Kuhn’s Geometric Index of Unifacial Stone Tool Reduction (GIUR): does it measure missing flake mass?

Citation: Metin I. Eren, C. Garth Sampson (2009) Kuhn’s Geometric Index of Unifacial Stone Tool Reduction (GIUR): does it measure missing flake mass?. Journal of Archaeological Sciences (RSS)
DOI (original publisher): 0.1016/j.jas.2009.01.011
Semantic Scholar (metadata): 0.1016/j.jas.2009.01.011
Sci-Hub (fulltext): 0.1016/j.jas.2009.01.011
Internet Archive Scholar (search for fulltext): Kuhn’s Geometric Index of Unifacial Stone Tool Reduction (GIUR): does it measure missing flake mass?
Tagged: Anthropology (RSS) Experimental archaeology (RSS), Lithics (RSS), Replication (RSS), Unifacial Retouch (RSS), Kuhn’s GIUR (RSS)

Summary

Context
Eren and Sampson’s article further examines the plausibility of Kuhn’s (1990) Geometric Index of Unifacial Reduction (GIUR). This index attempts to use 2D measurements of a flakes reduced edge to find the lost mass. Discovering the amount a particular flake has been reduced can help archaeologists answer questions of tool maintainability, optimal resources, and knapping practices. In 2005, Hiscock and Clarkson ran the first experiment to test Kuhn’s GIUR. They found that the mass loss in the reduction of thirty lithic blanks and the estimate given by the GIUR were extremely close (r=.9330). Although Hiscock and Clarkson’s GIUR equation differed slightly from Kuhn’s (while Kuhn calculated the GIUR by dividing the edge thickness and angle (t) at three points along the retouched edge by the overall artifact thickness (T), Hiscock and Clarkson calculated a different “T” at every point “t” was calculated), the result as of their experimental verification of the GIUR as a method for estimating mass loss in reduced flakes. However, Eren and Sampson note two further experiments (Eren ert. al.(2005), Eren and Pendergast (2008)) whose results generate r-vales of only .4277 and .5160. The goal of Eren and Sampsons article is to find the cause for this descrepancy and once more asses the plausibility of Kuhn’s GIUR.
Methods and Materials
Eren and Sampson posit the conflicting results of testing the GIUR is caused by differences in the initial flake modification. While Hiscock and Clarkson (2005) measure each reduction in increments, Eren et. al. (2005) and Eren and Pendergast (2008) retouched each blank once and only recorded GIUR once the flake was ready to discard. Eren and Sampson attribute this difference in data points generated for each stone the crux of the conflicting results. To overcome this, they set up their experiment to match the retouch conditions specified in Hiscock and Clarkson (2005). The blanks used were made of Green Sand Silicate from Dover, a material of relative high quality for knapping. The two hammerstones for retouching had masses of 174 and 41.4 grams and flakes removed along the ventral face until the lateral margin was sharp. Eren and Sampson altered the conditions of Hiscock and Clarkson (2005) slightly by ending their reduction not when the specimen broke, but when the edge met with the thickest point. Each flake was photographed and measure, while data points for Kuhn’s formula were calculated at multiple points along the edge.
Results
When conducted under similar conditions and similar flaking methods, Eren and Sampson find Hiscock and Clarksons verification of GIUR as a method for understanding mass loss in lithic reduction to hold. Their return of an r value equaling .9112 (n=147) matches almost perfectly Hiscock and Clarkson’s report of .9333 (n=348). However, the authors make a note that these results only confirm GIUR as a plausible method for calculating life histories of flakes. They remind that simple knowledge of artefact mass loss does not inherently say anything about the tools utility, use-life, or curation. They also cede that although their experiments had high levels of correlation between true mass loss and GIUR predicted mass loss, the losses were not inherently measured accurately. As GIUR values of the specimens increased, the variance in mass loss also increased. Within the experiment, GIUR inherently increases with further reduction. Because of this, Eren and Sampson posit that GIUR is only an accurate reflection of mass loss at low levels.

Theoretical and Practical Relevance

Connection This article provides a comprehensive overview of studies done to test and verify the GIUR. Their positive results provide archaeologists with a useful tool for measuring edge exhaustion. The quantification of retouch statistics creates a good visual of edge patterns within an assemblage. In the future, understanding of this aspect of lithic analysis should not stop but spur on further questions about the connection of measurements to utility, material and behavior.

Judgement Although short, this article provides a relatively comprehensive discussion of the uses and failures of Kuhn's GIUR. It outlines well the history of GIUR experiments and is clear in it's explanations of why and where some results differ. However, the article would benefit from a deeper discussion of the disconnect between GIUR values and knowledge of the lithic life history. Simple measurements of mass loss do not inherently say anything else. Eren and Sampson address this, but a more specific and in depth discussion would be interesting. In addition, Eren and Sampson wait until the conclusion of their paper to mention their realization that their measurements will inherently have a high correlation due to the act of reduction itself. In the future, it would be interesting to see if there is a way to design an experiment that lacks this particular bias.