Technical ceramics for salt production in Western Sahara

ABSTRACT

This paper presents evidence of ceramic technology in western Tiris (Western Sahara), dated by thermoluminescence to the third millennium cal. BP. Western Tiris is an arid region mostly covered by desert where recent archaeological fieldwork has nevertheless revealed a significant network of settlements from the Neolithic period inhabited by nomadic people. Domestic pottery and lithic materials are common in the archaeological register of these sites, but three sherds found in the Lejuad XVII rockshelter present features typical of technical ceramics. Laboratory analyses reveal that abundant mineral and organic temper was added to the natural clay which, in addition to the presence of thicker walls than those usually found in domestic pottery, is interpreted as an attempt to increase resistance to thermal shocks. However, the fragments present only mild signals of exposure to high temperatures, up to a maximum of 900 °C. Discussion of these contradictory data leads to the conclusion that the sherds may have been part of a briquetage mould to extract salt by evaporation, a pyrotechnical industry previously unknown in Western Sahara. Its appearance in an arid environment far from production centres is explained as result of sporadic economic activity rather than cross-cultural mobility and trading, which seems to have been intense in the area from Neolithic times. In addition, this paper introduces the use of micro-computed tomography (µ-CT) as a technique for measuring large porosity derived from burned organic materials.

RÉSUMÉ

Cet article présente des données concernant la technologie céramique dans le Tiris occidental (Sahara Occidental), qui se place, sur la base de datations par thermoluminescence, au troisième millénaire cal. BP. Le Tiris occidental est une région aride principalement couverte de désert où des travaux archéologiques récents ont néanmoins révélé un réseau important de sites datant du Néolithique qui furent habités par des populations nomades. La poterie domestique et les lithiques sont courants dans leur registre archéologique, mais trois tessons retrouvés dans l'abri sous roche de Lejuad XVII présentent des caractéristiques typiques de la céramique technique. Les analyses de laboratoire révèlent qu'un abondant dégraissant minéral et organique fut ajouté à l'argile naturelle. Ceci, ajouté au fait que les poteries ont des parois plus épaisses que celles habituellement observées dans la poterie domestique, est interprété comme indiquant une tentative d'augmenter la résistance aux chocs thermiques. Cependant, les fragments ne présentent que de faibles signaux d'exposition à des températures élevées, jusqu'à un maximum de 900°C. L’évaluation de ces données contradictoires amène à la conclusion que ces tessons ont pu avoir fait partie d'un moule de briquetage pour l’extraction de sel par évaporation, une industrie pyrotechnique jusque-là inconnue dans le Sahara Occidental. Son apparition dans un environnement aride loin des centres de production s'explique par une activité économique sporadique plutôt que par une mobilité et un commerce interculturels, apparemment intenses dans la région après le Néolithique. En outre, cet article présente l'utilisation de la tomographie micro-calculée (µ-CT) comme technique de mesure de la grande porosité dérivant de matières organiques brûlées.

KEYWORDS:

• briquetage
• Western Sahara
• salt
• mobility
• µ-CT
• porosity calculation

Acknowledgements

We wish to express our gratitude towards several institutions in the Basque Country that support the Project in the Sahara (grant number G01411677), specifically the Departamento de Cultura y Política Lingüística of the Basque Government and the University of the Basque Country (UPV-EHU). Equally, we are more than obliged to the Ministry of Culture and the Ministry of Defence and National Protocol Directorate of the Sahrawi Arab Democratic Republic. Both were directly involved in the implementation of the project and without their collaboration it would not have been possible. Very special thanks also go to Ana Álvaro Gallo and Pablo Pardo Ibañez at the CENIEH for their assistance with the analyses, motivation and excellent advice. In London, we also appreciated the availability and help of Hannah Page and Patrick Quinn in assisting with the thin-sections preparation.

Additional information

Notes on contributors

David Larreina-García

David Larreina-García holds a PhD in Archaeological Sciences from the Institute of Archaeology, UCL, London, and is currently microscopy and µ-CT laboratory technician at the CENIEH, Burgos, Spain. His research focus lies at the intersection of material science, history and archaeology.

Andoni Saenz de Buruaga

Andoni Sáenz de Buruaga has been Professor of Prehistory at the Universidad del País Vasco, UPV-EHU, Spain, since 1982. His research focuses on methodological areas of lithic typology and archaeological stratigraphy, as well as the genesis and evolution of different Palaeolithic cultures in Western Europe. Since 2004, he has led a pioneering research and co-operation project in Western Sahara aimed at recovering and interpreting the country’s cultural past and diverse heritage manifestations.

Andoni Tarriño Vinagre

Andoni Tarriño Vinagre holds a doctorate in Geology from the Universidad del País Vasco UPV-EHU, Spain. He specialises in geoarchaeology, in particular the characterisation and sourcing of lithic raw materials and the study of their mechanical properties. He has directed several archaeological projects and is currently a permanent doctoral researcher (PDR) at the Department of Prehistory, Geography and Archaeology at the Universidad del País Vasco.

Belén Notario

Belén Notario Collado holds a PhD in Physics from the Universidad de Valladolid, Spain, with a specialisation in materials science and the study of polymers. Since 2016 she has been the technician in charge of the Computerised Microscopy and Microtomography Laboratory of the National Centre for Research on Human Evolution (CENIEH), Burgos, Spain.