Sourcing the clay: Iron Age pottery production around Poole Harbour and the Isle of Purbeck, Dorset, UK.

Abstract

One of the most ubiquitous types of Romano-British coarseware pottery, Black- burnished ware 1 (BB1), was produced around the shores of Poole Harbour, in South East Dorset. Previous researchers have shown that this industry was already well- established by the 1st century BC, while reports documenting excavations at earlier Iron Age sites in Dorset indicate that its roots can be traced back to around 700 BC. However, little is known about the production and circulation of wares during these formative phases of the industry, a topic that is addressed by the research presented here with a specific focus on the clays selected by potters working between 700 BC and 100 BC. A typology of Iron Age Poole Harbour wares has been compiled, drawing together the range of forms found on sites across Dorset. A programme of fieldwork revealed that the landscape of Poole Harbour and the Isle of Purbeck offered a range of clays and sands to the potters. Petrological analysis of 255 sherds of pottery illustrated that the Poole Harbour ware fabrics are characterised by the presence of elongated argillaceous inclusions and a low incidence of silt-sized quartz, with variability in the range of larger quartz grains. Thin sections of 105 clay samples revealed the silt content of the clays is greater than that of the pottery, suggesting potters levigated the raw clay rather than simply utilising a naturally sandy clay. Examination of the elongated argillaceous inclusions in the pottery, using petrology and a scanning electron microscope with energy dispersive X-ray spectroscopy, indicated they are a component of the clay rather than shale fragments added as temper. Compositional analysis of 100 samples of pottery and clay, using inductively coupled plasma spectrometry, demonstrated the potters selected the iron-rich, red- firing clays, rather than the malleable white-firing clays. It also revealed that during the earlier Iron Age the potters utilised the Wealden Clay deposits from the southern side of the Purbeck Ridge, but exploited the Poole Formation clays to the north during the later Iron Age. The wider cultural context of this change is considered and it is suggested that shifting settlement patterns may have influenced the location of the expanding production sites and their ties to communication networks.