Proceedings of the 39th International Symposium for Archaeometry, Leuven (2012) 251-256

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Black- and red-slipped pottery from ancient Cassope (NW Greece): inference of provenance and production technology based on a multi-analytical approach

A. Oikonomou1, C. Papachristodoulou2, K. Gravani3, K. Stamoulis4 and K. Ioannides2,4

1. Department of Protection and Conservation of Cultural Heritage, TEI of Ionian Islands, Zante, Greece,

artoikon@teiion.gr 2. Department of Physics, The University of Ioannina, Ioannina, Greece,

xpapaxri@cc.uoi.gr, kioannid@cc.uoi.gr 3. Department of History-Archaeology, The University of Ioannina, Ioannina, Greece

4. Archaeometry Center, The University of Ioannina, Ioannina, Greece, kstamoul@cc.uoi.gr, kioannid@cc.uoi.gr

ABSTRACT The present work reports the results of a multi-analytical study of 90 pottery sherds recovered from the archaeological site of Cassope (mid-4th to 1st century BC), in Epirus (NW Greece). The elemental composition of the ceramic bodies was assessed using radioisotope-induced energy-dispersive X-ray fluorescence spectroscopy. The compositional data were statistically treated by principal component analysis and chemical groups were established, representing locally produced and imported items. Mineralogical analysis of the ceramic bodies by X-ray diffraction indicated firing temperatures in the range from 800 to 1000°C for most of the sherds, while one group consisted of over-fired items, possibly in excess of 1050°C. The morphology of the slip layers and the microstructure of the ceramic bodies were examined using scanning electron microscopy, which showed that different pottery groups exhibit surface slips of a different nature, in terms of thickness and degree of vitrification. Overall, the elemental classification combined with inferences concerning production skills and choices, shed light on different aspects of the political and socioeconomic history of Cassope. KEYWORDS Compositional analysis, multivariate statistics, pottery, provenance, technology. Introduction Cassope was a significant political and economic centre of Epirus, founded around the mid-4th century BC as the capital of Cassopea (Dakaris 1971, Hoepfner et al. 1994). The most flourishing period of Cassope was during the times of the Epirote League (234-168 BC) and particularly around the end of the 3rd to the beginning of the 2nd century BC, when Cassopaea broke away from the League and became independent, issuing its own silver coinage and trading with Italy through the Ionian ports and the island of Corfu. The city declined following the conquest of Epirus by the Romans in 167 BC; partial reconstruction took place after 148 BC and a certain level of economic prosperity was sustained until 31 BC when the residents of Cassope were

forced to settle to the newly-established roman Nikopolis (Fig. 1). Large amounts of pottery were recovered during the excavations conducted in Cassope between 1951 and 1955 by the “Archaeological Society at Athens” and between 1977 and 1983 by the University of Ioannina, in collaboration with the German Archaeological Institute. In the present work, a set of 90 sherds were selected and characterized by means of Energy-Dispersive X-Ray Fluorescence (EDXRF) spectroscopy, X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The study aimed primarily at identifying compositional groups of pottery and distinguishing between local and imported items.

Fig. 1. A map showing the location of Cassope in ancient Epirus.

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Furthermore, technological choices were explored, such as the firing conditions and the surface coating techniques used in pottery manufacture. Materials and Methods The ceramic collection The selected sherds included different vessel parts, such as rims, handles, bases and bodies of fine tableware. Based on the criteria of date, style and fabric, they were initially classified as “local” black-slipped (LBS) pottery, “local” red-slipped (LRS) pottery, Eastern Sigillata A (ESA) and Western Terra Sigillata (WTS) (Gravani 1994, 2004). The LBS sherds date from the mid 4th to the mid 2nd century BC, whereas the remainder of the samples span the period from the second quarter of the 2nd to the late 1st century BC. Characterisation techniques The concentrations of 15 minor and trace elements were determined in the ceramic bodies using radioisotope-induced EDXRF spectroscopy. A small area of each specimen, preferably on broken edges, was scrubbed until the surface slip and any surface contaminating particles were entirely removed and a clean layer of the ceramic body was exposed. A small piece was subsequently extracted and ground to a fine powder in an agate mortar. Powdered samples were pressed into 12mm diameter pellets by mixing 100mg of sample with cellulose at a ratio of 10% w/w. Photons emitted from annular radioisotopic 109Cd and 241Am sources were used for sample excitation. The sources were fixed coaxially above a CANBERRA SL80175 Si(Li) detector, having an energy resolution of 171eV for the 5.9KeV Mn Ka line. Spectral analysis was carried out using the WinQxas software package and elemental compositions were assessed with reference to the standard SOIL-7 material provided by the IAEA (International Atomic Energy Agency, Vienna, Austria). X-ray diffraction patterns were obtained for representative potsherds using a D8 Advance Brüker diffractometer operating with CuK! (" = 1.5406 Å) radiation and a secondary beam graphite monochromator. Powder samples, obtained as described above, were scanned over an angular 2# range from 5 to 60º, in steps of 0.02º (2#) at a rate of 2s per step. Fresh-fractured sections of selected sherds were examined through a field-emission scanning electron microscope (SEM, FEI Inspect F) to study the microstructure of the ceramic bodies and the morphology of the slip layers. Statistical treatment Elemental compositions obtained from EDXRF measurements were submitted to Principal Component Analysis (PCA) in order to identify structure in the data. PCA is a dimension-reducing technique, applied to study multivariate data sets that include N observations (samples), each characterised by D variables (elemental concentrations). The analysis defines a new set of

uncorrelated variables, called principal components (PCs), which are linear combinations of the original elemental variables, weighted through the PC loadings. The greater the structure in the original data, the more variance will be accounted for by the first few principal components. Normally, scatter-plots of the first two or three PC scores reveal groups of samples having similar chemical fingerprints. The corresponding loading plots allow identification of the elemental variables that are responsible for the similarities or differences detected. In the present work, PCA based on a variance-covariance matrix was carried out using algorithms in the STATISTICA software package (v. 6.0 for Windows). Before carrying out a PCA, the elemental concentrations were submitted to an additive log ratio transformation, following the approach introduced by Aitchison and further elaborated by Buxeda i Garrigós (Aitchison 1986, 1996, Buxeda i Garrigós, 1999, Buxeda i Garrigós et al. 2001). The compositional component d (i.e. the concentration of the d element) that introduces the lowest chemical variability to the entire dataset has been identified and logarithms of ratios were obtained using this component as a divisor. The variability introduced by each compositional component to the entire dataset was assessed by constructing the variation matrix, which, in a D-parts composition, x is defined as:

T = [!ij] = [var{log(xi/xj)}: i, j = 1, …, D]. The contribution of each element i to the total variation, is estimated through the ratio vt/!i, in which vt is the total variation, calculated as:

! ! "== =

D

i

D

jijD

vt1 12

1 ,

where !i is the sum of variances using element i as a divisor. A high vt/!i value indicates that the element i contributes the least to the chemical variability and can therefore be considered to be the most stable. Results and Discussion Compositional data and statistical analysis The elemental concentrations determined by EDXRF spectroscopy are given in Table 1. The data reveal a considerable spread, which does not result from counting statistics or method precision; it rather implies pottery from different production sites or reflects the natural heterogeneity of local clay deposits and the application of different manufacturing processes in local workshops. Arguments of this kind may be proposed on the basis of the statistical treatment of the elemental data. A total of 15 elemental variables were included in the statistical analysis and the variation matrix was calculated. The lowest variability in the entire dataset is imposed by Zr (vt/!Zr =0.891, i.e. a variability of 11%) and thus a log ratio transformation using Zr as a divisor was applied. Note that the elements that introduce the highest variability are Nd, Ca, Rb and Sr.

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The PC1-PC2 score plot shown in Fig. 2 allowed the distinction of four compositional groups, in line with the initial classification of the examined samples. Based on archaeological evidence, the LBS sherds date to the first period of prosperity of Cassope and represent pottery produced abundantly in local workshops. After the reconstruction of Cassope in 148 BC, some of these workshops were still in operation and followed the general demand for the manufacture of red-slipped pottery; the LRS group probably includes such local products. The ESA

sherds may be considered as imported to Cassope from eastern Mediterranean workshops, mainly after the first quarter of the 1st century BC, when this type of pottery became particularly widespread. The samples grouped as WTS are thought to represent items imported in Cassope during the 1st century BC from roman workshops at Arezzo (Gravani 1994); the Cassopeans were involved in commercial activity with the Italian coasts even earlier than the 2nd century BC and continued to trade during the period of the roman occupation.

Table 1. Elemental concentrations determined through EDXRF spectroscopy. Values are given in ppm (µg g-1) unless otherwise indicated. Sample K (%) Ca (%) Ti (%) Mn (%) Fe (%) Zn Rb Sr Y Zr Nb Ba La Ce Nd

Local black-slipped ware (n = 52)

K1529 1.15 3.20 0.69 0.16 7.14 89 49 154 20 138 18 415 27 55 27

K39a 0.82 2.73 0.70 0.12 6.89 84 41 105 19 141 14 291 21 51 29

K1542 1.31 2.96 0.65 0.11 6.28 94 52 124 24 147 15 357 24 46 30

K31 1.22 3.50 0.67 0.14 6.56 102 43 114 20 132 15 314 19 48 31

K35 1.48 2.89 0.61 0.11 6.30 87 43 128 22 157 17 389 22 50 27

K51 1.79 5.29 0.87 0.23 9.91 123 56 180 26 193 24 329 22 43 22

K1521 1.89 5.98 0.80 0.20 9.07 114 78 214 24 165 15 328 59 46 25

K34 1.78 8.46 0.67 0.17 8.20 133 66 258 24 165 14 251 72 38 26

K119 2.18 6.19 0.70 0.13 7.92 113 70 231 30 189 22 298 64 42 24

K49 2.00 7.67 0.72 0.16 8.47 136 66 233 22 159 17 301 31 40 27

K1550 1.67 11.20 0.63 0.19 8.46 77 39 283 23 144 14 297 40 46 25

K1522 1.21 9.94 0.43 0.15 5.48 179 39 259 17 110 11 264 18 37 27

K1205 1.44 4.66 0.60 0.12 6.98 144 54 173 22 132 15 337 25 51 26

K1216 1.16 5.69 0.68 0.13 6.69 159 82 221 21 149 11 330 23 49 25

K1220 1.15 5.12 0.75 0.14 7.94 100 63 196 34 161 24 361 27 54 29

K1203 1.37 7.74 0.67 0.12 6.55 93 59 252 20 149 10 304 19 48 29

K46 1.45 6.57 0.77 0.14 7.63 188 67 207 19 150 12 311 23 47 26

K460 1.20 4.98 0.68 0.09 6.85 107 69 167 20 138 16 364 22 47 26

K454 1.01 4.46 0.62 0.10 6.15 114 62 144 20 142 15 355 24 49 30

K457 0.99 4.68 0.55 0.11 5.99 108 56 135 21 138 15 341 25 50 27

K492 1.02 4.88 0.60 0.10 6.30 100 60 157 19 141 16 362 27 48 31

K462 0.97 4.18 0.64 0.14 7.34 100 51 128 21 153 15 349 25 52 29

K1326 1.08 5.00 0.45 0.09 5.78 105 65 175 21 134 13 347 28 56 32

K1334 0.98 4.22 0.61 0.08 7.03 150 45 131 19 113 15 364 20 45 25

K461 0.82 4.24 0.54 0.13 6.82 156 40 161 23 138 23 403 24 48 29

K482 0.84 3.47 0.54 0.11 7.24 92 48 131 28 134 15 265 17 40 27

K415 1.51 5.19 0.64 0.21 7.48 133 49 158 23 155 15 259 14 43 27

K391 1.14 6.12 0.98 0.15 8.89 141 45 139 27 167 23 262 24 52 29

K392 1.45 5.85 0.92 0.15 8.86 139 55 154 23 168 23 303 22 46 24

K388 1.34 4.79 0.91 0.13 8.39 144 59 172 25 178 20 322 20 43 25

K396 1.64 5.32 0.84 0.12 8.26 218 59 191 22 159 25 343 21 45 25

K443 1.27 7.83 0.59 0.10 6.27 100 38 226 39 136 16 243 19 40 24

K436 0.68 2.99 0.34 0.09 4.40 41 34 111 17 91 9 314 20 43 27

K1633 1.08 4.03 0.72 0.12 7.05 78 60 142 21 149 14 330 24 48 27

K342 1.20 5.41 0.57 0.14 6.02 90 59 155 21 130 16 282 20 46 26

K1635 0.98 5.21 0.60 0.13 6.25 84 57 147 20 134 16 305 20 41 25

K301b 0.76 6.15 0.57 0.11 5.98 94 46 198 16 146 11 274 13 39 23

K281 0.87 4.81 0.38 0.08 4.73 67 41 173 15 106 11 217 16 34 26

K147 0.76 4.04 0.56 0.10 7.05 91 33 108 17 107 11 165 14 29 23

K1256 1.03 4.78 0.52 0.09 6.55 97 76 188 23 121 14 253 17 37 28

K249 0.74 3.77 0.56 0.11 7.55 158 43 134 20 135 15 271 20 43 24

K1259 1.04 3.97 0.57 0.11 7.23 133 56 150 21 133 18 315 20 44 24

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Sample K (%) Ca (%) Ti (%) Mn (%) Fe (%) Zn Rb Sr Y Zr Nb Ba La Ce Nd

K1280 2.06 3.26 0.73 0.19 8.49 151 99 112 26 162 15 402 24 47 27

K166 1.89 3.91 0.87 0.21 9.69 147 72 105 30 181 17 325 33 48 27

K1579 2.08 7.78 0.68 0.19 7.62 77 84 232 25 167 17 313 16 44 22

K1560 2.25 6.32 0.72 0.20 9.16 131 73 189 24 157 15 401 19 41 26

K184 1.77 5.34 0.85 0.22 10.04 179 53 165 31 190 15 342 27 52 29

K177 1.88 5.29 0.79 0.18 8.99 139 82 187 26 188 21 342 27 52 28

K1304 1.76 3.29 0.69 0.24 8.16 144 59 118 27 162 17 433 35 51 29

K1661 1.94 7.62 0.65 0.16 7.79 123 71 257 23 172 12 299 26 39 28

K271 0.88 1.63 0.69 0.10 8.24 118 58 58 24 135 20 270 31 50 27

K1567! 1.81 4.16 0.67 0.17 7.98 142 68 146 26 165 13 248 28 40 24

Local red-slipped ware (n = 19)

4/43 1.19 3.98 0.62 0.16 9.14 164 64 160 22 126 16 166 15 35 11

2/76 1.30 4.98 0.65 0.16 8.16 161 75 218 23 126 14 234 15 40 9

8/17 1.39 3.36 0.61 0.15 8.30 147 117 138 27 119 17 209 15 38 10

8/75 1.76 6.04 0.69 0.16 8.42 225 55 227 28 132 18 245 17 44 12

8/18 1.27 5.97 0.54 0.20 7.83 179 49 228 28 152 16 174 16 34 9

46/6 2.28 6.01 0.84 0.20 9.99 168 71 193 24 163 20 283 16 40 9

"#/6 1.22 6.10 0.63 0.13 8.18 105 30 142 26 142 17 195 14 31 10

3/31 1.41 5.35 0.49 0.12 6.73 131 55 252 17 104 11 269 14 39 8

2/72 1.26 5.56 0.50 0.14 6.98 132 47 232 18 102 10 267 25 33 9

8/74 1.35 6.45 0.45 0.14 6.61 117 49 245 20 104 12 286 14 40 9

Pf/2 1.38 6.08 0.49 0.14 6.87 131 52 248 19 104 12 279 21 39 11

X139 1.27 5.26 0.46 0.12 6.60 119 47 234 17 102 10 265 12 34 9

5/170 1.97 8.26 0.65 0.17 7.52 92 52 242 28 159 15 254 13 38 10

X141 2.07 7.62 0.65 0.21 8.67 135 61 328 20 140 16 255 10 35 8

K8/17 1.47 6.00 0.88 0.15 8.97 140 56 260 28 165 19 219 14 37 11

7!/2 1.73 8.20 0.58 0.18 7.29 144 88 266 24 139 17 195 15 33 10

2/46 1.49 6.16 0.58 0.15 7.59 133 59 244 21 125 14 244 15 37 9

X140 1.79 7.53 0.71 0.18 8.57 153 72 284 25 148 17 282 19 39 10

2/63 1.67 6.80 0.59 0.21 8.25 157 55 278 24 146 16 215 13 35 9

Eastern Sigillata A (n = 11)

2/32 0.94 9.81 0.45 0.09 4.95 95 12 270 16 107 12 241 13 38 10

7/B 0.83 10.6 0.41 0.08 5.70 82 9 293 17 101 10 133 14 37 9

2/100 0.84 9.78 0.40 0.08 5.25 86 10 285 19 122 14 242 11 38 10

$6/34 0.91 10.0 0.39 0.09 5.52 88 10 279 18 103 10 160 13 33 9

2/33 0.67 9.25 0.37 0.07 4.99 71 9 299 16 95 10 126 11 33 8

5!/% 0.89 9.34 0.38 0.08 5.15 95 10 286 24 97 9 131 12 32 8

2/26& 1.55 6.63 0.62 0.18 8.24 87 52 208 26 162 18 223 12 39 9

3/46 1.36 12.5 0.56 0.11 7.78 102 28 199 23 137 18 127 11 27 6

"#/7 1.40 6.88 0.67 0.13 8.30 122 33 169 25 153 21 211 16 37 8

8/&'5 1.29 11.3 0.57 0.13 7.98 109 28 244 22 139 16 239 16 35 10

K/198 1.35 10.2 0.60 0.12 8.02 111 30 204 23 143 18 192 14 33 15

Western Terra Sigillata (n = 8)

1/20 1.42 5.79 0.54 0.15 5.73 130 68 283 26 163 25 409 23 73 18

1/4 1.43 5.75 0.52 0.17 5.92 133 78 257 24 150 23 340 21 66 15

"#/12 1.42 6.71 0.49 0.20 5.65 145 71 265 26 129 21 339 23 66 17

"#/8 1.32 6.19 0.55 0.15 5.52 134 60 282 26 148 24 347 24 65 16

5/23 7& 1.85 4.67 0.64 0.09 5.85 109 60 340 27 163 20 394 21 65 16

"#/4 1.65 6.48 0.61 0.19 6.11 153 77 311 25 161 21 333 21 64 19

1/11 1.13 4.49 0.48 0.10 5.43 112 58 230 23 142 19 375 23 68 16

"#/1 1.16 5.81 0.53 0.15 5.71 132 72 281 31 166 32 392 24 70 16

Entire sample set (n=90)

Mean 1.36 5.96 0.62 0.14 7.24 123 55 202 23 142 16 288 21 44 20

( 0.40 2.17 0.13 0.04 1.31 33 20 62 4 24 4 71 10 10 8

( (%) 29.2 36.4 21.5 28.8 18.0 26.9 35.8 30.6 18.7 16.6 26.9 24.7 46.9 21.7 41.1

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Fig. 2. A scatter-plot of the first two principal components (PC1-PC2) of the elemental data. The ellipses represent the 95% confidence level for group membership. The corresponding variable loadings plot is shown in the inset. Mineralogical analysis X-ray diffractograms are given in Fig. 3 for selected sherds considered to be representative of the chemical groups established by PCA. A firing temperature of at least 850ºC was estimated for all sherds, based on the development of diopside, a high-temperature Ca/Mg silicate that forms upon complete decomposition of primary calcite above 800-850ºC. Higher temperatures, possibly in excess of 1050°C, may be postulated for ESA sherds, as the XRD pattern depicted a considerable abundance of diopside and a partial collapse of quartz. Such a high temperature may be associated with the anomalous rubidium concentrations, which are lower by a factor of ~5 in ESA sherds, compared to sherds from the other groups. The same trend, although less pronounced, is observed for potassium concentrations. Severe changes in alkali metals have been correlated with the firing temperature, both in calcareous and non-calcareous pottery. These changes may be manifested either as a loss of alkalis from the sherd or as a concentration gradient between the surface and the core of the sherd (Buxeda i Garrigós, 1999, Buxeda i Garrigós et al., 2001, Zacharias et al., 2005, Schwedt et al., 2006, Schwedt and Mommsen, 2007). SEM analysis Firing temperatures may also be inferred by examining the micro-structure of the ceramic bodies under the SEM (images not shown). Following the main stages of vitrification established by Maniatis and Tite (1981), the analyzed LBS, LRS and WTS samples featured initial-to-extensive vitrification associated with firing at 850-1000°C. Total vitrification was evidenced for the ESA samples, indicating firing temperatures in excess of 1050°C. The above findings are in good agreement with the XRD data.

The surface slips observed under the SEM presented variable morphological features (Fig. 4). The WTS sherds possess a uniform, highly vitrified slip layer that measures 10-12µm in thickness and exhibits a sharp and even contact line with the main body. Examination of the ESA sherds revealed a coarse and unvitrified outer surface, with the coating being hardly distinguished from the body. This finding was rather unexpected given the visual appearance of these sherds, which exhibited coating layers of a deep orange-red hue. However, such a finish might have been obtained without the application of any slip, by simply smoothing the surface with a wet hand or cloth. This practice could possibly indicate a deliberate choice for decreasing labour investment in the frame of a massive production. Sherds in the LRS group displayed a less regular coating, which, in several places revealed the underlying body. The coating was still well vitrified and varied in thickness from ~8µm to 5µm. The LBS sherds were generally characterized by a poorly preserved surface slip and decoration. This was attributed to the use of damaged matrices during manufacture, as well as to the perturbation of archaeological layers during the destruction and reconstruction of Cassope.

Fig. 3. X-ray diffractograms for selected sherds. The indicated mineral phases are Q: quartz, P: plagioclase, F: potassium feldspar, D: diopside, C: calcite, H: hematite, I: illite.

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Fig. 4. SEM images of selected sherds showing the ceramic body-to-slip interface. Concluding remarks A multi-analytical approach was used to characterise a collection of 90 pottery sherds from ancient Cassope (mid-4th to 1st century BC). The examined sherds were classified in four different groups, on the basis of the EDXRF compositional data and multivariate statistical analysis. Further investigation through XRD and SEM measurements revealed different technological choices in the ceramic manufacture of each group. The analysis of pottery from ancient Cassope and the distinction of local pottery production provide additional input to a recently assembled compositional databank (Papachristodoulou et al. 2006, 2010) and contribute to establishing reference groups for Hellenistic pottery from Epirus. Acknowledgements All analytical measurements were carried out in the EDXRF and XRD laboratory units, at the University of Ioannina and in the SEM-EDX facility at the Institute of Materials Science, NCSR “Demokritos”. References Aitchison, J.A. 1986. The Statistical Analysis of Compositional

Data. Monographs on Statistics and Applied Probability. Chapman & Hall Ltd., London.

Aitchison, J.A. 1996. On criteria for measures of compositional difference. Mathematical Geology 24, 365-379.

Buxeda i Garrigós, J. 1999. Alteration and contamination of archaeological ceramics – the perturbation problem. Journal of Archaeological Science 26, 295-313.

Buxeda i Garrigós, J., Kilikoglou, V. & Day, P.M. 2001. Chemical and mineralogical alteration of ceramics from a late bronze age kiln at Kommos, Crete: the effect on the formation of a reference group. Journal of Archaeological Science 43, 349-371.

Dakaris, S. 1971. Cassopaia and the Elean Colonies. In: Athens Center of Ekistics (Ed.) Ancient Greek Cities 4. Athens.

Gravani, K. 1994. Die keramik von Kassope. Ein vorläufiger überblick. In: Hoepfner, W., Schwandner, E.L. (Eds.) Haus und Stadt im klassischen Griechenland, Wohnen in der Klassischen Polis I. München, 162-172.

Gravani, K. 2004. Hellenistic red-slipped pottery from Cassope. In: Hellenic Ministry of Culture, Archaeological Receipts Fund (Ed.) 6th Scientific Meeting for Hellenistic Pottery. Athens, 569-584.

Hoepfner, W., Schwandner, E.L., Dakaris, S., Gravani, K., Tsingas, A., 1994. Kassope, Bericht über die Ausgrabungen einer spätklassischen Streifenstadt in Nordwestgriechenland. In: Hoepfner, W., Schwandner E.L. (Eds.), Haus und Stadt im

klassischen Griechenland, Wohnen in der Klassischen Polis I, München 1994, 114-161.

Maniatis, Y. & Tite, M.S. 1981. Technological examination of Neolithic-Bronze age pottery from central and southeast Europe and from the Near East. Journal of Archaeological Science 8, 59-76.

Papachristodoulou, C., Oikonomou, A., Ioannides, K.G. & Gravani, K. 2006. A study of ancient pottery by means of X-ray fluorescence spectroscopy, multivariate statistics and mineralogical analysis. Analytica Chimica Acta 573-574, 347–353.

Papachristodoulou, C., Gravani, K., Oikonomou, A. & Ioannides K. 2010. On the provenance and manufacture of red-slipped fine ware from ancient Cassope (NW Greece): evidence by X-ray analytical methods. Journal of Archaeological Science 37, 2146-2154.

Schwedt, A., Mommsen, H., Zacharias, N. & Buxeda i Garrigós, J. 2006. Analcime crystallization and compositional profiles – comparing approaches to detect post-depositional alterations in archaeological pottery. Archaeometry 48, 237-51.

Schwedt, A. & Mommsen, H. 2007. On the influence of drying and firing of clay on the formation of trace element concentration profiles within pottery. Archaeometry 49, 495-509.

Zacharias, N., Buxeda i Garrigós, J., Mommsen, H., Schwedt, A. & Kilikoglou, V. 2005. Implications of burial alterations on luminescence dating of archaeological ceramics. Journal of Archaeological Science 32, 49-57.

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