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# High-Resolution Casts for Lithic Use-Wear Analysis

William Banks, Marvin Kay

► To cite this version:

William Banks, Marvin Kay. High-Resolution Casts for Lithic Use-Wear Analysis. Lithic Technology, 2003, 28 (1), pp.27-34. 10.1080/01977261.2003.11721000. hal-04947073

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# High-Resolution Casts for Lithic Use-Wear Analysis

William E. Banks¹ and Marvin Kay²

1. Department of Anthropology, University of Kansas, Lawrence, KS

2. Department of Anthropology, University of Arkansas, Fayetteville, AR

## Abstract

This paper describes a method for creating positive epoxy casts of lithic artifacts that can be subjected to use-wear examination. This method overcomes problems associated with examining patinated artifacts far microscopic traces of use and limitations documented far other casting methodologies. These limitations include having to work with negative casts or surface peels, air bubbles on cast surfaces, and long-term cast integrity. To demonstrate the utility and accuracy of the described casting methodology, use-wear features were documented on a sample of patinated Middle Paleolithic stone tools from the site of Solutré - Village (Saone-et-Loire), France. Epoxy casts were made of these tools, and the same use-wear features observed on the tools were located and documents on the casts. The results demonstrate that this methodology allows for the systematic functional analysis of stone tool assemblages independent of artifact color or chemical weathering.

## Introduction

This paper describes an improved method for producing high-resolution epoxy casts of lithic artifacts that can be subjected to high power use-wear examination. Our techniques faithfully replicate and easily document use-wear on heavily patinated tool surfaces, which often are excluded from microscopic analysis because of their high reflectivity. Our procedures also are suitable for lithic collections that cannot be removed from a curatorial facility, or for artifacts whose dimensions limit manipulation on a microscopic stage.

In contrast to making peels of a stone artifact surface that result in a negative impression or mold, similar to conventional casting (Beyries 1981; Moss 1983; Plisson 1983; Knutsson and Hope 1984), we produce true (or positive) casts for microscopic examination. Bienenfeld (1995) describes a similar casting method. Our experience differs in important respects. First, we have largely eliminated bubbles in cast production. We also address the long-term integrity of the artifact molds used to make the epoxy casts and the benefit of controlling for color when producing the casts. Our casting process employs materials and methods first adopted by paleo- anthropologists for scanning electron microscopy of dentition (Rose 1983; Teaford and Oyen 1989; Ungar 1994) that are easily applicable to stone tool use- wear analysis. This study does not focus on interpretations of the observed use-wear features, but rather is aimed at demonstrating the casting method's accuracy in replicating microscopic wear features.

To illustrate, we present comparative use-wear results of two patinated and unifacially retouched Mousterian stone tools. The patina present on this study's sample has not resulted in significant silica dissolution that would adversely affect wear features. We first examined the tools and documented use-wear features. We then cast these tools and examined the casts to locate the previously documented features. The two artifacts are part of a Middle Paleolithic collection dated to approximately 55,000 RCYBP from the village of Solutré (Saone-et-Loire), France (Montet-White et al. 2002). Analysis of this lithic assemblage has functional implications beyond those developed here (see Pautrat and Pugh 2002). The senior author has used the methodology described below to cast
and microscopically examine 170 tools from the Upper Paleolithic components at Solutré, along with four experimental tool replicas.

## Cast Production

Before casting, artifact surfaces must be cleaned of any adhering sediment and oils. The most practical method is to place the artifact in a clean polyethylene plastic bag filled with a solution of water and ammonium-based liquid detergent, then ultrasonically clean it for at least 30 minutes. This method is effective, it requires minimal equipment, and the appropriate cleaning solutions are readily available. Of course, other cleaning methods are available (e.g., soaking in diluted solutions of HCl or NaOH), but these are less practical, since they employ corrosive or caustic solutions that must be used with caution and can alter the surface of the artifact if used incorrectly. The tools discussed in this study were cleaned with the ultrasonic method.

To make the mold we use polyvinylsiloxane gel manufactured by Coltene-Whaledent named "President Plus Jet Regular Body." It comes in paired 48 ml tubes from which the gel can be extruded with a JM Express Polyvinylsiloxane Impression Material Introductory System that looks and works like a small grease or caulking gun. The gel reproduces features visible up to 10,000 X magnification (P. Ungar 1997, pers. comm.) and maintains its integrity indefinitely (Coltene-Whaledent polyvinylsiloxane gel literature) unless there is sustained expo- sure to ultraviolet (UV) radiation (D. Burnham 1999, pers. comm.).

A sufficient amount of the polyvinylsiloxane gel needed to cover an artifact surface is extruded onto an index card or piece of paper. The artifact's sur- face is then pushed into the gel and simultaneously wiggled back and forth to ensure that no air bubbles are introduced into the mold, while at the same time producing a mold of the tool surface and adjacent edge(s). The polyvinylsiloxanegel should harden for three to four minutes, after which time the artifact can be removed. The mold is then labeled, placed in a clear polyethylene plastic curation bag and, when not being used to make a positive cast, stored in a UV-safe sealed container.

To make the positive cast a mixture of epoxy, epoxy hardener, and pigment concentrate is slowly poured into the mold so that air bubbles are not introduced or trapped in the epoxy mixture. Before the epoxy mixture is poured, a dam of dental putty, which serves to contain the epoxy while it hardens, is attached to the perimeter of the mold.

Although we have tried other brands, we recommend Tap Plastic's "Four to One 'Super Hard' " that includes the epoxy, a hardener, and pigment concentrate. Tap Plastic specifies a four-to-one mixture of epoxy to hardener to which may be added a small amount of pigment concentrate, if desired. Through a trial-and-error process to eliminate from the cast surface air bubbles that confound analysis, we found the ideal mixture to be three parts epoxy to one-part hardener. When care is exercised, one can keep air bubbles from entering the mixture while pouring it into the mold, thus eliminating the need for placing the mold and liquid epoxy in a vacuum chamber. However, the three-to-one mixture of epoxy to hardener appears to be effective in eliminating any air bubbles that might be introduced into the mold during pouring. For analytical reasons, we stir a brown, black or dark gray pigment concentrate into the epoxy-hardener mixture until it becomes opaque. We chose an opaque brown for these casts because it resembles unweathered flint artifacts, which afford exceptionally detailed photomicrographs. The epoxy casts, along with the molds, are then safeguarded against prolonged UV exposure and possible damage.

Based on casting the Solutré and experimental tools, we can say the procedure does require moderate expenditures of money and time. The gel introductory system or dispensing gun was
purchased for US $44.00. A 48ml tube of polyvinylsiloxane gel can be used to mold approximately six artifacts that average between four and six centimeters in length. The tubes of gel are available in boxes of two at a cost of US $25.00 per box. Tap Plastics, Inc. sells a kit containing the "Four to One 'Super Hard' " epoxy and epoxy hardener at a cost of US

$24.75. The dental putty used to contain the epoxy in the mold is available from Coltene-Wahledent at a cost of US $46.00 per unit. Therefore, the only start-up cost is the dispensing gun for US $44.00. The remaining costs incurred during cast production (polyvinylsiloxane gel, putty and epoxy) of the Upper Paleolithic materials from Solutré resulted in an expenditure of US $3.08 per artifact. The expenditure of time to employ this methodology includes cleaning the artifacts in an ultrasonic cleaner, producing the molds, and producing the epoxy casts. In the Solutré analysis, several artifacts at a time were processed, averaging about 15 minutes per artifact.

## Use-Wear Examinations

A binocular differential-interference microscope with polarized reflected-light and Nomarski optics (Hoffman and Gross 1970) was used at intermediate-range magnifications (100X-400X) for this analysis. This microscope is ideal for use-wear studies because it affords a high resolution, three-dimensional view of microtopography far superior to conventional binocular microscopes commonly used to examine wear traces (Kay 1996, 1997; Kay et al. 1998). Striated soluble inorganic residue wear traces were located and photomicrographed at 400X on the patinated Mousterian artifacts. These soluble inorganic residues are most likely composed of silica that became a soluble gel during tool use and then hardened and became fixed to the portion of the tool that was in contact with the worked material (Kay et al. 1998: 756-758; Kay and Solecki 2000: 32; see also Mansur 1982; Vaughan 1985).

Cast of the artifacts were then made and microscopically examined. The same wear traces previously located on the original artifacts were photomicrographed at the same magnification on the casts to afford a direct comparison. Features were photo-documented at 400X because their characteristic attributes are not visible in detail or clearly diagnostic at lower magnifications (e.g., 100X or 200X).

The first artifact used in the casting comparison is the medial segment of a steeply retouched side-scraper. Its distal portion is snapped off. The proximal end has a transverse break about which are wear traces on the ventral surface. These show up reasonably well on the actual artifact (Figure 1a) but are better expressed on the cast (Figure 1b). Variation in image quality is caused by slight differences in the microscope stage planar orientation of the artifact and its cast, as well as by deliberate control of cast surface color. The observed details associated with a wear feature under the microscope can vary greatly based on the planar orientation of an artifact or cast. This is a result of microscope type and Nomarski optics. Therefore, variability in orientation between the original artifact and the epoxy cast explains why slight differences exist in photomicroscopic reproductions of wear feature details. Nevertheless, the suite of wear feature attributes needed to infer tool motion and worked material between the tool and its epoxy cast are identical despite slight differences in their expression. Additionally, because color could be controlled for the epoxy cast, the analyzed surface is not highly reflective, thus allowing for a higher resolution of wear feature details. This increased resolution decreases wear feature ambiguity, thereby allowing more detailed and accurate inferences of tool motion and worked material than would be possible on the original artifact.

Differences in the expression of wear feature attributes due to variation in the planar orientation of an artifact under the microscope are further illustrated in Figure 2. These photomicrographs
document the same cutting wear feature at the tip of a prismatic blade recovered from Ain Abu Nekheileh, Jordan (Henry et al 2001). The two photomicrographs were taken on separate days and after the specimen had been repositioned on a microscopic slide plate. Although an attempt was made to faith- fully place the artifact on the slide plate in the same manner as before, it was not possible to exactly replicate its previous planar orientation. As can be readily seen, a slight change in planar orientation can dramatically affect the visual expression of wear feature attributes. However, despite the difference in expression, the interpretation of use is not materially affected.

The second Mousterian tool that was cast is a naturally backed sidescraper opposite the retouched edge. Wear traces are located along the naturally backed edge rather than the retouched edge and were photomicrographed on the ventral surface (Figure 3). Other than slight differences that are a result of variation in planar orientation of the artifact and cast, the two images of the wear feature have nearly identical wear attributes and clarity of detail.

The sample used in this study is small. It is a result of limitations that prevented a large sample of artifacts from being transported out of France. However, the methodology has been evaluated on experimental tools and has been employed to analyze a large sample of lithic tools from the Upper Paleolithic components at Solutré. These analyses have provided additional evidence that the casting methodology does accurately replicate wear features on experimental tools and patinated artifacts.

## Conclusions

This casting approach allows for microscopic use- wear analysis of virtually any lithic collection of Middle Paleolithic or later age. Patinated artifacts, or others with highly reflective surfaces that are of- ten unsuitable for analysis, can be accurately analyzed. The polyvinylsiloxane gel replicates wear features for analysis at high magnifications and maintains its integrity indefinitely when kept from pro- longed exposure to ultraviolet light. The color-con- trolled epoxy casts exhibit wear features of the highest possible resolution. These techniques afford an opportunity to systematically sample stone assemblages on formal and functional criteria independent of artifact color and chemical weathering.

## Acknowledgments

We thank Peter Ungar, Anta Montet-White, Jean Combier, Yves Pautrat, Geneviève Lagardère, Catherine Varlot, Hélène Raoult, and David Burnham.

## References Cited

Bienenfeld, P., 1995. Duplicating Archaeological Microwear Polishes with Epoxy Casts. Lithic Technology 20:29–39.

Beyries, S., 1981. Etude de traces d'utilisation sur des empreintes en latex. Bulletin de la Société Préhistorique Française 78: 198–199.

Henry, D.O., J.J. White, J. Beaver, S. Kadowaki, A. Nowell, H. Ekstrom, R. Dean, M. Gregg. M. Harrower. J. McCorriston, and S. Mussadeh. 2001. Excavation of AinAbu Nekbeileh: Report of 2001 Field Season. Report to the Department of Antiquities of Jordan, pp. 1–8. Amman.

Hoffman, R., and L. Gross, 1970. Reflected-Light Differential-Interference Microscopy: Principles, Use and Image Interpretation. Journal of Microscopy 91: 149–172.
Kay, M., 1996. Microwear Analysis of Some Clovis and Experimental Chipped Stone Tools. In *Stone Tools: Theoretical Insights into Human Prehistory*, edited by G. H. Odell, pp. 315–344. Plenum Press, New York.

Kay, M., 1997. Imprints of Ancient Tool Use at Monte Verde. In *Monte Verde: a Late Pleistocene Settlement in Chile. Volume II: The Archaeological Findings*, edited by T. E. Dillehay, pp. 649–660. Smithsonian Institution Press, Washington, D.C.

Kay, M. and R. Solecki, 2000. Pilot Study of Burin Use-Wear From Shanidar Cave, Iraq. *Lithic Technology* 25: 30-41.

Kay, M., D. B. Hudler, B. N. Driskel, and M. B. Collins, 1998. Microwear Analysis of Chipped Stone Artifacts. In *Wilson-Leonard: an 11,000-year Archeological Record of Hunter-Gatherers in Central Texas, Volume III: Artifacts and Special Artifact Studies*, edited by M. B. Collins, pp. 731–805. Texas Archeological Research Laboratory, University of Texas at Austin, Studies in Archeology 31.

Knutsson, K. and R. Hope, 1984. The Application of Acetate Peels in Lithic Usewear Analysis. *Archaeometry* 26: 49–61.

Mansur, M. E., 1982. Microwear Analysis of Natural and Use Striations: new Clues to the Mechanism of Striation Formation. *Studia Praehistoria Belgica* 2: 213–233.

Montet-White, A., J. Evin, and T. Stafford, 2002. Les datations radiocarbone des Amas osseux de Solutre. In *Solutre: 1968–1998*, edited by J. Combier and A. Montet-White. Société Préhistorique Française, Mémoire (in press).

Moss, E. H., 1983. The Functional Analysis of Flint Implements: Pincevent and Pont d'Ambon: Two Case Studies from the French Final Paleolithic. *BAR International Series* 177. Oxford.

Pautrat, Y, and D. Pugh, 2002. Les alentours du gisement : Le site mousterien de Solutré-Village. In *Solutré: 1968–1998*, edited by J. Combier and A. Montet-White. Société Préhistorique Française, Mémoire (in press).

Plisson, H., 1983. An Application of Casting Techniques for Observing and Recording of Microwear. *Lithic Technology* 12: 17–21.

Rose, J.J., 1983. A Replication Technique for Scanning Electron Microscopy: Applications for Anthropologists. *American Journal of Physical Anthropology* 62: 255–261.

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Vaughan, P. C., 1985. Use-Wear Analysis of Flaked Stone Tools. University of Arizona Press, Tucson.
<figure><img src="image_3.png" /><figcaption>Figure 1. Photomicrographs of striated soluble inorganic residue wear traces on the ventral surface of a steeply retouched Mousterian sidescraper: a) the artifact, b) the cast.</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>Figure 2. Differences in use-wear attributes of a single feature due to a slight change in orientation for a ca. 9000 RCYBP flint artifact from Ain Abu Nekheileh, Jordan. Note the arrows point to the same microtopographic detail.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>Figure 3. Photomicrographs of striated soluble inorganic residue wear traces on the ventral surface of a naturally backed Mousterian sidescraper: a) the artifact, b) the cast.</figcaption></figure>