Journal of Archaeological Science 1985,12,361-375

The Analysis of Copper Artifacts of the Copper Inuit

M. L. Waymarf, R. R. Smith”, C. G. Hickeyb and M. J. M. Duke’

Metallography and neutron activation analysis have been used to investigate copper artifacts from 19th century archaeological sites associated with the “Copper Inuit” of the west-central Canadian Arctic. A knowledge of the source of the copper from which the artifacts were manufactured-native (local) copper or European (exotic) copper-is important, for example, to studies of the effects of European contact on utilization of native copper and on the general lifestyle of the Copper Inuit. Trace element analysis by neutron activation using the SLOWPOKE reactor has allowed local native copper, from the Coppermine River and Victoria Island, NW Territories, to be clearly distinguished from 19th century European smelted copper, which was found to contain higher concentrations of arsenic, antimony, nickel and selenium. Moreover, optical and scanning electron metallography revealed significant microstructural differences between native copper and the 19th century smelted copper. As a consequence it was possible to differentiate between native copper archaeological artifacts and those produced from smelted copper.

Keywords: METALLURGY, NATIVE COPPER, ELEMENTAL ANALYSIS, METALLOGRAPHY, NEUTRON ACTIVATION ANALYSIS, MICROSCOPY. This article is based upon a paper presented to the 24th International Archaeometry Symposium held at the Smithsonian Institution in May, 1984.

Introduction It is often of importance to be able to determine whether a copper artifact was originally manufactured from native copper or from smelted copper. In the present case this is applicable to anthropological studies of the 19th century Copper Inuit, who inhabited the mainland and islands of the west-central Canadian Arctic. This region contains native copper (sources in the Coppermine River area, at Bathurst Inlet and on Victoria Island; see Franklin et al., 1981) which has traditionally been used (perhaps for as long as 3000 or more years) for the manufacture of such implements as knives, fish rakes, rivets, staples and projectile points (see McGee, 1972; Morrison, 1983). Smelted copper was introduced into the region in appreciable amounts during the 19th century, especially as a result of contacts with Europeans involved in the search for Sir John Franklin’s third Arctic expedition, which disappeared in 1845. Of particular relevance was the fate of one Franklin search ship, HMS Investigator. This ship had sailed from England to the Arctic via Cape Horn and had therefore been outfitted for passage

“Department of Mineral Engineering, bDepartment of Anthropology, ‘SLOWPOKE Reactor Facility, University of Alberta, Edmonton, Alberta, Canada.

367

0305~4403/85/050367+09 $03.00/O 0 1985 Academic Press Inc. (London) Limited

368 M. L. WAYMAN ETAL.

through tropical waters, including the provision of copper-sheathing on the hull. In April 1853, after several winters trapped in the ice in Mercy Bay, Banks Island, a large cache of ship’s provisions was deposited on the shore and the ship itself abandoned.

Although this region was at the extreme margin of the area traditionally inhabited by the Copper Inuit, the cache was soon discovered by the Inuit who had been visited earlier by Investigator’s captain, Robert McClure. It is certain that extensive amounts of copper, iron, and other materials from the cache and perhaps also from the ship passed into Copper Inuit hands. The effect of this infusion of material wealth on the Copper Inuit (e.g. on their short- and long-term use of native copper) is of interest, and thus it is necessary to be able to determine the origin of the copper in copper artifacts. This is especially critical for two anthropological questions. First, did access to the Investi- gator’.r metals stimulate the production and use of native copper, as has been hypothesized (Hickey, 1983, 1984)? Secondly, was traditional Copper Inuit copper working limited to cold hammering or did it involve heat treatment? The latter point has implications for the archaeological record, in terms of the possibility of re-cycling of artifacts (Hickey, 1983, 1984).

Techniques for distinguishing between native and smelted copper have been reviewed by Maddin et al. (1980) who concluded that “no adequate criteria exist for distinguish- ing artifacts of native copper from those of worked and recrystallized smelted copper of high purity”. In the present case, however, the situation is enormously simplified since it is expected that 19th century European smelted copper was significantly less pure than native copper; thus a differentiation based on elemental composition might be possible. To this end instrumental neutron activation analysis (INAA) has been performed on a range of Arctic native coppers, 19th century European smelted coppers and artifacts from the vicinity of the Investigator cache. In addition, metallographic techniques might be expected to be useful, since such microstructural parameters as grain size and non- metallic inclusion content could differ significantly between native and smelted copper. For example, the presence in the microstructure of extensive amounts of copper oxide, which is indicative of melted copper, would indicate a non-local origin for the material (there is no evidence whatsoever for either the smelting of ore or the melting of native copper by the pre-contact inhabitants of the region). Thus, distinguishing between native and smelted copper might well be possible in this case.

Experimental Samples studied included:

(1) Five samples of Arctic native copper: three from the Coppermine River area and two from Victoria Island.

(2) Four samples of 19th century European smelted copper; one nail from the Fury Beach cache (dated at 1825); one nail from Russell Island (1851) and two formed shapes from the Znvestigator cache (1853).

(3) Eight small artifacts, scraps or tools of unidentified use, most weighing less than 5 g, from several Banks Island sites in the vicinity of the Investigator cache.

Techniques employed included dimension measurement, X-ray diffraction, X-radio- graphy, scanning electron microscopy with energy dispersive X-ray analysis, hardness and microhardness testing, optical metallography, and neutron activation analysis. The latter two proved to be the most useful for distinguishing between native and smelted copper.

For optical microscopy, specimens were mounted in cold-setting resin to avoid any recrystallization of the copper during the heating which is necessary for mounting in bakelite. Mounted samples were then ground to 600 grit silicon carbide, polished with

COPPER ARTIFACTS OF THE COPPER INUIT 369

Figure 1. Microstructure of native copper. Worked condition, 60 x The black holes are intergranular porosity.

6 urn diamond and then with 0.05 urn Al,O, and etched with either alcoholic ferric chloride or NH,OH-H,O,.

Elemental compositions were analysed by neutron activation analysis. Samples weigh- ing about 80 mg were removed with a jewellers’ saw, then etch-cleaned in a solution of 60% H,SO,, 15% NHO,, 25% H,O+ 1 drop of HCl. Samples were rinsed in distilled water and acetone, weighed, and placed in polyethylene vials for irradiation.

The irradiations and counting were carried out at the University of Alberta SLOWPOKE Reactor Facility. Samples and standards were irradiated for 4 h at a maximum thermal neutron flux of 1 x 10” neutrons cm-’ s- r. In order to maximize the number of elements determined, with optimum precision, the samples were counted twice following irradiation, initially for 1 h after 6 days decay time and then for S-10 h after approximately 21 days decay. A full description of the irradiation and counting schemes, methodology and equipment used is described elsewhere (Duke, in prep.).

Results and Discussion As expected, microstructure and elemental composition were the two material parameters which were most useful in discriminating between native and 19th century smelted coppers. The distinguishing characteristics of these two types of material are first discussed, followed by the analysis of the archaeological artifacts.

Microstructure of native and smelted copper Microstructures of native copper from the Coppermine River and Victoria Island were found to be characterized by a very coarse grain size, with grain diameters of the order of millimeters (Figure 1). Twins were present, as was some porosity, and the density of non- metallic inclusions was very low. This is in agreement with the results of other workers on native copper from the Arctic, Lake Superior and the Old World (see, for example, Smith, 1968; Schroeder & Ruhl, 1968; Maddin et al., 1980; Franklin et al., 1981; Vernon, 1984). The specimens of 19th century smelted copper, on the other hand, were observed

370 M. L. WAYMAN ETAL.

Figure 2. Microstructure of 19th century smelted copper. Annealed condition, 350x.

to have a finer grain size, of the order of 20 urn diameter, and a markedly higher density of non-metalic inclusions (Figure 2). Annealing twins were visible in all specimens, indicating that recrystallization had occurred at some time since initial solidification. Typically this would occur as a result of hot-work, or during an anneal subsequent to cold-work.

The non-metallic inclusions present in the microstructures were examined by energy dispersive X-ray analysis in the scanning electron microscope. Inclusions in the native copper were few, large (l&100 urn), generally intergranular and dominantly SiO,. The inclusions in the 19th century smelted copper were much smaller (< 10 urn), more abundant and widely dispersed throughout the microstructure. They were frequently elongated in the working direction. Energy dispersive X-ray analysis showed them to be copper oxides, most likely Cu,O. The utilization of oxide inclusions to distinguish between native and smelted copper was considered by Maddin et al. (1980). It is clear that impure smelted copper, such as was produced by 19th century European industry, would be expected to contain more oxygen than would native copper, and therefore a much higher volume fraction of oxide inclusions. The occurrence of copper oxide non- metallic inclusions in native copper is not unheard of, having been reported by Smith (1968) who found large partially spheroidized oxide particles in a specimen of Michigan native copper from a rock fault. Maddin et al. (1980) detected the presence of a disper- sion of second-phase particles in Australian native copper, these being mainly copper oxide with a few copper sulphides. However, in the present study the location of the inclusions in the microstructure, and their volume fractions and dispersions, were radically different in native and 19th century smelted copper.

Thus, two microstructural characteristics, the grain size and the non-metallic inclusion content, were effective parameters for distinguishing between the two forms of copper. Elemental composition also proved useful in this respect as discussed next.

Elemental composition of native and smelted copper The results of the neutron activation analysis are presented in Table 1. In comparing the compositions of native and smelted copper, the following points become evident.

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372 M. L. WAYMAN ETAL.

Arsenic, nickel, selenium, antimony. These four elements were found in the 19th century smelted copper at the levels of thousands, hundreds, tens and hundreds of parts per million (ppm) respectively. In contrast, the native copper samples contained in most instances concentrations of these elements below the detection limit (Currie, 1968). In the few cases where definite amounts were detected, their concentrations were two orders of magnitude below the levels found in the smelted copper.

Silver. The silver contents of the native copper samples fell in the range 100-1200 ppm with the majority below 400 ppm. Due to the small number of specimens analysed, no conclusions can be drawn on the use of silver content to differentiate the Victoria Island native copper from that found in the Coppermine River area. The 19th century smelted copper samples were found to contain 80&1300 ppm silver, thus overlapping the concentration range of the native copper.

Gold. The gold contents of native copper samples were found to lie below the detection limit (I 0.025 ppm) whereas 19th century smelted material contained concentrations ranging between 0.75 and 5 ppm.

Cobalt, zinc, tin, mercury. The concentrations of these elements were found to be comparable in the native and the 19th century smelted copper.

The results of these chemical analyses, although based on a limited number of measurements, suggest that native copper should be distinguishable from 19th century smelted copper on the basis of the concentrations of arsenic, nickel, selenium, antimony and gold. On the other hand, the levels of silver, cobalt, zinc, tin and mercury are not expected to be useful for this purpose.

The present results are consistent with those of other workers on the analysis. of trace element concentrations in native copper. Measurement techniques used by others have included neutron activation analysis (see for example, Friedman et al., 1966; Fields et al., 1971; Goad & Noakes, 1978; Franklin et al., 1981; Rapp et al., 1984) as well as emission spectroscopy (see, for example, Bastian, 1961; Friedman et al., 1966; Smith, 1968; Patterson, 197 1). The consensus is that more than 24 elements occur in trace amounts in N American native copper, with those present at highest concentrations being silver iron, arsenic and perhaps lead. It must be noted that there have been several reports (Broderick, 1929; Franklin et al., 1981; Rapp, 1982; Maddin, pers. comm.) of native copper containing arsenic at a level of more than 3500ppm. Thus, although in the present case no arsenic levels above 50 ppm were detected in native copper, the use of arsenic for discrimination must be carried out with caution.

Comparison between modern and 19th century smelted coppers reveals the extent to which technological developments have allowed the reduction of impurity levels. With the exception of the silver and mercury contents, the purity of the modern smelted copper is comparable to or worse than that of native copper, and thus significantly better than its 19th century progenitor. The microstructural evidence suggests a lower oxygen content as well, as the modern copper contains fewer non-metallic inclusions than the 19th century material.

Identljication of archaeological artifacts Using the microstructural and compositional information described above, analysis of a series of eight copper artifacts from Banks Island permitted the determination of whether they had been manufactured from native or smelted copper. These artifacts (ARl-AR8 in Table 1) were in all cases small fragments (< 5 g) of unknown purpose, or debitage from metal-working operations.

Microstructurally they fell clearly into two categories. Artifacts ARl-AR4 were typical of 19th century smelted copper with equiaxed recrystallized grains, a fine grain

COPPER ARTIFACTS OF THE COPPER INUIT 373

Figure 3. Copper arrowhead (artifact AR9). Archeological Survey of Alberta specimen 565-10.3. Overall length 16cm.

size and a high density of copper oxide inclusions. The inclusions were somewhat elongated. Conversely, AR55AR8 were similar to the native copper microstructures in their large grain size and low inclusion content. None of these latter artifacts had been recrystallized and all showed evidence of cold-work and folding or forging laps.

On the basis of microstructure, therefore, it is most likely that ARl-AR4 were manufactured from smelted copper and AR5-AR8 from native copper. Results of neutron activation analysis unambiguously confirmed this differentiation. The con- centrations of arsenic, nickel, selenium and antimony in ARl-AR4 were consistent with the previously analysed 19th century smelted copper whereas AR5-AR8 were consistent with native copper. The gold results were less useful, since artifacts AR3 and AR4 (which every other criterion suggested were smelted copper) had gold contents lower than the other 19th century smelted copper samples analysed. These two samples also contained minor amounts of scandium. It appears, therefore, that gold content is not useful for differentiating between native and smelted copper in this particular case.

One further artifact has been studied, an arrowhead of unknown provenance but bearing a strong stylistic resemblance to some variants of traditional Copper Inuit projectile points (Figure 3) The artifact (AR9) is identifiable as native copper on the basis of its chemical analysis (Table 1) and its low inclusion content. The microstructure reveals that it had been formed into a bar of square cross-section by either a hot-work or cold-work plus anneal process. The “bar” shape is characteristic of many northern cultures who practised this type of non-ambient copper working (see Franklin et al., 1981). The wings of the arrowhead, which are culturally diagnostic of Copper Inuit, were then formed from the recrystallized bar by cold-work. This evidence of the use of heat in the forming of Copper Inuit artifacts is important, although there exists the strong possibility that a recrystallized bar might have been obtained by the Copper Inuit by trade, for example with northern Indians, and finally cold-formed in the often-recorded, typical Copper Inuit manner (see, for example, Cadzow, 1920; Jenness, 1922, 1946).

374 M. L. WAYMAN ETAL.

Conclusions For the case of copper artifacts from Banks Island, Northwest Territories, Canada, it has been possible to distinguish between those manufactured from native copper and those from 19th century smelted copper. This was accomplished on the basis of microstructure and elemental composition, the native copper being of higher purity and having a lower concentration of non-metallic inclusions. The trace elements which proved most useful for differentiation were arsenic, nickel, selenium and antimony. Although the number of samples analysed was small and the differentiation parameters may not be applicable for artifacts from other areas of the world, the techniques were clearly successful in this study.

Acknowledgements The authors wish to acknowledge the financial support provided by the Natural Sciences and Engineering Research Council of Canada through an infrastructure grant to the University of Alberta SLOWPOKE reactor facility, and an operating grant to M. L. W. as well as by the Social Sciences and Humanities Research Council and the Boreal Institute for Northern Studies for research grants to C. G. H. We are grateful to those people and organizations who supplied samples for analysis, specifically to D. G. W. Smith of the University of Alberta, Department of Geology; J. Savelle of the University of Alberta, Department of Anthropology; J. Brink and J. Priegert of the Archaeological Survey of Alberta and H. G. Ansell of the Geological Survey of Canada. The technical assistance of R. A. Konzuk was invaluable in this study.

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