Modeling the costs and benefits of manufacturing expedient milling tools

It is often assumed that use-surfaces on informal or expedient milling tools were formed strictly through use. Informal or expedient milling tools lack clear evidence of exterior shaping and are often associated with short-term occupations or temporary, task-specific sites. Here, a simple model of technological intensification outlined in Bettinger et al. (2006) is adapted to predict minimum use times necessary to profit from time spent improving the use-surface of milling tools. The costs and benefits of making and using improved milling surfaces for two types of raw material (sandstone and granite) are compared using experimentally derived estimates of grinding rates and manufacturing costs. Experiments indicate that shaping a milling surface increases seed-grinding efficiency. Modeling these data along with manufacturing costs predicts that manufacturing effort should be expected sooner than often assumed-in fact, little more than one and a half hours of seed grinding are necessary to profit from time spent manufacturing a shallow basin in sandstone. It also predicts that sandstone should be selected over granite for short-term seed grinding due to its ease of shaping. These results imply that there are many cases where mobile hunter-gatherers who processed seed resources could have reduced their overall handling time by selecting certain materials and investing time in shaping milling surfaces. This highlights the need for greater attention to physical evidence of manufacturing among expedient milling tools. Documenting raw material selection and degree of manufacturing effort expended on such tools can increase the visibility of gendered economic decisions among prehistoric hunter-gatherers.