Thin-Section Petrography in the Use of Ancient Ceramic Studies

Abstract

The potential of thin-section petrography for the analysis of ancient ceramic materials, such as pottery vessels, figurative objects and building materials made of fired clay, was already recognized during the 19th century, but its use has become more intensive during the past 80 years. Since pottery is the most common and typologically datable artifact in archaeological excavations from the pottery Neolithic period onwards (some 7000–8000 years ago), the analysis of pottery, including its composition, is a central component of archaeological research. As ceramic materials are made of fired clay, which in turn is procured from soils, weathered rocks and geological formations, the mineralogical composition of the ceramic artifacts represents the clay sources. The study of the mineralogical and rock fragment composition of thin sections of ancient ceramic artifacts can yield the characterization of the clay and soil type and thus the geographic location or area of the clay source. Since in antiquity we assume clay was not precured from a distance of more than one day’s walk from the production site (‘site catchment area’), the production location can be detected as well. Thus, petrographic analysis can identify the trade of artifacts and commodities (if the ceramics are containers) in antiquity, which can shed light on political and cultural links and trade between ancient societies and their economic and social structure. In addition, since clay was often treated by ancient potters to improve its quality (levigation, clay mixing, addition of temper), technological aspects of the production sequence (chaîne opératoire) can also be acquired by petrographic analysis. Today, petrographic analysis is part of many standard studies of ancient pottery. While it is an old and relatively ‘low tech’ method, the accessibility of the equipment needed and its high analytic potential maintains its important and common position in archaeological research. This article describes the method and its analytical potential from the archaeological point of view and briefly mentions several archaeological case studies exemplifying its wide and diversified potential in the study of ancient ceramics in past decades.

1. Introduction

One of the important and diversified uses of thin-section analysis is the study of archaeological ceramics and other artifacts. In particular, this analysis is employed in relation to the determination of their production location. The potential of thin-section petrography for the analysis of ancient ceramic materials, such as pottery vessels, figurative objects and building materials made of fired (as well as unfired) clay, was already recognized during the 19th century, but its use has become more intensive during the past 80 years (e.g., [1], pp. 10–16). As pottery is the most common and typologically datable artifact in archaeological excavations from the pottery Neolithic periods onwards (some 7000–8000 years ago in the Near East, somewhat later in other regions of the world; see, e.g., [2,3]), the analysis of pottery, including its composition, is a central component of archaeological research. Since ceramic materials are made of fired clay, which in turn is procured from soils, weathered rocks and geological formations, the mineralogical composition of the ceramic artifacts represents the clay sources. The study of thin sections of ancient ceramic artifacts and the description of their mineralogical and rock fragment composition can yield the characterization of the clay and soil type and thus the geographic location or area of the clay source. It is generally assumed that in antiquity clay was not precured from a distance of more than one day’s walk from the production site (‘site catchment area’, Figure 1; see, e.g., [4], Table 2.1; [5], pp. 115–120; [6], pp. 6–9). Therefore, the production location can be detected as well. Thus, petrographic analysis can identify trade in commodities (if the ceramics are containers) and artifacts (if the objects are not closed containers) in antiquity, which can shed light on political and cultural links and trade between ancient societies and their economic and social structure. In addition, according to ethnographic evidence, clay was often treated by ancient potters to improve its quality: levigation, clay mixing, addition of temper (e.g., [5], pp. 115–120, see below). Therefore, technological aspects of the production sequence (chaîne opératoire) can also be acquired by the fabric and composition of the clay of the artifacts documented by employing petrographic analysis. This article describes the method and its analytical potential and diverse uses from the archaeological point of view and briefly mentions several archaeological case studies exemplifying its wide and diversified potential in the study of ancient ceramics in the past decades.

2. Materials Sampled, Methods and Implementations

2.1. Archaeological Ceramics

Since this article aims to illustrate a popular and important use of thin-section petrographic analysis in a non-geological discipline, this section focuses on the significance of petrography for archaeology and ancient ceramic studies and the manner thin sections are described, analyzed and interpreted in archaeology.

Ancient archaeological ceramics are clay-rich artifacts that were produced and used by ancient human societies (generally from the late Neolithic period onwards, e.g., [3]). They include pottery vessels, cultic/symbolic artifacts such as figurines and models (‘terracottas’), building materials such as bricks (e.g., [7]) and tiles and artifacts used for production in metallurgy and other technologies (‘refractory materials’) such as crucibles, molds, tuyères (e.g., [8]), smoking pipes, loom-weights, spindles, seals, stamps, clay writing tablets and other functional objects (see, e.g., [9], pp. 293–314; see below). Most of the ceramics analyzed by petrography are fired between 540 °C and 900 °C (terracotta class or ‘basic earthenware’); firing achieves better hardness, waterproof and heatproof properties. Earthenware, stoneware, fritware and porcelain, as well as faience, fired at temperatures over 1100 °C, appear in various periods, especially during the Middle Ages onwards, and are usually not suitable for petrographic analysis, since hardly any inclusions can be observed (yet see, e.g., [9], pp. 323–327). Ceramics are very common in archaeological sites as fired ceramics do not degrade for thousands of years, and vessels break into many pieces (pottery sherds). Pottery vessels are an important component in archaeological research as their form and style are chronologically indicative, and when found in context (‘in situ’) can reflect the function of the space they were used in (storage, cooking, etc.) as well as cultural influence and contacts and trade in vessels and commodities.

2.2. History of Research

While the earliest studies were conducted in the late 19th c. (e.g., [10]), the use of thin-section petrography in archaeology started to be more commonly used in the 1940s, with the works of Ann Shepard (e.g., [11], with thin sections hand-drawn, and [12] with further standardizing petrographic analysis; [1], pp. 10–16) and during the 1960s–1970s with the works of Fredrick Matson, David Peacock and others (e.g., [13]). Interestingly, some of the pioneering, large-scale studies deal with the Roman period in England (see [9], pp. 15–16), while today, generally, many studies are conducted in the Southern Levant, the Aegean and western Europe (e.g., [14]), while relatively less so in the Americas, east Asia and other regions. Research positions or laboratories dedicated to the petrographic research of ancient artifacts are not extremely common, yet several departments and laboratories as the ones at Sheffield University (Program of Mineralogy and Petrography of Archaeological Ceramics, directed by P. Day) and University College at London (UCL, directed by P. Quinn) serve an important role in the training and research of archaeological petrography. As an example, in some countries (especially Mediterranean Europe), laboratories appear in several universities, in archaeology or other departments (for example, in Greece, the British and the American Schools for Archaeology, at Athens and Crete, and several government-related research centers, or in Israel at Tel Aviv, Ben Gurion and Ariel Universities, as well as the Israel Antiquities Authority).

2.3. Provenancing

Petrographic analysis is a method employed for obtaining the mineralogical composition of ceramic artifacts. Compositional analyses of ceramic artifacts include chemical or geochemical analysis, obtaining the elemental or oxide abundancies of the clay material, via Neutron Activation (INAA), X-Ray Florescence (XRF) or Induced Coupled Plasma Mass Spectrometry (ICP-MS), commonly used, and mineralogical analysis (see, e.g., [5], pp. 413–425; [9], pp. 331–399). Compositional mineralogical analysis methods include thin-section petrography, X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) (see, e.g., [9], pp. 405–438), which are domains of micromorphology. Petrographic analysis, entailing visual observation under polarized light, is the most simple and inexpensive method; it also has several further advantages (see below) and is therefore the most commonly used.

Ceramics are made of clay which occurs as either natural geological formations, or more commonly, is derived from soils which represent eroded rocks and geological formations. These, in turn are usually geographically specific, and therefore the analysis of the composition can point to the geographical source of the clay (or ‘provenance’). The fabric or paste of ceramic artifacts can be divided into a clay (grain size under 4 microns, the ‘matrix’) component and coarse fraction components (also termed ‘non-plastics’ or ‘inclusions’). Both of these define the composition and can indicate the geographical source of the clay (see, e.g., [6], p. 7), as well as various interventions of the potter. The general principle of provenancing pottery according to its composition is that the clay in various geographic locations should have its own ‘fingerprint’ or profile, whether chemical or mineralogical. Thus, pottery pastes and raw materials can be traced to their location of quarrying. Usually the production location is sought, and it is assumed that clays were not transported a lengthy distance (Figure 1). The ‘provenancing postulate’ states that a compositional variability between two different sources will be distinctively higher than the variability within the same clay source, and naturally, within the same artifact ([15], p. 301; [16], p. 32). This postulate could apply also to a variety of types of raw material sources relevant to archaeology such as obsidian, stone, metals and clay.

If three degrees of compositional variability (S = spread) are defined:

a.

Differences within a single vessel or artifact (S_v)

b.

Differences within the same clay source (S_cs)

c.

Difference between clay sources (with possibly two categories: intra-regional S_r, and inter-regional S_ir). A clear detection of clay sources would be when S_ir > S_r >> S_cs >> S_v.

Since ceramics are a common artifact, and clay is common in most locations, it is reported according to ethnographic studies of modern traditional potters that clay is not carried more than a distance of a day’s walk ([4], Table 2.1; [5], pp. 115–120; [9], pp. 169–171), since it is needed in large quantities and weights. It is therefore assumed that in antiquity the source of the clay would define roughly the location of the workshop of the site producing the pottery, and a ‘site catchment area’ can be created by a 10–20 km radius around the archaeological site (Figure 1). While compositional provenancing of ceramics has several limitations, especially for identifying closely located pottery production centers or sources, provenancing the production locations of ceramics found in archaeological sites has great importance in archaeological research, since from early periods onwards short-distance and long-distance trade in vessels, artifacts and commodities carried within ceramic vessels (mostly liquids) was conducted and evidenced. The trade or movement of artifacts and commodities in antiquity has great importance for the reconstruction of socioeconomic phenomena in ancient societies, hierarchy, urbanization and cultural contacts and influences as well as migrations of populations.

Petrographic analysis is also used on other archaeological materials such as plaster or cement (see, e.g., [17]; [9], pp. 314–323). In situ sediments from living surfaces are studied by thin-section analysis. In this case, the objects studied are not minerals and rock but rather various organic elements, ash, dung-spherulites, phytoliths and other microscopic remains illustrating activities on floor surfaces (e.g., [18]).

The field of petrographic analysis in archaeology is constantly evolving, with both expansion of the reference data and advancements in data interpretation (e.g., [1,6,9,14,15,19,20,21]). However, the preparation and initial evaluation of thin sections have remained largely unchanged ([9], pp. 21–40). A sample, preferably about 1.0 cm² in size or larger, is cut from the archaeological artifact by a plyer or saw. Thus, this analysis is ‘destructive’ to a certain extent (often inhibiting the sampling of certain high value, rare and small museum objects for example). Much smaller samples from valuable and small ceramic artifacts can also be taken by flaking off minuscule amounts of material with a needle, or in the case of unfired clay artifacts such as writing tablets or seals ([6], p. 12; [9], p. 23), by slicing off a ‘peeling’ with a scalpel. These fragments can then be embedded in epoxy resin for hardening before the preparation of thin sections. It is important in general to select artifacts coming from stratigraphically clear archaeological contexts and well-defined architectural spaces in the archaeological excavation.

For the preparation of thin sections, one side of the sample is grinded and flattened and applied to a microscope glass slide and then cut and grinded to around 30 microns thickness. Thin sections are observed through a microscope (25–400× magnifications) in plane and crossed polarized light to identify rock fragments, minerals and other components. High-resolution photographs are obtained through the microscope by various cameras and software.

The description method largely derives from geological sedimentary petrography (see, e.g., [19,22]; [9], pp. 97–122). The clay component or the ‘matrix’ can be described according to its birefringence (variability under turning stage; this could reflect the firing temperature of the ceramics, and if the matrix is opaque, this indicates a high firing temperature for example), color, etc. ([9], pp. 114–119), while the coarse fraction can be identified and measured by size and roundness ([9], pp. 47–52,97–114). The matrix can often compose 50% of the thin-section area or more (see, e.g., Figure 2(4)). On top of rock fragments and minerals, ceramics also contain elements such as bone, fossil or shell fragments as well as voids (indicating the porosity of the fabric), which usually are created during firing when organic or other inclusions dissolve due to the high temperature ([9], pp. 76–86). Other inclusions which are not natural are crushed pottery sherds (‘grog’) and slag for example (Figure 3, see below). All these are recorded. Each component can be estimated in its quantity (either relatively or according to distribution charts, see [9], Figure 4.9), distribution or ‘texture’ and sorting. In many cases, before the final determination of the geographic source of the clay (see, e.g., [9], pp. 52–76), samples with similarities in the paste and inclusions are grouped together ([9], pp. 91–97), representing ‘petro-fabrics’, or even soil-related materials (Figure 2). It should be noted that the ‘grouping’ or definition of petro-fabrics can be somewhat subjective, even if described in detail (e.g., [9], p. 97). For example, the determination which differences are more crucial or more distinctive in quantities and sizes of inclusions can be a relative or subjective matter. There are various more formal methods for the description of petro-fabrics ([9], pp. 97–100,125–134). More quantitative methods are also used (e.g., [9], pp. 136–151), but they have not gained much popularity yet. Nevertheless, matrix/inclusions/voids (or fine/coarse/voids = f:c:v) numeric ratios are often used (as percentage of slide area, [9], Figure 4.9), then these (per sample, thus forming groups, or per group) can be used with various statistical analyses (e.g., [9], pp. 146–151, Figures 4.49,4.59–4.62).

The more complex stage of the petrographic analysis of archaeological ceramics is the determination of the geographic provenancing of the raw material used according to the petrographic classification of the samples and groups (see, e.g., [9], pp. 167–200). The geological provenancing is made according to geological and soil maps and comparison with ‘reference materials’ (e.g., [9], pp. 40–44). Reference materials are archaeological ceramics or clay samples of which we have a greater certainty of geographic source, such as collected clays, ceramics or wasters from workshops or kilns, or large and petrographically homogeneous groups of common pottery found in the same site. While, intuitively, the best reference material would be clay or soil samples collected from the field in a geographical region (see, [9], pp. 184–191), these can be often problematic for several reasons. Initially, it is not always easy to identify soils suitable for ceramic production in the field. Moreover, some soils exposed today were not exposed in antiquity and vice versa. Secondly, the preparation of the pastes by the potter that can include the mixing of clays, tempering levigation, etc., can change the clay substantially (see below).

Similar to geological thin-section petrography, some considerations are used to identify geographic provenancing, including the types, amounts and conditions of sedimentary, igneous and metamorphic rocks and the minerals derived from them. The soil source can be characterized as alluvial, marl or other more specific types (soil types and classes used in research shown here are, for example, alluvial, marl, colluvial, terra rossa and loess; Figure 2; [9], pp. 89–125). However, certain differences between the interpretation of geological and ceramic samples also occur. For example, if ceramics of a particular petro-fabric contain, for example, granite, serpentinite or fossiliferous limestone, this is useful information for the determination of their provenance, since this can attest to a specific geological background. Yet, one should also determine how these rock fragments or minerals appear in the clay and sample. Igneous rock fragments, for example, or a suite of derived mineral inclusions can be naturally occurring in clay or could have been added as temper (see below). If added as temper, these cannot necessarily reflect the close proximity of the clay source. Even if rock fragments are naturally occurring in the clay or soil, there is still a difference whether the fragments are weathered or eroded or not, since this could indicate whether primary or secondary deposits are evident. More weathered fragments can indicate a further distance from the geological formation (see [9], pp. 171–173). Another important distinction for the classification of ceramic raw materials is whether the clay matrix is calcareous or non-calcareous. Samples with a calcareous clay matrix contain abundant fine primary micritic.

‘Quantitative provenancing’ is based on the measurement of the inclusions and categorizing their ranges, for example, and can be used in addition to the more common ‘qualitative’ provenancing ([9], pp. 191–195). Another more advanced aspect of ceramics petrography is the identification and dating of the microfossils (or ‘foraminifera’) appearing in the sample that originate from calcareous sedimentary rocks ([9], pp. 195–197), since different species can reflect different geological dates and eras, and thus point to different geological formations and provenances. Macroscopic fabric description and classification are also used in certain ceramics reports and studies (see, e.g., [9], pp. 151–162).

2.4. Reconstruction of Ancient Potters’ Technology

An important advantage of the petrographic analysis of ceramics is the possibility to reconstruct the potters’ technology according to the composition of the artifacts (see, e.g., [9], pp. 205–278; [23], see below). In fact, petrographic analysis can yield information of all stages of the production sequence of ceramics production (the ‘chaîne opératoire’ = chain of operations conducted, see [25]), which includes the procuring of the clay and raw materials, preparation of paste, vessel forming and finishing, drying, and firing (see, e.g., [5], pp. 31–167). In particular, significant information can be recovered in many cases on clay collection and paste preparation ([5], pp. 120–124). The geographic provenancing aspect of the clay sources used was discussed above, yet, as within the ‘site catchment area’, several clay types can be found ([5], pp. 113–120; [9], pp. 211–212), and therefore, clay selection can reflect a technological choice as well, as different clay types have different properties and are optimally used for different ceramic artifacts or pottery types. Ethnographic studies clearly indicate that in most cases traditional potters do not often use natural clay ‘as is’ but treat it in various ways ([4]; [5], pp. 115–123). Experimental archaeology can also indicate these actions (see, e.g., [26,27]). The treatment includes mostly the mixing of various clays, the refining, reduction or levigation of the clay (using various sized pools to get rid of coarser materials in the clay) and the addition of coarse fraction—termed temper (Figure 3)—to achieve certain properties of the clay paste such as plasticity, toughness and weight. For example, adding straw to the clay would make the vessel lighter and more porous after firing, often used in the production of large thick storage vessels; resistivity to heat shock or even color or appearance can also be controlled. Temper could include, for example, calcareous-calcite (Figure 3(1,2)), basalt (Figure 3(4)), grog (Figure 3(6)), shell (Figure 3(5)), bone, dung, organic material and even salt (see, e.g., [28] for dung; [29] for slag). Potters also dry, crush and hydrate the clay (see [9], pp. 238–239 for possible petrographic evidence), as well as knead it in order to get rid of organic and coarse material and air bubbles.

Refining or levigation of the clay can be reflected by petro-fabrics with a fine matrix lacking a coarse fraction above a certain size; also, this clay may have a low porosity (less and smaller voids) ([5], pp. 406–412; [9], pp. 212–216). Probably the main component of the clay preparation that can be detected by petrography is tempering (Figure 3; [9], pp. 216–232). Deliberate tempering can be differentiated from a naturally coarse fraction by several ways: sand-sized fragments having a very uniform size, very large quantity of the same type of component, very large sizes of the grains, fragments that were crushed—having a very sharp angular form (Figure 3(1) and see also below Figure 9(2))—or elements which are not natural in the soils as grog (Figure 3(6)), shell (Figure 3(5)) slag, straw or ‘chalf’ (Figure 5(4), evidenced by voids; see also [9], pp. 224–232). Another way of detecting tempering is identifying a component which is not local to the clay source, for example, a large quantity of quartz ‘beach sand’ (rounded sand-sized quartz grains) in a fabric that otherwise has a non-coastal provenance (see below, Figure 3(2) and Figure 9(5); for probably natural beach sand quartz see Figure 2(3) and Figure 9(4)). In particular, cooking ware and refractory vessels (crucibles, tuyeres and furnaces) show much intentional tempering with calcite, limestone, shell or other rock inclusions (such as basalt and granite); experiments have shown that the addition of specific types of temper can improve the heating effectiveness of a pottery vessel by increasing its thermal conductivity and its resistance to thermal shock. For example, a component of particles sensitive to thermal shock, such as calcareous inclusions, can ‘absorb’ the thermal shock caused by rapid heating or cooling and prevent cracks in the main body of the vessel (see below; [9], pp. 220–224; [30,31]). It should be noted that temper, being less bulky than clay, can be brought from longer distances, up to several dozens of kilometers in certain cases (see, e.g., [5], Table 2:1).

The mixing of two or more clays in the preparation of the paste in order to better control its properties is also known ([9], pp. 232–237). Clay mixing can be detected by petrography usually when the clays were not thoroughly blended. In certain cases, this is visually seen in microscopes with streaks between layers of different appearance (see [9], pp. Figures 6.37,6.38); the clay may also react differently to dying or firing, and therefore voids and cracks will appear. The appearance of ‘Argillaceous bodies’, which are plastic inclusions or clay bodies within the fabric (‘clay pellets’), can also reflect clay mixing (Figure 4(1) and Figure 5(1); [9], p. 235, Figure 6.36; [32]). Other stages in the production sequence that may be observed in thin sections, though rarely, are forming ([9], pp. 239–250) and finishing ([9], pp. 250–260) techniques. Forming by fast wheel or wheel throwing (creating the initial vessel form by sheer use of the rotative kinetic energy of the wheel) may possibly be detected by a strong alignment of inclusions, especially elongated ones such as shell (Figure 4(2); [9], p. 241, Figures 6.43–6.45; see also [33]). The use of slab construction of the vessel may be indicated by a clear alignment of inclusions to the vessel’s exterior walls ([9], p. 244, Figure 6.53); construction by coils may be detected by streaks between the different coils showing slightly different clay in texture (Figure 4(3); see e.g., [9], Figure 6.61). The ‘finishing’ stage of production includes mostly surface treatment, such as smoothing, burnishing and the applying of slip and/or decoration, with or without the use of the wheel, usually when the clay is ‘leather hard’, as well as attachments of bases and handles and glaze (after firing). This may occasionally be detected in thin sections, especially slip, with its thickness observed in sections (Figure 4(4); [9], Figures 6.64, 6.67 and 6.70 [showing both slip and paint over it]). The final drying of vessels before firing can be detected by cracks or voids visible in macro- and microspecimens of the ceramics ([9], pp. 260–264).

Various aspects of the firing of the ceramics, including firing temperature, atmosphere (oxidizing or reducing) and regime (closed- or open-space firing, duration and temperature or atmosphere changes within cycle) can be detected as well ([9], pp. 264–278). Temperatures of 800 °C and above can be reflected by sintering or vitrification: the matrix becomes opaque and glass-like. Whether the matrix shows birefringence and extinction in crossed polarized light is also an indication of firing temperature, usually above 800–850 °C. Calcareous inclusions as calcite undergo transformation as expansion and spalling (leaving full or partial voids) in temperatures of 750 °C and above (Figure 5(2,3)), melting at 850 °C and above. Generally, certain minerals may change crystal phases and appearance at high temperatures, yet this cannot be always detected in regular petrography. One of the methods of detecting firing temperature is to refire a ceramic object in incriminating temperatures; when the appearance of the fabric in thin sections changes, this indicates that the original firing temperature has been exceeded (‘refiring’ experiments, e.g., [34]). The color of the clay in plain or polarized light can indicate the firing atmosphere (red—oxidizing; black, usually in the core—reducing), yet this can be detected usually in hand specimens as well.

In certain rare cases, information on the uses of the ceramic artifacts can also obtained from the petrographic data (see [9], pp. 278–279), as well as post-depositional phenomena occurring on the ceramics (as patina, or ‘secondary calcite’, [9], pp. 280–287, Figures 6.102–6.104).

Therefore, we can see that thin-section petrographic analysis has a clear advantage, yielding much information of the technology and production sequence of ancient ceramics, information that cannot be obtained by chemical analyses. Furthermore, as chemical analysis requires clear measured reference material (i.e., databanks, see, e.g., [35]), with petrography, provenance can be obtained by geological considerations, and in particular, geographic regions can be easily ruled out for the sourcing in many ways (see below). However, petrography has several limitations as well; in particular, it is not helpful for very fine wares or highly fired ceramics, as inclusions cannot be identified. As will be shown below, many cases show that a combination of petrography and chemical analysis, and the correlation between the two, can be very effective in the accurate identification of the production centers of ancient ceramics and ancient trade (see, e.g., [36], and below).

3. Selected Case Studies

Several case studies employing thin-section petrography of ancient ceramics will be mentioned and briefly described, illustrating the various uses and potential of this method, its advantages and limitations. Of the many hundreds or even thousands of studies published around the world, only a handful will be mentioned. The aim is to represent various periods, classes of ceramics and diverse uses of the method. These include mainly case studies from the Levant (modern Israel, Jordan, Lebanon and Syria) and the eastern Mediterranean (modern Greece and Cyprus) (Figure 6); studies conducted by the author will be described with more detail (Figure 7, Figure 8 and Figure 9).

Some petrographic studies were conducted on clay artifacts appearing even before the appearance of pottery, during the Pre-Pottery Neolithic period in the Levant. Recently, for example, a study on clay artifacts and clay plaster from Baja Jordan, dated to the 7th millennium BCE, employing petrography and other archaeometric methods, indicated clay bowls of a certain type were imported to the site ([37]).

An example from the Early Bronze Age I (ca. 3300–3000 BCE), with an initial emergence of urban settlements in the Near East, includes the analysis of pottery from the southern coast of Israel (the Nahal Besor region, sites such as Tel ‘Erani, ‘En Besor), on the border with Egypt (Figure 6). The sites in this region during this period yielded a significant amount of pottery in Egyptian style and forms, including various closed and open forms and flat, coarse ‘baking trays’. Petrographic analysis showed that most of this pottery was not imported from Egypt but was locally made in the region. The interpretations of this evidence is that likely a certain Egyptian population resided in these settlements, possibly immigrants, merchants or soldiers (see, e.g., [38]).

Another example indicating trade during the Early Bronze Age II (ca. 3000–2600 BCE) is the analysis of metallic wares from northern Israel ([39]). This pottery includes mostly storage vessels appearing in many sites in the southern Levant and is characterized by a special surface treatment and ‘metallic’ quality (probably indicating a high firing temperature). Petrographic analysis indicated all this pottery had the same geographic provenance, showing shale-derived clay related to Lower Cretaceous formations in the Hermon massif and southern Lebanon regions (Figure 7). It was therefore probably produced in workshops in the upper Jordan valleys and exported to sites 100 km away and more, due to both trade in the commodities the vessels contain and the special properties of the vessels (possibly for efficient storage of liquids).

Figure 7. Example of ceramics made of Lower Cretaceous-derived clay. Left: Khirbet el-Hawarit Sample1, Late Roman/Byzantine period (crossed polarized light; Sh = shale, Q = quartz, Mi = mica; Shapiro, Anastasia; Petrographic Sample: Hawarit S1, Site: Khirbet el-Hawarit (Israel/Golan) The Levantine Ceramics Project, accessed on 30 July 2025, https://www.levantineceramics.org/petrographics/5760-hawarit-s1.). Right: Zeraqon sample Ih6FN069-1, Early Bronze Age II (plane polarized light, showing shale [surrounded by a void gap] and sandstone, calcareous concentrations; Badreshany, Kamal; Vessel: Zeraqon Ih6FN069-1, Site: Khirbet ez-Zeraqon (Jordan/Northern Highlands), The Levantine Ceramics Project, accessed on 30 July 2025, https://www.levantineceramics.org/vessels/22227-zeraqon-ih6fn069-1, [40]).

Figure 7. Example of ceramics made of Lower Cretaceous-derived clay. Left: Khirbet el-Hawarit Sample1, Late Roman/Byzantine period (crossed polarized light; Sh = shale, Q = quartz, Mi = mica; Shapiro, Anastasia; Petrographic Sample: Hawarit S1, Site: Khirbet el-Hawarit (Israel/Golan) The Levantine Ceramics Project, accessed on 30 July 2025, https://www.levantineceramics.org/petrographics/5760-hawarit-s1.). Right: Zeraqon sample Ih6FN069-1, Early Bronze Age II (plane polarized light, showing shale [surrounded by a void gap] and sandstone, calcareous concentrations; Badreshany, Kamal; Vessel: Zeraqon Ih6FN069-1, Site: Khirbet ez-Zeraqon (Jordan/Northern Highlands), The Levantine Ceramics Project, accessed on 30 July 2025, https://www.levantineceramics.org/vessels/22227-zeraqon-ih6fn069-1, [40]).

During the Late Bronze Age (1550–1200 BCE), the eastern Mediterranean region witnessed a rise in international maritime trade. The trade included, for example, fineware Mycenaean and Minoan ceramics (closed containers and other objects), from Greece, arriving on the eastern costs of modern Syria, Lebanon and Israel as well as Egypt that could easily be identified visually as imports (in this case, as this is fineware, only chemical analysis can be employed). One of the forms, not commonly appearing, was large, coarse stirrup jars with a special ‘wavy’ decoration, stylistically provenanced to the island of Crete. Yet, this island is large and housed several different palatial sites, each having its own trade network. A petrographic study of vessels of this type found in a coastal site of Israel indicated several sources (Figure 8; [41]). The main fabric included metamorphic rock fragments such as phyllite and quartzite/poly-crystalline quartz and smaller amounts of volcanic rocks (Figure 8). According to the extensive research of ceramic fabrics in ancient Crete and its geology, this fabric points to a source in the central southern part of Crete, likely near the port town of Kommos, in proximity to the palace town of Phaistos. This specific source may suggest that these vessels, probably containing olive oil (Crete was a main supplier of this product in the region during this period according to ancient texts), arrived at the Southern Levant coast by a trade route via Egypt and the northeastern African coast, since Kommos is the closest Mediterranean port to this latter region.

Figure 8. Cretan Stirrup Jars found in Late Bronze Age, Tell Abu Hawam, Israel ([41], Figure 6), showing a petro-fabric provenanced to south-central Crete (all are in crossed polarized light). (1) Sample TAH2 (Q = quartzite, P = phyllite). (2) Sample TAH18 (Q = quartzite, V = volcanic rock, SS = siltstone, C = chert). (3) Sample TAH5 (SS = siltstone). (4) Slide No. 245 from Pediada survey, Crete, Greece (Q = quartzite, V = volcanic rocks). All photographs are copyright of the author or reproduced with permission.

Figure 8. Cretan Stirrup Jars found in Late Bronze Age, Tell Abu Hawam, Israel ([41], Figure 6), showing a petro-fabric provenanced to south-central Crete (all are in crossed polarized light). (1) Sample TAH2 (Q = quartzite, P = phyllite). (2) Sample TAH18 (Q = quartzite, V = volcanic rock, SS = siltstone, C = chert). (3) Sample TAH5 (SS = siltstone). (4) Slide No. 245 from Pediada survey, Crete, Greece (Q = quartzite, V = volcanic rocks). All photographs are copyright of the author or reproduced with permission.

An important study related to the same period of international Mediterranean trade reflects the potential of petrographic analysis for the understanding of ancient history, in particular geographical history: the analysis of inscribed clay tablets from the archive of the 14th c. BCE Egyptian capital located at Tell Amarna ([6]). Several hundred ancient letters were found at the site; these are clay tablets written in Akkadian script and language, representing formal correspondence between the Egyptian kings and other regional rulers and kings from the Southern Levant, Cyprus, Greece and beyond. While the letters received at Amarna, Egypt, are headed by the name and city of the ruler, this part is not always preserved, and moreover, many of the ancient city names are not geographically identified. The text was written on damp clay tablets and then fired. Since local clay was used, the provenance of the clay indicates the geographic provenance of the city from which the letter was sent. As these are rare museum objects, sampling was conducted by the ‘peeling’ method. The study was conducted on the background of extensive previous analysis of the clay sources, soils and petro-fabrics of the various regions in the Southern Levant from which most letters came (as this is the closest region to Egypt). The study, therefore, shed much new light on the location of ancient sites in the region and the importance of these cities and relationship with Egypt.

A large-scale study of a later period of extensive maritime trade in the eastern Mediterranean, the 8th–1st c. BCE (including mainly the Classical and Hellenistic periods) included petrographic analysis of large Greek-style containers: transport amphorae, likely containing wine in most cases ([20]). The different Aegean islands, such as Rhodes, Chios, Lesbos, Kos, Knidos and Samos, on the one hand, probably produced special wines; some were exclusive, and on the other hand, as islands, reflect a specific geological environment. The wine producer is sometimes indicated by a stamped inscription on the handle or by the morphological style of the vessel. This is actually a unique case where the archaeological and historical record can aid the mineralogical–petrographical research by pinpointing geographic sources within a generally similar geological environment (on each island). Thus, by analysis of the clay of the containers, combined with the study of the provenance of the wine producers exporting their product to very distant locations, the workshops can be localized to a very specific region within these islands.

Another Aegean island with special importance in the trade of ceramic vessels during the Bronze Age and Classical period is Aegina, 17 km from Athens, Greece. Aeginetan pottery, especially the cooking vessels, is distinguished by gold mica inclusions, unique decorations, specific manufacturing techniques and potmarks, making it one of the most recognizable and common imports in the Aegean region (reaching 50% of the pottery in some other islands and the mainland; e.g., [42]). A large-scale multi-analytical study of the Aeginetan pottery included petrography, chemical analysis, soil and clay surveys, experimental archaeology and ethnoarchaeological research (e.g., [27,43]). The most common petro-fabrics were various red clays mixed with volcanic rock fragments as well as feldspar and amphibole; these inclusions are likely naturally occurring locally. The study achieved a mapping of the workshops and clay sources of the pottery within the island and an understanding of how and why certain clays were selected for specific pottery classes and how this changed throughout different periods.

A multi-analytical study of cookware was conducted on Iron Age II (ca. 1000–586 BCE) cooking pots from Judah (central-southern part of modern Israel) ([23]), including typological, contextual, petrographic and chemical analysis as well as the analysis of the forming techniques of vessels, and experimental archaeology. Of the over 500 vessels analyzed from 11 sites, over two-thirds were made of a similar petro-fabric characterized by a reddish-tan non-carbonatic, ferruginous matrix (Figure 9). In many cases, it is anisotropic. Silty inclusions are mainly subangular quartz and accessory zircon, epidote and hornblende, along with a few feldspars and very rare silty dolomite. Opaques are common, while larger inclusions are calcite crystals and limestone and chalk fragments in various quantities (Figure 9(1,2)). While some of the sub-groups do not show intentionally added temper, others illustrate the addition of crushed sand-sized calcite and limestone (Figure 9(2,3)). The fabric represents terra rossa soil derived from calcareous rock dust and clay, which is common in various regions in the Southern Levant; in particular, the same petrographic profile can represent several centers and regions in Judah in the hills and lower lands to the west. The chemical analysis (INAA) employed aided in distinguishing two main production centers: one in the Jerusalem region, the capital of Judah, and the other at the region of Lachish, the main administrative center of the kingdom ([44]). The study illustrated how a rather common and coarse pottery form such as the cooking pot had specialized production centers and was distributed to sites over 50 km away. As cooking pots need to endure the heating of liquids and thermal shock, their production requires specific raw materials, paste preparation and forming techniques. Most of these were identified in this and other studies. In particular, these vessels have a large component of calcareous and other coarse inclusions absorbing the thermal shock (e.g., [30,45,46], and see above). The study of the Judean cooking pots showed how there was a certain slow shift from calcareous inclusions (mostly added, e.g., Figure 3(1) and Figure 9(2)) to quartz inclusions (mostly natural, Figure 3(2) and Figure 9(1,4–6)) during the Iron Age; this change may relate to the increase of firing temperatures in workshops. This phenomenon could have only been recognized and quantified by thin-section petrography and no other compositional method. The selection of local clay sources for specific vessel types can by also represented by the Iron Age II pottery of Jerusalem ([24]). A large-scale compositional analysis of Iron Age II pottery, mainly tableware, storage vessels and cooking pots from Jerusalem indicated that tableware and storage vessels were made of clays derived from highly calcareous Motza marl and rendzina soils, while cooking pots were mostly made of the terra rossa non-calcareous clay (and never of the Motza marl clay) (Figure 2(2,6)). All petro-fabrics reflect sources local to Jerusalem. The storage jars were made of the Motza marl rich with coarse dolomite inclusions (Figure 3(3); possibly to reduce plasticity as these are large and thick vessels); these inclusions could naturally occur in the contact between the local Motza and Aminadav formations.

Figure 9. Iron Age II cooking pots from Judah ([44], Figure 3). Photomicrographs of samples representing main petro-fabrics (showing sample id and petro-group in parenthesis). (1,2) Clay derived from terra rossa soil. (3,4) Clay derived from loess-type soil. (5) Clay derived from brown soil. (6) Clay derived from Hamra soil. (7). Motza marl-derived clay. (6) Clay derived from the Hazeva Formation. Nos. (1–6,8) taken in crossed polarized light, No. (7) in plain polarized light. Abbreviations on photomicrographs: CL = calcite, CP = clay pellet, DL = dolomite, FR = microfossil, LS = limestone, OP = opaque mineral, QZ = quartz, SH = shale. All photographs are copyright of the author or reproduced with permission.

Figure 9. Iron Age II cooking pots from Judah ([44], Figure 3). Photomicrographs of samples representing main petro-fabrics (showing sample id and petro-group in parenthesis). (1,2) Clay derived from terra rossa soil. (3,4) Clay derived from loess-type soil. (5) Clay derived from brown soil. (6) Clay derived from Hamra soil. (7). Motza marl-derived clay. (6) Clay derived from the Hazeva Formation. Nos. (1–6,8) taken in crossed polarized light, No. (7) in plain polarized light. Abbreviations on photomicrographs: CL = calcite, CP = clay pellet, DL = dolomite, FR = microfossil, LS = limestone, OP = opaque mineral, QZ = quartz, SH = shale. All photographs are copyright of the author or reproduced with permission.

Turning to a much later period is a petrographic study of geometric-painted handmade vessels from the Mamluk period (1250–1517 CE) in the Levant ([47]). The results suggest that this easily distinguished ware appearing in many sites was manufactured by multiple workshops and not centralized; even the production mode is not uniform. Although the macroscopic style and decoration patterns are similar throughout large regions in the Levant (in various parts of modern Israel and Jordan), the distribution was on a very regional basis.

Cultic ceramic objects (such as figurines, libation vessels and cultic stands and models) are rarely analyzed due to their museum value. However, several petrographic studies of these objects show how their analysis can shed light on cultic practices, such as temple-related production and the movement of cultic objects (possibly by pilgrims) (see, e.g., [48]).

Finally, a recently developed online publication and database platform should be mentioned. The Levantine Ceramics Project website (‘LCP’, link: https://www.levantineceramics.org/, 14 September 2025) is an open-access resource including uploaded information on visual wares and styles, petro-fabrics, production sites and vessels, including currently 22,387 vessels, 6399 petrographic samples (belonging to 119 petro-fabrics, all have photographs on the site) from 747 archaeological sites from all countries in the east Mediterranean and all archaeological periods (see also [49] for a previous online database). The data on the website can help in petrographic provenancing studies, as most of the data is not published elsewhere in detail, as well as enable insight and criticisms on petrographic evaluations and groupings (since often the petro-fabric is represented by multiple samples and photographs, different to regular publications).

4. Conclusions

Today, petrographic analysis is part of many standard studies of ancient pottery. While it is an old and relatively ‘low tech’ method, the accessibility of the equipment needed (basically this includes a thin-section machine and/or cutter, lapping equipment and a petrographic microscope with camera), its low cost, relative simplicity and high analytic potential maintains its important and common position in archaeological research. As has been shown above, the two main uses of this method, as a compositional analysis tool in ancient ceramics analyses, is the determination of the provenance or production location of artifacts and obtaining insight into the production sequence, methods and traditions of ancient potters. The first aspect of provenance analysis is especially important in archaeological study as it can illustrate trade patterns and movements of artifacts and commodities. When a vessel is identified as imported from another site or region, this could usually indicate trade, especially in the commodities the ceramic vessels contained (usually liquids). When a vessel which is stylistically similar to vessels appearing commonly in other sites or regions, but according to petrography is locally made, this could indicate cultural influence or the movement of peoples or immigration from other regions. Revealing aspects in the production sequence of the potters as clay selection and clay preparation is also important for the reconstruction of ancient society, since it can illustrate technological changes, versus ongoing traditions, that can be clan-, tribe- or ethnic-related.

Thin-section petrographic compositional analysis has distinct advantages, even in relation to much more expensive geochemical methods. As a visual method, details are retrieved within the mineral and rock composition of the clay and can reflect various aspects of technology, which cannot be obtained by bulk chemical methods. Furthermore, geographical provenance (or exclusion of regions for sourcing) can be often obtained by geological and pedological reasoning, even without comparison with reference materials or databases. Even a petro-fabric containing a single example can be provenanced, or at least restricted, for its possible sources. Disadvantages include the relative subjectivity of the method and the difficulty of presenting results in a quantitative manner. Also, this method cannot be used for ceramics which are too fine (without any silt or larger-sized inclusions) or ceramics which are fired in a high temperature (usually above 900 °C).