An Early Neolithic ‘cracking technology’: Assessing the thermal shock behaviour of organic-tempered low-fired ceramics

During the Early Neolithic, Starčevo-Körös-Criș pottery became a widespread and long-lived phenomenon in the central Balkans. While there was variation in their decoration, form and use, the fabric of these ceramic materials, which more notably includes the use of organic temper was much more consistent. Explanations for this consistency abound, but most are unrelated to how these vessels performed mechanically in different activities. Given the centrality of cooking activities in Early Neolithic societies, a deeper understanding of the thermal shock behaviour of these ceramics is warranted. In this paper, we identify the effects of organic temper and manufacturing techniques in the thermal shock behaviour of low-fired pottery. With the novel use of a thermal cycler, disc-shaped replicas of Starčevo-Körös-Criș pottery bases were submitted to multiple moderate heating and cooling cycles to emulate past thermal shock conditions. With this apparatus, thermally induced cracks were generated, and thermal shock resistance was estimated through two parameters: crack growth and crack path tortuosity. In addition, three-point-bend tests were conducted independently. Our results indicate that, regardless of manufacturing method, fibres from organic temper toughen the ceramic material through energy dissipating mechanisms, such as crack deflection, bridging and micro-cracking, attaining stable crack growth and increasing the material’s thermal shock resistance. Furthermore, results from three-point-bend tests indicate that, while values of organic- and untempered discs did not differ, there was a notable reduction in the variation of flexural strength in organic-tempered specimens, which would have made these ceramics a more ‘predictable’ material. Thus, organic temper likely improved the mechanical behaviour of these vessels by creating mechanisms that regulated crack propagation, constituting a ‘cracking technology’, and is a plausible explanation for the long-term reproduction of these recipes in the Balkans.