 ± 8 51±8 12 0.001 0.64

Discussion

1 As most materials found in the storage facility are imported 20 18 ± 3 24±5 − 0.001 0.66 (by sea or land), or originate from the sea (such as shells), and in the absence of any proof for glass working in the neighbourhood, it is worth comparing the glass found in Dibba with temporal and/or regional equivalents. 33 41±4 0.01 ± 0.01 0.02 ± 0.00 0.01 ± 0.00 42 ± 27 0.001 n.a. 1.79 Temporal equivalents mainly originate from the Roman Empire, which was exporting large quantities of raw natron glass produced in the Levant. This glass was produced with a mineral soda flux and hence completely differs compositionally from the glass found in Dibba. There are, nevertheless, 29 32±5 30 ± 8 0.002 n.a 41.40 sparse examples of plant ash glasses found throughout the Roman Empire. Not much is known about them, as they are usually reported as the one odd glass in the assemblage of a site. A list of these samples and their composition is provided in electronic supplementary information (ESI); it is a compi- 11 n.a. 0.001 4.60 lation of data from Brill (1999) and the ARCHglass database (Ganio 2013; Ganio et al. 2012a,b;Ereminetal.2011; Degryse and Shortland 2009; Degryse et al. 2009; Shortland and Schroeder 2009;Brill1999). Surveying this data, a wide variety in composition is encountered, and it is impossible to Sr (ppm) Cu (ppm) Ni (ppm) Zn (ppm) Zr (ppm) Cr (ppm) V (ppm) Y (ppm) Ba (ppm) Sc (ppm) La (ppm) 440 n.a. 0.01 ± 0.00 0.00 ± 0.00 0.780 0.00 discuss Bthe composition of Roman plant ash glass^. (continued) Roman plant ash glasses compiled in ESI 1 have CaO

concentrations above 8.0 wt% and K2O concentrations below

Table 4 – Amber 364±126 11±2 Green 414 ± 157 9 ± 2 3 wt%, whereas glass from Dibba contains 5 7wt%CaOand Archaeol Anthropol Sci

Fig. 3 μXRF spectra of an amber and a green glass highlighting the presence of S and Cl

more than 3 wt% K2O. As no glass of this type has been the odd Indian sample (Seland 2014). The Tylos burials attested in the Roman Empire, this indicates that the glass yielded some thick-walled unguentaria (Andersen 2007); found in Dibba is probably not a Roman import. however, no elemental compositions are reported for the Other temporal equivalents which should be considered are glass from the Tylos burials in Bahrain. In the camel glasses produced in ancient India. Indian glasses are mostly cemetery in Mleiha, unguentaria were recovered; how- produced using a mineral soda source and contain elevated ever, their shape is different from what was found in

Al2O3 concentrations (Dussubieux et al. 2010; Brill 1999). Dibba (Jasim 1999). The two most common glass groups found in India for the The plant ash glass making tradition originated in period are m-Na-Al-1 and m-Na-Al-3, their composition is Mesopotamia in the late Bronze Age. It was superseded found in ESI 4 (Dussubieux et al. 2010). Both of them are as the main glass making tradition by natron glass during rich in Al2O3 and do not correspond to the glasses found in the Roman period. However, it continued to be used es- Dibba. pecially in Mesopotamia during this period. Plant ash A large proportion of published Indian glasses relevant for glass again becomes the most important glass group in this study are reproduced in ESI 3 (Brill 1999;Govind1970; the region during the Sasanian and Islamic periods. Sayre 1964; Kanungo and Brill 2009;Bhardwaj1979). Especially, Sasanian glass is of interest as compositionally

Amongst the samples containing > 1.5 wt% K2O and MgO, the glass from Dibba is closest to Sasanian group II glass. there are samples from Taxila (in modern-day Pakistan), The Sasanian Empire was centred on modern-day Iran and Ahicchatra, Kopia, Kausambi, Rupar, Bhar, Orissa and part of Iraq between the third and seventh century CE. At Arikamedu. None of these glasses correspond to the glasses its height, its influence extended as far as Yemen in South from Dibba, as they all contain at least 1 wt% more Al2O3 or, Arabia and the Caucasus in the North. Glasses from in the case of Ahicchatra, contain much more Fe2O3.Itthus Sasanian Veh Ardasir (Ctesiphon in present day Iraq) seems unlikely that the glass from Dibba was imported from were analysed chemically (Mirti et al. 2008, 2009)and sites found thus far in India. The Sr isotopic composition of isotopically (Ganio et al. 2013). During their analysis, the glasses from Kopia is also much higher than what was they showed that the glass was plant ash glass, which found in the glasses from Dibba. could be divided into two groups based on magnesium As far as regional equivalents go, ed-Dur and Mleiha and phosphorus concentrations (Mirti et al. 2009)andthat (U.A.E.) as well as the Tylos burials on Bahrain offer the Sr isotopic composition was between 0.7084 and the closest parallels from around the same period. 0.7088, with one outlier at 0.70916 and εNd between − 5 Analysis of the glass assemblage from ed-Dur showed and − 8.5(Ganioetal.2013). The Sasanian glasses con- that it is almost exclusively Roman natron glass with tain more Al2 O 3 than the glass from Dibba Archaeol Anthropol Sci

Table 5 Sr and Nd isotope composition of the samples; reported errors are standard deviations within one measurement sequence. Reference materials measured during the session are also included

87 86 143 144 Sr/ Sr Nd/ Nd εNd

Amber 001.03 0.70876 ± 0.00003 0.5124070 ± 0.0000235 − 4.506 ± 459 001.06 0.70884 ± 0.00005 0.5124277 ± 0.0000277 − 4.103 ± 0.540 05.1 0.70871 ± 0.00002 008.05.02 0.70903 ± 0.00013 0.5124191 ± 0.0000323 − 4.270 ± 0.631 008.43.07 0.70856 ± 0.00004 0.5124224 ± 0.0000373 − 4.206 ± 0.728 009.004.10.05 0.70866 ± 0.00007 0.5124307 ± 0.0000455 − 4.043 ± 0.888 009.26.03 0.70869 ± 0.00001 0.5128165 ± 0.0005538 3.482 ± 10.803 012.06.02 0.70878 ± 0.00003 0.5124411 ± 0.0000317 − 3.840 ± 0.618 012.07.02 0.70871 ± 0.00002 0.5124051 ± 0.0000308 − 4.513 ± 0.600 013.009.05.03 0.70876 ± 0.00003 0.5124521 ± 0.0011044 − 3.626 ± 20 013.16.03 0.70868 ± 0.00004 0.5124095 ± 0.0000305 − 4.456 ± 0.495 013.20.03 0.5123925 ± 0.0000327 − 4.789 ± 0.638 013.20.04 0.70870 ± 0.00001 0.5124229 ± 0.0001023 − 4.195 ± 1.995 017.10.03 0.70872 ± 0.00002 0.5124157 ± 0.0000265 − 4.337 ± 0.513 Green 05.06 0.70858 ± 0.00007 0.512813 ± 0.0002089 − 3.057 ± 4.076 008.05.09 0.70856 ± 0.00003 0.5124363 ± 0.0000284 − 3.935 ± 0.555 009.1.2 0.70853 ± 0.00006 0.514229 ± 0.0000346 − 4.197 ± 0.675 009.004.02.03 0.70866 ± 0.00007 009.13.16 0.5124097 ± 0.0000259 − 4.472 ± 0.505 009.26.11 0.70861 ± 0.00003 0.5124456 ± 0.0000322 − 3.752 ± 0.623 013.12.09 0.5124385 ± 0.0000381 − 3.892 ± 0.744 .16.03 0.70861 ± 0.00002 0.5124130 ± 0.0000379 − 4.389 ± 0.740 Amber Average ± std 0.708736 ± 0.00012 0.512821 ± 0.00081 Green Average ± std 0.708588 ± 0.00005 0.512867 ± 0.00091 Corning D 0.70975 ± 0.00002 JNDI-1 0.5120903 ± 0.000006 Difference with reference value − 0.0007 − 0.000025

(approximately 2 wt% in the Sasanian glass compared to et al. 1999;Garzantietal.2003). In fact, most of the less than 2 wt% in the glass from Dibba), and the Nd coastal and wadi sands in the U.A.E. are unsuitable for isotopic composition is different. Hence, the silica used glassmaking. In Oman, the sands are richer in quartz for producing these glasses is likely from a different and poorer in feldspars and heavy minerals (Garzanti source. et al. 2003). At present, it is impossible to say whether The glass found in Dibba has a composition never the glass found in Dibba was produced in the region reported before, possibly indicating a local production, though there are indicators in this sense. or import from a yet unknown production centre. People in Dibba had access to goods from all over the Production in the U.A.E. cannot be excluded as the Sr ancient world, and also imported Roman glass. Yet, it seems isotopic composition of the glass corresponds to the that they produced or imported a different type of coloured composition of ashes from local trees as determined glass as well. Why this was done and whether different glass by Kutterer and Uerpmann (2017). They found that types were for different purposes or more costly cannot be ashes from the Dibba region have a Sr isotopic compo- assessed with the available knowledge. It is also not possi- sition of 0.70863. The Nd isotopic composition of the ble to ascertain whether the two glass colours were purpose- coastal sands, between Dibba and Muscat As Sifah, is ly obtained or whether the aim was to make amber glass, and highly variable with some locations, like Ra’sDadnah, this sometimes failed yielding green glass instead. To obtain 3+ 2− yielding εNd = − 4.31 (Cox et al. 1999). This is close to the Fe –S chromophore, reducing conditions are needed the value obtained for the glass from Dibba. The under- in the glass. In natron glasses, this was ensured by admixing lying geology, however, is ophiolitic and the sand is some charcoal to the glass (Paynter and Jackson 2017). In rich in Al2O3 and unsuitable for glassmaking (Cox the case of plant ash glass, the reducing agent might have Archaeol Anthropol Sci been present in the ashes of the plants. The production of Sr/Nd isotope systematics. Contrib Mineral Petrol 137:267– 287 amber glass is a difficult process where green glasses can be – 3+ 2+ Degryse P, Schneider J (2008) Pliny the elder and Sr Nd iso- obtained instead of amber ones if Fe reduces to Fe .This topes: tracing the provenance of raw materials for roman process is highly sensitive to temperature and duration of glass production. J Archaeol Sci 35:1993–2000 the firing (Paynter and Jackson 2017). Hence, amber Degryse P, Shortland A (2009) Trace elements in provenancing raw ma- – glasses must be prepared deliberately whereas green terials for roman glass production. Geol Belg 12:135 143 Degryse P, Schneider J, Lauwers V, Henderson J, Van Daele B, glasses could be an accidental by-product. Furthermore, Martens M, Huisman HDJ, De Muynck D, Muchez P (2009) the thicker walls indicate that the blowing technique Neodymium and strontium isotopes in the provenance deter- was not fully mastered yet, as this is more costly in mination of primary natron glass production. In: Degryse P, material and has no obvious purpose. Henderson J, Hodgins G (eds) Isotopes in vitreous materials. Studies in archaeological sciences. University Press, Leuven, pp 53–72 Dussubieux L, Gratuze B, Blet-Lemarquand M (2010) Mineral soda alumina glass: occurence and meaning. J Archaeol Sci 37:1646–1655 Conclusion Eremin K, Degryse P, Erb-Satullo N, Ganio M, Greene J, Shortland A, Walton M, Stager L (2011) Amulets and infant burials: glass beads The determination of the elemental composition of glass from the Carthage Tophet. Proceedings of the SEM and microanal- ysis in the study of historical technology, materials and conservation excavated in Dibba, U.A.E., dating from the first centu- conference, London, UK, 9-10 September 2010 ry CE, highlights the unique composition of this glass Freestone IC, Leslie KA, Thirlwall M, Gorin-Rosen Y (2003) Strontium with no known regional or temporal equivalents. isotopes in the investigation of early glass production: byzantine and – The unique elemental and isotopic compositions and early islamic glass from the near east. Archaeometry 45:19 32 Ganio M (2013) A ‘true’ Roman glass: evidence for primary production the possibility of finding raw materials with matching in Italy. PhD Thesis, KU Leuven (isotopic) composition in the region present a case for Ganio M, Boyen S, Fenn T, Scott R, Vanhoutte S, Gimeno D, possible local production of glass in ancient Oman. Degryse P (2012a) Roman glass across the empire: an ele- The presence of plant ash glass in this region during mental and isotopic characterization. J Anal At Spectrom 27: 743–753 this period shows a continuation of the millennia long Ganio M, Boyen S, Brems D, Scott R, Foy D, Latruwe K, Molin G, tradition of producing plant ash glass in Mesopotamia. Silvestri A, Vanhaecke F, Degryse P (2012b) Trade routes across The glass in Dibba is a remarkable early example of plant the Mediterranean: a Sr/Nd isotopic investigation on roman ash blown glass in the Arabian World. Furthermore, at- colourless glass. Glass Technol: Eur J Glass Sci Technol A 53: 217–224 tempt at control of the furnace conditions for obtaining Ganio M, Gulmini M, Latruwe K, Vanhaecke F, Degryse P (2013) amber testifies to the skill and innovation of the craftsman Sasanian glass from Veh Ardašīr investigated by strontium and neo- who produced and/or worked this glass, even if the blow- dymium isotopic analysis. J Archaeol Sci 40:4264–4270 ’ ing technique is at its early stages with thick walls and Garzanti E, Andò S, Vezzoli G, Dell era D (2003) From rifted margins to foreland and basins: investigating provenance and sediment dispers- irregular shapes. al across desert Arabia (Oman, U.A.E.) J Sediment Res 73:572–588 Govind V (1970) Some aspects of glass manufacturing in ancient India. Acknowledgements The authors are thankful to the Emirate of Sharjah Indian journal of the. Hist Sci 5(2):281–308 for providing the samples for analysis. The authors are also thankful for Henderson J, Evans J, Barkoudah Y (2009) The roots of provenance: the helpful comments of the reviewers which have contributed to the glass, plants and isotopes in the islamic middle east. Antiquity 83: coherence and thoroughness of the paper. 414–429 Jasim SA (1999) The excavation of a camel cemetery at Mleiha, Sharjah, Funding information Alicia Van Ham-Meert is funded on a project from U.A.E. 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