From Andalusia to the Atlantic During Early Globalization: Multidisciplinary Archaeometric Approach to Ceramic Production from Jerez de la Frontera (Spain)

Abstract

The technological development of ceramic production during the early modern period in the Iberian Peninsula is a crucial topic in historical archaeological research. The present study analyzes pottery from Jerez de la Frontera, Andalusia, focusing on ceramic materials from the Convent of Santo Domingo (late 15th to early 17th centuries). Through the analysis of production wastes, including dolia and olive jars (botijas), this text unveils key aspects of regional ceramics practices. Using a multidisciplinary archaeometric approach, we applied petrography, X-ray diffraction (XRD), and inductively coupled plasma mass spectrometry (ICP-MS) to investigate compositional, technological, and provenance characteristics. The petrographic analysis identified clay matrix variability and mineral inclusions, indicating diverse raw material sources and production techniques. The XRD analysis confirmed key mineral phases that reflect controlled firing temperatures, while the ICP-MS analyses provided trace element profiles that were used to distinguish between local and non-local raw materials. Together, these results reveal technological shifts and resource diversity over time, challenging the assumption that Seville was the sole supplier of ceramics for Atlantic trade. This study establishes Jerez as a potential complementary production center, offering a new understanding of early globalization processes and ceramics manufacturing in southwestern Andalusia.

1. Introduction

The economic transformation of Andalusia during the early modern period was profoundly shaped by the expansion of transatlantic trade, catalyzed by increasing demand from urban centers. While local and regional trade remained significant, it was Andalusia’s strategic geographic positioning along key Atlantic routes that played a decisive role in facilitating external commerce and driving economic development (Figure 1). This role has clearly materialized in the enormous spread of their ceramics over vast areas of the Atlantic [1,2,3]. In this context, understanding the production processes and technological innovations in ceramics manufacturing in Jerez de la Frontera becomes key for unraveling the dynamics of early globalization. While archaeometric studies on early modern ceramics in Andalusia remain partial, apart from important investigations that have addressed this topic [4,5,6], this research offers essential insights into the evolution and transmission of artisanal skills, ceramic forms and manufacturing techniques, as well as the continuity and adaptation of long-standing craft traditions.

This study presents the preliminary results of both archaeological and archaeometric analyses conducted on ceramics from the Convent of Santo Domingo in Jerez de la Frontera, dating from the late 15th to the early 17th centuries. By adopting a multidisciplinary methodology—integrating petrographic analysis, X-ray diffraction (XRD), and inductively coupled plasma mass spectrometry (ICP-MS)—this research delves into the mineralogical and chemical composition of the ceramics, providing critical data on the production techniques, material provenance, and technological characteristics of Jerez’s ceramics tradition. These findings contribute significantly to the broader understanding of ceramic production during the nascent phases of globalization, particularly in relation to the expansion of Iberian colonial networks in the Atlantic world.

The ceramic assemblage was recovered during the excavation of the vaults of Santo Domingo’s convent, offering a rare and valuable perspective on the material culture used in Jerez de la Frontera during a particularly transformative period. These ceramics are pivotal to decode the productive and economic strategies that supported the colonial expansion of Iberian kingdoms in key Atlantic territories. While medieval ceramic production in Andalusia has been the subject of considerable scholarly attention, the study of early modern pottery production sites remains an underexplored area. This research aims to contribute towards bridging this gap by examining the typology and technological innovations in Jerez’s ceramic production, as a major regional production center, where comprehensive archaeometric studies have been largely absent until now.

1.1. Historical Background of Jerez de la Frontera and the Convent of Santo Domingo

Jerez de la Frontera has long been a prominent center for agricultural production and trade, a role that it has played especially since its conquest by the Crown of Castile in 1246. Its strategic location along the Guadalete River, particularly the port of El Portal, facilitated the city’s access to maritime trade networks. As part of the Kingdom of Seville, which became a significant region within the Crown of Castile during the 15th century, Jerez witnessed substantial economic growth. The city’s September fair became a pivotal event for wine contracting, cementing Jerez’s status as a major hub in the wine industry and fostering a long-lasting viticulture tradition. Artisans were integral to this urban productive system, particularly those involved in the manufacture of ceramic containers, which were essential in both local consumption and broader commercial networks [7,8,9].

Despite the socio-political and economic disruptions caused by the “Reconquista” and the decline of certain industries, such as viticulture, during wartime, Jerez maintained its relevance within the regional trade system. The city’s connections to the nearby ports of Santa María and Sanlúcar de Barrameda, key commercial nodes in the Guadalquivir Basin, were instrumental in sustaining its economic vitality. During the reign of the Catholic Monarchs, merchant capitalism and an oligarchic structure became foundational to royal policy in Andalusia, positioning Jerez as a focal point of urban and economic centralization. The artisanal production of ceramic containers not only supported local economies but also played a crucial role in foreign trade during this period, as documented in historical accounts from the 15th and 16th centuries [10,11,12]. These vessels were essential in large-scale commercial trade, reflecting the broader socio-economic significance of ceramic production in Jerez.

Regarding the archaeology of early modern civic and religious buildings, the excavation of their vault fillings provides invaluable chronological, cultural, and environmental data. These contexts provide insights into commercial practices, crafts, and consumption habits during the building’s remodeling period. However, such renovations are often poorly described and documented.

The Convent of Santo Domingo, established shortly after the Christian conquest under the reign of Alfonso X of Castile, serves as a key archaeological site. Originally functioning as a fortified structure and warehouse, the convent underwent crucial renovations, such as the construction of the gothic cloister, during the 15th century. Later, around the middle of the 17th century, a second floor was added to the cloister. The gothic cloister of the Royal Convent of Santo Domingo in Jerez was already under construction in 1436. The ground floor was likely completed by the late 15th century. The second construction phase began in the late 16th century; historical records indicate that the upper cloister was probably fully built by the early 17th century. To build these vaulted ceilings, broken ceramics (also known as loza quebrada) were used to fill the vaults in the lightest way possible. For that, they applied preferably large containers, mostly ceramic wastes from local potters [13,14,15,16] (Figure 2). Contemporary written sources attest to the existence of these local pottery workshops since medieval times. More significantly, there are references from the middle of the fifteenth century to “olleros, cantareros y tinajeros”, which literally translates as ‘potters of cooking pots, water jars, and large storage vessels’ [17]. This same procedure was also used in another monastery in Jerez, the Cartuja de Santa María de la Defensión, from the first half of the 16th century onwards [18,19].

The possibility of comparing the archaeological materials recovered from different construction phases of the convent enables us to also better understand changes in the economic and social dynamics of Jerez during this period, revealing significant insights into daily life, craft production, and trade activities within a broader Atlantic and Mediterranean framework.

1.2. A Brief Geological Background of Southwestern Andalusia

The geological complexity of southwestern Andalusia is the result of a long and dynamic evolution, giving rise to two prominent mountain systems: the Iberian Massif and the Baetic Cordillera (Figure 3). The Iberian Massif, situated to the north of the Guadalquivir Basin, encompasses the mountain ranges of Córdoba, Seville, and Huelva. This massif is composed of highly metamorphosed Precambrian formations, including gneisses, slates, and quartzites, interspersed with volcanic intrusions, as well as Cambrian sequences dominated by sandstones, conglomerates, and limestones. These ancient formations were tectonically and thermally modified during the Hercynian orogeny, a major geodynamic event that shaped much of the Iberian Peninsula’s structural framework. In particular, the Hercynian uplift contributed significantly to the exposure of deep-seated metamorphic rocks, providing a rich source of raw materials [20].

The Guadalquivir Basin itself, positioned between these two tectonic domains, has been subjected to multiple phases of marine transgression and regression since the Miocene. These processes have deposited thick sequences of marine and continental sediments, including clays, marls, and limestones, interspersed with olistostromes—chaotic deposits resulting from gravity-driven mass wasting events. Stratigraphic and sedimentological investigations have revealed the significance of these deposits in reconstructing the paleogeography and tectonic evolution of the region during the Mesozoic and Cenozoic eras [21,22].

In the Jerez region, the geological setting is defined by extensive alluvial plains formed primarily by the depositional dynamics of the Guadalquivir River system. These plains are characterized by upper Miocene formations, particularly calcareous sandstones, which are rich in both macrofossils and clay minerals, indicative of alternating marine and fluvial depositional environments. The presence of these materials suggests complex sedimentary processes shaped by both tectonic uplift and subsidence, as well as eustatic sea-level changes during the Miocene and Pliocene [23]. Furthermore, the region was significantly affected by tectonic activity during the Pliocene to Quaternary period, which has modulated local geomorphological features and influenced the spatial distribution of these sedimentary units.

Geological and climatic conditions have also played a pivotal role in the formation and classification of soils in the Jerez area. The predominant soil types—Vertisols, Cambisols, and Luvisols—are closely linked to the underlying geology and the hydrological regime of the Guadalquivir Basin. Vertisols, typically found in the deeper valleys and low-lying marshes, are characterized by high clay content, which leads to significant expansion and contraction with moisture changes, influencing their agricultural use. Cambisols, recognized by their yellowish-brown to reddish hues, are primarily associated with siliceous sandstones and iron oxides, reflecting significant weathering processes. Luvisols, with their higher clay content and characteristic argillic horizons, are widespread and contribute to the region’s high agricultural productivity [24].

These soil types are not only critical for modern agricultural practices but also represent key environmental factors that influenced the availability and selection of raw materials by ancient potters. The mineralogical composition of these soils, rich in clay minerals, such as illite, kaolinite, and smectite, would have been essential for ceramic production in Jerez. These unique geological features provide essential criteria for archaeometric analysis, as the region’s clay deposits contain diagnostic components such as high concentrations of calcite and iron oxides. Petrographic studies frequently reveal the presence of marine microfossils (e.g., foraminifera), indicating clay sourced from sedimentary environments influenced by past marine changes. Additionally, elemental analyses (e.g., ICP-MS) can identify elevated levels of calcium (Ca), strontium (Sr), and trace elements that reflect the local clay’s composition. These features are critical for distinguishing ceramics produced in Jerez from those of other Andalusian centers such as Seville. The interplay between these factors informs provenance studies, enabling researchers to detect both the raw material selection and regional technological choices that shaped ceramic production.

2. Materials and Methods

2.1. Sampling Strategy and Typological Characterization

In archaeometric research, sampling strategies are often constrained by the availability of well-preserved diagnostic materials, along with ethical and conservation considerations, especially when working with heritage collections. The challenge lies in selecting representative samples that balance preservation concerns with the need to obtain scientifically robust data. In this study, seven ceramic samples were chosen to maximize interpretive potential, encompassing a variety of typologies such as dolia, olive jars, and jugs (Figure 4). These forms reflect key production phases and technological features associated with the second construction phase of the Convent of Santo Domingo. The selection criteria prioritized samples with distinct technological attributes, including variations in clay matrices, temper types, and firing conditions. This targeted approach ensures that the chosen materials offer a comprehensive dataset for comparative analysis through petrographic, XRD, and ICP-MS techniques. Each of these methods operates at different analytical scales, as follows: petrography identifies the mineralogical composition, fabric structure, and inclusions, providing insights into raw material selection and manufacturing techniques; XRD detects the mineral phases associated with firing conditions, such as gehlenite and diopside, which help to reconstruct thermal processing; and ICP-MS offers precise elemental profiling, facilitating provenance studies and technological comparisons. Given the destructive nature of ICP-MS, the sample size was carefully controlled to minimize impacts on the archaeological collection. Importantly, in petrographic analyses, the selection of appropriate samples is crucial, as thin-section examination provides valuable evidence on paste preparation, temper use, and potential sources of raw materials. Studies have shown that petrography is particularly effective at identifying local versus non-local production and detecting technological practices, which are central to understanding production networks and craft specialization. The integration of these complementary techniques allows for a multi-scalar analysis, enhancing the reliability and interpretive power of the study.

The ceramics samples analyzed in this study were recovered from vault fillings in the cloister of the Convent of Santo Domingo belonging to its second construction phase, which took place from the late 16th century to the mid-17th century. This phase relied heavily on ceramic production waste, with fragments comprising approximately 80% of the materials used to fill the vaults. This high proportion explains the excellent state of preservation of many vessels, allowing for complete form reconstructions. The archaeological context and sample attribution are based on the excavation reports and the typological study conducted by the archaeologist F. Barrionuevo, who classified these ceramics as part of Jerez’s local production. This author proposed a grouping system based on the following functional types: (1) Storage; (2) Transportation; (3) General domestic use; (4) Tableware domestic use; (5) Domestic use of kitchen; (6) Agricultural/industrial use; and (7) Diverse uses. These types of ceramics have been documented in construction fills at other Sevillian sites, and in Spain, that helped to associate precise chronological data with typology and production places [25,26,27,28,29].

1. The olive jars, commonly referred to in written sources as botijas, are large storage and transportation containers that trace their design origins to the amphorae used by various ancient Mediterranean civilizations. These jars were integral to the transatlantic and regional trade networks, particularly for the storage of olive oil, wine, and other liquid and solid goods. Some of these olive jars display interior coatings of lead glaze, likely applied to improve the jar’s impermeability and prevent contamination of the contents. Morphologically, a circular mouth, a pronounced high shoulder, and a concave or flat base define them. These features can vary considerably and have been the focus of typological and chronological studies aiming to differentiate their regional production centers, phases of trade expansion, and their distribution across consumption sites.

2. Dolia. The dolia is a transport container with a well-defined shape, closely related to the vessels used in Mediterranean trade, although it has not been documented in the territories until now. The dolia found in the Convent of Santo Domingo lack interior glazing and were typically recovered from the deepest sections of the vaults. These vessels are easily identifiable by their rims and clay paste composition, similar to that of orzas (handleless storage jars). Evidence suggests that dolia were among the earliest ceramic containers from the Christian period used for fluvial and maritime trade. Their remains have been reported in various regions, including the Levant (eastern Iberian Peninsula), England, and Italy, indicating their role in long-distance commercial networks.

The discovery of these jars in the deepest vaults of the cloister suggests their use in the foundational phases of the convent’s construction, indicating a potential relationship between building materials and the broader commercial networks of the period.

3. Jars/“jarros”. The jugs were functional vessels, often used for serving liquids like water and wine. Typically, they have a single handle, an outlined spout, and are partially glazed on the interior and exterior. Those from Jerez have a honey-colored glaze on the interior surface and along its mouth and neck on the exterior surface [30,31,32,33,34].

For comparative purposes, we also analyzed ceramic fragments from Seville, a major Andalusian pottery production center. These materials include 15 forms from an early production phase (15th century) and 25 forms from the later one (16th century). This study is therefore supported by chronological and typological analyses of multiple ceramic waste assemblages recovered in Seville. These ceramic types have been widely documented across the region; here, we compare them with previous chemical characterization studies conducted by Iñañez and colleagues [35].

Concerning archaeometry, the methodology employed in this study adheres to rigorous parameters that balance diagnostic value with statistical validity. While the sample size is limited, archaeometric research prioritizes interpretive depth over quantity, particularly in contexts where preservation constraints and ethical concerns restrict destructive analysis. The selection of samples was guided by established criteria aimed at maximizing informational output through the analysis of key typological variants. Each sample was chosen for its potential to reveal critical technological features such as firing temperatures, raw material composition, and production techniques. Although statistical representativity across the entire production landscape cannot be fully claimed due to the sample size, the observed patterns align with findings from previous studies on Andalusian ceramic production, thereby supporting the extrapolation of results to broader production practices. Future research will strengthen these conclusions by incorporating larger datasets and comparative analyses from multiple production centers.

2.2. Techniques

2.2.1. Petrography (Optical Microscopy-OM)

The petrographic analysis was carried out using a polarized optical microscope (Nikon LVPol-100 and SZ750, manufactured by Nikon Corporation, headquartered in Tokyo, Japan), equipped with objectives providing x5, x10, x20, and x50 magnifications. The methodology followed established protocols in ceramic petrography, geology, and soil science [35,36,37,38,39,40]. This analysis focused on identifying and characterizing inclusions, tempers, clay matrices, voids, and surface finishes. Observations were made using both plane-polarized light (PPL) and cross-polarized light (XPL). These techniques are critical for determining the fabric and production characteristics of ceramics, particularly regarding the selection of raw materials, formation techniques, and decorative methods. The clay matrix, observed at a microscopic level, provides insights into its homogeneity and the presence of natural or intentional temper materials, which play a significant role in defining the mechanical and thermal properties of ceramics.

This detailed microstructural analysis is essential not only for reconstructing the technological choices made by ancient potters but also for understanding post-firing treatments and surface finishes. By cross-examining the clay matrix, tempers, and visible traces of production processes (such as molding or wheel-throwing), the petrographic analysis contributes towards the identification of production techniques and technological innovations.

2.2.2. X-Ray Diffraction Analysis (XRD)

XRD was employed to determine the mineralogical composition of the ceramic fragments. This analysis aimed to identify both primary and secondary crystalline phases, crucial for inferring firing temperatures and production techniques. The formation of neo-crystalline phases during firing, such as mullite and spinel, serves as an indicator of the specific thermal conditions to which the ceramics were exposed. This technique is widely used in ceramic analysis and several parameters were considered [41,42,43,44].

The analysis was conducted using a PANalytical Xpert PRO diffractometer, which is equipped with a copper tube (λCuKα = 1.5418 Å), a vertical goniometer in Bragg–Brentano geometry, a programmable divergence slit, a secondary monochromator, and a PixCel detector. The operational conditions were set at 40 kV and 40 mA, with the scan range covering 5 to 70° 2θ, which is sufficient to capture the most relevant mineralogical phases present in ceramics. The diffractograms obtained from these scans were interpreted using established mineralogical reference databases and protocols for ceramic analysis. This technique is pivotal for assessing the thermal history of ceramics. By identifying phases, such as quartz, feldspar, hematite, and the presence of vitrified clay components, the XRD data allow for an accurate estimation of the firing temperatures, which in turn provides insights into the technological capabilities and choices of the potters. Additionally, the presence of certain mineralogical phases can help to characterize the provenance of the raw materials, indicating whether the clays were sourced locally or imported.

2.2.3. Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

ICP-MS was employed to analyze the elemental composition of the ceramics, with a particular focus on determining their provenance and the technological processes involved in their production. The analysis followed the established protocols outlined by Iñañez and colleagues, which are designed to ensure the precision and reliability of elemental data [45,46]. In the first stage, we removed the external and internal surfaces of the ceramic material mechanically to prevent any post-depositional contaminants. We then ground approximately 5 g of each ceramic sample using a planetary ball tungsten carbide cell mill. We then calcined the ceramics at 900 °C for one hour in an electric furnace under oxidizing conditions. In archaeometric research, particularly in heritage sciences, sample conservation is a critical concern. The decision to collect 5 g of material was based on the specific requirements of the analytical techniques employed. ICP-MS and XRD both require sufficient sample materials to ensure accurate and reproducible results. Specifically, ICP-MS demands finely milled powders to prevent contamination and heterogeneity, while XRD analysis benefits from a sample large enough to detect minor phases, which may be critical for understanding chemical and mineral characteristics.

The samples were subsequently processed and subjected to ICP-MS analysis using a NexION 300 ICP/MS (PerkinElmer Waltham, MA, USA) in a laboratory clean room (class 100). Using 500 mg of LiBO₂ in Pt–Au crucibles, four drops of LiBr solution as a non-wetting agent, and propane melting equipment, the alkaline fusion method was utilized to create solutions of 250 mg of unknown samples, blanks, and certified materials for external calibration (Geological Survey of Japan: andesite JA2, granodiorite JG-1a, granite JG-2, and basalt JB-3). Subsequently, the resultant solution was diluted (1:200) using standard solutions of In (50 μg L⁻¹) and Bi (10 μg L⁻¹) together with a mixture of 0.32 N HNO₃ and extremely dilute HF. On the one hand, the following analyte concentrations were carried out in standard mode: ²⁷Al, ³¹P, ⁸⁸Sr, ¹²⁰Sn, ⁹0Zr, ⁹³Nb, ¹³³Cs, ¹³⁷Ba, ¹³⁹La, ¹⁴⁰Ce, ¹⁴¹Pr, ¹⁴²Nd, ¹⁴⁷Sm, ¹⁵³Eu, ¹⁵⁸Gd, ¹⁵⁹Tb, ¹⁶⁴Dy, ¹⁶⁵Ho, ¹⁶⁶Er, ¹⁶⁹Tm, ¹⁷⁴Tb, ¹⁷⁵Lu, ¹⁸⁰Hf, ¹⁸¹Ta, ^206+207+208Pb,²³²Th, and ²³⁸U (internal standards: In and Bi). On the other hand, ²³Na, ²⁴Mg,²⁸Si, ³⁹K, ⁴⁴Ca, ⁴⁷Ti, ⁵¹V, ⁵²Cr, ⁵⁵Mn, ⁵⁶Fe, ⁵⁹Co, ⁶⁰Ni, ⁶³Cu, and ⁶⁶Zn (internal standard: In) were analyzed in collision mode with He as the cell gas. The introduction of the samples and the experimental setup were optimized to yield 20 scans, 1 read, and 3 replicates for each sample, with an integration period of 1000 ms for ICP-MS data gathering [45,46].

The ICP-MS analysis focused on detecting a wide range of major, minor, and trace elements, including, but not limited to, Si, Al, Fe, Ca, Mg, Na, K, Ti, Mn, and trace elements such as Zr, Nb, Y, and rare earth elements (REEs). These elements are crucial for determining the geological provenance of the raw materials used in the ceramics and for identifying any technological enhancements made during production (such as the deliberate addition of temper or other materials to improve the performance of the ceramics).

By analyzing the elemental composition, this technique provides a comprehensive overview of the materials’ provenance and technological decisions made by potters. Variations in elemental concentrations can point to different clay sources, revealing whether the ceramics were produced locally or imported. Furthermore, specific elemental signatures related to high-temperature firing or tempering materials can offer insights into the technological sophistication of ceramic production processes.

3. Results

3.1. Petrography Analysis

The petrographic analysis of the dolia (Figure 5) reveals distinct mineralogical and lithic compositions compared to the olive jars, suggesting differences in the sourcing of raw materials and production techniques. Sample 5 shows a mineralogical structure dominated by medium- and fine-sized quartz, pyroxenes, and clinopyroxenes, which are typically associated with igneous origins. These minerals suggest that the raw materials were sourced from regions with access to mafic or intermediate igneous rocks such as volcanic or plutonic formations.

The presence of plagioclase feldspar, with its characteristic twinning and birefringence, further supports this igneous origin. The feldspar grains were likely derived from basaltic or andesitic rocks, providing a direct link to specific volcanic regions.

The clay matrix in these samples exhibits high birefringence, indicating a significant presence of well-crystallized phyllosilicates, likely derived from weathered igneous or metamorphic rocks. Iron oxide nodules appear as reddish-brown inclusions, indicative of an oxidizing firing atmosphere or post-depositional oxidation. The presence of these iron oxides suggests that the jars were fired at relatively high temperatures, sufficient to induce the formation of these iron phases.

An important discovery in the dolia samples is the presence of microfossils, including foraminifera, radiolarians, and sponge spicules. These fossils point to the incorporation of marine sediments into the ceramic paste, either intentionally as a tempering material or because they were naturally present in the clay. This is significant, as it suggests that the raw materials were sourced from marine depositional environments, possibly coastal areas or sedimentary basins that experienced past marine transgressions.

Sample 6 shows a complex paste composition, with fragments of quartz, biotite, sedimentary rocks, phyllite, and calcite. The presence of phyllite indicates the inclusion of low-grade metamorphic materials, likely from tectonically active regions or eroded metamorphic terrains. The biotite displays typical pleochroism, ranging from brown to green, further supporting a metamorphic origin.

The vitrification of the clay matrix suggests that the dolia were fired at high temperatures, of around 800–900 °C, consistent with controlled production techniques aimed at creating durable storage vessels. The incomplete vitrification in some samples suggests that while the firing temperatures were high, they may not have been sustained long enough to fully vitrify the matrix.

The presence of iron oxide concretions, in combination with the microfossil inclusions and calcite, reinforces the hypothesis that the raw materials were derived from marine sedimentary environments. Calcite plays a key role in influencing the mechanical properties of ceramics, as it decomposes at high temperatures, releasing CO₂ and creating voids that enhanced the insulating properties of these ceramic containers.

The petrographic analysis (Figure 6) provides significant insights into the mineralogical composition and technological aspects of the olive jars. A consistent mineralogical profile across all specimens suggests uniformity in raw materials selection and production techniques, pointing to a standardized manufacturing process for these transport vessels. The analysis reveals key details regarding the raw materials, their geological origins, and the production processes employed, which are crucial for understanding the provenance and technological sophistication behind olive jar production.

The predominant mineral observed in the samples is polycrystalline quartz, which appears colorless under plane-polarized light (PPL) and exhibits first-order gray interference colors under cross-polarized light (XPL). The quartz grains show low-relief characteristics and occasionally display recrystallization textures, suggesting thermal or mechanical alteration. This could indicate post-depositional processes or repeated exposure to moderate temperatures during the jars’ use such as contact with heated materials.

The presence of plagioclase was confirmed; it is identifiable by its characteristic polysynthetic twinning and gray interference colors. The presence of this feldspar points to an igneous origin, potentially from volcanic or plutonic sources, which were likely nearby. The durability of both quartz and plagioclase indicates that raw materials selection prioritized resilient minerals, ideal for long-distance transport.

Lithic fragments, including sandstone and limestone, were identified within the samples, supporting the hypothesis that the temper materials were locally sourced from sedimentary formations, such as those in the Seville region or the Guadalquivir Basin, where sedimentary and metamorphic rocks coexist. These lithic inclusions are consistent with a sedimentary context, particularly the fluvial or alluvial deposits commonly found in these regions.

Of note is the presence of medium-grade metamorphic schists, characterized by a foliated texture and composed of minerals such as biotite, muscovite, chlorite, talc, and occasionally hornblende. The schist fragments exhibit typical metamorphic lamination, with both white and black micas, indicating a regional metamorphic provenance, likely from the Sierra Morena or other metamorphic terrains in southwestern Spain. These metamorphic inclusions may have been intentionally selected as tempering agents due to their mechanical properties, or they could have been naturally present in the local clay sources.

The clay matrix of the olive jars displays a brown coloration with medium birefringence, indicating a well-consolidated and homogenous matrix. Embedded within the matrix are iron oxide concretions, likely hematite or goethite, which provide crucial information about the firing conditions. The iron oxides suggest that the jars were fired in an oxidizing atmosphere, resulting in the typical reddish hue seen in Mediterranean ceramics. These concretions may also reflect post-depositional weathering, pointing to the regional clay’s richness in iron, further linking the materials to geological formations near Seville.

The mineralogical consistency across the samples points to a deliberate selection of tempering materials, focused on resilient minerals (quartz and plagioclase) and metamorphic lithic fragments to enhance the mechanical strength and durability of the olive jars. Additionally, the presence of marine microfossils, identified in earlier studies, suggests a complex provenance, with raw materials sourced from geologically diverse areas, including marine sedimentary environments.

The Guadalquivir Basin remains a likely source for these raw materials, given its rich deposits of sedimentary, metamorphic, and igneous rocks. The presence of iron oxide concretions and signs of vitrification suggest controlled firing processes, indicative of sophisticated ceramic production techniques.

3.2. X-Ray Diffraction Analysis (XRD)

The XRD analysis provided essential information about the crystalline phases present in the ceramic samples, offering insights into the raw materials and firing technologies used. The identification of mineral phases, such as quartz, plagioclase, gehlenite, and diopside, allowed for an estimation of the firing temperatures and a reconstruction of the technological choices made by the potters. The firing temperatures were estimated through XRD analysis, which revealed the presence of key high-temperature mineral phases such as gehlenite (Gh), diopside (Di), and hematite (He). These phases act as reliable markers for the thermal conditions during ceramic production, indicating firing temperatures between 850 °C and 1100 °C. Previous studies have established the formation ranges for these phases. Gehlenite begins to crystallize at temperatures exceeding 850 °C, while diopside typically forms at temperatures above 950 °C, confirming the estimates derived from our analysis [47,48].

The diffractograms (Figure 7) show the presence of stable minerals, like quartz (Qz), which remains stable up to 573 °C before transitioning to β-quartz. Its continued presence in the 850–950 °C range indicates stable firing conditions that did not induce quartz decomposition. The presence of plagioclase (albite, Pl), gehlenite (Gh), and diopside (Di), which form at temperatures above 800 °C, confirms that the ceramics were fired at sufficiently high temperatures to promote the mineralogical transformations typical of well-fired ceramics.

The comparative analysis between olive jars and dolia reveal distinct firing environments. The olive jars exhibit stable, high-temperature phases, such as gehlenite and diopside, indicating controlled firing above 850 °C, while the dolia show greater variability, with a higher presence of calcite (Cal), suggesting that the firing temperatures were not as consistently high, or that the firing environment was more heterogeneous.

Calcite (Cal) may persist in lower-fired ceramics or those fired at temperatures insufficient to fully decompose carbonates (typically >850 °C). Calcite is a calcium carbonate that can be present in the raw materials of these ceramics. Its presence can indicate that the ceramics have not reached high enough temperatures to decompose this carbonate. However, it can also form as a secondary phase due to alteration or recarbonation processes [49]. Hematite (Hem) is a key indicator of oxidizing conditions during firing. Its formation occurs at high temperatures and suggests that some samples were fired in an oxygen-rich atmosphere, leading to the oxidation of iron-bearing phases.

3.3. Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

A total of 73 ceramic samples were selected for this compositional study using ICP-MS, including those from Jerez and reference groups from Seville. Among these, Sev 03 corresponds to majolica ceramics and decorated wares, while Sev 05 includes olive jars (botijas) and ceramic transport containers. This analysis aimed to define reference groups based on chemical composition to determine the provenance of the samples, with a particular focus on ceramics from the Jerez and Seville reference groups. The results of this chemical analysis have been corroborated by petrographic studies to ensure consistency and reliability.

To assess the elemental variability across the samples, a compositional variation matrix (CVM) was employed. This method allows for the identification of chemical concentration variability in the analyzed elements, providing insights into the monogenic or polygenic nature of the ceramic paste. The total variation value (vt) serves as an indicator of this variability [50].

In the present study, the analysis of 73 ceramic samples revealed a mean relative total variation (vt) value of 0.77 (Figure 8A), indicative of significant contributions from compounds such as CaO, Zr, K₂O, Th, and Tm. Conversely, a second subset of data yielded a mean relative value of 1.25 (Figure 8B), highlighting the dominance of elements like Hf, Cr, and CaO. In both cases, certain elements, such as Mn, Cr, Hf, and Fe, were excluded in subsequent analyses to refine the interpretation of the compositional variation and ensure more accurate clustering results. These findings suggest that the analyzed specimens, predominantly olive jars, are enriched with calcium carbonate and show notable concentrations of zirconium (Zr), potassium (K₂O), and thorium (Th).

Further petrographic XRD analyses corroborate that most of the samples exhibit paste compositions consistent with olive jars, with a minimal presence of other ceramic types. The decision to exclude Mn, Cr, Hf, and Fe was based on their disproportionate influence on the overall chemical variability, which could have obscured the underlying compositional patterns of the samples.

A cluster analysis was conducted using the ArchFlow package in R [51,52,53,54]. This multivariate statistical approach employed a squared Euclidean distance and centroid algorithm to group the samples based on chemical similarities after performing a centered log-ratio transformation of the analyses’ retained post-matrix variation calculation. The resulting clusters were plotted based on the subcomposition of key elements, including Al₂O₃, CaO, Ce, Dy, Er, Eu, Fe₂O₃, Gd, Hf, Ho, La, MgO, Nd, Pr, SiO₂, Sm, Sr, TiO₂, V, Yb, and Zr. The principal component analysis (PCA) (Figure 9) shows the results of the multivariate analysis, where samples from Jerez and Seville are plotted. The first principal component (PC1) accounts for 80.55% of the total variation, while the second principal component (PC2) explains 17.08% of the variance. The PCA chart effectively differentiates the chemical profiles of the samples, clustering the olive jars and dolia into distinct groups based on their elemental composition.

The hierarchical cluster analysis (Figure 10) further supports the differentiation of production centers. This analysis reveals two primary clusters, corresponding to the ceramic production centers of Jerez and Seville. The hierarchical dendrogram clearly shows the separation between these two groups based on the chemical relationships established through the compositional analysis. Notably, the samples from Seville form a cohesive cluster, whereas those from Jerez show slight internal variability but remain distinct as a group. In addition, the mean Fe₂O₃ content was calculated for both the Seville and Jerez samples. The Seville samples exhibited a notably higher concentration of Fe₂O₃, suggesting differences in the clay sources or firing conditions between the two production centers. This finding reinforces the distinct technological practices employed at each site, as reflected in the hierarchical clustering and multivariate analyses.

The Sev03 group exhibits a compositional overlap with other groups, indicating potential shared raw material sources. Petrographic and XRD analyses reveal similar mineral phases, including quartz, gehlenite, and diopside, suggesting that the clays may originate from comparable sedimentary deposits within the Guadalquivir Basin. The ICP-MS results also show matching concentrations of calcium, iron, and strontium, supporting the hypothesis of regional production networks (Figure 11).

4. Discussion

The petrographic analysis of the olive jars exposes a consistent mineralogical composition, highlighting uniformity in the selection of raw materials and, very likely, the production methods employed. The dominant mineral observed is polycrystalline quartz, a highly durable and common material, which appears colorless in PPL and shows first-order gray interference colors in XPL. This mineral is well known for its resistance to both chemical weathering and mechanical abrasion, generally being part of the raw material itself. Some quartz grains exhibit recrystallization textures, which may indicate post-depositional thermal or mechanical alteration.

In addition, plagioclase feldspar was identified, characterized by banded twinning and moderate gray interference colors. The presence of plagioclase likely originates from nearby igneous formations. Moreover, the identification of sandstone, limestone, and pebble fragments supports a sedimentary origin for the tempering materials, further linking the ceramics to the geological formations of the Seville region and the Guadalquivir Basin. These sedimentary inclusions, along with the presence of metamorphic rocks, such as schists, provide a complex picture of materials sourcing. The medium-grade metamorphic schist fragments, characterized by laminar minerals, such as mica (biotite and muscovite), chlorite, talc, and hornblende, point to raw materials originating from regional metamorphic terrains. These metamorphic inclusions, with their characteristic schistose texture, likely contributed to the mechanical strength of the olive jars, a property that would have been particularly useful for long-distance trade and transport.

The clayey matrix of the olive jars is brown, with medium birefringence, and contains iron oxide concretions, probably hematite or goethite, indicative of an oxidizing firing atmosphere. These concretions also suggest post-depositional weathering processes or the natural oxidation of iron-bearing minerals within the clay, reinforcing the link to local clay sources rich in iron. The reddish hue of the olive jars, characteristic of Mediterranean ceramics, further supports this interpretation. The presence of marine microfossils in some samples suggests that the raw materials were sourced from sedimentary basins with marine influences, possibly from coastal areas near the Guadalquivir River.

As for the dolia, although they share some similarities with the olive jars, they show notable differences in material composition. The petrographic analysis of Sample 5 shows quartz, pyroxenes, and clinopyroxenes, suggesting an igneous origin for the raw materials. These minerals are commonly associated with volcanic or plutonic environments, indicating that the dolia may have been produced using materials sourced from regions with mafic and intermediate igneous rocks. The clayey matrix of the dolia exhibits high birefringence and contains iron oxide nodules, again indicating an oxidizing firing atmosphere, although with more variability compared to the olive jars.

One of the more intriguing findings in the dolia is the presence of microfossils such as foraminifera, radiolarians, and sponge spicules. These inclusions point to the use of marine sediments in the clay mixture, further supporting a coastal or marine sedimentary origin for the raw materials, a characteristic of the Jerez de la Frontera region. The presence of calcite in some dolia, particularly in Sample 6, suggests that these vessels were fired at lower or more variable temperatures, as calcite typically decomposes above 850 °C. This, together with the presence of hematite, indicates a more oxidizing but less controlled firing process compared to the olive jars.

The XRD analysis supports these petrographic findings by identifying key crystalline phases that provide insights into the firing temperatures and materials selection. Quartz remains a dominant phase, stable up to 573 °C, while plagioclase confirms the presence of feldspathic materials in both the olive jars and dolia. The identification of gehlenite and diopside in both types of vessels is particularly significant, as these minerals suggest firing temperatures of 850–950 °C, indicating that the ceramics were subjected to controlled high-temperature firing. The consistent presence of these high-temperature minerals in the olive jars suggests a more uniform firing process, while the variability in the calcite content in the dolia points to potential differences in kiln management or functional requirements between the two vessel types.

The ICP-MS analysis further corroborates these findings by providing a detailed chemical characterization of the samples. The compositional variation matrix (CVM) analysis revealed significant contributions from elements, such as CaO, Zr, K₂O, Th, and Tm, with a total variation value (vt) of 0.77 for the olive jars. In contrast, the dolia samples exhibited greater chemical variability, with Hf, Cr, and CaO contributing to a vt of 1.25. This compositional variation reflects the different production practices and materials sourcing strategies employed for the two types of vessels. Despite the limited sample size, robust statistical techniques—such as PCA and Cluster Analysis—allow for the detection of significant chemical groupings, further reinforcing the validity of the results. The PCA reduced the complexity of the dataset, with PC1 explaining 80.55% of the variance and PC2 accounting for 17.08%, effectively distinguishing between the ceramic production centers of Seville and Jerez.

The statistical validity of the conclusions is further supported by the rigorous application of cluster analysis and log-centroidal transformation, which enabled the identification of clear chemical groupings despite the limited number of samples. The hierarchical clustering analysis revealed clear distinctions between the Seville and Jerez production centers, with the Seville samples showing higher concentrations of Fe₂O₃, suggesting differences in clay sources or firing conditions between the two regions.

The study shows that the technological differences between Jerez and Seville were primarily driven by the availability of raw materials rather than deliberate technological choices. The petrographic results show that Seville ceramics often exhibit higher Fe₂O₃ content, reflecting the natural abundance of iron-rich clays in the region and the tendency towards oxidizing firing conditions. In contrast, the Jerez samples show greater variability in calcite content, suggesting the use of local clay deposits influenced by marine sediments, which impacted the firing conditions and final ceramic properties. These differences reflect regional geological variations that shaped the ceramic production practices in each center.

The observed differences in production standards between dolia and olive jars align with archaeometric evidence from other studies, which has demonstrated varying degrees of standardization depending on the ceramic’s function and production context. Olive jars, often destined for long-distance transatlantic trade, exhibit greater uniformity in composition and firing conditions, likely to ensure durability and structural consistency. In contrast, dolia, primarily intended for regional use, show higher variability in raw materials and production techniques. These patterns reflect technological adaptations observed in comparable Andalusian production centers.

5. Conclusions

Since the late Middle Ages, mobility and connectivity between cities, people, goods, and ideas, both by sea and land, became increasingly prominent across the Iberian kingdoms. This phenomenon intensified in the western ports, forming part of the broader context of early globalization in the Atlantic. Through the integration of archaeological and archaeometric studies, this research provides a more comprehensive understanding of ceramic production, particularly transport and daily-use vessels.

The Convent of Santo Domingo in Jerez de la Frontera is a significant archaeological site that has undergone various structural modifications over time. The recovery of archaeological materials from the cloister’s vault fillings has provided critical data on regional ceramic production. Olive jars found at the site were manufactured in the Guadalquivir Basin of Lower Andalusia, particularly around Seville, a key center of ceramic production for Atlantic trade. Their presence in Jerez suggests active integration into these commercial networks. It is plausible that defective or surplus vessels from Seville workshops were transported to Jerez for secondary purposes, such as construction materials, reflecting both resource reutilization and the interconnectedness of regional production centers.

Despite variations in paste, color, and surface finish, the olive jars exhibit homogeneous firing temperatures, indicating a standardized production process. Previous studies have demonstrated this standardization through correlations between vessel dimensions, specifically body and mouth shape [55,56,57,58]. Furthermore, ongoing research has explored the variability and technological adaptations between workshops, highlighting the heterogeneity in artisanal knowledge among Iberian potters and the continuous exploitation of production sites over time.

An important challenge in this research is the chronological inconsistency observed between dolia from Seville and Jerez. Archaeometric data and typological analysis suggest that dolia production in Seville ceased around 1550, by which time olive jars had become the dominant transport container in Atlantic trade. The dolia recovered in Jerez were likely incorporated into the construction of the Gothic cloister as early as 1436. This indicates that these vessels were not newly produced at the time but were repurposed, possibly dating from an earlier period. During the 1609 remodeling of the convent, older dolia were reused, resulting in the coexistence of vessels from distinct chronological phases within the same architectural context, particularly in the vaults constructed in the 15th century.

Such reuse practices, common in Andalusian religious and civic architecture, complicate typological dating by introducing earlier materials into later construction phases. Stratigraphic control and compositional analysis are essential for distinguishing between primary and secondary deposition, improving dating accuracy and understanding long-term material reuse strategies.

The discovery of both Sevillian and Jerezanian dolia in the convent indicates that Jerez may have contributed to large-vessel production as part of its integration into Atlantic trade networks. This pattern parallels developments in Palos de la Frontera, where ceramics influenced by Sevillian typologies were produced between the late 15th and early 16th centuries [59]. These findings suggest that local production centers adapted rapidly to meet the demands of expanding global commerce. However, given the limited number of analyzed samples, further typological and archaeometric studies are necessary to solidify these observations. The growth of Jerez’s wine production and olive oil industry had significant impacts on both rural life and the diffusion of ceramic containers across the Atlantic. Historical records highlight the economic importance of the local wine market, which expanded trade routes to destinations such as the Canary Islands, England, Flanders, and the American territories [60,61]. This economic success was supported by royal roads, ports, and inland settlements, which facilitated the circulation of goods, people, and ideas throughout the region.

Future research should expand the sample size to enhance the understanding of ceramic typologies, production chronology, and technological variations in Jerez. The diverse ecosystems of Andalusia offered abundant resources for agricultural and ceramic industries, including the rich clay deposits essential for pottery production. By the 15th century, Andalusian ceramics had established extensive connections with European and African markets, accelerating their integration into global trade. Despite overarching trade influences, local variations in ceramic form and style persisted, reflecting both adaptation and innovation in major ports of the Atlantic expansion during the early modern period.

In conclusion, this study highlights the complex and dynamic nature of ceramic production in Andalusia, where local traditions intersected with the demands of global commerce. The detailed archaeometric analysis of dolia, olive jars, and other ceramic forms from sites in Jerez and Seville offers valuable insights into the technological innovations, production strategies, and economic imperatives shaping the region’s ceramics industry. These findings contribute to ongoing discussions on the role of Andalusian ceramics within the broader context of early globalization.