The Valley of Oaxaca (Mexico) has a long prehispanic sequence of reduced grayware (<i>gris</i>) pottery that is antecedent to the region's renowned contemporary blackware made today in the village of San Bartolo Coyotepec. Although generally plain, this prehispanic <i>gris</i> ceramic tradition underwent several significant changes in surface finish, thickness, and paste composition. A series of preliminary analyses, including petrography, porosity measurements, and firing temperature experiments, were employed to identify more precisely the technological parameters of these ceramic shifts. The results of these technological analyses were integrated with distributional studies of pottery selected from more than 1,400 collections by the Valley of Oaxaca Settlement Pattern Project. Together these findings offer a new perspective on the often-controversial Classic-Postclassic transition in <i>gris</i> plainwares.