Basalt/Andesite Tool Sets
Sandstone Tool Sets
Images of experimentally generated use-wear: wild grass seed processing on a variety of basalt and sandstone mortars and grinding slabs 1, 2
1. Formal Models of Traditional Milling Tool Design, NSF award 1452079, PI Tammy Buonasera, University of California, Davis.
2. Website Design by Christopher Beckham, University of California, Davis
The collection of photomicrographs and photographs posted here is intended to facilitate data sharing and comparisons between different experimental use-wear programs. The images can also function as a teaching aid, or as a supplemental resource for use-wear analysis of ground stone. Please use appropriate citations when using this data.
Grinding experiments were conducted as part of a larger study aimed at comparing the efficiency and functionality of different mortar and grinding slab designs (Formal models of Traditional Milling Tool Design, NSF award 1452079, PI Tammy Buonasera). Tool sets (three types of mortars and pestles, and two types of grinding slabs and handstones) were made out of sandstone or basalt/andesite (Table 1). The use-surfaces of experimental tool sets were manufactured to average dimensions recorded in several sites from hunter-gatherer contexts in central and southern California and southern Arizona. Initial manufacture of use surfaces was accomplished with power-tools. Use-surfaces were then finished with rock-on-rock pecking to remove marks from mechanical tools. Two unshaped tool sets (one basalt/andesite, and the other sandstone) were also used in the grinding experiments (Table 1).
Processing was performed by volunteers (college students, archaeological professionals, and interested community members). Volunteers used the tool sets to process Indian ricegrass (Achnatherum hymenoides) into flour over two, non-consecutive, 30-minute sets. During each grinding session, two different individuals processed Indian ricegrass on each tool set. This provided a total of two hours of measured grinding time per session. In addition to the measured experimental processing time, 20 minutes of grinding practice was provided on the tool sets before the measured results. A more accurate accounting of use-times for assessing wear would be two hours and 20 minutes and four hours and 40 minutes.
Table 1. Tool sets
Tool surfaces were photographed macroscopically and at 20x and 40x under a stereomicroscope before use, after two hours and 20 minutes of use, and after four hours and 40 minutes use. Photomicrographs were recorded using a Leica IC80 HD digital camera fitted to a Leica M80 stereomicroscope. Leica LAS EZ 3.4 software was used to record the images. Photographs were taken with a Nikon D50 DSLR with a 18-55mm f/3.5-5.6G AF-S Zoom-Nikkor lens.
Photomicrographs designated as "stacked" have been digitally processed to enhance the depth of field and highlight topographical details that may be useful in discriminating between microscopic wear-patterns on the surface of the stone. A normal photograph, especially under high-magnification, is limited to a narrow depth of field and therefore can only bring topographical features within a certain range of depth into good focus. Focus stacking is a technique that involves taking numerous photographs at different focus levels and then using software to digitally "stack" them into a single composite image that contains the full range of focus of all of the photos.
Natural and pecked surfaces before use
Photos and photomicrographs (20x and 40x) of natural and pecked surfaces before use serve as comparative examples of starting rock textures. When assessing the used state of a grinding surface, it is helpful to know the starting characteristics (texture, sheen) of the starting material. Starting surface characteristics were similar for different tools manufactured from the same type of rock. Instead of individual photomicrographs of each tool set, several examples of each stone type are provided as a baseline for reference.
Individual tool surfaces after use
Alterations to the grinding areas of tool sets were recorded with photographs and microphotographs at 20x and 40x for each tool set. Because tools were different shapes, made from different raw material types, and used with different sets of primary motions (pounding, grinding, crushing), different patterns of wear are expected to develop.
Firstly, we thank the numerous volunteers who contributed their time, sweat, and observations to the grinding experiments. Funding for this research was provided by NSF award BCS-1452079. Grinding sessions were held in collaboration with several different organizations: University of Arizona, Tucson; Boise State University; the 34th Great Basin Anthropological Conference; Celebration Park, ID; and Far Western Anthropological Research Group in Davis, CA. Dr. Eleni Hasaki (University of Arizona) hosted several experimental sessions at the Laboratory for Traditional Technology. Dr. Mary Stiner (University of Arizona) provided laboratory space for analysis and helped recruit volunteers. Dr. Eric Wohlgemuth and Kaley Colligan (Far Western Anthropological Research Group, Inc.) helped to recruit volunteers and hosted several experimental grinding sessions. Currently, experiments are continuing at the University of Davis California in collaboration with CEAD and Dr. Nicolas Zwins. Finally, we thank the University of California, Davis CEAD for providing a digital platform for sharing many of the use wear Images.