Swept under the rug: The problem of unacknowledged ambiguity in lithic residue identification

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Microscopic analysis of organic residues on stone tools is used to interpret prehistoric stone tool functions. The morphology of some residues can be difficult to interpret, yet this ambiguity is rarely acknowledged in the literature. Our research seeks to understand the nature of this ambiguity by objectively identifying ambiguous residues in our reference collection. We trained four archaeologists in residue analysis using one part of our reference collection, then tested their ability to identify sixty-eight residues in another part of the same collection. Forty-eight of the residues in the test (70%) were correctly identified by three or all four subjects. We considered the remaining twenty residues, which were correctly identified by two or fewer of the subjects, to be ambiguous. These are most often in the hide-scraping, bone-scraping, and hardwood-scraping (macerated) categories, and tend to have an atypical morphology which falls in the range of variability of another residue category. Some of these residues also have optical properties which make them more difficult to image than others. We explore the potential for scanning electron microscopy (SEM) to improve residue identification in a second test. This test shows a modest improvement in identification success rates of ambiguous residues when SEM images are included. We conclude that while images from different types of microscopes can improve reliability of identification, some residues will always be ambiguous. Rather than being ignored, these ambiguities should be brought to light, closely examined, and published as such.

Original languageEnglish (US)
Pages (from-to)3284-3300
Number of pages17
JournalJournal of Archaeological Science
Issue number10
StatePublished - Oct 2012

Bibliographical note

Funding Information:
We thank the four reviewers of an earlier version of this paper, whose thoughtful comments helped to improve it considerably. We also thank our four test subjects, Gil Tostevin, Michele Stillinger, Kristina Golubiewski-Davis and Kia Atsales. Many others helped at various stages of this study, including Tracy Anderson, Gail Celio, Ellery Frahm, Matt Hunstiger, Lora Korynta, Carlos Manivel, Keith Manthie, John Nelson, Mark Sanders, and John Soderberg. Thanks to Harold Dibble and Gil Tostevin for reading the second version of this paper and providing useful comments. This research was funded by a University of Minnesota Grant-in-Aid to G. Monnier. Parts of this work were carried out at the College of Biological Sciences Imaging Center at the University of Minnesota; at the Institute of Technology Characterization Facility at the University of Minnesota, a member of the NSF-funded Materials Research Facilities Network; and at the College of Science and Engineering's Department of Geology and Geophysics Microprobe Lab. The bulk of the work was carried out at the Evolutionary Anthropology Laboratories in the Anthropology Department, College of Liberal Arts, University of Minnesota.


  • Experimental archaeology
  • Lithic residue analysis
  • Microscopy
  • Scanning electron microscopy
  • Stone tools


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