An archaeometric contribution to the study of Late Classic-Hellenistic ceramics of Northern Greece

Journal of Archaeological Science: Reports 29 (2020) 102097

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An archaeometric contribution to the study of Late Classic-Hellenistic ceramics of Northern Greece

T

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Y. Santosa, D. Kondopouloua, L. Papadopouloua, N. Saridakib, E. Aidonaa, , C. Rathossic, C. Serletisa a

Aristotle University of Thessaloniki, Faculty of Sciences, School of Geology, Thessaloniki, Greece Aristotle University of Thessaloniki, Faculty of Philosophy, School of History and Archaeology, Thessaloniki 54124, Greece c University of Patras, Department of Geology, Sector of Earth Materials, Rio Patras 26504, Greece b

A R T I C LE I N FO

A B S T R A C T

Keywords: Late-Classic Hellenistic Ceramics Petrography X-Ray Spectroscopy Archaeomagnetism

The present study is a multi-analytical approach for the characterization of several potsherd samples, dated from Late Classical to the Hellenistic period at three different archaeological sites of Northern Greece: Pella, Thasos and Samothrace. Ceramic petrography, Scanning Electron Microscopy coupled with Energy Dispersive Spectrometry (SEM-EDS) and X-Ray Powder Diffraction Analysis (XRPD) were applied for the determination of the chemical and mineralogical characteristics of the studied ceramics as well as the morphology of the clay with high resolution SEM images. Magnetic measurements on the sherds enriched the present study and when combined with the archaeometrical approach described above, contribute to the characterization of the material on its suitability for archaeomagnetic experiments. The overall obtained results confirm a local provenance and techniques used for the pottery production.

1. Introduction The interdisciplinary approach by means of chemical, geological and physical analytical techniques in the study of archaeological remains is common nowadays. More specifically, the characterization of ancient pottery, based on the methods above, can provide valuable information regarding the provenance of raw materials used for the ceramic production and specify the employed technological processes related to the product manufacture (Pollard et al. 2007; Iordanidis et al., 2009; Gauss and Kiriatzi, 2011; Neyt et al., 2012; Quinn, 2013; Marzec et al., 2018). The identification of the elemental variability in the ancient sherds studies can provide fingerprints of the geological profile of the study region and, furthermore, distinguish local pottery from imported one (Hein and Kilikoglou, 2017). The mineralogical composition of ceramic products provides us with information regarding the raw material used, the firing temperatures during its fabrication and the firing conditions (oxidizing or reducing) in the kiln (Whitbread, 1995). The combination of multiple techniques is fundamental in order to fully characterize the studied samples reinforcing and/or complementing each line of analysis. The first analytical method applied was petrography, which can provide a better orientation for analytical

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techniques, some of which are destructive. Petrography could easily determine pottery provenance based on the composition of mineral inclusions and rock fragments and answer questions related to technological issues (Whitbread, 1995; Quinn, 2013).Mineralogical analyses using X-ray Powder Diffraction (XRPD) and Scanning Electron Microscopy (SEM-EDS) are also reported. The presently studied pottery samples were initially selected for archaeomagnetic experiments. This selection was made upon their accurate datings (Late Classical to Hellenistic) and known firing locations, the elementary conditions “sine qua non” for such studies. Systematic archaeomagnetic research has been conducted for several years in multiple archaeological sites in Greece (De Marco et al., 2008; Fanjat et al., 2013; Kondopoulou et al., 2014; Aidona et al., 2018 among others). An important factor to be taken into account during archaeomagnetic studies is the suitability of the related clays to accurately record the signal of the magnetic field. This issue has been often discussed (Cui and Verosub, 1995; Kostadinova–Avramova, and Kovacheva, 2013). The use of petrography in combination with magnetic measurements has been applied in a study on prehistoric ceramics, as a tool for improving the selection of pottery suitable for archaeomagnetic experiments (Kondopoulou et al., 2017). In order to complement this study by extending it to historical periods, we adopted

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

https://doi.org/10.1016/j.jasrep.2019.102097 Received 6 May 2019; Received in revised form 6 November 2019; Accepted 12 November 2019 2352-409X/ © 2019 Elsevier Ltd. All rights reserved.

Journal of Archaeological Science: Reports 29 (2020) 102097

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Fig. 1. Map focus on the northern coast of Greece. Samples originate from 3 different regions in: Pella west of Thessaloniki; the island of Thasos east of Halkidiki peninsula (Chalcidice) and the island of Samothrace further to the east.

due to river-transported sediments which have filled in the estuary, the city stood on a shallow, but navigable lagoon (Fouache et al., 2008; Vouvalidis, 2013). The archaeological site of Pella has a great reputation as it is related to the kingdom of Philip II and his son Alexander the Great. A recent reopening of the excavation lead to important restorations, and created a fully visitable site (Akamatis and Lilimpaki-Akamati, 2015). In 2008 an organized pottery workshop was unearthed and studied in the quarter of the public baths, at the northwest part of the town block (Fig. 2). The workshop comprised a well, two cisterns for cleaning the clay and depositories in pits. Two pottery kilns were found in the northeast room, both pear-shaped with medium to small dimensions, that is 1.30–1.55 m width to 1.80–2.10 m length. Both kilns presented similar architectural characteristics and evidence for high firings

a protocol for obtaining data from both analytical methods and basic magnetic experiments such as thermomagnetic and hysteresis loop experiments. A strong emphasis is also recently given by several researchers on the investigation of the firing conditions within the kiln, during ceramic manufacturing, by both petrographic and magnetic measurements (Jordanova et al., 2018; Rada et al., 2011). This approach, though promising, is not directly related to the scope of the present study which aims first to investigate the physical and chemical properties of three groups of ceramics, and to establish relations between the material’s composition and the regional geology in the vicinity of the corresponding archaeological sites. At a second level, this outcome could enhance their relevance for archaeomagnetic studies through the possible correlation of the ceramics magnetic properties and the characterization of the clay fabric. The production of all studied samples belongs to three different sites in Northern Greece (Fig. 1): Pella, Thasos and Samothrace from west to east. The samples date from late 5th to late 3rd century BCE. (Late Classical to the Hellenistic Period). 2. Geological setting and archaeological background 2.1. Pella (Site code PE) Pella is situated in the Northwest part of the Thessaloniki Plain (Fig. S1). To its south lie the alluvial plains of the Axios and Aliakmon rivers; to the north low hills of Miocene-Pliocene sedimentary rocks were deposited by predecessors of the present rivers (Fig. S1). The successive depositional environments infilled a Neogene depression with fluvial deposits, brackish clays, sands, limestones in the Miocene and fluviolacustrine sands, silts and lacustrine marly limestones in the Pliocene (Ghilardi et al., 2008). From Neolithic to Early Roman times Pella was situated on the coast of the Thermaikos Gulf. By Late Roman times and

Fig. 2. Pottery workshop in Pella. 2

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Fig. 3. Representative studied samples from Pella (A) Samothrace (B) and Thasos (C).

according to observed vitrification. Traces of fired floors were clear and pottery fragments were found in both kilns, abundant in kiln 1 and less numerous in kiln 2. The size of the fired pots was rather small, as can be expected from the dimensions of the kilns, and the products were unpainted. Because of the big amount of ceramics found within the kilns it is assumed that they were in operation during their destruction and possibly their last firing (dated at 250–225BC) was not completed (Lilimbaki-Akamati and Akamatis, 2008). The material we selected comes from the two kilns, is labelled as PE01 (from kiln 1) and PE02 (from kiln 2) and consists of small handles, bottoms and body fragments of sherds.

2.3. Samothrace (Site code SM) The island of Samothrace is situated in the northeast part of the Aegean (Fig. S3). The island is part of the Circum-Rhodope Belt (Heimann et al., 1972; Kauffmann et al., 1976), a series of TriassicJurassic continental margin sedimentary and volcanic rocks that surround the crystalline Serbo-Macedonian and Rhodope Massifs. Lithologically, five units have been distinguished in Samothrace from bottom to top: I) the basement which consists of a series of Late Jurassic lowgrade metamorphic sedimentary and volcanic rocks (Tsikouras and Hatzipanagiotou, 1995) II) a low-grade meta-ophiolitic complex; III) a calc-alcaline granite; IV) tilted volcano-sedimentary formations and V) mostly horizontal Upper Miocene-Pliocene sediments which consist mainly of conglomerates, sandstones, shales and nummulitic limestones (Christofides, 2000; Eleftheriadis et al., 1994). The lower north-east, west and south-west slopes of the island are covered by Tertiary volcanic rocks in the form of domes, dykes, lava flows and abundant pyroclastic formations mainly of andesitic composition (Eleftheriadis et al., 1994) (Fig. S3). The island hosts one of the most peculiar archaeological sites in Greece, which flourished in the second half of the 4th BC century and continuously expanded until the end of Hellenistic times. This site, Palaeopolis, is situated at the northern part of the island and comprises the Sanctuary of the Great Gods, a Tholos, and several buildings used for the mystic ceremonies of Kaviria. An extended complex of ceramic workshops was excavated in the late 1980s close to the North coast, around 5 km east of Palaeopolis. The workshops’ activity was placed between the late Hellenistic and the Early Imperial period. Around 500 m further to the East three ceramic kilns, of updraft type, were also brought to light (Karadima-Matsa, 1994) and for this reason the area was named Keramidharia. The biggest kiln was studied archaeomagentically in the past (Spatharas, 2005; Spatharas et al., 2011). The kiln was buried afterwards for preservation, but in the surrounding slopes of the mound several fragments of common, unpainted pottery (jars, plates, handles) were spread, originating from the kiln’s production. The samples of the present study were collected precisely in this

2.2. Thasos (Site code TH) Thasos is the northernmost island in Greece and is separated from the mainland by only 10 km. The interior of the island is mountainous and belongs to the Rhodope geological zone, thus largely composed of metamorphic rocks (Fig. S2). These formations are divided into several units formed basically of muscovite schists, biotite schists and gneisses whereas coarse-grained marbles and dolomites are overlying these series. Stratigraphically higher units follow the same lithological trend of gneisses, schists, marbles and dolomites. Alluvial deposits occur in the major bays, in the northeast, east and southwest, and especially along the northwest coast (Zachos, 1982). Remains of several production sites for transport amphorae have been located and reported by Picon and Garlan (1986) and Garlan (1986), all concentrated around the coast of the island, except from the northwest to southeast. Workshops were in operation from the end of the fifth or beginning of the fourth centuries through to the second or even the beginning of the first century BC. More than 20.000 fragments of stamped handles are classified and stored in the archeological museum of Thasos. The presently studied collection comes from four groups of amphorae handles labelled as TH (05, 06, 07, 08) and covers the period from 285 to 266 BC.

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the same chemical composition do not have the same crystallographic structure (e.g. calcite and aragonite). Mineralogical characterization of the ceramic samples as well as their firing conditions were performed by X-ray powder diffraction (XRPD) using a water-cooled Rigaku Ultima in conjunction with powder diffractometer with CuKa radiation, a step size of 0.05° and a step time of 3 s, operating at 40 kV and 30 mA. The collections studied here were initially selected for an archaeomagnetic study. In order to cross-check the information compiled through the experiments described above with a focus to magnetic minerals included in our fragments, two classical magnetic experiments were performed: a) Magnetic susceptibility and its variation with temperature (thermomagnetic analysis) is a key tool for the identification of iron oxides within fired clays and for monitoring possible alterations during heating and cooling cycles. Important information can be obtained through their shape, reversibility and calculation of Curie temperatures. The Curie points for the corresponding samples have been calculated through the second derivative procedure (Petrovsky and Kapicka, 2006). For this experiment we used the equipment in Paris IPG. A Kappabridge KLY 3 was used in order to determine the Curie point of the magnetic carriers, as well as their stability during heating. The experiments were carried out in air. Susceptibility values were recorded continuously from room temperature up to 550 °C and back to room temperature. The equivalent equipment in the Geophysical Laboratory, University of Thessaloniki, MS2 Bartington susceptibility meter with the MS2WF attached furnace, was also used for complementary measurements from room temperature up to 700 °C. b) Hysteresis loops are also a standard experiment for rock magnetism studies. Their shape and calculated parameters provide important information on the nature and size of magnetic grains. These experiments were conducted in the Physics Department of Aristotle University of Thessaloniki, on a PAR 155 magnetometer with a 2T electromagnet.

area. The archaeomagnetic dating of the kiln in combination with OSL on the fragments suggests a possible date for the sherds between 340 and 221 BCE. Additional information on the kiln’s dating can be found in the supplementary material. 3. Materials and analytical methods A total of 23 fragments from the three sites were examined within a framework of archaeological information on typology (Fig. 3). None of the three groups could be considered as “fine ware” since they are mostly unpainted (PE) amphorae handles (TH) and other commonware (SM). From each fragment 2 to 3 specimens (apart only one exception) were cut in order to be used for the different methods applied in this study. In total, 48 specimens were studied. The mean size of each fragment was 3X4 cm in surface and 1–2 cm in thickness, while specimens followed the geometry of the fragment. More details on the material are included in the corresponding paragraphs for each site. Microscopic examination combines several analytical techniques such as ceramic petrography, scanning electron microscopy (SEM) and X-Ray powder diffraction analysis in order to better investigate the raw material sources. Defining the petrographic fabric groups was initially based upon their occurrence in the archaeological collections that were sampled, the extent of production centres and availability. This has allowed the regional geology of each area to be taken into consideration during the fabric characterization. Petrography has been performed on 15 pottery specimens and revealed a fine fabric for Pella, a coarse, a medium to fine and a fine fabric for Thasos, a coarse, a medium and a fine fabric for Samothrace ceramics. All but one polished thin-sections used for petrographic analysis were coated with carbon in order to achieve conductivity at the Scanning Electron Microscopy Laboratory of Aristotle University of Thessaloniki. At least one sample per petrographic fabric has been analysed by SEM with the aim of complementing the results of the petrographic analysis. Images and chemical analyses were performed with a SEM (JEOL JSM-840A, Tokyo, Japan) equipped with an Energy Dispersive Spectrometer - EDS (INCA 250, Oxford) with 20 kV accelerating voltage and 0.4 mA probe current. Backscattered electron (BSE) images were taken in order to determine the different mineralogical phases in the clay matrix. Chemical composition of the clay paste was measured using a beam size of 5 x 5 μm. On each sample 30 analyses of clay paste were performed. All data were normalized to 100%. SEM provides valuable information regarding the degree of refinement of the clay used, tempering and the firing conditions during the ceramic production. Therefore it is widely used in archaeometric studies on ceramics (Froh, 2004; Knappet, 2011 among others). This technique permits surface details to be obtained and statistical analyses to be performed to fully characterize the samples. X-ray Powder Diffraction spectroscopy is based on the fact that crystals diffract X-ray with an angle characteristic of the crystal and consequently of the material. The angle and the intensity of the peaks can give information about the phases present in the sample. That can be used for identification of general mineralogical composition and neo-formed minerals. By identifying the mineral phases present in ceramics, one can estimate the firing temperature which the ceramic products reached during the vitrification process. So, the main goal of XRPD analysis is the recognition of the mineral phases, especially new microcrystalline minerals formed by firing and from those the determination of the firing temperature and atmosphere condition in the kilns. However, it is important to bear in mind that XRPD can identify minerals only above 3% of the overall sample weight. Also XRPD analysis can confirm the data found by petrography and SEM-EDS analyses as well as complete a full mineralogical composition of the studied samples by distinguishing polymorph compounds. X-Ray diffraction can distinguish polymorphs by identifying the crystallography of each compound. Compounds with

4. Results 4.1. Ceramic petrography Thin section petrography is based on compositional analysis and provides data for the raw material selection and the reconstruction of technology (Peterson, 2009). Petrographic analysis allowed the classification of the samples into fabric classes based on a common range of explicit properties and not only from typology and macroscopic analysis. Since petrography can reveal significant points for archaeometric analysis, it was the first step done in this research and provided preliminary information concerning the fabric and the minerals included in the samples. In order to better investigate these issues, 15 pottery sherds were thin-sectioned and studied under the polarizing microscope (Zeiss Axioskop Pol.) following the systematic description proposed by Whitbread (1986; 1995). Each Fabric Class was based on the clay matrix, the compositional differences (the presence of different inclusions) and the fabric coarseness. It is important to bear in mind that the nomenclature for each fabric class is based on the set of samples from a specific area. For example we have fine fabric classes from Pella, Thasos and Samothrace, but that does not imply that all of these fabrics can be classified in the same category. Regarding the contribution of petrographic analysis an overview on the fabrics is required (Tables 1 and 2). Regarding Pella fine fabric samples, though the geology of Pella is mostly based on alluvial sediments, volcanic rock fragments are not uncommon. In fact, intense volcanic activity took place northwest from Pella and fragments from these rocks, most likely trachyte due to its texture and orientation of feldspars, would reach Pella as sediments (Higgins and Higgins, 1996; Vougioukalakis, 2002; Eleftheriadis et al., 4

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analysis. As for the metamorphic fabric, pyroxene is clearly present as well as some opaque minerals (Fig. 4c). Similarly to Pella samples, it was not possible to identify the opaque minerals present in the metamorphic fabric by petrography alone. The fine fabric from Samothrace has similar aspects to Pella fine fabric samples; it could even be questioned whether this is due to similar production techniques. Apart from Samothrace volcanic fabric sample, all the samples bear clay pellets, mostly with clear boundaries, subrounded and with high density. This pattern can be justified due to standard production procedure used by Hellenistic potters at that era (Drougou, 2014). By petrographic analysis we studied the characterization of ceramic fabrics which includes the identification of most minerals and rock fragments. Further analyses by SEM and XRPD can confirm the previous conclusions and determine those minerals not clearly specified.

Table 1 Overview of the analyzed fabric. Groups divided as Pella Fine Fabric (PFF); Thasos Coarse Fabric (TCF); Thasos Medium to Fine Fabric (TMFF); Thasos Fine Fabric (TFF); Samothrace Coarse Volcanic Fabric (SVF); Samothrace Coarse Metamorphic Fabric (SMF) and Samothrace Fine Fabric (SFF). INCLUSIONS

PFF

TCF

TMFF

TFF

SVF

SMF

SFF

Polycrystalline Quartz Quartz K-Feldspar White Mica Brown Mica Epidote Plagioclase Amphibole Sillimanite Calcite Titanite Pyroxene Volcanic Rock Fragments Metamorphic Rock Fragments Opaque Minerals Clay Pellets

X X X X X X X X

X X X X X X X X X

X X X X X X X X

X X X X X X X

X X X X X

X X X X X X X X

X X X X X X X X

X

X

X X X X

X

X

X

X

X X

X X X X X

X X X X X

4.2. Scanning electron microscope (SEM - EDS) X X

By SEM-EDS analysis it was possible to confirm the results found through petrographic analyses and identify minerals which the previous technique could not. Pella samples were found to consist of rutile, amphibole, epidote in small grains, titanite, pyroxene, chlorite and ilmenite. The presence of similar minerals in the different Pella samples suggests the same clay source or temper used for the production of the vessels. Iron oxides have been chemically identified only in sample PE01-07, while ilmenite and titanite were found in samples PE02-07 and PE02-08. Regarding Thasos samples, these consist of amphibole, iron-oxides, titanite, monazite and rutile which also suggest a common clay source or temper used for the production of the amphorae. The presence of calcite is likely due to post-burial processes, when calcite from the soil fills the gaps of voids and clay pellets. Furthermore, sample TH06-05 bears minerals which stand out from all the other samples from Thasos group set, i.e. sillimanite, xenotime and allanite. Xenotime and allanite contain rare earth elements, La, Ce, Nd and Y, while sillimanite points to a metamorphic rock source. In Samothrace samples, pyroxene was the focus for SEM analysis, as well as the opaque minerals determined by petrographic analyses, which point to an iron oxide. In order to confirm the petrographic results, elemental analyses of the clay was performed by SEM-EDS and the results are given in Table 3. Samples from Thasos and Pella, as well as one sample from Samothrace, present a grey inner core and a red outer rim. As revealed

X

2003). The metamorphic rock fragments could not be clearly identified by petrography alone, but their texture clearly belongs to basic aspects of metamorphic rocks. The opaque minerals found could not be identified by petrography alone as well, so we registered the particular minerals for elemental analyses (Fig. 4a). The major characteristic for Thasos samples is the presence of calcite linings and much larger epidote crystals, especially compared with Pella samples. The calcite linings, also known as hypo-coating, derive from calcite precipitation, after the ceramic’s burial. Calcite can easily crystallize between gaps since it is dissolved in solutions that circulate in the soil (Quinn, 2013). Fragments with epidote crystals could have originated from metamorphic rocks such as metabasites (Zachos, 1982; Wawrzenitz and Krohe, 1998; Brun and Socoutis, 2007). As for sericitized plagioclase, it could originate from either metamorphic or igneous rocks. Single mineral crystals cannot be used for the provenance identification of the raw material as they can derive from many different rock types (Fig. 4b). Samothrace samples were quite peculiar since all the fabrics present many similarities as well as unique features. The volcanic fabric not only contains fragments of andesite but also rare grains of titanite. Pyroxene may be present as a primary mineral but is quite altered due to firing conditions so its presence can be verified only by elemental

Table 2 Petrographic analysis of the studied samples. Groups are labeled as in Table 1. “X” checks the presence of the particular mineral or rock fragments within the sample. Petrographic Groups

Fine Fabric

Pella

PFF: Fine, well sorted, optical medium active. Common: quartz, feldspars, epidote, white and brown mica. Rare: volcanic(trachyte) and metamorphic rock fragment (PE 01–01, PE 01–07, PE 02–07, PE 02–08, PE 02–09) TFF: Fine, poorly sorted, optical active. Common: quartz, white and brown mica. Rare: micritic calcite, epidote, plagioclase, amphibole (TH06-01)

Thasos

Samothrace

SFF: Fine, poorly sorted, optical active. Common: quartz, plagioclase, white and brown mica. Rare: amphibole, volcanic and metamorphic rock fragments (SM12)

Medium Fabric

Coarse Fabric

TMF: Medium, well sorted, optical medium active. Common: quartz, feldspar, white and brown mica. Rare: epidote, mictitic, calcite, metamorphic rock fragments with epidote (TH05-05, TH0705, TH08-01) SMF: Medium, poorly sorted, optical inactive. Common: quartz, plagioclase, white and brown mica, volcanic rock fragments. Rare: amphibole, titanite, pyroxene, metamorphic rock fragments (SM13)

TCF: Coarse, well sorted, optical medium active. Common: quartz, plagioclase, white and brown mica. Rare: epidote, amphibole, mica schist (TH06-05, TH0608)

5

SCF: Coarse, poorly sorted, optical inactive. Common: quartz, white and brown mica, polycrystalline quartz with biotite, metamorphic rock fragments (epidotite), plagioclase. Rare: amphibole, volcanic rock fragments, pyroxene (SM15, SM18)

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Fig. 4. (a) Pella Fabric, XP, Sample PE01-01. Volcanic rock fragment; potentially trachyte (x10) 1.4 mm wide, (b) Thasos fine fabric, XP. Sample TH 07-05. Clay pellet with calcite linings, also known as hypo-coating (x10; 1 mm wide), (c) Samothrace coarse metamorphic fabric, XP, Sample SM-15.Metamorphic rock fragments have been identified. Fabric feature. (x5; 2 mm wide).

4.3. X-ray powder diffraction analysis

by SEM micrographs, the surface morphology between rim and core shows variations (Fig. 5). The outer rim shows a smooth, continuous, non-porous texture while the inner core is characterized by fine pores with a diameter less than 1 μm. On the other hand, the chemical composition of the clay matrix, as shown by EDS analysis is similar. The morphological difference between the core and the rim is ascribed to the different firing conditions as will be discussed in a following paragraph. Therefore, additional data from XRPD are needed to confirm the mineralogical composition of the samples, distinguish polymorphs by identifying the crystallography of particular minerals and provide characterization of the clay used.

As stated before, the mineralogical composition depends on the regional geology and the potters’ habits and experience. The estimated firing temperature for PE01 sample is T ≈ 750 to 800 °C. The presence of tremolite confirms that this temperature could not exceed 800 °C as such a mineral would not be present (Grapes, 2006; Xu et al., 1996). Data from petrographic analyses also confirm the firing temperature mentioned above since the micromass for Pella fine fabric has been described as optically slightly active, when almost complete dehydroxylation of clay minerals happens (Rathossi et al. 2004; 2010) (Fig. 6). Furthermore, sample PE02-09 belongs to the same fabric group as all the other samples and the micro mass can be described as medium/ slightly optically active (Fig. 6) so its firing temperature was probably

Table 3 Chemical composition of the different clays. Values represent average of 30 area (5 μm × 5 μm) analyses. All data are normalized to 100%. Analyses of inner and outer layers of representative samples are also given. SAMPLE

FORMULA Na2O MgO Al2O3 SiO2 K2O CaO FeO TiO2 Cr2O3 MnO BaO SO3

PE01-07 inner wt% 4,23 2,1 19,69 64,07 2,78 0,85 4,5 3,63 0,49 0,46

PE02-07

PE02-08

PE02-09

outer wt% 5.57 1.71 17.89 69.93 2.25 0.3 2.59 0.02 0.08

wt% 0,69 3,42 21,1 57,24 2,59 1,76 8,07 0,61 0,23 0,18 0,48

wt% 0,96 3,31 22,59 58,35 2,6 1,4 9,64 0,69 0,38 0,24 0,58

wt% 1,56 2,23 22,74 61,29 2,91 2,23 6,59 0,56 0,42 0,36

TH06-01 inner

outer

wt% 1,85 4,99 17,95 55,75 3,8 9,23 5,73

wt% 1.87 4.58 15.97 58.32 3.82 8.96 5.05

TH06-05

TH06-08

TH07-05

SM-12

SM-15

SM-18

wt%

wt%

wt%

3,44 23,05 65,43 2,53 1,51 4,41

14,65 53,48 26,12 2,94 4,22

3,66 23,55 53,05 3,34 5,94 7,56

wt% 0,88 4,5 29,9 53,23 0,66 1,61 8,17 1,18 0,33 0,26

wt% 2,97 3,66 21,97 61,04 0,68 2,84 7,46 0,71 0,29 0,36

wt% 2,14 4,81 22,97 60,39 1,55 1,72 6,23 0,7

5,81

6

0,75

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and pyrite. As observed by the petrographic analyses, calcite in this sample is secondary, deposited in voids after the burial of the ceramics. The presence of pyrite can be explained as secondary mineral as it can not persist above 600⁰C (Nungasser et al., 1985) and the firing temperature of this sample can not be very low as the optical behaviour of its micromass is medium optically active (Table 4). As a result the estimated firing temperature of Thasian samples is T ≈ 650° − 750 °C. A preliminary XRPD study on Thasian amphorae included two fragments from group TH05 of the present collection that is TH05-02 and TH0507. The calculated firing temperatures are very divergent, around 900–950 °C for the first but only 600°- 650 °C for the second, in agreement with the ones calculated in this study. The corresponding spectra are displayed in Fig. S7. Results of XRPD analyses on samples from Samothrace were not performed during this study. The relevant information on fragments from the same ceramic production was obtained from Rathossi et al., (2018). The compiled new results on the obtained minerals and associated firing temperatures are given in Table 4. 4.4. Magnetic properties of the studied ceramics 4.4.1. Pella Among the fragments which were retrieved from the two Pella kilns for the archaeomagnetic study, four representative samples were selected according to their color and shape. First the monitoring of the magnetic susceptibility variation with temperature (thermomagnetic analysis) on these specimens was performed up to 550 °C in order to detect the reversibility of the heating and cooling curves. A very similar pattern was observed for all (Fig. S4). Following this, three specimens were selected and heated up to 700 °C in order to calculate their Curie temperatures (Fig. 7). For two out of three the calculated Curie points provide values in the expected range of 496 °C−506 °C, indicating the dominance of titanomagnetite. For sample PE01-08 the Tc is very low, around 210 °C. This will be discussed together with similar results from Thasos. Hysteresis loops were performed, to our best, on the same material as for the thermomagnetic analysis, and to the one used for petrography and SEM. Therefore we used the following samples: PE01-01, PE01-08, PE02-07, PE02-08 (Fig. 7). From the shape of the loops and the calculated parameters the following characteristics can be observed: For PE01-01 dominance of single domain (SD) titanomagnetite. For PE0108 a mixture of two magnetic components most probably one superparamagnetic and one SD titanomagnetite. For PE02-07 the shell is pseudo -single domain (PSD) titanomagnetite with a higher quantity while the core is SD titanomagnetite with low quantity. Finally for PE02-08 a mixture of two magnetic components, most probably PSD and SD titanomagnetite is documented.

Fig. 5. Backscattered electron micrographs of sample PE01-07 – Outer (top) and inner (bottom) layer comparison.

4.4.2. Thasos Nine groups of stamped amphorae handles from Thasos were sampled in the past and the magnetic properties of several fragments, belonging to groups 1–5 are under study by A. Genevey and D. Kondopoulou. The groups were organized through their dating and not through provenance areas. Therefore we tried to investigate some fragments from groups 5, 6, 7 and 8 in order to enlarge our database. We used the same approach as for Pella: the first set was heated up to 550 °C (TH05-05, TH06-05, 08, Fig. S5). Then thermomagnetic analyses up to 700 °C were performed on specimens from group 6 for a better coverage: TH06-01, TH06-03, TH06-04 and TH06-08 (Fig. 8). In all cases, the susceptibility values are very low, the curves show a marked alteration around 350–450 °C corresponding to possible mineralogical transformations. The calculated Curie temperatures are T = 486 °C only for sample TH-06-08 while for the 3 remaining very low values were calculated (114°–172 °C). Hysteresis loops were performed on fragments: TH06-01, TH06-05, TH06-08 (Fig. 8). For sample THGR06-01 a mixture of SD/PSD and MD

Fig. 6. XRPD spectra of representative specimens from Pella and Thasos.

slightly higher T ≈ 800 °C to 850 °C which could also be explained by the higher content of hematite formed. All samples from Thasos clearly bear white mica, which can be preserved up to 900 °C, however the strong reflection recorded for such a mineral and the absence of neo-formed minerals suggests that the firing could not have exceeded 750 °C (Rathossi and Pontikes 2010; Kondopoulou et al., 2014). In addition the small amounts of calcite in sample TH06-07 indicate also that the firing temperature was below 750 °C. Results from sample TH07-05 indicate the presence of calcite 7

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Table 4 Results by XRPD for sites PE and TH, presenting the estimated firing conditions, micro mass description and minerals abundances (%). Q: Quartz, K-fd: K-Feldspars, Pl: Pagioclase, C: Calcite, M: Muscovite, Tr: Tremolite, He: Hematite, Py: Pyrite. SAMPLE

ESTIMATED FIRING TEMPERATURE (°C)

MICROMASS DESCRIPTION (OPTICAL ACTIVITY)

IDENTIFIED MINERALS (%)

PE01-07 PE02-09 TH06-01 TH06-05 TH06-08 TH07-05

750° – 800° C 800° −850⁰ C 650°-700⁰ C 700° −750⁰ C 650°-700⁰ C 650°-700⁰ C

Slightly optically active; light brown Slightly optically active; light brown Optically Active; Brown. Slightly optically active; very light brown Slightly optically active; very light brown Medium optically active; brown

Q 77 79 72 80 73 56

K-fd 6 18 4 18 5

Pl 9 9 8 4 2 7

C

2 17

REFERENCE M 1 2 7 6 6

Tr 3

He 4 12

Py

4 9

Present Present Present Present Present Present

study study study study study study

15 and SM-18 three of which are fully reversible (Fig. S6) and up to 700 °C on SM-13 and SM-15 (Fig. 9). The Tc calculated are between 430 and 440 °C, indicating the possible dominance of titanomagnetites in the samples. Hysteresis loops were obtained for fragments SM-12 and SM-A (Fig. 9) in addition to SM-19 published in Rathossi et al. (2018). Both samples contain MD grains of magnetite/titanomagnetite. Sample SMA contains a significantly higher quantity of magnetic grains than sample SM-12 in which a very small quantity of magnetic grains is found.

titanomagnetite is observed while for THGR06-05 considerably bigger amounts of MD are present. In THGR06-08 SD or PSD titanomagnetites in small amounts are dominant. The comparison of the two datasets is very promising as both indicate weak magnetization for samples TH06-05 and TH06-08 which are the two overlapping cases.

4.4.3. Samothrace Three of the ceramics retrieved from Samothrace were previously studied for archaeomagnetism, and relevant information in parallel with petrography is given in Rathossi et al., (2018). Thermomagnetic analysis up to 550 °C was done on new fragments: SM-12, SM-13, SM-

Fig. 7. (Top) Thermomagnetic analysis of three Pella samples. Susceptibility is given in 10-5SI units. (Bottom) Hysteresis loops for four Pella samples. 8

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Fig. 7. (continued)

5. Discussion

area, i.e., have not undergone much transport. Furthermore, the data from petrographic analysis can imply the firing temperatures to which the ceramics have been exposed during their production. In most of the samples, the micromass was optically active to medium optically active and its colour was light brown to yellowish red according to the Munsell Soil Colour Charts suggesting that the firing temperature was between 700 and 800 °C in an oxidising atmosphere. Usually, the clay matrix loses its birefringence between 800°–850 °C during firing. The samples with optically active clay matrices were interpreted as having an approximate firing temperature less than 800°–850 °C. The samples with an inactive matrix were interpreted as having an approximate firing temperature greater than 800°–850 °C (Quinn, 2013).

5.1. Interpretation of results The present ceramic collection was examined following a progressive protocol for an optimum exploration of the artifacts features. This protocol included petrography, SEM, XRPD analyses and magnetic mineralogy experiments (Table 5).

5.1.1. Petrography The presence of coarse minerals may suggest the use of temper during the production of the samples. For most of them the minerals do not show such evidence, except for the samples from Samothrace where metamorphic fabric presents a bimodal pattern of sand temper added during the vessel production. This converges with the known technology for the ceramic production during Hellenistic times (Hemingway and Hemingway, 2007). Moreover, the difference between the inclusions from each sample, regarding angularity and roundness, are attributed to the process used for the preparation of the clay (e.g. levigation). The degree of angularity in sediments is related to the distance through which clastic material has been transported from its source. In the present ceramic samples most of the grains are characterized as sub-angular to angular and the inclusions usually are poorly-sorted. This is considered as evidence that sediments have been deposited fairly close to the source

5.1.2. SEM Macroscopic and petrographic examination, as mentioned before, suggested that non-calcareous clay sources could have been used for the production of the ceramics in study due to the dominant reddish tone of the ceramic matrix from all samples. Additionally, samples from Thasos and Pella, as well as one sample from Samothrace, exhibit a red margin and a grey core (Fig. 3). This structure is possibly the result of firing conditions. The grey reduced core and the reddish oxidised margin can be the result of firing in kilns under an oxidising atmosphere with a low heating rate and long residence time (Maritan et al., 2006). According to Maniatis and Tite (1981), clays containing less than 9

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Fig. 8. (Top) Thermomagnetic analyses for four Thasos samples. Susceptibility is given in 10-5 SI units. (Bottom) Hysteresis loops for three Thasos samples.

6 wt% of calcium oxide are considered as non-calcareous clays. In all studied samples, with the exception of sample TH06-01, CaO content is less than 6 wt%, confirming the original petrographic observation that the clays used for the production of the vessels are non-calcareous. Sample TH06-01 has a high CaO content, 9.23 wt%, indicating a different clay source for this sample. Thasos amphorae have been divided in two groups based on their clay composition and on a previous relevant study on prehistoric pottery (Kondopoulou et al., 2017). The first group has been produced from calcareous clay which points to a source near marbles, dolomites and Neogene sediments while the second group has been produced from a non-calcareous clay, pointing to a source near metamorphic rocks.

kiln, and have been fired between 650° −800 °C (Rathossi et al., 2018). The calcite deficiency that was witnessed in the majority of samples may indicate that either the raw clays were extracted from a non-calcareous deposit or were not refined with calcite temper. Quartz was detected in all samples. This mineral persists on firing up to 1000 °C, and thus it indicates that the ceramic derived from silica-rich raw material. Quartz may be an indigenous mineral of natural clays or may be an intentionally added temper. Except quartz, feldspars are also evident in all samples, while the preservation of primitive minerals such as: clay minerals, white mica, hornblende and neo-formed such as: iron oxides, mullite helps on estimating the firing conditions of analysed samples.

5.1.3. XRPD A set of 8 ceramic samples collected from Pella and Thasos have been subjected to mineralogical (XRPD) analysis in order to gather further data on the mineralogical composition. The main purpose was to assess their firing conditions because the degree of thermal transformation to which the clay paste of ceramics has been subjected during the firing procedures is largely affected by the prevailing conditions in the kilns. The overall calculated firing temperatures for Pella vary between 750 and 850 while for Thasos they are between 650 and 750. We further used previously reported XRPD results from 3 samples from Samothrace (SMb, SM3, SM19) which constitute products of the same

5.1.4. Magnetic properties The calculated Curie temperatures for the majority of the studied fragments converge to dominant titanomagnetites as magnetic carriers. We report also a group of samples (PE01-08, TH06-01, TH06-03, TH0604) with very low Curie temperatures (below 200 °C). This feature, already reported in archaeological clays from various areas in Europe has been related to the presence of a new high coercivity-low Curie temperature iron oxide (e-iron oxide, McIntosh et al., 2007; 2011). The kiln from which the Samothrace ceramics were retrieved was studied for archaeomagnetism by Spatharas, (2005) and relevant results are also included in Spatharas et al. (2011). It can be assumed quite 10

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Fig. 8. (continued)

present study we selected three different geological zones with specific characteristics and we enriched the obtained data with magnetic mineralogy measurements. This combination is increasingly adopted for the archaeometric studies on ceramics and we favored it aiming to the improvement of the success in archaeomagnetic studies by appropriate material selection. Petrography performed on 15 pottery samples revealed a fine fabric for Pella, a coarse, a medium and a fine fabric for Thasos, a coarse, a medium and a fine fabric for Samothrace ceramics. The majority of these fabrics seem to have been locally produced. From the petrographic point of view, the observed samples share many similarities, but a few minerals are more specific of the origin area for each set of samples. The presence of metamorphic rocks in a high quantity, for instance, is persistent in Thasos amphorae. Consistency in the composition and micromorphology of Thasian amphorae from various production sites suggests that similar clay sources were used in different parts of the island (Whitbread, 1995). Following the geological evidence, sedimentary clays (other than recent alluvial deposits) are only present in the south-western part of Thasos and, in most cases these deposits are situated at some distance from the production sites. According to Peacock (1970) the potters used two clays, each taken from different localities on the island. The author reports clear differences between the clays collected at these localities referring to their color and grain size: yellowish brown and relatively fine, or reddish brown and rather coarse.

safely that the materials used are the same both for the kiln and its products, since these common use ceramics are not very elaborated and were attributed to the local workshop (Karadima et al., 2002). Therefore the information provided by Spatharas, (2005; 2011) in terms of magnetic mineralogy should be relevant to the one we cite here. A close examination of this dataset indicates prevailing titanomagnetites, mostly MD, and a few cases with mixtures of SD/PSD grains, both for the kiln’s clays and the produced ceramics. 5.2. Implications and general context. The pottery of the Hellenistic period proves to be common and uniform and at the same time varying depending on the tradition and the circumstances of different regions in the Hellenistic world. Increasingly affluent consumers during this period were eager to enhance their private homes and gardens with luxury goods. These lavish items were manufactured on a grand scale as never before, so it is safe to conclude that pottery recipes were well diffused in the Hellenistic world and, as a result, assume that the potters shared common knowledge on ceramic production. Several archaeometric studies in connection with raw materials were performed on Hellenistic pottery in this part of the Mediterranean (Neyt et al., 2012; Marzec et al., 2018 and references therein) apart from Greece where the list is long (for an overview see Drougou and Touratsoglou, 2012; Ackermann, 2018 and references therein). For the 11

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Fig. 9. (Top) Themomagnetic analyses on Samothrace samples. Susceptibility is given in 10-5 SI units. (Bottom) Samples SMA and SM- 12 hysteresis loops.

Table 5 Compilation of samples and techniques applied in the present study. Number of specimens depends on the methods used. XRPD results from Samothrace (SM) are from Rathossi et al. (2018). Sample

Specimens

Petrography

PE01-01 PE01-07 PE01-08 PE02-07 PE02-08 PE02-09 TH05-02 TH05-05 TH05-07 TH06-01 TH06-03 TH06-04 TH06-05 TH06-08 TH07-05 TH08-01 SM – a, b SM – 3 SM − 12 SM − 13 SM − 15 SM − 18 SM − 19

2 3 2 2 2 2 2 2 2 3 1 1 3 3 3 1 2 2 2 2 2 2 2

X X X X X

XRPD

X

X X X X

X X X X

SEM-EDS

Thermomagnetic

Hysteresis

X X X X X X X X

X X X X

X

X X

X

X X X

X X X

X X X X X X

X X X X

12

X X X X X X X X

X X X X X X X

X X X

X

X X X X X

X

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(Lilimbaki-Akamati and Akamatis, 2008). An important contribution of petrography and XRPD analysis in the present research was to assist on the estimation of the firing temperatures. Table 4 presents a general characterization of the studied samples by XRPD analyses. The maximum firing temperature of each sample is also indicated according to the presence or absence of particular minerals. For instance the estimated firing temperatures of Samothrace samples are T ≈ 650°-800 °C. The micromass of studied samples are optically active (clay minerals, T ≈ 600°–650° C) to slightly active (almost complete dehydroxylation of clay minerals, T ≈ 750°–800 °C). Moreover, the coexistence of both hematite and magnetite at temperatures below 1000 °C suggests firing in a mild oxidizing atmosphere. (Rathossi et al., 2018; Rathossi and Pontikes, 2010) Apart all technological and archaeological input provided by combined sets of optical methods, one application of the obtained information directly connects with the field of archaeomagnetism. As stated in a previous section, the possible contribution of optical methods to improve the outcome of such studies, is still under examination as it has already been underlined in recent publications (Kondopoulou et al., 2017). Combination of analytical and rock magnetic methods is increasingly explored worldwide in the last decade for estimating various technological aspects of ceramic production and especially provenance and firing temperatures. As an example, Rada et al. (2011) suggested that IRM acquisition curves as well as thermomagnetic measurements can be used to distinguish various pottery groups and as indicators for reducing or oxidizing conditions respectively. In more recent studies (Jordanova et al., 2018; 2019) extensive experimental procedures on Bulgarian collections establish protocols leading to such information. Nevertheless such an approach is beyond the scope of our research based mostly on analytical methods and basic rock magnetic results. The combination of petrographic observations, SEM and X-ray diffraction analysis was used, apart assessing the firing conditions (temperature, atmosphere), for estimating the proportion of Fe-bearing minerals in order to cross-check this outcome with the magnetic properties of the three collections. This cross-checking proved to be partly efficient as will be explained below. In Table 5 we have compiled the totality of experiments performed on the 23 fragments studied. In the majority of them, at least two different measurements were done. We will now focus to cases where all (5/5) or 4/5 experiments are available, mostly for Pella and Thasos and one from Samothrace. For Pella, samples PE01-07 and PE02-07 are studied with 4/5 methods. Both samples contain FeO but in lower amounts for PE01-07. They also belong to the same petrographic fabric class: Pella Fine Fabric (Table 1). All Thasos samples display alteration indications at low temperatures ~300°–400 °C. Together with their magnetic content of MD grains and rather low firing temperatures (less than 700 °C) these samples do not sound promising for archaeointensity studies. Finally, most of Samothrace samples do not seem to alter during heating, but did not reach very high temperatures apart from SM – 19 which is the only one that has provided successful archaeomagnetic results in a preliminary study (Rathossi et al., 2018). The cross-checking of information provided both by optical and magnetic

Ceramic groups from Samothrace were previously investigated, together with clay surveying (Karadima et al., 2002), through XRF analysis. Several groups were isolated among which some of local and others of non-local origin. Two among these groups, named 2 and 3 by the authors, due to their high contents in chromium and nickel, have been assigned to the areas of Palaeopolis and Keramidharia, where our samples were collected. These are compatible with the proximity of gabbro outcrops, which increased the concentrations of Cr and Ni within the sediments resulting from alteration. Elemental analyses of the clay from our Samothrace samples show existence of Cr2O3 in small quantities in samples SM-12 and SM-15 as well as higher amounts of FeO, while sample SM-18 lacks Cr2O3 and has smaller amounts of FeO. The first two samples possibly point to areas near the alteration of the gabbro formations that exist at the centre of the island while the latter derive from a different location. This observation is in accordance with Karadima et al., (2002) as reported above. The minerals identified by spectroscopy suggest that all samples correlate with each other while each set group bears some particular minerals compared to each other group set, in relation to the area where the samples were produced. The local geology is characterized by the exclusive minerals from each sample set, e.g sillimanite in Thasos samples. Thasos samples correlate to the maximum with both Pella and Samothrace samples, in terms of fine fabric. Fine fabric from Samothrace has similar aspects as Pella fine fabric samples. Therefore we can conclude that the potters used a preferred type of clay or/and a similar production technique to obtain fine fabrics. SEM-EDS analyses provided also information regarding the clay texture and composition. It confirmed the use of non-calcareous clay for the production of the samples under study, with the exception of sample TH06-01. Furthermore, SEM results enhance the suggestion that potters had followed similar if not identical recipes, and the major difference refers to the non-plastic inclusions, that could have originated either from the clay source or from the added material (e.g temper). The petrographic, mineralogical and geochemical analyses indicate that all the observed samples were produced from non-calcareous clay with similar composition due to the overall low percentage of calcium oxide and the bloating porous microstructure displayed by the BSE microphotographs. All samples differ very little both in texture and chemical composition. The discrimination of sample TH06-01, which has the highest CaO content, 9,23 wt%, probably indicates an exception From the macroscopic examination, samples from Pella and Thasos and one sample from Samothrace, show an outer red/dark red margin and an inner grey core. When examined with SEM-EDS, these areas reveal a different microstructure. Margins are non-porous and the sheet like habit of the clay minerals is evident while the cores exhibit fine pores with a diameter of less than 1 μm. The difference in color and morphology is attributed to the differing firing conditions (Maniatis and Tite, 1981). The more reddish outer margin points to oxidizing conditions during firing while the gray-colored inner core points to reducing conditions. Based on this fact, firing of these samples is assumed not to be completed, in accordance with archaeological information, for instance in Pella where the kilns appear to be destroyed during firing Table 6 Comparative information provided by optical and magnetic methods. Sites Methods

Pella

Thasos

Samothrace

Petrography

Fine fabric (volcanic and metamorphic inclusions) High % FeO, Low % TiO2 700 °C–850 °C 750 °C–800 °C 494 °C–506 °C 290/558 °C, SD/PSD titanomagnetites

Coarse, medium and fine fabrics (indication for metamorphic/volcanic origin) Low % FeO, No TiO2 650 °C-700 °C 486 °C 114 °C–172 °C Mixture of SD/PSD and MD titanomagnetites

Coarse, medium and fine fabrics (volcanic fabric with fragments of andesite and titanite/metamorphic) High % FeO, Low % TiO2 650 °C–800 °C 434 °C–440 °C MD titanomagnetites

SEM XRPD (Firing temperatures) Magnetic Mineralogy (Tc) Hysteresis

13

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experiments is displayed in Table 6. It is noteworthy to observe that the existence of titanomagnetites can be traced through magnetic measurements even if they are not tracked by SEM analysis.

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6. Conclusions Detailed analytical experiments applied to 23 potsherds from Late Classic to Hellenistic collections (Northern Greece) when combined to three previously studied ones from Samothrace, have confirmed the local provenance of the clays in almost all cases and provided information on the technology used. When compared to magnetic mineralogy experiments performed on selected fragments, a more concise pattern of their content and characteristics as far as their iron oxides inclusions are concerned can be drawn. Among the three collections studied here, we claim that Thasos amphorae are the less promising for archaeomagnetism- archaeointensity calculations which imply long series of heating and cooling cycles and this can be explained by the tendency of Thasian clays to alter during heating and by the rather low firing temperatures. This last observation was already mentioned for a prehistoric pottery collection in Thasos, therefore it suggests a diachronic feature in preparation and use of Thasian clays (Kondopoulou et al., 2017). Nevertheless and in spite of this promising outcome we confirm, by the present study, that if optical methods have to be combined to magnetic ones in order to improve the success of archaeomagnetic experiments, then a much bigger and variable dataset is requested. In order to build an easily applicable protocol, the abundant greek ceramic collections, already well studied through archaeometry, should be explored. For instance samples originating from different geological areas could be collected from archaeological periods between the end of Bronze Age and the Classical period, which lack sufficient archaeomagnetic information. We remain confident that there is a real potential in such approach, therefore we expect to have the opportunity to expand this research. In this context, the present article aimed to be among the first of many future steps to come, regarding a harmonic cooperation between different scientific approaches to enrich the already flourishing ceramic studies in the broader area. Acknowledgements The current article is based on the results of a Master thesis within ARCHMAT – Erasmus Mundus Master in Archaeological Materials – to promote a better approach between Archaeology and Material Sciences. For such realization the first author is indebted to many individuals and institutions for their support and encouragement. We would like also to thank Prof. G. Vourlias and Dr. A. Bourliva for their major role in assisting on the XRPD experiments realization and interpretation. The analysis of these Greek ceramic samples could not be possible without the aid of the archaeologists, Dr. N. Akamatis and Dr. Ch. Karadima who allowed the use of ceramic collections from Pella and Samothrace respectively. Dr. A. Genevey agreed to provide samples from Thasos (French School at Athens material) for archaeometric purposes and commented on an earlier version of the paper. D. K. and E. A. acknowledge partial support by the project “HELPOS – Hellenic System for Lithosphere Monitoring” (MIS 5002697) which is implemented under the Action “Reinforcement of the Research and Innovation Infrastructure”, funded by the Operational Programme “Competitiveness, Entrepreneurship and Innovation” (NSRF 2014–2020) and co-financed by Greece and the European Union (European Regional Development Fund). The efforts of the editor and two anonymous reviewers are highly appreciated and improved substantially our manuscript. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.jasrep.2019.102097. 14

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