Variance in Response to Heat Treatment in Perkinsville Jasper

The heat treatment of lithic raw material is a globally dispersed technology that improves the flaking quality of toolstone. While not all types of stone respond to heat treatment, many forms of microcrystalline silicates do, including jasper. Here, we aim to better understand how Perkinsville jasper responds to heat treatment. Perkinsville jasper occurs in the Perkinsville Valley of Yavapai County, Arizona, and was utilized prehistorically by the Prescott, Sinagua, and Hohokam cultures. For our study, we collected seven boulders of jasper from private land (with permission) in Yavapai County. These boulders were flintknapped into 74 spalls which were subsequently heated in an electric kiln using 20 treatment protocols with systematically varying combinations of maximum temperature and maximum heating times. Afterward, we compared multiple quantitative and qualitative characteristics of unheated and heated flakes taken from the same nodule pre- and post-heat treatment. Our heating protocol allows us to determine an ‘optimal heating context’ for Perkinsville jasper and to better understand how variation in time and temperature influences flaking quality of the stone. Lastly, this research develops an experimental reference dataset that can be used by other researchers studying raw material use and heat treatment in the Southwest United States.