The study, published in Archaeological and Anthropological Sciences, examined 59 fragments selected from documented production contexts at two sites about 150 metres apart in the city’s historic pottery district. The material dated mainly from the late eleventh to the mid-twelfth centuries, spanning the Taifa, Almoravid and early Almohad periods. One workshop contained a rod kiln that had been reused as a waste dump after abandonment; the other had a clay-setting pit and production debris. The researchers regarded these contexts as more securely documented than many assemblages of decorated medieval pottery found in residential areas.

Each fragment was mounted in resin and examined by optical microscopy, while all 59 were analysed with scanning electron microscopy and energy-dispersive X-ray spectroscopy, or SEM–EDS. Twenty specimens were prepared as 30-micrometre petrographic thin sections, 14 were tested by wavelength-dispersive X-ray fluorescence, and 18 underwent X-ray diffraction. The methods were chosen to connect visible vessel traits with microscopic fabric, elemental composition and mineral phases formed during firing. Because SEM–EDS can give broader readings across heterogeneous pastes, its results were combined with petrography and XRF rather than treated as a complete chemical map.

Petrography separated the assemblage into three principal fabric groups that broadly followed function. Kitchenware belonged to Fabric F1, whose dark, fine-grained matrix contained abundant phyllite, mica schist and granite inclusions. Its cooking pots were generally low in calcium and sodium but high in silicon, with average values of about 1.5 weight per cent CaO, 0.6 per cent Na₂O and 63.2 per cent SiO₂ in the SEM–EDS dataset. Quartz-rich particles and rock fragments would have increased resistance to thermal shock. Most cooking pots were handmade, although three of the analysed examples were wheel-thrown, documenting a technological transition within the same production setting.

Water jugs formed a distinct group, Fabric F2. Their bodies were poorer in silica and richer in calcium and magnesium than the cooking pots, with a CaO/MgO ratio near 1.25. The authors interpreted this composition as evidence that at least two clays were combined: a medium-grained, non-calcareous red material resembling that used for kitchenware and a lighter clay containing dolomitic inclusions. This blended paste was also chemically similar to that used for kiln rods, suggesting that available workshop clays were adapted according to the demands of different objects. The water vessels were wheel-thrown and decorated with painted red or black designs, while their handles were sometimes made by hand.

Tableware used a finer, calcareous fabric divided into two subgroups. Both had relatively low porosity and fewer inclusions than the kitchenware, but F3-S1 contained more potassium while F3-S2 contained more sodium. Their average K₂O concentrations were about 2.6 and 0.8 per cent, respectively, while Na₂O averaged approximately 1.1 and 2.4 per cent. Neither subgroup consistently belonged to one workshop, indicating that the chemical contrast was not a simple division between the two sites. Instead, the researchers proposed that it could reflect different local clay sources, clay mixing or paste-preparation practices. Geological sampling would be required to determine whether the workshops exploited the same deposits.

The glazes showed that shared clays did not imply a single firing recipe. SEM–EDS identified 26 glazed samples, including 11 kitchenware and 15 tableware examples, along with glaze droplets from workshop equipment. Many transparent glazes contained lead and were coloured honey-yellow by iron oxide. Transparent tableware glazes ranged from 27.1 to 56.2 per cent PbO. Comparison with the ceramic bodies indicated that lead compounds were combined with quartz sand rather than applied as a simple lead coating. The tableware glazes also showed evidence of a deliberately added potassium-bearing material, possibly derived from woody plant ash, while some recipes apparently included a sodium-rich component such as salt.

Colour was produced through a limited but technically varied palette. Copper oxide generated green transparent glazes, with some samples also containing zinc, possibly indicating the reuse of brass. Brown decoration on honey-coloured tableware contained iron and manganese oxides and may have been painted onto the biscuit-fired vessel before glazing. Opaque white glaze came from cassiterite crystals formed when tin oxide was added to lead glaze. Turquoise combined copper with tin, the latter dispersing fine cassiterite particles that increased opacity. A droplet adhering to a workshop handle contained partially dissolved quartz, cassiterite and lead glaze, consistent with preparation of tin “calx,” while its wider composition included substances associated with lustre pigments. The evidence demonstrates use of lustre-related materials, but the researchers stressed that it did not conclusively prove lustreware production at either workshop.

Principal component analysis reinforced the separation of the three fabric groups: the first three components accounted for 96 per cent of the total chemical variance, with 76.9 per cent contributed by the first component alone. Mineral phases also suggested varying firing temperatures. Kitchenware containing dehydrated muscovite was probably fired below 850 degrees Celsius, while some waterware and tableware indicated temperatures of about 850 degrees or higher; analcime in one tableware subgroup pointed to vitrification above 950 degrees Celsius. Workshop equipment showed repeated exposure to heat: kiln rods contained abundant glassy phases, and one tripod stilt appeared to have been fired more than once. Overall, the evidence points to a coherent but flexible craft system, with functional choices in clay selection and multiple glazing traditions rather than highly specialised production. The study’s principal limitation is that the two selected workshops and 59 fragments cannot establish the exact source of the clays or represent every medieval pottery tradition in Almería.

Subject of Research: Archaeometric characterization of medieval pottery production, clay fabrics, glazes and colorants in Almería, al-Andalus

Article Title: Materials and technological choices in ceramic production of Medieval Almería (al-Andalus): clays, glazes and colorants

Article References: Peregrina, M. J., Molera, J., Garcia-Porras, A., Pradell, T., & Salinas, E. (2026). Materials and technological choices in ceramic production of Medieval Almería (al-Andalus): clays, glazes and colorants. Archaeological and Anthropological Sciences, 18(11), Article 219. https://doi.org/10.1007/s12520-026-02575-6

Image Credits: AI Generated

DOI: 10.1007/s12520-026-02575-6

Keywords: medieval pottery, archaeometry, Almería, al-Andalus, ceramic technology, clay fabrics, lead glazes, tin opacification, pottery workshops, X-ray diffraction, SEM–EDS, petrography

Utrecht occupies a special place in medieval Dutch ceramic history. The earliest evidence for pottery production there dates to the late 12th century CE, and by the 14th century the town had joined Haarlem, Leiden and Breda as a major manufacturing centre supplying both local markets and wider regional trade. Its products have been recovered as far afield as Alkmaar, Haarlem, Dordrecht and Amsterdam. The workshops themselves clustered in the suburbs of Bemuurde Weerd and Tolsteeg, north and south of the town walls, and along the banks of the Vecht river, where excavations have uncovered nine vertical updraft kilns with brick or clay floors, round or oval in plan and measuring up to five metres long.

The excavated waste heaps tell a story of technological transition. The first production phase at Zeedijk, dated 1150 to 1175 CE, yielded almost exclusively grey, round-based jars. After an apparent hiatus of roughly a century, the second phase, from 1275 to 1350 CE, saw a wider repertoire including lead-glazed reddish tripod forms, jugs, bowls and pans, though grey jars remained dominant. By the third phase, represented by the Oosterkade workshop (1350 to 1400 CE) and riverside workshops such as Anthoniedijk, Hogelanden and Lauwerecht (1375 to 1425 CE), lead-glazed redware had become far more prominent, and unglazed and lead-glazed floor tiles were also being produced.

To characterise the raw materials and firing technology, the team subjected the 59 samples, plus one clay sample from a waste pit at Bemuurde Weerd, to a battery of techniques: polarised light optical microscopy, wavelength-dispersive X-ray fluorescence spectrometry, X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectrometry. Thin-section petrography revealed two main fabric groups, a Coarse Group with large, moderately to poorly sorted quartz inclusions and a Fine Group with smaller, better-sorted inclusions. The size, rounded shape and bimodal distribution of the coarse quartz grains suggest they were deliberately added as temper, most likely derived from fluvial deposits, consistent with the Holocene river clays of the region.

The chemical data, measured on 26 major, minor and trace elements at the Fitch Laboratory of the British School at Athens, showed a strongly homogeneous, silico-aluminous dataset pointing to local clay sources. Principal component analysis identified three compositional groups, with a large, homogeneous group A accounting for more than 70 percent of the samples. All the Utrecht products were made from calcium-poor, iron-rich clay, with calcium contents below 2.5 percent, and the chemical similarity between the fired clay sample and the pottery, despite differences in calcium, may itself be evidence of quartz tempering. X-ray diffraction confirmed the mineral assemblage of quartz, illite-muscovite, K-feldspar and plagioclase, with redware bodies generally containing more hematite than greyware.

Firing temperatures emerged as consistently low. Most of the ceramics, 44 of them, were fired below 800 degrees Celsius, while a handful containing the high-temperature minerals gehlenite, diopside and mullite may have reached roughly 850 to 900 degrees or slightly above. The co-occurrence of surviving calcite and dolomite with these high-temperature phases implies short soaking times in the kiln. The glazes told their own story: single-layered, transparent coatings up to about 250 micrometres thick, of very high to high-lead type, with lead oxide contents between roughly 51 and 69 weight percent. Comparisons of corrected glaze and body compositions indicate that potters mixed lead oxide with silica before application, and that the yellowish-brown to greenish colour came from iron in the glaze over the reddish ceramic body.

The most novel element of the study was the application of small-angle neutron scattering, or SANS, to the question of how the vessels were formed. Measured non-destructively at the YS-SANS instrument of the Budapest Neutron Centre, 38 jar samples yielded data on the orientation and alignment of nanoscale domains in the ceramic fabric, which record the forces applied during forming. Thirty-two samples showed high isotropy values, indicating disorganised internal structures characteristic of percussion-building techniques such as pinching, moulding or tamper-and-concave-anvil forming. Combined with the wheel-made traces on rims and necks, this points to a two-stage strategy the authors call percussion-wheeling: the body formed by percussion, then the neck and rim refined on a rotational device.

Only six samples showed the low isotropy and significant tilting angles diagnostic of other techniques. One redware jar from the second phase at Zeedijk proved to be coil-built and wheel-shaped, while five jars, from both Zeedijk and Oudenoord, were genuinely wheel-thrown, three with clockwise and two with anticlockwise wheel rotation. Notably, all the wheel-thrown examples date to the second production phase after about 1275 CE, confirming a previously observed typo-technological shift from grey hand-formed jars to reddish tripod forms. Contrary to common expectations, the potters did not favour fine fabrics for wheel-throwing; nearly all the wheel-thrown jars were made from the coarse fabric. The persistence of percussion-wheeling across the 100-year hiatus between the first and second phases suggests a conservative, culturally embedded technological tradition, one perhaps also suited to producing the round-based jar shapes that were difficult to throw on a wheel.

The study also cautions against reading forming techniques from surface features alone. Interior depressions often interpreted as fingertip impressions from moulding appeared on wheel-thrown vessels too, and may instead reflect hands supporting the vessel wall during brushing, while interior ridges below the neck, sometimes taken as evidence of added coils, also occurred on wheel-thrown jars and may result from clay displacement during wheel work. The reasons for discarding the wasters were largely firing failures: warping and cracking from overfiring, loosened tripod legs and handles, and glazes accidentally fired in a reducing atmosphere. Taken together, the results portray a production tradition defined by both continuity and change, in which local potters favoured iron-rich, calcium-poor clay, tempered it with river sand, fired at low temperatures, and gradually adopted wheel-throwing and lead glazing, offering archaeologists a new quantitative template for reconstructing medieval craft knowledge and its transmission.

Subject of Research: The production technology and chaîne opératoire of medieval greyware and redware ceramics from 12th to 15th century Utrecht, the Netherlands

Article Title: Advancing the chaîne opératoire analysis of medieval greyware and redware ceramics: A case study from 12th to 15th centuries CE Utrecht, the Netherlands

Article References: Borgers, B., Gait, J., Bajnok, K., Allepuz, E. T., Bajnóczi, B., Len, A., & Griffioen, A. (2026). Advancing the chaîne opératoire analysis of medieval greyware and redware ceramics: A case study from 12th to 15th centuries CE Utrecht, the Netherlands. Archaeological and Anthropological Sciences, 18(9), Article 194. https://doi.org/10.1007/s12520-026-02554-x

Image Credits: AI Generated

DOI: 10.1007/s12520-026-02554-x

Keywords: medieval pottery, Utrecht, chaîne opératoire, ceramic technology, greyware, redware, small-angle neutron scattering, lead glazes, petrography, X-ray fluorescence, pottery workshops, the Netherlands