A study involving fabrication of a model body and comparison to pottery shards from the Mississipian site of Aztalan ( ~ 900-1450 AD) has been outlined and implemented. The focus of this study was the effect of rock salt additions on a shell-tempered clay body fired to 700°-1200°. The model body consisted of 65% Ocmulgee clay, 20% Blackbird or M + D ball clay, and 15% crushed oyster shells. Oyster shells were combined with the clay components as a raw, coarse addition, and as a coarse and fine addition after preheat treatment to 540°. Rock salt was added to the various batches covering the range 0-20 weight%. It was found that, by the addition of rock salt, a clay body containing 15% shell temper can be successfully fired to temperatures less than 1000° without exhibiting spalling. The amount of salt required to prevent spalling depends on the particle-size distributions of salt and shell present; the most favorable situation involves fine grinding of both components. Docking the samples after firing decreased the occurrence of spalling. The development of a bulk liquid phase due to salt in the body is not the mechanism which leads to successful firing of shell-tempered ware. Thermal analysis indicates that in the presence of salt, calcite does not decompose. Reaction occurs between calcite and halite at temperatures as low as 700°, producing CaCl₂. Possible eutectic formation in the binary system NaCl-CaCl₂ results in the encapsulation of shell fragments by local glass-phase development. Analysis of Aztalan pottery shards proved the presence of salt by the identification of cubic voids with chlorine-rich rims. If salt was deliberately added to Aztalan shards it was done so in small amounts (<5 weight%), and probably was not well dispersed. -- AATA