Journal of Archaeology in the Low Countries 3-1 (November 2011)

The Production Process and Potential Usage of Bronze Geistingen Axes

Janneke Nienhuis, Jilt Sietsma, Stijn Arnoldussen

Keywords: bronze, Geistingen, axe, microstructure, secondary dendrite arm spacing, copper-sulphide, smeltingre-meltingLate Bronze Age, deposition

Abstract

Late Bronze Age Geistingen axes, found near Geistingen, Belgium (fig.1), are socketed bronze axes whose function remains somewhat enigmatic. Their thin walls and absence of use-wear traces suggest that axes of this type may have had other than purely functional purposes. This paper describes a microstructural investigation on samples taken from two broken Geistingen axes in order to elucidate the production process and assess the axes’ functionality.

One axe has been identified as copper with 9 at%^[1] tin and the other as a ternary alloy of copper with 4 at% antimony and 6 at% nickel. It is concluded that the two axes have been produced from different raw materials (probably re-melted scrap) and have subsequently been cast into a bronze bi-valve mould. Features of the microstructure, like the distribution of inclusions and the secondary dendrite arm spacing, allowed the determination of applied temperature ranges and the average cooling rate during solidification, which indicated that both axes were rapidly cooled using water.

It is suggested that these Geistingen axes were produced for votive or ritual practices or as a certain type of ingot and were not primarily used as tools or weapons.

1 Introduction

Fig. 1 Location of Geistingen.

Bronze axes of the Geistingen type (fig. 2) are dated to the Late Bronze Age, approximately 925-800 BC (Butler & Steegstra 2002/03, 309). They are named after a hoard of 26 or 28^[2] axes found in 1935 in Geistingen, Belgium (Wielockx 1986; Butler & Steegstra 2002/03, 303). To date there are 29 additional examples with a relatively certain origin (Fontijn 2003, 325; Butler & Steegstra 2002/03, 304). Their distribution appears to be confined to the western half of Nordrhein-Westfalen and the Dutch-Belgium Meuse river valley (Butler & Steegstra 2002/03, 304 map 6). Such a confined distribution is atypical of Late Bronze Age socketed axes (cf. Butler & Steegstra 2003/04, 204 map 11; 248 map 14) and suggests a single workshop from which these axes could have originated (Butler 1973, 341; Kibbert 1984, 168; Butler & Steegstra 2002/03, 304).

Fig. 2 Example of an axe of the Geistingen type. Length: 14.3 cm, width 4.1 cm, wall thickness 1-2 mm. (cat. no. 551, from: , 306 fig. 33a) .

Their confined distribution is not the only aspect that sets these axes apart from other contemporary axe(-type)s. First, the few known Geistingen hoards are situated on drier plateaus instead of the typical wetland settings (rivers, streams, bogs) that characterise other axe hoards (Fontijn 2003, 160). Second, contrary to expectations of use as tools prior to deposition, the examples presently known rarely show use-wear (yet are frequently sharpened; Fontijn 2003, 325. Only two axes show a ‘battered’ cutting edge: Butler & Steegstra 2002/03, 304). Third, the walls of these axes are extraordinarily thin (1-2 mm), which renders a functional use as a cutting tool improbable (Butler 1973, 339-340; Kibbert 1984, 166; Butler & Steegstra 2002/03, 304). Moreover, the Geistingen axes from Ool and Nijmegen display casting flaws (bronze projecting into the socket) that would have prevented these axes from ever having been hafted (Butler & Steegstra 2002/03, 309, cf. Guilbert 1996, 13).

These peculiar characteristics gave rise to hypotheses that Geistingen axes were perhaps never intended to be used as tools, but served solely as beautified votive copies of functional types (perhaps of type Wesseling axes) or as standardized metal (currency?) units or ‘axe money’ (Beilgeld; Kibbert 1984, 167; Rivallain 2001). Indeed, one may argue that the role of the axe as an exchangeable, convertible ingot was first materialized through a specialised ingot form during the Late Bronze Age, of which the production of Geistingen axes is an example (Fontijn & Fokkens 2007, 364). Such a usage of axes as ingot and/or votive units is also documented for the contemporary – yet better known – Armorican axe depositions (Briard 1965, 241-282; 1979, 207; 1991, esp. 23). Consequently, a study of the metallurgy and production processes of Geistingen axes may help to determine whether these axes were indeed never intended to be put to use.

However, in order to do so, the information obtained for Geistingen axes should be compared with data for what were contemporary, and explicitly functional, socketed axes from the same region and period. Such axes have been inventoried by Butler and Steegstra (2003/03) and comprise several axe-types such as the Niedermaas type (c. 44 find spots known in the Netherlands and adjacent Germany and Belgium; Butler & Steegstra 2003/03, 268 map 3; 269-271) and the Plainseau type (c. 51 find spots known from the same areas; Butler & Steegstra 2003/03, 279-281 map 4). In particular the latter, mostly found in the Paris basin and Picardy during Bronze Final IIIb (Blanchet 1984, 368-373; Van Impe 1994, 16 fig. 4), can be assessed for pre-deposition functionality through documented use-wear (e.g. Van Impe 1995/96, 10; 31; Butler & Steegstra 2003/03, 267; 283 no. 508; 289 no. 529) and compositional analyses (e.g. Wouters 1990; Van Impe 1994). These thus provide an excellent basis for comparison.

In general, bronze objects can be produced either from ore by smelting or from scrap by re-melting. Smelting copper oxide ore involves heating to about 1250 °C, at which temperature two liquid layers will form according to their density and immiscibility: copper forms the bulk of the melt and a slag, rich in iron and silicon, floats on top (Caley & Easby 1959, 60; Lechtman & Klein 1999, 499; Davis 2001, 10; Bassiakos & Catapotis 2006, 348). The molten copper can be tapped from the furnace and further processed. When sulphide-rich ore is used, an extra step prior to smelting is required: roasting. Roasting takes place at about 350 C in an oxidising atmosphere and the resulting ore will be partially oxidised and partially desulphurised (Caley & Easby 1959, 61; Lechtman & Klein 1999, 498). When this ore is subsequently smelted, three liquid layers will form: copper at the bottom, matte in the middle and slag on top (Caley & Easby 1959, 61). Matte contains copper, sulphur and impurities like iron and nickel (Lechtman & Klein 1999, 499; Bassiakos & Catapotis 2006, 342). The standard practice applied during the Bronze Age did not adequately remove all the sulphur, which means that sulphur in the form of matte inclusions and other impurities may remain in the copper (Caley & Easby 1959, 62; Craddock 1995, 153). The alloying of copper with other elements to produce bronze can take place by either natural co-smelting or intentional co-smelting (Lechtman & Klein 1999, 498-499). After smelting, an object is formed by casting the liquid bronze into a mould.

Re-melting of scrap or ingots and subsequent casting can also produce bronze artefacts. This method is mostly practised in regions where no sources of ore are present, like in The Netherlands (Kuijpers 2008, 20). A lower temperature than in smelting (about 1000°C, depending on the alloy) can be applied to melt the metal (Davis 2001). The concentration of impurities and inclusions in the resulting metal will be lower in re-melted bronze than in bronze produced by smelting (Wheeler et al. 1975, 38; Craddock 1995, 152; Figueiredo et al. 2009, 953). Working of the finished product involves plastic deformation of the metal which results in features in the microstructure, like slip bands, recrystallised grains, deformed phases or broken dendrites (Gordon & Knopf 2006).

This study applies microstructural research on small samples from two broken axes, enabling us to better understand the production and former function(s) of Geistingen axes. The average composition of the bronze has been determined using several analytical techniques, including X-Ray Fluorescence and Electron Probe Micro Analysis. The microstructure of the metal was characterised by means of Scanning Electron Microscopy and contained a fingerprint of the solidification process of the bronze. Several specific features of the microstructures in the two axes will be presented and discussed. This process enabled us to form a hypothesis on the production and potential usage of these Geistingen axes.

2 Methodology and analyses

Samples were taken from two axes (fig. 3), one from Museum Het Valkhof in Nijmegen (The Netherlands; labelled AC20) excavated at Ubbergen near Nijmegen and one from the Gallo-Romeins Museum in Tongeren (Belgium; labelled BH76), which is one of the axes from the Geistingen hoard.

Fig. 3 Sampling locations on axes AC20 from Museum Het Valkhof (left, courtesy: Rijksuniversiteit Groningen) and BH76 from the Gallo-Romeins Museum (right).

Samples

Both axes have a clear casting seam (figs. 2 and 3), indicating that both objects have been cast in a bi-valve mould. Seven samples were taken using a jeweller’s saw. These were taken from each half of the axe and from the casting seam. One sample from axe AC20 is heavily oxidised and is thus excluded from this analysis. The other six specimens are triangular in shape and have dimensions of about 2 x 1 x 1 mm³, so that a cross-section of the wall both lengthwise and crosswise is present. All samples used in this research originate from the upper part of the axe (i.e. the part closest to the original socket mouth, see fig. 3).

Analytical techniques

Compositional measurements on the same axes were recently taken by Postma et al. by means of Neutron Resonance Capture Analysis (NRCA; Postma et al. 2005a; Postma et al. 2011/in press). NRCA is able to detect elements within the ppm to 10^-4 range if the elements show neutron resonances at energies in the range 1-500 eV. Elements that do not satisfy this criterion are for example lead, nickel and iron, which have resonances in the keV region and therefore require an energy resolution beyond the one presently used to distinguish their resonances from those of other elements in the object. Lead, nickel and iron can be determined in the per cent region. Compounds like oxides and sulphides can only be detected by diffraction experiments. NRCA is a bulk technique, it measures the composition of the entire object, including the patina. (Postma & Schillebeeckx 2005b)

This study provides two additional and complementary micro-scale techniques to determine the composition: X-Ray Fluorescence (XRF) and Electron Probe MicroAnalysis (EPMA). The detection limits of XRF generally are in the order of a few tenths of a per cent. The XRF instrument used has a silver tube to generate x-rays, which leads to a detection limit for silver of 1-2 wt%. EPMA can only measure a limited number of elements due to limited number of detection crystals and the detection limits range between 10^-3 and 10^-1. Whereas the composition per phase has been measured with EPMA, the fraction of each phase present has been deduced from electron micrographs. Combining this data leads to the overall composition that will be indicated as measured with EPMA.

The microstructure is analysed on the basis of Scanning Electron Microscopy (SEM), detailing phase fractions, dimensions and morphologies of the primary copper phases and inclusions. The microstructure is the crystalline structure of a metal that can be seen under a microscope. It is formed during the production process of the metal, more specifically during the cooling of the melt. During this process the atoms will order themselves in a crystalline arrangement. The resulting microstructure depends on a number of factors, including the chemical composition of the metal, the initial temperature, the cooling rate and the mould. The microstructure is also responsible for the final properties of the product. Consequently, by studying the microstructure of the Geistingen axes, a part of the production process can be reconstructed and the properties of the material can be discussed.

3 Results and discussion

Composition

The results concerning the composition of the two Geistingen axes, determined with NRCA (Postma et al. 2005a; 2011/in press; personal communication 2010), XRF and EPMA are summarised in table 1 and illustrated in figure 4.

Table 1 Average compositions (in at%) of two Geistingen axes determined with NRCA, XRF and EPMA.

Axe		Pb	Sn	Sb	As	Fe	Ni	S	Ag	Cu (by balance)

AC20	Mean	0.21	9	1.4	0.72	0.4	2	0.95	0.378	85
	error	0.01	2	0.2	0.01	0.2	1	0.06	0.003	3

BH76	Mean	0.4	0.62	4	2.9	0.2	6	1.26	0.605	84
	error	0.3	0.08	1	0.1	0.1	2	0.09	0.004	4

Figure 4 Compositions (in at%) of two Geistingen axes determined with NRCA, XRF and EPMA.

Table 1 and figure 4 show the relevance of using three complementary techniques to determine the chemical compositions. NRCA is able to quantify silver while EPMA is in this case the only technique that measures sulphur. Both elements are important in deducing the raw material used for production (see sections 3.2 and 3.3). NRCA, XRF and EPMA all confirm the presence of the main alloying elements tin, antimony and nickel. The main differences are seen in the number of elements and their percentages, which originate from the technical specifications and limitations of the techniques used (see section 2.2).

Due to systematic instrumental uncertainties for each technique that cannot be accurately determined, a larger variation in the concentration values is found than expected on the basis of the statistical errors per technique. Therefore, for every element detected with more than one technique, the arithmetic mean is calculated and the corresponding error is calculated by using the least squares method. The use of these complementary analytical methods thus provides a more accurate determination of the composition than by using only one.

The results lead to the conclusion that AC20 can be identified as a binary copper-tin bronze with 9 at% tin, while BH76 is essentially a ternary copper-antimony-nickel alloy with 4 at% antimony and 6 at% nickel.

Comparing these numbers with known compositions from functional and contemporary axes can highlight the differences and help form a hypothesis on the function of Geistingen axes. Only a modest corpus of metal analyses on Late Bronze Age axe types is available for the area under study (table 2). The corpus mostly consists of axes of the Plainseau and Geistingen types and very few other types (Niedermaas, Armorican, Wesseling; Butler 2003/2003) are represented. Moreover, the quality of the analytical techniques is varied (chemical extraction versus XRF/EPMA). Nonetheless, the data allow characterising the composition of certain axe types. The (functional) axes of the Plainseau-type can be roughly characterised as copper containing tin (2-10 at%) and lead (2-7 at%) with virtually no other elements present (Van Impe 1994; Wouters 1994, 42). The Geistingen axes studied as part of the SAM series can be characterised as copper with 0.5-5.8 at% tin, 1.8-2.9 at% arsenic, 0.2-2.3 at% antimony and low (

Table 2 Metal composition of Late Bronze Age socketed axe types, measured using different analytical techniques.

As		Sb		Ni		Fe		References		Remarks
0,036		0,001		0,001		0,001		Wouters 1994, 41 tab. 1;		Pres. Niedermaas-type axe; average of 5 measurements
								Van Impe & Creemers 1993;
								Butler & Steegstra 2002/2003, 269-271.
0,031		0,001		0,08		0,001		Wouters 1994, 41 tab. 1;		Pres. Niedermaas-type axe; average of 6 measurements
								Van Impe & Creemers 1993;
								Butler & Steegstra 2002/2003, 269-271.
0,054		0,001		0,001		0,001		Wouters 1994, 41 tab. 1;		Pres. Niedermaas-type axe; average of 5 measurements
								Van Impe & Creemers 1993;
								Butler & Steegstra 2002/2003, 269-271.
0,009		0,001		0,002		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,007		0,001		0,057		0,082		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,007		0,001		0,001		0,89		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,022		1,51		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,009		0,001		0,02		0,35		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,009		0,001		0,035		0,19		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,001		0,001		0,006		0,16		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,009		0,001		0,006		0,089		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,008		0,001		0,012		0,007		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,008		0,001		0,001		0,39		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,001		0,001		0,06		0,31		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,02		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,011		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,003		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,011		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,011		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,014		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,012		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,011		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,009		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,011		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,011		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,001		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,012		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,012		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,011		0,001		0,001		0,43		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,009		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type; average of 2 measurements
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,011		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,56		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,009		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,008		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,008		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,009		0,001		0,001		0,001		Wouters 1994, 42 tab. 2;		Axe of 'Plainseau' type
								Van Impe 1994;
								Butler & Steegstra 2002/2003, 280-282
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2		Axe of 'Plainseau' type; pres. part of Heppeneert hoard
0,01		0,001		0,001		0,001		Wouters 1994, 42 tab. 2		Axe of 'Plainseau' type; pres. part of Heppeneert hoard
n.a.		n.a.		n.a.		n.a.		Van Impe 1995/1996, 31		Axe of 'Plainseau' type
n.a.		n.a.		n.a.		n.a.		Van Impe 1995/1996, 31		Axe of 'Plainseau' type
0,08		0,08		0,05		n.a.		Verlaeckt 1996, 88-89		Axe of 'Plainseau' type; Ag 0,07
1,18		0,56		0,07		n.a.		Verlaeckt 1996, 90		Axe of 'Plainseau' type; Bi 0,1
0,18		n.a.		0,25		0,18		Verlaeckt 1996, 90		Axe of 'Plainseau' type; Bi 0,1
0,06		0,09		0,02		n.a.		Verlaeckt 1996, 109		Axe of 'Plainseau' type; Bi 0,002; Ag 0,05
0,35		<0,62		0,12		0,39		Verlaeckt 1996, 119		Axe of 'Plainseau' type?; Bi 0,06
0,316		0,596		0,161		0,96		Verlaeckt 1996, 119		Axe of 'Plainseau' type?; Bi 0,046
0,07		0,15		0,1		0,08		Verlaeckt 1996, 120		Axe of 'Plainseau' type?; Bi 0,004
1,5		0,7		0,25		0,01		Verlaeckt 1996, 120		Axe of 'Plainseau' type?; Bi 0,015
1		0,8		0,25		0,002		Verlaeckt 1996, 103		Local type (cast in Heusden mould?)
0,535		1,26		1		0,072		Verlaeckt 1996, 90		Axe of type Sompting
2		1		0,25		0,035		Verlaeckt 1996, 106		Axe related to type Sompting ('Atlantic')
1		1		0,35		0,1		Verlaeckt 1996, 106		Axe related to type Sompting ('Atlantic')
0,55		0,15		0,06		0,03		Verlaeckt 1996, 120		Axe related to type Sompting ('Atlantic'); Bi 0,01
0,56		n.a.		0,66		0,23		Verlaeckt 1996, 101		Atlantic'?
3,3		4,1		1,9		n.a.		Kibbert 1984, 214;		Axe of type Geistingen; Co 0,06
								Junghans et al.1960-1974 (SAM 16559)
0,55		2,6		0,5		n.a.		Kibbert 1984, 214;		Axe of type Geistingen, Co 0,04
								Junghans et al.1960-1974 (SAM 16552)
2,1		0,046		0,03		n.a.		Kibbert 1984, 214;		Axe of type Geistingen; Co 0,08
								Junghans et al.1960-1974 (SAM 21612)
1,7		2,7		1,2		n.a.		Kibbert 1984, 214;		Axe of type Geistingen, Co 0,26
								Junghans et al.1960-1974 (SAM 16560)
1,07		2,17		1,97		n.a.		Postma et al. in press table 1;		Axe of type Geistingen
								Butler & Steegstra 2002/2003, 305
1		3,62		4,47		n.a.		Postma et al. in press table 1;		Axe of type Geistingen
								Butler & Steegstra 2002/2003, 305
2,36		4,27		7,58		n.a.		Postma et al. in press table 1;		Axe of type Geistingen
								Wielockx 1986
2,69		4,47		7,73		n.a.		Postma et al. in press table 1;		Axe of type Geistingen
								Wielockx 1986
3,09		4,65		6,59		n.a.		Postma et al. in press table 1;		Axe of type Geistingen; XRF&EPMA
								Wielockx 1986		measurements done (this study)
3,05		5,54		7,83		n.a.		Postma et al. in press table 1;		Axe of type Geistingen
								Wielockx 1986
1,97		3,21		4,3		n.a.		Postma et al. in press table 1		Axe of type Geistingen
2,39		2,66		3,95		n.a.		Postma et al. in press table 1		Axe of type Geistingen
1,24		2,4		6,53		n.a.		Postma et al. in press table 1;		Axe of type Geistingen
								Butler & Steegstra 2002/2003, 309
1,19		1,76		1,5		n.a.		Postma et al. in press table 1;		Axe of type Geistingen
								Butler & Steegstra 2002/2003, 309
0,62		0,87		<0.90		n.a.		Postma et al. in press table 1;		Axe of type Geistingen
								Butler & Steegstra 2002/2003, 309
0,82		2,21		<2.5		n.a.		Postma et al. in press table 1;		Axe of type Geistingen; XRF&EPMA
								Butler & Steegstra 2002/2003, 305		measurements done (this study)
traces		n.a.		n.a.		n.a.		Jacobsen 1904, 18		Axe of 'Plainseau' type; Ag 0,17
traces		n.a.		n.a.		1,5		Jacobsen 1904, 18		Axe of unclear (Niedermaas) type; Ag 0,19
n.a.		n.a.		n.a.		0,77		Jacobsen 1904, 20		Axe of 'Plainseau' type
n.a.		n.a.		n.a.		1,05		Jacobsen 1904, 24		Axe of Armorican type?
n.a.		n.a.		n.a.		1,05		Jacobsen 1904, 39		Axe of Armorican type?; S 0,275
2,35		3,4		0,19		1,99		Verlaeckt 1996, 109		Axe of 'Plainseau' / 'Atlantic' type?; Bi 0,11 (Armorican?)
0,15		0,09		0,02		0,08		Verlaeckt 1996, 87-88		Axe of Armorican type (Tréhou); Ag 0,06
0,46		0,11		0,02		0,16		Verlaeckt 1996, 93		Axe of Armorican type (Tréhou); Bi 0,71
0,39		0,37		0,04		n.a.		Verlaeckt 1996, 89		axe of Armorican type (Plurien); Bi 0,32
0,48		0,29		0,03		0,07		Verlaeckt 1996, 89		Axe of Armorican type (Plurien); Bi 0,35
0,59		<0,17		0,02		0,54		Verlaeckt 1996, 97		Axe of Armorican type (Plurien); Bi 0,22
0,53		0,23		0,06		0,11		Verlaeckt 1996, 119		Axe of Armorican type (Plurien); Bi 0,19
0,29		n.a.		0,03		0,11		Verlaeckt 1996, 101		Axe of Armorican type (Plurien); Bi 1,01
0,31		n.a.		0,05		0,18		Verlaeckt 1996, 89		Axe of Armorican type (Couville); Bi 0,32
traces		n.a.		n.a.		0,35		Jacobsen 1904, 43		Axe of type 'winged with biconical collar'
n.a.		n.a.		n.a.		0,315		Jacobsen 1904, 44		Axe of linear faceted type
n.a.		n.a.		n.a.		0,507		Jacobsen 1904, 44-45		Axe of type Wesseling
1,1		1,9		0,55		n.a.		Kibbert 1984, 168-170; 214		Axe of type Amelsbüren; Bi 0,027; Ag 0, 58
0,29		0,3		0,14		n.a.		Kibbert 1984, 168-170; 214		Axe of type Amelsbüren; Bi 0,033; Ag 0,22
0,42		0,46		0,17		n.a.		Kibbert 1984, 168-170; 214		Axe of type Amelsbüren; Bi 0,025; Ag 0,3
0,33		0,53		0,13		n.a.		Kibbert 1984, 168-170; 214		Axe of type Amelsbüren; Bi 0,022; Ag 0,36
0,95	.	6,4	.	0,65	.	0,01	.	Craddock 1979, 380 table 2	.	Socketed looped axe of continental type

When drawing comparisons with the data available for axe (type)s known to be functional (see table 2), Geistingen axes differ in a number of ways, although there are also some similarities. First, the tin content of the Geistingen axes falls in the range present in several Plainseau and Armorican axes, but since there is such a wide margin (5 at% antimony or >4 at% arsenic, is the result of the re-melting of scrap bronze (Curtis & Kruszyński 2002, 91). Axe BH76 from the Geistingen depot shows such a combination (see table 1). However, sometimes antimony is seen as an intentional replacement for tin (Craddock 1979, 380). This indicates that the combination of tin and antimony seen in axe BH76 is the result of intentional addition of only antimony. This however does not explain the high nickel and arsenic content found, so it is argued that re-melting in this case seems more likely because of the additional elements present. When looking at the arsenic content of the axes shown in table 2, a dichotomy is seen: the Geistingen axes contain more than 1 at% (up to 3 at%) arsenic, while the content of all other axes measured is (much) less than 1 at%. Next to making the copper appear more silvery, addition of more than 2 at% arsenic will make the object harder without loss of integrity (Lechtman 1996, 506; 509; Junk 2003, 23; 24). The same arguments apply to nickel. Furthermore, the Geistingen axes contain 1-7 at% nickel, while other axes contain (much) less than 1 at%. The effect of nickel as an alloying element is comparable to that of arsenic, resulting in good cold and hot working properties of the alloy (Cheng & Schwitter 1957, 351). The amount of lead found in the Geistingen axes is lower than 1 at% and the majority of the axes listed in table 2 contain more than 1 at%. The addition of less than 1 at% lead to copper will lead to increased fluidity of the melt, making the casting of hollow shapes more easy (Craddock 1979, 383). Adding more than 1 at% will significantly reduce the melting point of copper, with a reduction of almost 200 °C for a bronze containing 18 at% lead (Craddock 1979, 383). However, upon solidification of a leaded copper alloy, the lead will form insoluble globules that are dispersed throughout the microstructures. Increasing the lead content will increase the size of these globules, which will cause major areas of weakness. Therefore, bronze objects containing large amounts (>1 at%) of lead might be cast as ingots and not intended to be functional objects (Craddock 1979, 383). In case of the Geistingen axes, lead is not intentionally added to make the axe unusable since its concentration is below 1 at%. Its presence can however be attributed to the reduction of the melting point and the increase of fluidity. Another element found in more than 1 at% in Geistingen axes but not, or in less than 1 at%, is antimony (see table 2). One exception is the socketed looped axe of continental type (Craddock 1979, 380). In general, the addition of antimony to copper will lower the melting temperature and in amounts over 0.5 at% will slightly increase toughness and ductility, as well as the hardness of copper (Junk 2003, 26; 28). However, in percentages over approximately 4% the result is a brittle alloy (Charles 1980 in Moorey 1999, 241). The Geistingen axes analysed in this research contain respectively 1.4 at% and 4 at% (see table 1), which means one of them is on the verge of being unusable because of brittleness. These numbers indicate that the antimony was either added on purpose (perhaps to make the axes less suitable as tools or weapons), or the presence of the element could not be controlled, i.e. the ore or scrap contained large amounts of antimony. In both cases, the result is that the finished Geistingen axe could not have been functional on compositional grounds as well as the low weight of the objects.

Therefore, the combination of >1 at% antimony, >1 at% Ni and >1 at% As in the Geistingen axes has no counterpart in the composition of any of the contemporary axes in table 2. This sets the Geistingen axes even further apart from other socketed axes.

Microstructure

The microstructure is the assembly of microscale crystals and inclusions in a material with characteristic features like grain dimensions, morphology and composition. This microstructure is the result of specific steps of the production process. Consequently, by studying the features of the two Geistingen axes, this process can be reconstructed.

Dendrites

The axes from Nijmegen and Tongeren both exhibit a microstructure (fig. 5) that contains tree-like structures with a rounded outline, called dendrites, which is typical for cast structures (Allen et al. 1970). The dendrites are intact and the intradendritic pores are spherical, suggesting that no mechanical working of the upper part of the axes has taken place during the production process of the axes.

Figure 5 Microstructures of AC20 (top) and BH76 (bottom), Scanning Electron Micrographs. The distance indicated as d2 is the secondary dendrite arm spacing.

The dendritic phase in axe AC20 is the α-phase of copper, with tin and nickel in solid solution. In axe BH76 the dendritic α-phase contains antimony, arsenic and nickel in a solid solution with copper.

Dendrites consist of main (or primary) branches which at a certain stage of solidification develop secondary side-branches. The number density of these secondary arms, quantified by the secondary dendrite arm spacing (d2, see fig. 4), depends on the thermal and compositional conditions during cooling. Dendrites in copper alloys typically form in the temperature range 800-500 °C, in which both the undercooling below the melting temperature and the atomic mobility are sufficiently high to form the solid-state microstructure (Porter & Easterling 2001). The cooling rate in this temperature range therefore governs the characteristics of the resulting microstructure. This means that d2 provides an indication for the average cooling rate that was applied and d2 can thus be used to determine the cooling rate during the production of the Geistingen axes. The values for d2 in this research have been determined using detailed scanning electron micrographs of the microstructure (fig. 5). For the AC20 axe, the average secondary dendrite arm spacing is determined as 9±1 µm and for BH76 it is 14±2 µm. The relation of this spacing with the cooling rate can be expressed in a general empirical form as (Miettinen 2001, Kumoto et al. 2002, Frame & Vandiver 2008):

where d2 is the secondary dendrite arm spacing in µm, α a factor dependent on the alloy composition, R the cooling rate in °C/s and n a constant with an empirical value of 0.3. Using the average calculated values α = 30 µm °Cⁿ/sⁿ for AC20 and 39 µm °Cⁿ/sⁿ for BH76 (using equations for α from Frame & Vandiver 2008), the average cooling rate is calculated to be approximately 39 °C/s for the Nijmegen axe and 22 °C/s for the Tongeren axe. The relative uncertainty in R is estimated at 30%. Since for both axes the temperature range of 800-500 °C is the range at which the secondary dendrite arm spacing evolves, this result implies that most features of the microstructure are formed in approximately 10 seconds, which is only a part of the time in which the whole axe is solidified.

Inclusions

Several types of inclusions can be found in the microstructures of the Geistingen axes.

Small silver and lead-antimony particles are sporadically seen throughout the structure of AC20. The most plausible explanation for their presence is that they are remnants of the ore since their presence is not uncommon in copper ores (Lindgren 1933). The melting point of pure silver (962 °C) is higher than that of bronze with a composition like AC20 (~950 °C) and of BH76 (~800 °C), and the silver particles thus remain solid in the liquid bronze. Lead has a very poor solid solubility in copper. Both cases result in these elements (either solid silver or liquid lead) being dragged along with the solidification front in the melt subsequently to be found in the interdendritic phase between the solid dendrites.

Both AC20 and BH76 display another distinct type of inclusion, namely copper-sulphide particles. Almost all of these particles in the two axes contain the same elements but their concentration differs: copper, sulphur, iron, oxygen and sometimes also tin, nickel and antimony. The majority of the particles can be identified as Cu₂ S with the aforementioned elements in solution. A difference seen between the two axes lies in the morphology of these inclusions (see fig. 5). They are spherical and star-shaped in AC20, while BH76 only contains star-shaped particles. Substructures have been qualitatively identified in the spherical particles, but further research is needed to provide more information about the origin of these structures. The different inclusion morphologies indicate that for both axes the temperature of the melt has been around the melting temperature (1130 °C) of copper-sulphide. The spherical particles have been completely molten and solidified into spheres, while the star-shaped particles represent particles of which only the outside has been molten. This implies that the temperature of the melt of both axes ranges between 1100 °C and 1150 °C, and the absence of spherical Cu₂ S-inclusions in BH76 indicates a somewhat lower temperature than for AC20. For both axes the applied temperature is higher than the melting temperatures of the main phases.

The copper-sulphide particles solidify during cooling at a higher temperature than the bronze does and can therefore end up between the dendrites, within the interdendritic phase as described above. This type of inclusion represents an important clue to the production of Geistingen axes since they can be identified as matte, a by-product of the smelting of copper-sulphide ore. It is therefore assumed that the presence of silver, lead-antimony and matte particles with their different morphologies can be attributed to the imperfect smelting of sulphidous copper ore, used for the initial melt that eventually formed the Geistingen axes after re-melting.

Production

When looking at macroscopic aspects of the two axes from Museum Het Valkhof (AC20) and the Gallo-Romeins Museum (BH76), it is evident that their size and socketed shape are almost the same. Casting seams are also present on both. These features suggest a casting technique which is the same for both axes and for which most probably a bi-valve mould has been used. The microstructural research presented in this paper provides valuable additional information.

A decisive indication for the casting process is the porous dendritic microstructure with different types of inclusions. It indicates that the bronze has been molten and relatively rapidly solidified. The average cooling rate is approximately 30 °C/s for both axes, which suggests that they have been cooled using the same method. This rapid cooling can be attained by quenching with water (Frame & Vandiver 2008).

Several materials can be used as mould material, of which clay (cf. Van Impe 1995/96, 20) and bronze are frequently used for bi-valve moulds (Kuijpers 2008). Clay has a very low thermal conductivity, which means that several steps need to be undertaken to cast a sound and strong bronze object. After casting the bronze in the pre-heated clay mould, the ensemble needs to be cooled with water for a few minutes. As soon as the bronze is solidified, the clay mould should be removed to allow a faster cooling of the object by submerging it in (cold) water again. This is a practice that calls for considerable skill and experience since the more rapid cooling should be applied during the formation of the microstructure, i.e. during the solidification process. Using a bronze mould (cf. Butler 1973, 322; 338; Butler & Steegstra 2005/06, 209) will eliminate the extra step of removing the mould and is therefore more likely to be applied. In addition, the identical shape of the various Geistingen axes supports the use of a re-usable bronze mould.

There are two options for the type of raw material used; either ore is smelted, or bronze scrap or exchanged ingots are re-melted. One indication for smelting lies in the presence of matte particles in the microstructure, which are remains of the roasting step in the smelting process. Since other impurities like titanium, silver, cobalt and zinc are present as well, no further refining steps have then been undertaken (Lindgren 1933, Craddock 1995, Figueiredo et al. 2009). The composition of the two bronzes indicates it is a possibility that both axes are smelted using the same type of ore with different ratios and additions of tin and/or nickel. Fahlerz is a sulphidic ore known to have been used during the Copper Age and the Early Bronze Age (Biek 1957, Tylecote et al. 1977) and contains elements like copper, arsenic and antimony (Gainov et al. 2008). If ore from the same source is used for both Geistingen axes, the Sb/As ratio should be the same in both cases. However, the Sb/As ratio is different for both objects (2.0 for AC20 and 1.5 for BH76). If nickel would have been added, AC20 and BH76 should contain at least 4 times the arsenic amount than they do now since nickel is usually associated with arsenic (Lindgren 1933). These two features indicate that it is unlikely that the same type of ore from the same source has been used for both axes. So either different types of ore have been used during smelting or (different pieces of) bronze scrap formed the raw material of these Geistingen axes. The lack of data in the literature on microstructures of re-melted bronze makes it difficult to reach a firm conclusion on the raw materials used. However, some information on the change in composition during re-melting is available. Two cycles of re-melting and hot-working in air can result in the loss of antimony and arsenic content until less than one per cent is left (Junk 2003, 26; 29; Tylecote 1977, 329). Since these two Geistingen axes still contain relatively high amounts of both elements (1-4 at%) it is assumed that extensive re-melting and hot-working have not taken place. This assumption is supported by the relatively large amount of copper sulphide particles in the microstructure.

From an archaeological perspective, it is very plausible that ingots or, even more likely, scrap was transported to areas themselves lacking metal ores. In the Netherlands, the famous Drouwen hoard (Butler 1986) found in Drenthe yielded 1.1 kg of bronze scrap of non-local (southern Scandinavian and central European) origin (Butler 1986, 138). The equally well-known Voorhout hoard (traditionally interpreted as a trader’s stock), was recently convincingly shown to have contained not pristine axes (as is to be expected for a ‘merchant’s hoard’) but old, worn and no longer functional axes (i.e. scrap) of French and English origin instead (Fontijn 2008, cf. Kuijpers 2008, 43; 74). Finds like Drouwen and Voorhout, together with the unlikelihood of transporting large quantities of ore, suggest that the Geistingen axes have probably been re-melted from different scrap resources.

4 Conclusions

It is concluded that the two Geistingen axes have been produced by using different raw materials. The use of three complementary analysis techniques has allowed an optimal determination of the average composition of the bronze used for these two axes. Axe AC20 consists of copper alloyed with 9 at% tin, while the bronze of BH76 is identified as copper with 4 at% antimony and 6 at% nickel.

The microstructures display the presence of matte particles and silver and lead-antimony particles. Based on these features, the melt temperature and the different composition of AC20 and BH76, production by the (non-extensive) re-melting of scrap (part of which was possibly made from imperfect smelted sulphidous ores) for both axes is suggested. The microstructure of both axes proved to be essential for the deduction of characteristics of the thermal cycle during the production process. The composition and morphology of interdendritic inclusions indicate that the material has been molten in the temperature range 1100-1150 °C. The secondary dendrite arm spacing, combined with the composition of the alloy, is used to estimate the cooling rate during solidification. The average cooling rate of both axes is around 30°C/s, which implies that both axes have been quenched with water after casting into a (bronze) bi-valve mould.

Combining the compositional, metallurgical and archaeological considerations it is clear that Geistingen axes were not intended to be used as a tool or a weapon. Five aspects render a functional use of the Geistingen axes improbable:

their thin walls (Butler 1973, 339-340; Kibbert 1984, 166),
their low weight (Butler & Steegstra 2002/03, 304; Kibbert 1984, 166),
the presence of the embrittling element antimony in the alloy (this study),
they rarely show traces of use (Fontijn 2003, 325) and working (this study), in spite of their fine external finish and sharp cutting edge (Butler & Steegstra 2002/03, 304),
some show casting flaws that would have impeded hafting altogether (Butler & Steegstra 2002/03, 309).

This leaves ingots ('axe money') or an unspecified votive or ritual function as options. It is possible that the conversion of scrap stock into local types that by composition, knowledge of origin or by visual clues could be identified as non-local, was facilitated or cosmologically rendered acceptable through the deposition of parts of the scrap as hoards, as cogently argued by Fontijn (2008). Consequently, even larger hoards as the eponymous Geistingen hoard may merely represent parts of much larger original quantities. This tallies with the observation that for the Geistingen axes were probably produced using a reusable mould or pattern. In short, sizeable quantities of Geistingen axes were presumably produced, but never with the intention to ever fell a tree with them.

Acknowledgements

The authors would like to thank Ronny Meijers and Louis Swinkels from Museum Het Valkhof in Nijmegen, and Else Hartoch and Guido Creemers from the Gallo-Romeins Museum in Tongeren for kindly supplying samples. Hans Postma is thanked for his valuable contributions to this paper. David Fontijn and Maikel Kuijpers from the Archaeology department from Leiden University have been very helpful with various archaeological issues, for which the authors are grateful.

Janneke Nienhuis

Delft University of Technology, department Materials Science and Engineering

j.nienhuis@tudelft.nl

Jilt Sietsma

Delft University of Technology, department Materials Science and Engineering

j.sietsma@tudelft.nl

Stijn Arnoldussen

Groningen Institute for Archaeology, Groningen University

s.arnoldussen@rug.nl

Review data:

Submission 6/12/2010

Revision 23/5/2011

2nd submission 7/6/2011

Notes

1. at% and wt% are abbreviations for respectively atomic percent and weight percent. Atomic percent is the percentage of one kind of atom relative to the total number of the mixture of atoms. Weight percent is the percentage of the mass of one kind of atom relative to the total mass of the mixture of atoms.

2. Since the axes were dispersed among the finder’s family and friends, the exact number of objects found is unclear. Possibly, the axes were tied together with a piece of rope (Fontijn 2003, 161).

References

Allen, I., D. Britton & H. Coghlan 1970, Metallurgical reports on British and Irish Bronze Age implements and weapons in the Pitt Rivers Museum, Oxford (Oxford University Press).

Bassiakos, Y. & M. Catapotis 2006, Reconstruction of the copper smelting process based on the analysis of ore and slag samples. In: P.P. Betancourt (ed.), The Chrysokamino metallurgy workshop and its territory. Hesperia Supplement 36, Princeton, 329-353.

Biek, L. 1957, The examination of some copper ores: a report of the Ancient Mining and Metallurgy Committee, Man 57, 72-76.

Blanchet, J.C. 1984, Les premiers metallurgistes en Picardie et dans le Nord de la France, Paris (Mémoires de la Société Préhistorique Française 17).

Briard, J. 1965, Les dépôts Bretons et l'Âge du bronze Atlantique, Rennes (Travaux du Laboratoire d'Anthropologie Préhistorique).

Briard, J. 1972, Un dépôt de Bronze final: les haches à douille armoricaines des Treillières (Loire-Atlantique), Congrès Préhistorique de France, XIXè session, Auvergne, 1969, Issoudun, 117-127.

Briard, J. 1979, The Bronze Age in barbarian Europe, London (Routledge).

Briard, J. 1991, La protohistoire de Bretagne et d'Armorique, Luçon (Gisserot).

Butler, J.J. 1961, De Noordnederlandse fabrikanten van bijlen in de Late Bronstijd en hun produkten. Een bijdrage tot de omschrijving van de Hunze-Eems Industrie, Nieuwe Drentse Volksalmanak 79, 199-233.

Butler, J.J. 1973 Einheimische Bronzebeilproduktion im Niederrhein-Maasgebiet, Palaeohistoria 15, 319-343.

Butler, J.J. & H. Steegstra 2002/03, Bronze Age metal and amber in the Netherlands (iii.2) catalogue of the socketed axes, Part A, Palaeohistoria 43-44, 263-319.

Butler, J.J. & H. Steegstra 2003/04, Bronze Age metal and amber in the Netherlands (iii.2) catalogue of the socketed axes, Part B, Palaeohistoria 45-46, 197-300.

Butler, J.J. & H. Steegstra 2005/06, Bronze Age metal and amber in the Netherlands (iii.2) catalogue of the socketed axes, Part C, Palaeohistoria 47-48, 207-240.

Caley, E.R. & D.T. Easby 1959, the smelting of sulfide ores of copper in preconquest Peru, American Antiquity 25 (1), 59-65.

Cheng, C.F. & C.M. Schwitter 1957, Nickel in ancient bronzes, American Journal of Archaeology 61(4), 351-365.

Craddock, P.T. 1979. Deliberate alloying in the Atlantic Bronze Age. In: M. Ryan (ed.), The origins of metallurgy in Atlantic Europe: Proceedings of the Fifth Atlantic Colloquium, Dublin, 369-385.

Craddock, P.T. 1995, Early metal mining and production, Edinburgh (Edinburgh University Press).

Curtis, J. & M. Kruszyński 2002, Ancient Caucasian and related material in the British Museum, London (The British Museum Occasional Paper No. 121).

Davis, J.R. 2001, Copper and copper alloys, United States of America (ASM International).Doonan, R.C.P., S. Klemm, B.S. Ottaway, G. Sperl, H. Weinek 1996, The East Alpine Bronze Age copper smelting process: evidence from the Ramsau Valley, Eisenerz, Austria. In: Ş. Demirci, A.M. Özer & G.D. Summers (eds), Archaeometry 94: Proceedings of the 29th International Symposium on Archaeometry. Tübitak, 17-22.

Figueiredo, E., J.C. Senna-Martinez, R.J.C. Silva & M.F. Araújo 2009, Orientalizing artifacts from Fraga dos Corvos rock shelter in North Portugal, Materials and Manufacturing Processes 24, 949-954.

Fontijn, D.R. 2003, Sacrificial landscapes. Cultural biographies of persons, objects and 'natural' places in the Bronze Age of the southern Netherlands, c. 2300-600 BC, Leiden (Analecta Praehistorica Leidensia 33/34).

Fontijn, D.R. 2008, 'Traders hoard': reviewing the relationship between trade and permanent deposition: the case of the Dutch Voorhout hoard. In: B. Quilliec, C. Hamon (eds), Hoards from the Neolithic to the Metal Ages in Europe: technical and codified practices (British Archaeological Reports International Series 1758), Oxford, 5-17.

Fontijn, D.R. & H. Fokkens 2007, The emergence of early iron age 'chieftains' graves' in the southern Netherlands: reconsidering transformations in burial and depositional practices. In: C. Haselgrove & R. Pope (eds), The Earlier Iron Age in Britain and the Near Continent, Oxford, 354-373.

Frame, L. & P.M. Vandiver 2008, Variability in copper and bronze casting technology as seen at Bronze Age Godin Tepe, Iran, Materials Issues in Art and Archaeology VIII, MRS Proceedings, 253-261.

Gainov, R.R., A.V. Dooglav, I.N. Pen’kov, I.R. Mukhamedshin, A.V. Savinkov & N.N. Mozgova 2008, Copper valence, structural separation and lattice dynamics in Tennantite (Fahlore): NMR, NQR and SQUID Studies, Physics and Chemistry of Minerals 35, 37-48.

Gordon, R. & R. Knopf 2006, Metallurgy of bronze used in tools from Machu Picchu, Peru, Archaeometry 48 (1), 57-76.

Guilbert, G. 1996, The oldest artefact of lead in the peak: new evidence from Mam Tor, Mining History. The Bulletin of the Peak District Mining Historical Society 13.1, 12-18.

Jacobsen, J. 1904, L'age du bronze en Belgique, partie chimique, Brussels (Oscar Lamberty).

Junghans, S., E. Sangmeister & M. Schröder 1960-1974, Studien zu den Anfängen der Metallurgie, I, II 1-4, Berlin (Gebrüder Mann).

Junk, M. 1993, Material properties of copper alloys containing arsenic, antimony, and bismuth -The material of Early Bronze Age ingot torques, Freiberg.

Kibbert, K. 1984, Die Äxte und Beile im mittleren West-deutschland II, München (Prähistorische Bronzefunde IX: 13).

Kuijpers, M.H.G. 2008, Bronze Age metalworking in the Netherlands (c. 2000-800 BC): a research into the preservation of metallurgy related artefacts and the social position of the smith, Leiden (Sidestone Press).

Kumoto, E.A., R.O. Alhadeff & M.A. Martorano 2002, Microsegregation and dendrite arm coarsening in tin bronze, Materials Science and Technology 18, 1001-1006.

Lechtman, H. (1996) Arsenic bronze: dirty copper or chosen alloy? A view from the Americas, Journal of Field Archaeology 23(4), 477-514.

Lechtman, H. & S. Klein, 1999, The production of copper-arsenic alloys (arsenic bronze) by cosmelting: modern experiment, ancient practice, Journal of Archaeological Science 26, 479-526.

Lindgren, W. 1933, Mineral deposits, New York (McGraw-Hill).

Miettinen, J. 2001, Thermodynamic-kinetic simulation of solidification in binary fcc copper alloys with calculation of thermophysical properties, Computational Materials Science 22, 240-260.

Moorey, P.R.S. 1999, Ancient Mesopotamian materials and industries: the archaeological evidence, Winona Lake (Eisenbrauns).

Porter, D.A. & K.E. Easterling 2001, Phase transformations in metals and alloys, Cheltenham (Nelson Thornes).

Postma, H., D.R. Fontijn, P. Schillebeeckx, R.C. Perego & J.J. Butler 2005a, Neutron resonance capture analysis of Geistingen axes, Lunula: Archaeologia Protohistorica XIII, 41-46.

Postma, H. & P. Schillebeeckx 2005b, Non-destructive analysis of objects using neutron resonance capture, Journal of Radioanalytical and Nuclear Chemistry 265 (2), 297-302.

Postma, H., P. Schillebeeckx & W. Kockelmann (in press/2011), The metal composition of a series of Geistingen-type socketed axes, Journal of Archaeological Science (accepted manuscript).

Rivallain, J. 2001, Les haches a douille armoricaines: monnaies hors des normes de la numismatique, Revue archéologique de l'Ouest Supl. 9, 87-92.

Tylecote, R.F., H.A. Ghaznavi & P.J. Boydell 1977, partitioning of trace elements between the ores, fluxes, slags and metal during the smelting of copper, Journal of Archaeological Science 4, 305-333.

Van Impe, L. 1994, Een depot met kokerbijlen uit de Plainseau-cultuur (late Bronstijd) te Heppeneert-Wayerveld (Maaseik, prov. Limburg), Archeologie in Vlaanderen 4, 7-38.

Van Impe, L. 1995/96, De schat van het konijn: het bronsdepot van Luthommel-Konijnepijp (gem. Lommel, prov. Limburg), Archeologie in Vlaanderen 5, 7-40.

Wheeler, T.S., R. Maddin & J.D. Muhly 1975, Ingots and the Bronze Age copper trade in the Mediterranean: a progress report, Expedition, 31-39.

Wielockx, A. 1986, Bronzen bijlen uit de brons- en vroege ijzertijd in de Maasvallei. Verhandelingen tot het verkrijgen van de graad van licentiaat in de Oudheidkunde en de Kunstgeschiedenis aan de Katholieke Universiteit Leuven, Leuven.

Wouters, H. 1990, Chemical characterization of archaeological copper alloys: Application of X-ray fluorescence spectrometry and elemental & micro trace analytical techniques, Antwerpen.

Wouters, H. 1994, Metalen gebruiksvoorwerpen uit de late bronstijd uit de Maasvallei: een analytische en metallurgische benadering van de depots van Dilsen en Maaseik-Heppeneert, Archeologie in Vlaanderen 4, 39-48.