The History and Practice of Shell Tempering in the Middle Atlantic: A Useful Balance

Middle Atlantic shell-tempered pottery emerges in primitive form in the Albemarle region of North Carolina as the flat-bottomed Currituck "beaker" ware and Water Lily type, possibly flourishing prior to A.D. 400. Classic shell tempering is first represented in the Mockley series, variously interpreted as evidence of the first Algonquian migratory event or local innovation, appearing on the Delmarva Peninsula about A.D. 100 and subsequently on Maryland's Western Shore and in Tidewater Virginia. The tradition of shell tempering reaches its zenith in the region as the Townsend series, generally understood as the ceramic tradition of Algonquian immigrants to the middle Atlantic region about A.D. 800. The use of shell as temper continues into the historic era as Colono-Indian ware of Tidewater Virginia. Replication experiments evaluating the practical implications of shell tempering indicate that the appearance, adoption, and geographic distribution of this technology in the middle Atlantic necessarily accompanied low-temperature firing techniques. Results suggest that long-held views regarding the necessity of prefiring shell are unfounded but confirm other aspects of traditional archaeological assumptions about the technological process derived from materials science studies. Introduction Throughout much of eastern North America, the use of crushed shell for tempering pottery increased dramatically during the Late Woodland and Emergent Mississippian periods, about A.D. 800-1000 (Feathers 2006; Steponaitis 1986:386-387). Noting the broad scale of the distribution of shell tempering over much of the Southeast, and the relatively synchronous timing of its adoption, Feathers (2006) has proposed an evolutionary explanation that situates shell-tempering technology in an adaptive environment in which households with shell-tempered pottery enjoyed the advantage of more durable ceramic vessels, thus assuring the selection and spread of the technique. Shell tempering spread through the middle Atlantic about A.D. 100-800, increasing in frequency and becoming the dominant, or exclusive, tempering technology throughout the coastal and estuarine zones by about A.D. 900. The first part of this paper concerns the question of shell tempering in the middle Atlantic, whether introduced through migration or diffusion, or arising as a local phenomenon, and the nature of the causes for its emergence, adoption, and spread. In a second part the practical aspects of the rather involved (and risky) process of tempering pottery with oyster shell is explored through a simple experiment. An evolutionary explanation positing selection as the cause for the rise in frequency of shell-tempered pottery is described as requiring two parts (Feathers 2006:14). First, shell tempering must be demonstrated to affect the performance of pottery, and second, these effects must be shown to improve the chances that shell-tempered pottery would be reproduced. In other words, it must be shown that one or more physical properties influenced by shell tempering improve fitness. Materials science studies have amply demonstrated that two properties are enhanced by shell tempering: (1) mechanical strength or toughness measured as resistance to breakage, and (2) thermal shock resistance (Bronitsky and Hamer 1986; Feathers 1989, 1990; Feathers and Scott 1989; Steponaitis 1983, 1984; Tite et al. 2001). It is also well known that, however desirable these benefits may be, the use of shell as temper entails the risk of lime spalling not associated with other tempering agents such as grog or quartz. Feathers (2006:21) suggests that if improvements in performance were driving the adoption and spread of shell tempering, we should expect to see a history in which the rise in the frequency of shelltempered pottery occurs with a firing strategy that lowers the risk of lime spalling. For example, "If a potter is using sand temper and regularly firing vessels to 800°C in an oxidizing atmosphere, a switch to shell temper cannot be undertaken without altering the firing strategy" (Feathers and Peacock, this issue). …