The geochemical diversity of neogene clay deposits in Crete and its implications for provenance studies of Minoan pottery*

The determination of provenance probably forms the primary role of geochemical analyses in archaeological ceramic studies. In what has comprised a successful field of study, the ultimate basis for such research has been the comparison of pottery compositions with the geochemical diversity displayed by clay deposits within a given study area. Although such studies are now common, the understanding of chemical and mineralogical variability in ceramic raw materials has been somewhat neglected, with the dominance of assumptions rather than the actual analysis of clays. In this paper, a study is presented of Neogene clays in Crete (Greece), a clay type commonly used in ancient and modern pottery production. Sixty‐one samples were taken from 28 locations in the central and eastern parts of the island, to reveal both intra‐ and inter‐deposit variability. In one deposit chosen for multiple sampling, the 14 samples display great variability in the alkali elements, Fe and Co, and to a lesser extent in the REEs. Many of the geographically separate deposits differ from each other in chemical composition, with Eastern Cretan deposits showing higher REE concentrations and higher Th/Sc ratios, whereas Central Cretan deposits of younger geological stages are characterized by a lower Th/U ratio. Mineralogical analysis by XRD is used to explain aspects of the geochemical variability of the clays.     

Tracing the clay source of Nasca polychrome pottery: results from a preliminary raw material survey

This paper describes the results of the first season of a survey in which clays suitable for the production of Nasca polychrome pottery were collected in an effort to (1) determine the geological variability of clay sources in the Nasca region and (2) match clays compositionally to paste groups from previous provenance analyses. Clays were collected, processed, fired, and analyzed using neutron activation. The results demonstrate that clays in the region were compositionally heterogeneous, and that the clay source for the majority of Nasca polychrome pottery sampled thus far can be traced to lower valleys in the region near the ancient ceremonial center Cahuachi. The results have implications for understanding the nature of polychrome pottery production in the Nasca region, and suggest centralized production near the ceremonial center of the majority of painted ceramics consumed in the Southern Nasca Region.     

Identifying the sources of Inka period ceramics from northern Chile: results of a neutron activation study

To examine regional patterns of ceramic production and distribution during the era of Inka domination in northern Chile, we determined the elemental compositions of 157 samples of archaeological ceramics and geological clays from the sites of Catarpe and Turi using instrumental neutron activation analysis. We identified two major and three minor composition groups in the ceramics. The major groups, High Cr and Low Cr, are linked to clays from two broad geological contexts within the region, while the minor Low Na group is made up of ceramics imported from northwestern Argentina. The distribution of the composition groups indicates that, in the Catarpe–Turi region, patterns of ceramic production differed for different vessel types: jars were made from clay and temper acquired near the sites where the jars were used, while bowls were made of material coming from more distant sources. The geographical distribution of the analyzed ceramics indicates that bowls were exchanged between Catarpe and Turi in a pattern more similar to tribute/extraction than to market exchange, with Catarpe being the dominant site. The compositional analysis also demonstrates that Inka-style ceramics were being locally produced at sites in this region during the era of Inka domination.     

Chemical Variability in Clays and Pottery from a Traditional Cooking Pot Production Village: Testing Assumptions in Pereruela*

This paper explores analytically the contemporary pottery‐making community of Pereruela (north‐west Spain) that produces cooking pots from a mixture of red clay and kaolin. Analyses by different techniques (XRF, NAA, XRD, SEM and petrography) showed an extremely high variability for cooking ware pottery produced in a single production centre, by the same technology and using local clays. The main source of chemical variation is related to the use of different red clays and the presence of non‐normally distributed inclusions of monazite. These two factors induce a high chemical variability, not only in the output of a single production centre, but even in the paste of a single pot, to an extent to which chemical compositions from one ‘workshop’, or even one ‘pot’, could be classified as having different provenances. The implications for the chemical characterization and for provenance studies of archaeological ceramics are addressed.     

Technological examination of Neolithic-Bronze Age pottery from central and southeast Europe and from the Near East

Scanning electron microscopy is used to examine sequences of pottery sherds from central and southeast Europe, Greece and the Near East spanning the period from the Neolithic to the Bronze Age, in order to obtain information on the ceramic technologies employed in antiquity. On the basis of the vitrification observed and the chemical composition, the types of clay and firing procedures (temperature and atmosphere) employed in the manufacture of the pottery are defined. Two under-lying trends in the associated ceramic technologies are thus identified. The first is based on the use of non-calcareous or “unstable” calcareous clays fired in a reducing atmosphere at temperatures below 800 °C and the second on the use of “stable” calcareous clays fired in an oxidizing atmosphere at temperatures in excess of 800 °C.     

Western technical traditions of pottery making in Tang Dynasty China: chemical evidence from the Liquanfang Kiln site,Xi'an city

This study is based on the SEM-EDS and LA-ICP-AES analyses of a sample of twenty-nine Tang sancai sherds unearthed from the Liquanfang site, Xi'an city. The results indicate that ceramics with yellowish bodies are calcareous and those with red bodies were made of ferruginous clays. The use of calcareous clay in Tang sancai bodies is otherwise unknown in Chinese history, which suggests that the technique of Tang sancai making at this site might have been influenced by ceramic technology from the Near East or Central Asia. The paper therefore argues that the traditional approach of treating calcareous clay as the main characteristic of pottery made in the ancient Near East or Central Asia is not necessarily accurate. It is likely that some calcareous Tang sancai ceramics were made in the capital city of the Tang dynasty.     

The forest or the trees? Behavioral and methodological considerations for geochemical characterization of heavily-tempered ceramic pastes using NAA and LA-ICP-MS

In this paper, the utility of LA-ICP-MS for instrumentally separating clay and temper within pottery samples is examined through a well-known case study that has been previously characterized through NAA and petrography. Coarse Orange pottery is composed of kaolinitic clays heavily tempered within volcanic ash from the basalt-rich Tuxtla Mountains of southern Veracruz, Mexico. We attempt to address the following topics with analyses on this pottery: 1) can LA-ICP-MS replicate the same groups previously identified by NAA and petrography; 2) can instrumental isolation of the clay fraction within the pottery replicate known patterns in raw clay source geochemistry in the Tuxtla Mountains; 3) can data for both the clay and volcanic ash fractions of each pottery sherd be combined to simulate the bulk INAA data? The results demonstrate that the clay fraction of the pottery sherds can be isolated. Furthermore, the LA-ICP-MS data for the clay fractions display nearly identical chemistry to available NAA data for raw clay samples collected from geological contexts in the region. Instrumentally isolating the clay fraction in this case eliminates the homogenizing effects of adding a common temper and increases the chemical separation among groups making it easier to identify clay procurement strategies for each specimen. However, focusing only on the clay fraction ignores significant tempering variation. Attempts to simulate the bulk NAA by combining LA-ICP-MS data for clays and temper was reasonably successful in reestablishing the tempering variation lost by exclusive focus on clays, but such an approach could not replace the more precise data generated from NAA and petrography.     

A Clay source provenance survey in Northwest Alaska: Late Holocene ceramic production in the Arctic

Ceramic compositional analysis can contribute to the study of late Holocene Arctic hunter-gatherer social interaction through reconstruction of past ceramic distribution patterns. The results of an ethnographically informed clay source survey in Northwest Alaska are presented here. The survey provided contextual data on clay depositional environments, clay variability, and local environmental factors that influenced pre-contact clay availability. Geochemical analysis of clays and tempers clarified the location of ceramic production zones. Concurrence between survey results and ethnographic data highlights the persistence of clay knowledge despite post-contact absence of pottery making. This research demonstrates that ethnographically informed source survey can aid in interpreting ceramic geochemical data and yield important insights into pre-contact ceramic production processes.     

Using provenance data to assess archaeological landscapes: an example from Calabria, Italy

Ceramic provenance studies have helped archaeologists examine trade and exchange in multiple scales, the organization of production, and even vessel function. Yet, they may go even further, to provide a venue for the examination of past people’s perception of their landscape. To do so, a methodology is needed that links the choices prehistoric potters made, as reflected in their ceramics, with the choices their landscape could afford them, as reflected in the extent and distribution of local clays, and the physical, chemical and mineralogical characteristics of these clays. Using the region of Bova Marina in southwestern Calabria as a case study, we have combined a raw materials survey with field and laboratory experiments, along with chemical and mineralogical analyses of the collected sediments to understand the distribution and the physical, chemical and mineralogical variability of locally available clays and provide baseline data against which prehistoric ceramic materials from the region may be compared. We show that the local sediments can be divided into three major units, based on their macroscopic, mineralogical and chemical characteristics, that correspond well with the major geological units outcropping in the study area. While two of these units have internally consistent properties, the third is variable.     

Characterization of bricks and tiles from the 17th-century brick Chapel,St. Mary's City,Maryland

The brick Chapel at St. Mary's City, Maryland, built around 1667, would have been an impressive structure on a colonial frontier where all the other buildings were built only of wood. While the building is no longer extant, the bricks remaining in the buried foundations hold information about the technologies and materials used by brickmakers in the 17th-century Chesapeake region. Instrumental neutron activation analysis (INAA) and petrographic analysis of thin sections were used to compare the Chapel bricks and other 17th-century bricks and tiles from several Chesapeake contexts to locally available clay sources. While the composition of the Chapel bricks is generally consistent with that of clays available in southern Maryland, these historic materials could not be linked to any one deposit, and may reflect the mixing of clays from multiple sources. In contrast, building materials from other 17th-century buildings at St. Mary's City could be more precisely “matched” to specific local clay deposits. This paper reports on our initial investigations toward understanding the technology of the Chapel bricks and their relationship to other bricks from St. Mary's City.     

ETHNO-ARCHAEOLOGY OF POTTERY FIRING IN DARFUR, SUDAN: IMPLICATIONS FOR CERAMIC TECHNOLOGY STUDIES

Summary. In 1982 the author spent six months in Darfur, Sudan, studying a group of itinerant female potters. This paper examines their method of manufacturing and firing, and discusses data observed from 21 pyrometric readings. The use of a bonfire for firing ceramics is described and it is concluded that, despite the apparent simplicity of the technique, the Kebkebiya potters control the appearance of their ware to a surprising degree, since surface colour and quality of vessels to suit a particular function can be regulated by the firing technique. A study of the preparation of raw material shows that these potters never take a single clay but use a mixture from three distinct sources, and petrological analysis and firing tests of the original clays indicate that none of the source clays is workable individually. Different fillers (millet-husk and donkey-dung) are added to clay used to form different sections of the pot (body and neck respectively) and the effect of these is discussed. The extent of the potter's control over the technological process is emphasised.     

X-ray powder diffraction analysis of Late Holocene reservoir sediments

X-ray powder diffraction (XRD) analysis of clays from anthropogenic Late Holocene reservoir sediments can provide a paleoclimatic proxy. Illite and smectite are climate sensitive clay minerals and their relative amounts correlate with climatic episodes. Relative percent composition of clays in Late Holocene reservoir sediment is diagnostic of different mineral source areas and their hydraulic transport processes, which are climate controlled. Climosequences of clay minerals from Late Holocene reservoir sediments are correlative with magnetic susceptibility records and provide a relatively simple and cost-effective tool for gaining insight into paleoclimate.     

Insect Clay Geophagy in Sierre Leone

Field study in eastern Sierra Leone shows that 50% of pregnant women regularly consume clay found in the interior of termite mounds. Some 40 to 80 grams of clay are eaten per day. Another, but less commonly used, geophagical source of clay is the nest of the mud daubing wasp. Both clays provide important amounts of minerals and trace elements essential for fetal development. It is concluded that the practice is a cultural response to nutritional need.     

Diatoms as indicators of provenance in Finnish sub-neolithic pottery

The clays of Finland originated from glacial deposits formed during the deglaciation of the Weichselian ice-sheet and during the different stages of the Baltic Sea. The analysis of the fossil diatom flora is of central importance in the study of its developmental history. The diatoms in the clay indicate its sedimentary environment, which can be linked to the stages of the Baltic Sea. The siliceous valves of diatoms tolerate heating up to 1400°C and can consequently be identified in ceramics fired at lower temperatures. Several diatom analyses have been made in Finnish Sub-Neolithic comb ware pottery in order to determinate the origin of their clay materials. According to the results of these studies, prehistoric potteries used clays deposited during the Yoldia and the Ancylus stages. The criteria used in selecting raw materials were identical to those of modern ceramic industries. Further details as to provenance of clay materials have been illustrated in connection with research on pottery from the Aland Islands. In the example from Kymi, South-eastern Finland, changes in the composition of the diatom flora have been found to correlate with changes in pottery decoration styles.     

Petrographic and geochemical analysis on the provenance of the Middle Bronze and Late Bronze/Early Iron Age ceramics from Didi Gora and Udabno I, Eastern Georgia

We report thin section petrographic and geochemical analysis of a total of 20 Middle Bronze, Late Bronze/Early Iron Age ceramics excavated from Didi Gora and Udabno I located in the Eastern part of the Republic of Georgia and 31 clay samples from eight different regions in the surrounding areas of the sites. The major and trace element compositions of the ceramics and clays were determined using a wavelength dispersive X-ray fluorescence technique. The results indicate that the ceramics were manufactured from local clays in Eastern Georgia, mainly from two local clays without any preference of one of the sources during the Middle Bronze, Late Bronze/Early Iron Age.     

Taken with a Grain of Salt: Experimentation and the Chemistry of Archaeological Ceramics from Xaltocan,Mexico

Neutron activation analysis (NAA) of ceramics from Xaltocan (n?=?651) displays high values for sodium and potassium and low concentrations of many transition metals and rare earth elements compared to other sites in the Basin of Mexico. Given that Xaltocan was situated on an island in the middle of a saline lake, the potential reasons for this chemical signature are diverse. On one hand, if the sodium and potassium were elevated due to some behavioral aspect of the potters, the Xaltocan chemical groups provide a glimpse at the behaviors of Xaltocan potters that permit more precise source designations. On the other hand, if this chemical fingerprint arose due to contamination in a saline post-depositional environment, the Xaltocan chemical groups would not be valid references for provenance studies. To evaluate these alternative hypotheses, we employ several lines of evidence: (1) comparison of the Xaltocan ceramics to over 5,000 NAA assays of clays and ceramics from the Basin of Mexico, (2) experimental doping of clays with water of different salinities and fired to different temperatures, (3) leaching experiments of archaeological pottery sherds (n?=?22) recovered from the site of Xaltocan, and (4) laser ablation–inductively coupled plasma–mass spectrometry of the clay and temper fraction of a small sample of Xaltocan ceramics to determine which component is responsible for the elevated sodium and potassium values. The results suggest that the high sodium and potassium values were present in the ceramic paste before firing. We then use these newly established reference groups to better understand the role of Xaltocan in the regional economy. The type of experimentation employed in this study has proven to be an important method for determining the behaviors of ancient potters and distinguishing them from post-depositional processes.     

ASSESSING NATURAL CLAY COMPOSITION IN THE VALLEY OF OAXACA AS A BASIS FOR CERAMIC PROVENANCE STUDIES

The Oaxaca Clay Survey was initiated to provide baseline data on clay composition within the Valley of Oaxaca, Mexico, to assist in provenance determination of prehistoric ceramics. Natural clays were sampled from 135 locations throughout the valley, and analysed using INAA in combination with ceramic petrography. Observed geographical trends in trace‐element and mineralogical composition confirm that while parent material (surficial geology) strongly affects clay composition, a continuum of variation exists within the valley. The study develops and tests a continuous spatial model of clay composition that provides greater resolution in ceramic sourcing than bedrock alone. By establishing a regional framework for Oaxaca Valley clays, the survey will support significant advances in our understanding of pottery production and exchange within the valley, and provide a more robust means for monitoring exchange between the valley and neighbouring regions.     

Characterization of a black residue in a decorated Neolithic pot from Dikili Tash,Greece:an unexpected result

A black depositional layer on the inner surface of a Neolithic carinated vessel from the archaeological site of Dikili Tash in Eastern Macedonia was examined scientifically. The layer was initially considered as decomposed organic matter and interest was focused on identifying the original organic contents. The scientific investigation, which included FTIR spectroscopy, analytical SEM examination and optical microscopy, revealed that the black substance was not organic but a pure iron oxide layer deposited on the vessel’s inner surface, and reduced in places to black iron oxides, during a destructive fire. The conclusion is that this layer represents the remnants of the vessel’s original content, which was a red hematite pigment. This unexpected find provides, for the first time, a missing link in the evidence of pigments used in Neolithic times, previously attested to only by finished products.     

THE EFFECT OF PURIFICATION AND FIRING OF CLAYS ON TRACE ELEMENT PROVENANCE STUDIES

The effect of purifying, mixing and firing of clays on trace element concentration was systematically investigated using instrumental neutron activation analysis. Eight different clays from two sites in Crete were used together with sherds found around several kilns near the sites. Trace element analysis showed that the extent to which the concentration changes after purification and firing depends on the initial particle size and chemistry of the clay. The calcite concentration plays an essential role in this. An application is made using roof tiles found at the excavation of the ancient city of Pella in Macedonia.     

Minero-petrographic characterization of fine ware from Cales (South Italy)

79 samples of black glazed pottery, Terra sigillata, fine common ware, and production indicators were recovered in the archaeological site of Cales and investigated via a multi-analytical program (polarized light microscopy, thermal analyses, XRPD, XRF, FESEM, FESEM-EDS). Among the materials, finds of important production indicators, represented by welded pieces of black glazed pottery and spacers, attest a local production. Polarized light microscopy shows that the inclusions consist of feldspar, quartz, mica, calcite, and lithic fragments of both volcanic and sedimentary nature. Additional information about the mineralogical assemblage comes from the XRPD that revealed the presence of neoformed Ca-silicates, indicating equivalent firing temperatures ranging from 750 to 1050°C. All the samples show a Ca-rich character and an extreme compositional homogeneity, including the production indicators. The comparison with some Ca-rich Campanian clay raw materials shows a greater affinity with the Mio-Pliocene marine clay sediments of the Apennine sector, which include local clays. This allowed us to formulate the first hypotheses about clay sources used to produce fine pottery during the third century BCE to the early imperial period in Cales.