Copper and Flint – Exploring Technological Interfaces in South Scandinavian Early Metal Using Societies

Abstract

This chapter explores research pertaining to the possible evidence of copper tools being used in flint knapping processes in early metal-using societies in South Scandinavia. The existence and use of copper as a flint working tool in prehistoric Scandinavian contexts has often been proposed and accepted, but no real study on the implementation as such or the effects on the knapping process has been conducted. In the absence of archaeological evidence, the proof and interpretation must rely on secondary markers, such as technical attributes or trace elements on the flint. Research so far has analysed finished tools to detect and verify the use of copper. This study offers a different approach, relying on production flakes to get a deeper understanding of the production process itself and thus investigating the effects copper knapping tools would have had.

1. Introduction

In flint knapping, the oldest known and most persistent technique is direct percussion with a hard hammer stone. First, evidence has been traced back 3.3 million years, long before the existence of the genus Homo, e.g. [1, 2]. For the longest time, it has been the only way of working stone tools. Only some 100,000 years ago, during the late Lower Palaeolithic, a change in manufacturing methods appeared, and organic percussors enter the knapping process [3, 4]. By comparison, the discovery and processing of metals happened quite recently, only 5000 to 6000 years ago, during the Chalcolithic, after which it started to spread at varying speeds through Europe [5, 6].

Invention and adoption of metallurgy most certainly was one of the most powerful technological milestones in prehistory [7, 8]. Not only did the objects made from a novel material have an influence on the societies, but also the knowledge and possibilities tied to the invention acted on people as well as on the existing technological traditions. Yet, no technology appears out of thin air; ideas, procedures, and developments are often based on existing knowledge adapted to new circumstances. This is also the case concerning metallurgy. The material is new, and the properties are very different, but the idea of heating material in order to change its properties is not a novelty. This process has a longer tradition in ceramic production and even flint knapping [7, 9]. The challenge in the processing of the new material was to achieve higher and steady temperatures so the ore could smelt [10, 11, 12]. Metallurgic knowledge and the tools created were thus not separate entities but part of the entire technological system. They were influenced by and did influence other technological aspects, like flint knapping.

While questions of technological developments in local metallurgy and its effects on the social sphere have been analysed, e.g. [13, 14, 15], the effects on existing local technologies and traditions have only received little attention and then mostly pertaining to the decline of the flint knapping craft, e.g. [16, 17, 18]. This article examines the influence of different technological complexes, here, flint working and early metallurgy, on each other and explores the possibilities for identification in archaeological contexts.

2. Research background

The emergence of civilisation and social hierarchisation has often been treated as an inevitable development connected to the invention and spread of metallurgy. The new prestigious material as well as the new developing technology, implied new social structures. On one hand, the complex extraction and/or trade and processing of metals needed specific working structures for a successful outcome and on the other hand, this eased the path to individuals seizing control over raw material access, craft knowledge, (trade) routes, and other influential and necessary aspects of life. This can be sensed in changing burial rites, including a shift from communal megalithic burial to family or individual-oriented mounds, but also in the changing symbolism and objects connected with certain social rules and genders as well as settlement patterns and house construction [15, 19]. However, the adoption of early metallurgy has not been a straightforward path in the development of societies [9]. Northern Europe, and especially Southern Scandinavia, is a good example of a culture-geographic area where an initial familiarisation with the novel material was not immediately followed by an adoption of the new technology. The earliest copper objects in Scandinavia have been found in Late Ertebølle (Mesolithic) contexts and date around 4500 BCE [14, 20]. Based on typological similarities and metallographic analyses, the pieces have been identified as imports from Southeast Europe [14]. Early objects are typically tools like axes, but awls, beads, and rings are also known [14, 20]. Large-scale adoption of metallurgy did not happen; likewise, local copper sources, especially in today’s north Sweden, were not exploited in prehistoric contexts, although mining was a familiar practice, as flint quarries indicate [21, 22, 23, 24]. All copper had to be imported to Scandinavia, either as finished tools or in the form of ingots [16, 25, 26]. New data suggest that some experimentation with metallurgy in the early phase in the form of cold forging and probably also smelting was present [6, 27, 28]. Likewise, knowledge about physical properties is hinted at in prehistoric finds [29, 30]. After an initial boost, copper objects disappeared from archaeological contexts between 3200 and 2350 BCE [6, 9], which is often interpreted as an indication of changing or collapsing networks, leaving Scandinavia at the fringes of the technological development without possibilities to participate, e.g. [9, 31]. Opposing opinions and explanations have been voiced. Missing evidence does not indicate absence per se. Changing depositional practices or intensified re-melting are likewise possible explanations for the absence of objects [6, 28]. However, metallurgical analyses have detected changing isotope compositions in the copper alloy of the objects from the initial phase and objects from the Late Neolithic and Bronze Age context, which favours the interpretation of changing networks, also indicating that metal is imported from different regions than initially after the hiatus [6, 9, 32]. Likewise, throughout the Bronze Age, certain types and forms of objects and materials appearing in different European regions indicate a developing and changing long-distance trade network connected to the distribution of metal across Europe, where Scandinavia contributed by supplying central Europe and the Mediterranean with amber [15, 19, 33, 34].

Another option for the decline is that copper tools simply were not as much in demand as always assumed. The early copper tools especially did not present technical advantages to the existing tools made of bone, stone, or flint, as the copper was far too soft to offer the same efficient use [35, 36]. Early copper objects in Scandinavia are often found in hoards and in pristine condition, which suggests a purely symbolic function. It is the aesthetics and rarity of the material which made it desirable, not the technical function [37]. The notion of metal as a superior and prestigious material is a modern view of prehistoric times, which needs to explain the adoption or abandonment of metallurgy [9, 36, 38]. However, copper has technical advantages when used in flint knapping. In comparison to antler or wood, copper is a harder yet still flexible material. Antler pressure flakes need a certain size as the contact area of the tip during the flaking process, as the applied force otherwise will cause the tip to splinter (Figure 1). The physical properties of copper extend the possible force that can be applied during the flaking while reducing the contact area of the tip; the material will deform a bit but will not splinter. In other words, as the material is harder than organic materials, the tip can be smaller and more pointed, and as it is still flexible, the tip will withstand the pressure without shattering. Likewise, the reduced contact area provides a more concentrated transmission of force, which relates to less force being needed from the knapper’s side to remove flakes. On the downside, as the copper tip is harder, it is more likely to result in a conchoidal fracture, which often leaves deeper negatives than pressure with an organic flaker would. This means additional work has to be invested to achieve an even working surface.

Figure 1.

Flint knapping tool kit by PW in 2007. Photo by: B.V. Eriksen.

The need to import metal objects and the shortage of the very same material has been used as an explanation for the development of bifacially¹ crafted flint daggers in Scandinavia between 2350 and 1600 BCE. It also has been frequently stated that the daggers are skeumorphic alternatives to copper daggers made from locally available material [39, 40, 41, 42, 43, 44]. But the bifacial flint knapping method² is older, and other types of bifaces were manufactured in Scandinavia before the advent of daggers [46, 47, 48]. Similarly, the typological development of the daggers appears continuous without breaks or jumps in the overall shapes. Metal objects seem to have had a guiding effect on the forms of flint tools but were not necessarily the origin.

Scandinavian flint daggers were produced and circulated in northern Europe for about 800 years. Throughout this time, a variety of forms developed, which were divided into six types based on the form of the blade and handle by E. Lomborg [49]. Each type consists of at least two subtypes (Figure 2), but from a morphological point of view, the daggers can be summarised into four categories: lanceolate (types I and II), lanceolate blades with square-profiled handles (type III), leaf-shaped blades with so-called fishtail handles (types IV and V) and leaf-shaped blades with tang-like handles (type VI). They are chronologically more or less successive, although with larger overlaps and regional variations in type preferences [16, 49, 51]. Especially the so-called fishtail daggers (Figure 3) have received considerable attention due to their impressive shapes, difficult and complex manufacturing process, and likeness to contemporary bronze daggers in northern and central Europe [42, 52]. Without a doubt, Late Neolithic and Early Bronze Age flint knappers were experts in the craft and pushed the boundaries of the physically possible. A similar perfection and command of the flint knapping process has not been observed before or after in Europe.

Figure 2.

Overview of flint dagger types based on E. Lomborg’s [49] drawings assembled by J. Apel [50].

Figure 3.

Type IV flintdagger. Holstein-Rathlou collection, Moesgaard Museum, Denmark. © Rógvi N. Johansen, Moesgaard Museum.

Starting with the type III daggers, punched seams are created on mostly rhombic handles, which are often interpreted as copies of metal dagger seams created by the casting mould [53, 54]. It is these handles that have puzzled generations of archaeologists and modern flint knappers. Fracture mechanics specify certain angles at which successful removal of flakes can happen. Ideally, depending on the technique used during the reduction, an angle between 60 and 80° is aimed for [45, 55]. The seams on the rhombic handles are often worked at a 90° angle on all four sides. Furthermore, the knapper had to change from planar to four-sided working mode on the same piece. Although the technique employed to work those forms was long incomprehensible from a modern point of view, studies have shown that the knowledge and working tradition was nothing new for flint knappers in the Late Neolithic and Early Bronze Age. The method has a long tradition in the manufacture of the four-sided axes and adzes of flint from the region [56]. Creating 90° seams on flint objects is thus nothing really new in South Scandinavian flint knapping traditions, but the filigree character of the stitching, as seen in Figure 3, represents a refinement of existing knowledge and methods. Quite likely related to the possibilities copper offered in flint knapping.

It is unclear whether the manufacture of the handle was done like this for aesthetic or, indeed, for technical reasons. Flint is a hard and, in flaked form, very sharp material. It is quite uncomfortable to wield a freshly made dagger in bare hands, and it can result in deep cuts if not treated carefully. The lanceolate daggers were likely used hafted (i.e., with a wrapping of the handle made of organic material), as finds from different regions suggest [57], for example, the dagger from Wiepenkaten [58] and a recent find from the Femern belt excavation [59, 60, 61]. The stitched seams are still mostly interpreted as an aesthetic attribute, which was meant to be shown, especially on the type IV fishtail daggers. Points in favour of this interpretation are that the handles of the earlier dagger types are often not worked as carefully as the blade, probably due to the later wrapping, which would cover the surface. Likewise, the stitched seams often show grinding to blunt the sharp ridges, which would lessen the danger of injuries during handling. Another explanation for the seams is the possible advantages of the wrapping of the handle. The organic material would have a better grip and be less prone to slip on the seams. An example in favour of this interpretation is a reported type V dagger, which allegedly was found with a thread wrapping which, unfortunately, was removed by the collector [48, 62].

The manufacturing process of the flint daggers is a complex series of interrelated steps. Depending on the type of dagger, up to eight stages may have to be completed before a finished tool is produced [63]. Simply put, the more elaborate the dagger was meant to be, the more stages and more careful work were needed. A point which has often been stressed is that the development of flint crafting was only made possible due to the rise of metallurgy and the inflow of copper daggers into Scandinavia. The scarcity of metal and the determination of lithic craftspeople not to be left behind started a technological race which prompted the perfection of the flint knapping process and resulted in more and more elaborate and stunning dagger designs [40, 64]. Moreover, there are strong arguments to suggest that the development also did benefit directly from the upcoming metallurgy. Certain steps in the manufacture of some dagger types are not possible or, at any rate, very difficult to master without the use of copper-tipped implements, i.e., the so-called pressure flakers. This concerns the finishing parallel retouch of the blade surface of the type IC daggers but also the finely stitched seams of the type IV daggers [53, 63, 65, 66]. The necessity of including copper-tipped pressure flakes to achieve fine parallel flaking is still debated in the flint knapping community. While all agree that some of the finest seams of the fishtail daggers show too small negatives of removed flakes to be done by anything other than copper tips, the parallel flaking is more debatable. Some flint knappers suggest that it could be possible to achieve similar results while using spatula-shaped antler flakers [67], which do exist in the archaeological record and could be related to pressure flaking [68]. Regardless of the possibility of using different materials and tools for the parallel retouch, copper-tipped flakers would still have had a positive effect on the flaking process and made the manufacture easier. The force needed to remove flakes is less, when copper is used. Likewise, flakes can be spaced more evenly, and the removals tend to be more regular, meaning that the lateral edges of the flakes tend to be more straight and even, which would be a highly desired feature for the aesthetic parallel retouch [66]. Though we have as yet no archaeological support for the existence of copper tips for flint manufacture in Scandinavia, it is not too far-fetched to assume they were available. As argued above, copper and some metallurgical knowledge was present in Scandinavia at the time. A tip for a pressure flaker would not require much material, and not much metallurgical knowledge would be needed to fabricate a short pin which can be inserted into a wooden handle. Likewise, in other European regions, copper objects exist, which suggests a connection and use in flint knapping contexts [68, 69, 70]. The possibility is therefore high that copper flakers were either not recovered archaeologically because the short pieces of copper were not preserved or were not recognised either due to heavy oxidation or because they were mistaken for other artefacts, like awls. Modern knappers use their copper-tipped pressure flakers for several years before the material is worn down so irrecoverably that it has to be replaced by a new tip. The demand for copper in the flint knapping context in prehistoric Scandinavia was thus quite likely very low, and resupplying would not have posed a major problem. The identification of copper in flint knapping processes in Scandinavia thus relies on technical observations and trace element analysis, which both have come up with heavily debated results, e.g. [68, 71, 72, 73].

3. Technical identification of copper in flint knapping

The data used in this chapter are part of a recent project concerning Late Neolithic and Early Bronze Age bifacial production [67]. For the study, production flakes from modern knappers replication of bifacial sickles and daggers were recorded and analysed, as well as their (i.e., the flint knappers) decision process (Figure 4). Questions about individual technical choices and transmission of knowledge were addressed. A minor part of the project was also concerned with the identification of copper in the knapping process. For this, not only technical markers were analysed, but some flint flakes were examined by scanning electron microscopy (SEM). A problem when trying to confirm traces on object surfaces by SEM is the limited size an object can have to be placed in the chamber [72, 74]. Likewise, it is time-consuming when no exact spot is known, and the entire surface has to be analysed. Part of the project was, therefore, to have a closer look at production flakes, not only to identify where copper implements leave traces of metal but also to ascertain which other attributes and characteristics are connected to the use of copper and thus can give hints in the absence of visible proof. Visible denotes here traces that are identifiable with the naked eye or a magnifying glass.

Figure 4.

Finished bifacial objects of the inventories included in the recent project that is referred to here. Outer left: Type IC dagger. Rest: Early bronze age type asymmetric sickles. © a. Heitman, UFG Kiel.

Flint is a generic term for silicious material with certain properties. It is mostly fine-grained, homogeneous and knappable [45, 75, 76]. Depending on the variety and the object that is being made, no further treatment of the flint is necessary. If tough and coarse-grained flint is used, heat treating may help to improve the knapping quality so flakes can be removed more easily [77, 78]. Heat treatment of flint has not been confirmed in Neolithic or Bronze Age contexts in Scandinavia. This is probably due to the generally good quality of available flint as well as the abundance of the raw material [79]. When force is applied punctually to the material, it fractures conchoidal. The more homogeneous and isotropic the material, the more predictable the process is [80, 81]. The force applied results in a fracture following the Hertzian cone. The resulting crack in the material will bend inward rather quickly, and the force will run more or less parallel to the surface until the flake detaches completely. A second mechanical property used in flint knapping is the bending fracture. Without a clear point of impact, the stress on the material tears the flake away from the nodule [81, 82]. Both types of fracture mechanics leave characteristic traces on the flakes, which help to determine which fracture happened during the reduction. For example, a bulb is a sign of conchoidal fracture, while a lip formation indicates bending of the material. The bulb is the partial expression of the Hertzian cone, where the force of the blow has travelled through the material [82], while the lip is an overhang, left on the back edge of the flake platform. Further, the markedness and joint occurrence of certain technical attributes make it possible to identify which techniques were applied during the reduction process.

The first distinction in knapping techniques is drawn between direct and indirect application. This differentiates if the knapping tool was applied directly to the nodule or if an intermediate piece was placed between nodule and percussor. Classically, direct percussion is separated in hard percussion with a stone and soft percussion with organic implements, like antler or wood [45, 55, 83]. Depending on the knapping material, the flake detaches either by conchoidal or bending fracture. Generally speaking, the softer the material, the bigger the area of impact, and bending fractures are more likely to happen.

Another technique applied in a direct manner is pressure. During pressure flaking, a device, often a short handle with a pointed tip, is placed directly on the edge, and pressure is applied until the flake detaches. Pressure can also be applied with the so-called Ishi-stick. The principle is the same, but the Ishi stick is most often a rod of forearm length. Due to this, more leverage can be applied as the whole upper body can be used to exert pressure. The length of pressure flakers is not standardised and depends on the knapper and what they feel comfortable with. The detachment of the flake can happen by both conchoidal or bending fractures. Like direct percussion, pressure flaking can be split into a hard and a soft variety. Former is done, by using copper-tipped pressure flakers, while the latter uses tips of antler, wood, or bone [45, 84]. Indirect technique includes the use of an intermediate piece positioned on the edge where the flake is wished to be removed, on which the blow is then dealt. Like the pressure technique, the control is higher than in free percussion, as the exact spot for removal can be chosen, but the force delivered is higher than achieved by pressure. Intermediate pieces are called punch and are usually made from antler or copper, but other materials are possible [45].

As mentioned above, the choice of technique can be reconstructed by analysing technical markers on the flakes. Relevant to this chapter are only characteristics related to knapping with copper tools, so a further discussion of attributes related to other implements will not be given. It should be noted, though, that the overlap in attributes is very high, and they are not mutually exclusive [81]. Statements about the production process should, therefore, be based on a multitude of flakes being examined and not on single observations.

Characteristics of pressure flaking are small and plain platform remnants without facets, barely extending the contact area of the implement tip. The harder the tip’s material, the smaller the remnant can be, and the more likely conchoidal fracturing becomes [81, 84, 85]. The bulb is often short and set rather high on the ventral surface (the surface that was attached to the nodule), and if copper is used for pressure, very small ring cracks are possible [81, 85, 86]. Ring cracks are small, semi-circular fissures indicating the top of the Hertzian cone [87]. During the recording of production flakes, it was noted that flint flakes with visible confirmation of copper traces indeed had quite marked but small and high-set bulbs. However, this was not true in every case, which can be explained by the state of preservation of the knapping device. Regardless of the technique used, the continuous impact of the implement on the more or less sharp edge of flint wears down the material. An important part of flint knapping is thus the maintenance of the knapping implement’s surface. During pressure flaking, no blow is dealt, but a lot of force is exerted on a rather small area, which also wears down the tips of antler as well as of copper. For the maximum effect, the tips have to be kept in good working order and sharpened every once in a while. For copper, this can happen through grinding or hammering. The latter has the advantage of hardening the material further, as it resembles cold forging. If the tip wears down and the area of contact with the material gets slightly bigger, this has effects on the knapping attributes; the less sharp the point is, the less marked the attributes appear [88], which explains why traces are visible, but the attributes do not match in every case.

Most research concerning attribute formation in copper flaking has been done in connection to blade production, e.g. [86, 89, 90]. Occasionally, copper flaking has been identified in contexts of pressure flaking, e.g. [72, 91], but the focus of analysis was always on finished objects and not production flakes. Experimental production of artefacts has shown that copper-tipped flakers leave visible traces when the tip slips and scratches across the surface, which often also happens when the termination fails, and the tip connects to the resulting step in the material [72]. For the experimental replications in this study, all craftsmen were allowed to use their own tools at their own discretion. As copper pressure flakers cannot be confirmed or excluded from the production process archaeologically, this had no influence on the authenticity of the replications, even if there is no evidence for the use in sickle production during prehistory. All resulting production sequences were documented and compared to each other, and an ideal sequence for bifacial dagger production [67]. Compared to the ideal sequence, copper was implemented and used more often and earlier in the process than expected. The choice to use copper pressure flakers was also dependent on the individual knapper’s preferences. While two of the knappers preferred to work with copper to have more control over of the process and be able to progress more carefully, the third preferred not to use copper because it tends to leave deeper negatives, which have to be compensated later.

Visual inspection of the finished artefacts (Figure 4) did yield traces of copper on the surface, mostly in connection with failed terminations, but not on all pieces and surprisingly not on the included type IC dagger replication, where the last production step is executed with copper pressure flaking alone. The confirmation of copper traces left on production flakes, especially on the platform remnants, was better. Out of 12,184 recorded flakes, 942 had visible traces of copper, mostly on the platform remnant or below the platform on the edge (Table 1). The dagger replication by AB especially included a very high number of traces, which is probably due to the relatively poor quality of the raw material, which forced the knapper to progress carefully. In his case, this included the default to copper pressure but also the implementation of copper punches during indirect percussion, which was chosen more often for safety reasons.

Artefact	Count with copper	Total number recorded
AB dagger	670	3330
AB sickle	9	1730
GN dagger	9	2109
GN sickle 2006	89	1059
GN sickle 2007	158	1771
PW sickle 2006	1	997
PW sickle 2007	6	1081
Total	942	12,077

Table 1.

Number of flakes with visible copper traces on the surface in each recorded inventory.

Differing total number of flakes from the total amount mentioned in the text is due to an additional test inventory, which has not been included in the paper.

As mentioned above, ring cracks are used as a representation for flint knapping with copper in the absence of other evidence [86, 91]. The recorded ring cracks from the case study were also analysed to see if any prediction concerning the use of copper implements in the knapping process could be made. Table 2 shows the expected low frequency of ring cracks, as most of the production is executed in soft percussion. Most of the cracks are probably related to pressure and indirect technique, but they do not seem to be the only factor. As mentioned already, AB used copper punches rather frequently during the production of the dagger. This was not done in the sickle production, and pressure with copper was not done extensively. Still, the frequency of ring cracks is nearly double in the sickle inventory. AB stated that he uses copper when he wants to be more in control of the knapping process and use less force during the removal. Thus, choosing the harder material here seems to translate to less forceful flaking, which reduces the formation of ring cracks. In contrast, GN dagger shows a rather high percentage, which relates back to the raw material. This inventory is the only one using differing materials: Texas flint, which is a tougher and less homogeneous variety compared to Scandinavian flint. More force is thus needed to remove flakes, which favours the formation of ring cracks.

Inventory	None	Present	With conical break	Not preserved
AB dagger	84.6	4.84	0.00	10.6
AB sickle	56.1	8.66	0.18	35.0
GN dagger	69.2	13.86	0.14	16.9
GN sickle 2006	75.3	8.03	0.09	16.5
GN sickle 2007	83.7	3.06	0.06	13.2
PW sickle 2006	65.8	8.68	0.31	25.2
PW sickle 2007	70.1	5.98	0.00	23.9

Table 2.

Frequency in percent of ring cracks in the recorded inventories.

Further analysis showed that ring cracks appear mostly in the first stages of production and not so much in the last. Only a few have been recorded on the smallest flakes, which are more likely to originate from the final pressure retouch or on the flakes from the parallel retouch (Figure 5). This strengthens the impression that it is the indirect technique which is responsible for the ring cracks in the inventories. No, or just a few ring cracks during the parallel flaking and pressure retouch is not so surprising, as the amount of force needed is rather small compared to the earlier stages, where more and larger areas of the surface are being removed. This shows that the force needed to remove the parallel flakes is not high enough to leave ring cracks in a repetitive way, and the attribute is not a significant indicator for the use of copper-tipped pressure flakers in the archaeological record if the bifacial method is analysed. This draws attention to a problem relating to the experimental identification of knapping attributes. As mentioned, the attributes for copper flaking have been identified in experiments of blade production [85, 86, 89, 92]. Blades, and especially blades knapped with copper, are long, narrow, and regular flakes. They need a certain kind of preparation, precision, and force to be removed from the nodule. The conditions for pressure flaking or indirect percussion in a bifacial method differ completely. It is shown here that the attributes are not transferable one-to-one to other production strategies.

Figure 5.

Scatterplot of ring crack diameters by production stage or flake size class. Ring cracks exceeding 10 mm were removed from the data sets. The flake size classes used here refer to the length of the flake. Size class 1 comprises the biggest flakes (≥ 100 mm) and the length gradually declines until flake class 8 (5–6.99 mm).

To get a better impression how the ring crack diameter relates to pressure flaking and indirect technique using copper implements, all flakes with visible traces were assembled, and the ring crack diameters were plotted against the distance from the edge (Figure 6). This was done to see if distinct groups would be observable. Indirect technique is mostly used in the early stages of production and is meant to remove larger flakes, and as the punch is bigger than the pressure flaker tip, this means the flake is removed at a greater distance from the edge than a pressure flake. As Figure 4 shows, no group formation can be detected. As AB was the only knapper including copper punches in the production process and only during the production of the dagger, all other inventories and plotted points indicate that pressure flaking with copper indeed relates to small ring cracks near the edge. But, the relatively low number of incidences indicates that other factors need to be met so that ring cracks really appear. Likewise, no clear separation between pressure and indirect technique with copper seems to be present, at least not in the formation of ring cracks.

Figure 6.

Scatterplot of all ring cracks on flakes with visible confirmation of copper traces in correlation to the distance of the impact point from the edge of the platform remnant.

Thus, even if it is known when and why copper was included in the production process, this does not mean an identification is easy. Table 1 shows that copper has an ambiguous tendency to leave traces on the surface of flint. The frequency of implementation, skill of the knapper, force needed for the removal, as well as raw material qualities are all aspects, which have an influence on the possibility of copper traces being visible on the surface. Likewise, the copper itself is important; the softer the material, the more likely it will leave traces. Hardened tips are thus more likely not to leave visible traces. Also, the handling by the knapper has influence; skilled and experienced knappers are less prone to errors and accidents during the reduction. This lessens the chance of scratches on the surface by slipping. Further, the technical markers and attributes are not always explicit.

The possibility of detecting traces on the platform remnant of flakes would thus offer a higher chance of identifying knappers working with copper, as even the experienced knappers need to place the tip on the surface of the flint and exert pressure for the detachment. As mentioned above, interpretation of used techniques should not be made on single flakes, as the characteristics overlap, and clear-cut evidence for copper in the knapping process only shows on very few flakes. It would be useful to have a more reliable way to identify copper-knapped flakes, and trace element analysis can be a method for that. Using flakes for the detection of copper in flint knapping processes offers possibilities the finished tools cannot offer. Flakes are mostly not subjected to further use, which, especially for the sickles, can remove traces left on the surface. Likewise, the possible areas to look for traces are smaller and thus more quickly inspected, even in the absence of visual evidence.

4. Material analysis and results

Residue analysis on flint started to develop in the 1960s, following S. Semenov’s [93] seminal work on flint technology [74]. Studies like P.C. Anderson’s [94] work showed that residues of different kinds leave traces on the flint and can be used to identify the material which was worked. Most often, residue analysis is done to make statements about the function and handling of flint tools, e.g. [95, 96, 97]. Studies relating to the identification of knapping tools are scant, which relates back to the facts that use-wear traces need time and repetition to form – which is not given during knapping, as the knapping tool only connects briefly with the surface – and organic residue on very small areas, as the platform remnant, quite likely have perished by the time archaeologists uncover the artefacts. Likewise, even modern residues can be hard to interpret visually, as their morphology can vary depending on many factors other than degradation [74].

Though residue and use-wear analysis have become an integral part of archaeology, no real best practice guide or norm of analysis has been formulated yet [74].

Some flakes with visible confirmation of copper traces from experimental replicas were selected for trace analysis. They were each subjected to visual analysis under the Andonstar ADSM302 digital microscope, and later, the chemical analysis was conducted using SEM Zeiss Gemini Ultra55 Plus. The SEM uses radiation (secondary electrons and X-rays) created by the interaction of the primary electrons and the sample in order to receive information about surface morphology and chemical composition of the same micro-scale area. For the imaging, secondary electrons with relatively low energy provide the most surface-sensitive contrast, so-called SE-imaging. Compared to light microscopy, SE-imaging provides a much higher depth of field, giving surfaces the impression of three-dimensional micro-topographies. However, due to the conventionally used electron detectors, images are restricted to greyscale. Localisation of residue can thus be quite challenging, which is why initial analysis with visual microscopes is recommended [74]. The instrument applied here uses a beam of electrons operating in the accelerating voltage of 5–20 kV. The electron images recorded via SEM were used to attain the surface topography of the specimen, showing the contrast between the possible metal traces on the flint material. Furthermore, chemical analyses via elemental mapping were conducted in the energy-dispersive X-ray (EDX) mode in SEM. In this case, the beam of electrons scans the surface of the specimen, and secondary X-rays are detected by the EDX detector to determine the chemical composition laterally resolved. In the scope of this study, the EDX point measurements and elemental mapping have been conducted. The X-ray spectrum always includes weak stray signals from the instrument itself, the sample holder, etc., which has to be kept in mind when interpreting the complete spectrum [74]. Furthermore, non-conducting artefacts had to be coated with carbon or gold for high-quality imaging. However, more recent studies have shown that it is possible to collect images and spectra without coating the surfaces [74, 98].

Two representative examples of the analyses are shown here. In Figure 7, a flake (number 761) produced by AB from the replication of an Early Bronze Age flint sickle is displayed and records the observations from the SEM. In the electron image, certain regions appear brighter, corresponding to the original flaked surface of the flint, which contains Si and O as determined by the elemental mapping. Moreover, the EDX elemental mapping also shows the signals from the copper metal, which are residues from the copper knapping tool. Similarly, Figure 8 also shows the traces of copper as confirmed by the SEM EDX elemental mapping showing the copper metal traces on the surface of the replication of the flint 1609.

Figure 7.

SEM EDX elemental mapping on the flake 761 with electron image (a) and images (b-d) showing the corresponding elements along with the the copper traces.

Figure 8.

SEM EDX elemental mapping on the flake 1609 with electron image (a) and images (b-d) showing the corresponding elements along with the the copper traces.

In another experiment, the flakes were heated at 600 °C for 24 and 48 hours to simulate oxidation. The result was that the copper traces on the surface do reduce through time (Figure 9 and Table 3) by the thermal treatment; however, the mechanical stability of the copper oxide formed is sufficient to avoid complete removal from the surface. The same is presumably true for flint, which has been exposed to the environment for a long time. Consequently, the confirmation of copper traces by SEM-EDX does not provide an unambiguous indication for the use of copper tools in the production process. Likewise, only examining technical attributes is not sufficient and may lead to wrong conclusions. Further analytical strategies should be based on well-designed combinations of correlated analytical techniques. For instance, dedicated (e.g. Synchrotron-based) XRF and/or Synchrotron-based tomography may provide information about the presence of copper. Using identical location approaches, the chemical nature of the copper (oxide, element, etc.) may be determined by SEM, particularly if the measurements are already supported by machine learning approaches. The ultimate test for such a novel strategy would be to identify the nature of copper traces on flint without visible indication.

Figure 9.

SEM EDX elemental map of experimental flint replica (a) before heating, (b) after heating for 24 hours, and (c) after heating for 48 hours.

Atomic percent (at.%)	Before heating	After heating 24 hours	After heating 48 hours
Cu	76 at.%	36 at.%	17 at.%
O	23 at.%	64 at.%	83 at.%

Table 3.

SEM electron images of heat treated flint at 600 °C (a) before heating, (b) after heating for 24 hours, and (c) after heating for 48 hours.

5. Discussion

Identification of copper pressure flakers or punches in the production process of flint objects is not as straightforward, as often described especially in technological studies. As could be shown in the flake inventories included here, the technical attributes identified as typical markers for the involvement of copper during blade production are not present or are not only related to copper in the flaking process. The very small ring crack, which has mostly been used to identify copper pressure flakers, is mostly absent on the production flakes analysed. Or the ring cracks associated with copper traces have a bigger diameter than assumed in connection. Likewise, markers such as the bulb, which can be quite distinctive, do not always show the same features when knapping with copper. The state of the copper tip as well as the hardness of the material or force of application can obscure the distinct features, so a definite assignment is not possible.

Likewise, trace element analysis has only been done in connection with finished artefacts so far, which poses several problems. First, the size of the objects for which analyses are possible. Second, there is a concentration on few and mostly finely made objects, in this case also only daggers from Bronze Age contexts, e.g. [71, 72]. Confirming copper in contexts from which we know copper had to be present to achieve the outcome is a bit of a self-confirming result. It tells us nothing new but still fails to answer if copper as knapping tool was widely available or only restricted to very few craftspersons. Likewise, as could also be seen in this study, when skilled craftspersons are involved in the process, there does not need to be traces left on the surface. They are mostly connected to errors in the knapping process and can also be removed from the surface again when those errors are eliminated, e.g. [72]. There is also the possibility for accumulation of element traces due to depositional circumstances, e.g. [99], as well as removal through oxidation. Mostly, if copper and other materials had sufficient contact with the flint surface to leave elemental traces, those remains would seem to be amply preserved to be detectable in analysis, even after long years in the soil [72, 74], but it has to be located before analysis nonetheless. Also, no studies exist so far that deal with the question of how use affects the traces. The study by G.H. Strand Tanner [72] included only a very limited experiment on cutting flesh.

Looking for traces of production flakes is therefore the next logical step. They are mostly not restricted by the size requirements, especially as flakes removed by copper pressure tend to be relatively small. Likewise, the area of interest is so much smaller, i.e. mostly relating to the platform remnant and the edge below, though steps and hinges of failed terminations can be of interest, too. Another advantage is the certainty that if copper was involved, the tip had to connect to the platform. On the surface of finished artefacts, every trace detectable is an impact by chance, contrary to the impact point on the platform remnant. If the knapping device would not have connected, the flake would not have detached. This simplifies and shortens the analysis with the SEM a lot. Furthermore, in combination with technical markers, flakes can be pre-sorted for probability of bearing traces, which can reduce the negative results for a time-consuming and expensive analysis.

6. Conclusion

Copper in the knapping process can best be identified by combining approaches. Trace element analysis can confirm the presence of copper traces on the surface but works best when distinct locations for sampling are known. These can be found either by visual confirmation or by selecting technical markers. A problem with the bifacial method is that the markers identified so far are not represented very well in the production process. This is most likely due to the differences in production, as the previously published experiments were conducted with blade manufacture, which is very dissimilar to the bifacial method. Further experiments of copper implementation in bifacial production would be needed to distinguish typical characteristics on flakes. If those are identified, it will help to answer a wider variety of questions concerning not only the technological knowledge of flint knapping but also metallurgy. Also, questions about social developments could be pursued, for example, in the context of the availability of copper to flint knappers, and this also gives insight into social networks of dependency.

Likewise, identifying the implementation of copper tools in flint production processes can help us to better describe the development of flint knapping technology and understand how the elaboration of the craft was structured. There is no doubt that metal and metallurgical knowledge influenced flint technology, not only in the form and function of objects but also in the manufacturing process. Copper offers advantages compared to antler or wood and eases the process of knapping while allowing for more control. This is true not only for production steps, which are not possible without copper. Many modern flint knappers rely a lot on copper during flint knapping, depending on how authentic they want to work. There are technically no reasons why prehistoric knappers should not have done the same, when copper became available, save social and traditional rules structuring the manufacturing process. If such rules were in existence and/or how they changed, the prospect of changing technologies can be explored better if we understand how the new techniques were integrated into existing technologies. The effect is visible in the typological and technical development of the flint daggers, but when, where, and how the development started is still not fully understood. Analysing production flakes in favour of finished tools offers a more holistic and objective approach to the questions.

Acknowledgments

This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy-EXC 2150-390870439.

Conflict of interest

The authors declare no conflict of interest.