Journal of Archaeological Science (2001) 28, 457–464doi:10.1006/jasc.2000.0571, available online at http://www.idealibrary.com on

The Use of Lithic Artefacts for Making Rock Art Engravings:Observation and Analysis of Use-Wear Traces in ExperimentalTools Through Optical Microscopy and SEM*

Myrian Alvarez†

CONICET. Asociacion de Investigaciones Antropogicas (AIA), Rivadavia 1379 11 ‘‘F’’ (1033), Buenos Aires,Argentina

Danae Fiore‡

University College London, Institute of Archaeology, 31–34 Gordon Square, London WC1H 0PY, U.K.

Eduardo Favret

CONICET, Centro Atomico Constituyentes (CNEA), Constituyentes y Av, Gral Paz. C.P. (1650), Buenos Aires,Argentina

Ramon Castillo Guerra

Centro Atomico Constituyentes (CNEA), Constituyentes y Av, Gral Paz. C.P. (1650), Buenos Aires, Argentina

(Received 23 June 1999, revised manuscript accepted 17 January 2000)

In this paper we present the results of observations made via optical microscopy and SEM of microwear traces onexperimental lithic tools used in the replication of rock art engravings. The overall aim of this experimental programmeis to generate diagnostic microscopic criteria that could subsequently be used (a) in the identification of archaeologicalartefacts that have been involved in the production of rock art engravings, and (b) in the inference of the engravingtechniques in which they have been used. The methods of replication of engraved figures and lines, and the observationof the microwear traces on the experimental artefacts used are presented. The complementary use of stereomicroscope,metallographic microscope with bright field, dark field and laser illumination, and SEM is also discussed. The resultingmicrowear traces observed on the tools used in the experiment are characterized, and are linked to the two differentengraving techniques with which the rock art replication has been carried out. � 2001 Academic Press

Keywords: ROCK ART ENGRAVINGS (PETROGLYPHS), MICROWEAR ANALYSIS, MICROWEARTRACES, EXPERIMENTAL ARTEFACTS, REPLICATIVE EXPERIMENT, ENGRAVING TOOLS,ENGRAVING TECHNIQUES.

*An earlier version of this paper was presented at the XII CongresoNacional de Arqueologia Argentina, La Plata, in October 1997.†,‡These two authors have contributed equally to this researchproject.

4570305–4403/01/050457+08 $35.00/0

*As an example of this, bibliographical research on rock art sitesfrom Argentina (Fiore, 1996–1998) showed that in spite of the veryhigh number of sites with rock art engravings found in that country,only in three cases are tools mentioned in relation to their making(Debenedetti, 1917; Menghın & Gradın, 1972; Llamazares, 1980). Inall cases, the identification was made according to the tool mor-phology and to the macroscopic observation of possible use-weartraces.

Introduction

T he aim of this paper is to present the first resultsof an experimental programme in which micro-wear traces on experimental lithic artefacts used

in the production of rock engravings (which can alsobe called petroglyphs) replicating rock art lines andfigures were observed via optical microscopy and SEM.These results may be relevant for developing useful

criteria for the identification of archaeological toolsinvolved in the production of rock art engravings(Fiore, 1996). Such tools are not usually recognizedwithin artefact assemblages*. This, in turn, will be

� 2001 Academic Press

458 M. Alvarez et al.

informative about the techniques involved in rock artproduction, particularly about the types of artefactsused and the ways in which they were used (Alvarezand Fiore, 1995).

To fulfil the proposed aim, we developed an exper-imental program which had the following generalgoals:

(1) to generate criteria that help in the identificationof the morphology of the artefacts used to makerock art engravings;

(2) to establish possible modes of use of theseartefacts;

(3) to distinguish the use-wear traces found on thoseartefacts, through the methodological frame-work of microscopic observation (developed bySemenov, 1964; Keeley, 1980; Anderson-Gerfaud,1981; Vaughan, 1981; Mansur-Franchomme,1983a, b; and Plisson, 1985 among others), inorder to identify the characteristic traces of theengraving task on the used tools, as well as todevelop microscopic criteria to infer the differentengraving techniques used (in this case, incisionand scraping).

In the following sections we present the details of theexperimental programme and the results obtainedthrough its application.

BackgroundThe microscopic study of experimental and archaeo-logical tools used in rock art engraving has not been acommon practice, and hence there are only a few casesin which this approach has been applied. Pratt &Sonneville-Bordes (1969, in Mansur, 1983a), madeengravings on calcareous boulders and cave walls withthe aim of observing the resulting traces on the exper-imental tools through the use of a metallographicmicroscope. Replicative experiments and the obser-vation of wear traces on the engraving artefacts usingoptical microscopy has also been carried out byBednarick (1998: 27–31), who has characterized manyengraving techniques, particularly that of percussion.

Allain (1979) studied the lithic material of Lascauxand identified 27 artefacts related to the production ofrock art engravings through their observation under astereomicroscope. These tools show a clear edgerounding, similar to that observed by Rigaud after theexperimental use of the same raw materials found inthe site (Allain, 1979). Finally, other authors havestudied the grooves of the engraved figures, bothmacroscopically and via optical microscopy, in orderto make inferences about the engraving techniquesused to produce them (G. and B. Delluc, 1978, 1991;D’Errico & Sacchi, 1995; Bednarik, 1998: 29, 30).

*Scraping can also be unidirectional, but the cinematic of this workusually implies that even in this situation, the tool is moved in thecontrary direction when being re-positioned for starting the nextunidirectional movement, since it is not operative to lift or raise thetool for re-positioning it each time.

Experimental MethodsThe development of the experimental programmeimplied the making of reproductions of various

engraved figures and lines using experimental lithictools. The aims of this programme were:

(1) to make engravings on a rock surface(both—engravings and surface—similar to thearchaeological ones);

(2) to assess the potential of the particular shapes ofartefact and of particular techniques to achievethe engravings reproduction;

(3) to determine the dynamics of wear trace forma-tion on experimental lithic tools as a consequenceof the work on the rock surface;

(4) to establish if there are different traces left bydifferent engraving techniques.

The figures were made on boulders from the north ofPatagonia (Argentina), where many rock art engrav-ings have been found. The type of rock—a tuff which isfrequently found in the area (and belongs to the CollonCura formation, Miocene)—is very friable and itshardness is between 3 and 4 on Mohs’s scale. Amongthe various engraving techniques used in the region,two were selected to start the experimental programme:incision and scraping. These two share certain elementsin common, related to the work cinematic and to thetechnical gestures:

(1) they both imply the movement of the artefactalong the worked material (instead of the punc-tual action made by a tool on a restricted portionof the worked surface, such as in pecking andpounding);

(2) the application of force is continuous and impliesthe use of pressure, involving the constant contactof the tool with the worked material.

We define ‘‘inclusion’’ as a cut or split made in thebedrock through the unidirectional or bi-directionalmovement of the tool, whose edge is moved longitudi-nally in relation to the working direction. The workingangle is about 90 deg. ‘‘Scraping’’ is the abrasion of thebedrock through the bi-directional movement of thetool*, whose edge is moved in a transversal way inrelation to the working direction. The working angle isbetween 35 and 70 deg, and the contact between thematerial and the artefact is unifacial.

According to the type of mechanical action put intopractice, both techniques require pressure, that is, acontinuous contact between the artefact and theworked material, where the load is applied in a pro-longed way, and at the same time requires moving theartefact along a portion of the worked material(Mansur Franchomme, 1983; Gutierrez Saez, 1993).

The experimental engravings included 13 reproduc-tions of actual patagonian rock art figures and 41marks, mainly in the shape of straight lines (see Figures

Use of Lithic Artefacts for Making Rock Art Engravings 459

Figure 1. Experimental three-digit figure reproducing a typicalPatagonian rock art engraving, made on a standing wall in aPatagonia rock shelter. Scale: 1 section white/black=2 cm.

Figure 2. Boulder with experimental engraved lines.

The experimental tools were 34 unretouched flakes,from which 40 edges were used. The flakes were madeof basalt and obsidian by direct percussion, usinga hard hammer. Both raw materials were usedin Northern Patagonia, although according to thearchaeological records the basalt tools were muchmore frequent than the obsidian ones. The inclusion ofobsidian in this study permits comparison to andanalysis of the formation of the wear traces withdifferent characteristics. In relation to the wear traces,the following were considered: edge rounding, micro-flakes, striations, micropolishes and residues (Mansur,1986–1990).

After each experiment, the used tool was observedunder a stereomicroscope (Olympus SZ40) with mag-nification from 4� to 40�, and with a metallographicmicroscope (Reichert MEF II) with objectives andoculars that allow a magnification between 35� and800�. These were used in a complementary way sincein each the orientation of the beam of light, the degreeof resolution and the depth of field are different. Wealso used a scanning electron microscope (Jeol U 3SEM) in secondary electron mode, which is a usefulinstrument for characterizing fracture surfaces and forrevealing surface topography.

In the case of the metallographic microscope, bothbright field and dark field illumination were used. Aunidirectional laser oblique illumination (ULOI) lightHe–Ne Melles-Griot 30 mW was also used. This illu-mination technique, which has recently been used inoptical microscopy of metals, alloys and polymers,allows one to distinguish regularities and/or preferreddirections in the rough texture whose dimensions are,in some cases, under the resolution of the objective lensused. The laser beam is focused on the surface of thesample from outside the microscope, with an angle ofapproximately 10 deg to the horizontal. The image isformed with the diffracted beams of higher order,resulting, as a consequence, in a technique similar tothe dark field (Favret et al., 1995; Povolo, Canzian &Favret, 1997).

1 & 2). The former were made in order to find out thepossible span of time taken in the production of thesefigures. The latter were made in pre-established periodsof 5, 10, 15, 20, and 30 min with the aim of systemati-cally observing the evolution of the formation of weartraces.

ResultsAs a result of carrying out the experimental pro-gramme, grooves having similar characteristics tothose of archaeological engravings were produced bythe use of the natural edges of the flakes, which provedeffective for the making of incised and scraped linesand figures. The use of a soft, homogeneous andfine-grained boulder as the bedrock for the engravings,allowed easy making of the lines and figures, sinceremoval of the material from its surface was quitegentle. The irregularity of the texture of the boulder insome areas, hindered the sliding of the tool in thoseareas. This hindrance disappeared when the surface goteven due to the work process, since the worked surfacebecomes increasingly flattened as a result of the contactwith the tool.

460 M. Alvarez et al.

Figure 3. Edge damage, striations and micropolish band inexperimental obsidian artefact used in unidirectional incision.Magnification: 100�. Dark field illumination.

Figure 4. Edge rounding in experimental basalt artefact used inscraping. SEM. Magnification: 50�.

Figure 5. Micropolish band in experimental basalt artefact used inunidirectional incision. Magnification: 50�. Dark field illumination.

In relation to the wear traces, the observation ofthe experimental tools at 5-min intervals allowed theobservation of the evolution of the modifications tothe artefacts’ surface. During the first minutes edgedamage occurred, giving the edge a very irregularshape (see Figure 3). The scars are distributed alongthe edges in a continuous way and are more abundantin the obsidian tools than in the basalt ones.

In relation to their morphology, there are many‘‘half moons’’ generally of very small dimensions,although small stepped and small scalar edge micro-fractures (Keeley, 1980) are also observed. In thoseartefacts used with the incision techniques, these tracesare distributed along both faces of the tool, while inthose used for scraping they generally appear on thecontact face. This is due to the fact that, while inincision the edge is placed with a longitudinal orien-tation, which involves both sides of it, in scraping theedge is placed with a transversal orientation, whichinvolves only one side of it, therefore the use-weartraces will be formed (and found) in the respectiveactive sides. While orientation of the tool is thenrelevant for the position of the traces on the side/s ofthe edge, the direction in which the tool was used seemsnot to have been determinant of this figure. Also aclear edge-rounding is observed in the non-fracturedareas of the edge both in incising and in scrapingtools.

The modification of the edge angle that is generatedduring this first stage of the work leads to edgestabilization. This means that when the edges andthe vertex that offer fragile points disappear, the gen-eration of microflakes is clearly reduced. From thatmoment onwards, the working edges are rounded andsmoothed by the pressure produced by the continuoustool rubbing (see Figure 4); this fact is similar to thatobserved by Allain (1979) in the experimental andarchaeological tools from Lascaux. This edge round-ing, as well as its polished surface, is visible with the

naked eye, and also with the stereomicroscope. Also,the section next to the edge of the artefact lookscompletely smoothed.

Concerning the micropolishes, they are comparableto those described in the literature for tools thatworked on mineral substances. Micropolishes areobservable from the moment in which the edge isstabilized (approximately 10 min of work). It is prob-able that their formation could be previous to thatmoment, but the microchipping of the edge in the firstminutes of the work makes the zone of micropolishesdisappear together with the microflakes.

In most of our observations the micropolishes arewell developed at 15 min after starting work, and canbe studied under low magnification, using a metallo-graphic microscope with dark field illumination orusing SEM. At 50� and 100� they look like scratcheson the surface that form parallel bands to the edge,oriented in the sense of the direction of the work. In theincision cases, they appear clearly oriented in thelongitudinal sense respect to the edge (see Figure 5),while in the engraving cases they are oriented in thetransversal sense respect to the edge (see Figure 6).

Use of Lithic Artefacts for Making Rock Art Engravings 461

Figure 6. Micropolish band in experimental basalt artefact used inscraping. Magnification: 50�. Dark field illumination.

Figure 7. Micropolish band in experimental basalt artefact used inunidirectional incision. Magnification: 50�. Unidirectional laseroblique illumination.

Figure 8. Micropolish band in experimental basalt artefact usedin scraping. Magnification: 50�. Unidirectional laser obliqueillumination.

Figure 9. Waves of micropolish surface in experimental obsidianartefact used in unidirectional incision. SEM. Magnification: 500�.Bright field illumination.

These micropolish bands have been observed in allexperimental tools, but with some specific featuresaffected by the structure of both the tool and theworked material. On the basalt tools, the micropolishappears flat in comparison to the non-worked zonesof the artefact (see Figures 5 & 6); as opposed to this,on the obsidian, a material whose natural fracturesurface is flat, homogeneous and highly reflective, themicropolish shows a rough texture, including severalstriations (see Figure 3).

The use of laser illumination, that falls in an almostgrazing or oblique way on the tool, proved a great helpin the characterization of these bands, and in theobservation of their orientation and microtopography,allowing as a consequence a better enhancement of thehighly rough surfaces (see Figures 7 & 8).

When observed both with bright field illuminationand with SEM, at more than 300�, micropolisheslook slightly shiny, not very thick, and show a slightly

wavy surface with a homogeneous distribution (seeFigure 9). During the first moments of their formation,they are found in the high parts of the tool microtopog-raphy, and afterwards they cover the entire surface. Ingeneral they are very extended from the edge onwards.In the incision cases, the average extension of themicropolishes is 2·9�0·2 mm (the maximum value is4·33 mm and the minimum is 1·7 mm), in the scrapingcases, their average extension is 2·3 mm (2·6 mmand 1·9 mm are the maximum and minimum valuesrespectively).

The artefacts used to make engravings withboth techniques show the same type of micropolish.Nevertheless, according to the lineal features (stria-tions and waves, see below) position and orientationon the artefact, it is possible to discriminate in whichsense of direction the artefact moved, that is, in alongitudinal in the incision cases and in a transversalway in the scraping ones. Striations are numerous,they appear included in the micropolishes and presentvariable dimensions.

462 M. Alvarez et al.

Figure 11. Waves of micropolish surface in experimental basalt artefact used in bidirectional incision. Magnification: 400�. Bright fieldillumination.

Figure 10. Waves of micropolish surface in experimental basaltartefact used in unidirectional incision. Magnification: 400�. Brightfield illumination.

ConclusionsThe results obtained from microwear analysis ofexperimental tools have allowed a first characterizationof diagnostic wear traces resulting from making rockengravings. It has also allowed the observation of thedevelopment of the use-wear traces that happens dur-ing the work process. Although these traces show thegeneral features of wear related to work in mineralsubstances, they show some specific characteristics thatare related to the used materials, the tools employedand the activities carried out.

We have observed a series of traces that can beclassified in two types (according to Mansur, 1999):traces generated by the edge fracture and traces gener-ated by the modification of the crystalline structure ofthe rock, or plastic deformation. Among the firsttype we found edge damage of different morphologythat are formed mainly during the first minutes of thework. They are of small dimensions, probably due tothree reasons: the edges selected for working wererelatively rectilinear, the worked material is soft,the pressure required to make the engraved figures isslight.

Among the traces generated by the plastic deforma-tion, we have observed a clear edge rounding and thepresence of micropolishes in the form of bands. Thelatter are homogeneous, very extended from the edge,slightly shiny, not very thick. Their lineal featuresallowed the identification of the direction in which theartefact was moved. This latter fact is of great interestfor rock art research, since it would allow the recon-struction of the tool movements involved in the figures’production.

An interesting aspect that resulted from these obser-vations is the possibility to distinguish between theunidirectional and bi-directional actions from thestudy of the waves of the micropolished surface. Wavesare arcs whose convex side points to the directionin which the tool worked, that is, their orientationindicates the direction to which the artefact movedtowards. These observations are consistent with thosemade by Knutsson (1984/85/86: 40), who stated that‘‘In high friction areas there are gentle undulations inthe smoothed surface indicating the working directionof the tool.’’ Waves can show that the artefact hasmoved in a unidirectional way, when they only pointtowards a single direction (see convex sides of whitewaves pointing to the upper left of the field of view inFigure 9, and pointing to the left in Figure 10). Asopposed to this, when the artefact was moved in abi-directional way, the waves are formed in bothdirections (see Figures 11 & 12). Nevertheless, in this

latter case it is sometimes possible to observe a pre-dominant direction because the work process is notentirely symmetrical in both ways.

Use of Lithic Artefacts for Making Rock Art Engravings 463

In relation to the raw materials, we have observedmore edge fractures in the obsidian tools than in thebasalt ones, since the former is a very fragile material.Also, as we have stated above, the micropolish bandsobserved at 50� and 100� on the obsidian tools,have a rougher look. Nevertheless, both clearly showthat they are the result of working a rock or similarsurface.

Finally, given that the mechanisms of formation ofeach of the traces is different—edge fracture and plasticdeformation—the observation of each of these tracesthrough the complementary use of different micro-scopes and various illumination techniques was ofgreat help not only for the analysis of their formationbut also for the characterization of their variousaspects. The inclusion of the laser illumination tech-nique proved of great use for the identification ofthe micropolish bands, since it enhances the contrastbetween the areas of more or less roughness on the toolsurface. The use of SEM not only confirmed theobservations made through optical microscopy, butalso allowed a contextual view and characterization ofthe wear traces by allowing broader portions of thetools edges to be in focus at high magnification withoutlosing resolution and depth of field.

This paper presents a first approach to the study ofthe artefacts involved in the production of rock artengravings through optical microscopy. The resultsobtained up to the moment can be used as initialparameters with which to compare both other exper-

imental results, as well as microwear traces observed inarchaeological artefacts which may have been involvedin the production of petroglyphs. A further studyinvolving new experiments with materials of differentcharacteristics (both of the engraving artefact andthe engraved bedrock), as well as involving differentengraving techniques, will allow a broader and moreaccurate approach to this subject.

AcknowledgementsThe research presented in this paper was generouslyfunded by Fundacion Antorchas (Argentina), towhom we remain very grateful, and it was carriedout under the general supervision of DrM. Ipohorsky (CONICET-CNEA) and Dr M.Tarrago (CONICET-UBA—Museo Etnografico ‘‘J. B.Ambrosetti’’). Any shortcomings of the paper remainexclusively the authors responsibility.

Figure 12. Waves of micropolish surface in experimental obsidian artefact used in scraping. Magnification: 400�. Bright field illumination.

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