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Journal of Archaeological Science xxx (2010) 1–12
Contents lists available at ScienceDirect
Journal of Archaeological Science
journal homepage: http://www.elsevier.com/locate/jas
Smelting and recycling evidences from the Late Bronze Age habitat
site of Baiões (Viseu, Portugal)
Elin Figueiredo a, b, c, *, Rui J.C. Silva b, João C. Senna-Martinez d, M. Fátima Araújo a,
Francisco M. Braz Fernandes b, João L. Inês Vaz e
a
Instituto Tecnológico e Nuclear, Estrada Nacional 10, 2686-953 Sacavém, Portugal
CENIMAT, Departamento de Ciências dos Materiais, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Monte de Caparica, Portugal
Departamento de Conservação e Restauro, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Monte de Caparica, Portugal
d
Centro de Arqueologia (Uniarq), Faculdade de Letras, Universidade de Lisboa, 1600-214 Lisboa, Portugal
e
Departamento de Letras, Universidade Católica Portuguesa, Estrada da Circunvalação, 3504-505 Viseu, Portugal
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 June 2009
Received in revised form
7 January 2010
Accepted 19 January 2010
Many aspects of bronze production during Late Bronze Age in Western Europe are so far unknown. In the
present study selected artefact fragments and metallurgical debris, which include a slag fragment, from
the emblematic Late Bronze Age habitat site of Castro da Senhora da Guia de Baiões (Viseu, Portugal)
have been studied by optical microscopy, micro-EDXRF, SEM–EDS and XRD. Evidences were found for
bronze production involving smelting and recycling. Compositional analysis showed that the artefacts
are made of a bronze with 13 3 wt.% Sn (average and one standard deviation) and a low impurity
pattern, namely <0.1 wt.% Pb, being comparable with the composition of other bronzes from the same
region (the Central Portuguese Beiras). This alloy is generally different from elsewhere Atlantic and
Mediterranean bronzes, which show frequently slightly lower Sn contents and higher impurity patterns,
namely Pb which is often present as an alloying element. The present study gives further support to early
proposals suggesting the exploration of the Western Iberian tin resources during Late Bronze Age, and
besides that, it indicates that metalworking and smelting could have been a commonplace activity
requiring no specific facilities, being bronze produced at a domestic scale in this Western extreme of
Europe.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Late Bronze Age
Archaeometallurgy
Smelting
Microstructure
EDXRF
SEM–EDS
Iberian Peninsula
1. Introduction
During Late Bronze Age (LBA) the circulation and consumption
of bronze increased, as evidenced by the numerous metal artefacts
and deposits found all over Europe (Huth, 2000). This period is also
characterized by the full adoption of bronze in many regions,
namely in the Iberian Peninsula, as well as a significant diversification in artefacts typologies (Melo, 2000).
Although the high number of metal artefacts dating to LBA all
over Europe, many aspects of prehistoric technologies for Cu–Sn
production are so far unknown. Three hypotheses for bronze
production have been proposed in literature (Coghan, 1975; Rovira,
2007): (1) smelting ores of tin and copper together, in a co-smelting
operation; (2) adding one of the metals to the other still as ore, in
* Corresponding author. Instituto Tecnológico e Nuclear, Estrada Nacional 10,
2686-953 Sacavém, Portugal. Tel.: þ351 219 946 207; fax: þ351 219 946 185.
E-mail address: elin@itn.pt (E. Figueiredo).
a partial smelting operation; (3) smelting the ores separately and
then alloying the metals in a melting operation.
Slags are a crucial evidence for the study of the technology
involved in bronze production. Nevertheless, these are very scarce
in Western European contexts, namely in the so called Atlantic
areas (Craddock, 2007; Faoláin, 2004; Pendleton, 1999). Most of the
latest works on the topic are based on some copper–tin slags that
have been found in a number of settlements in the Iberian Peninsula, particularly in the Spanish territory, having the earliest ones
been found in north-eastern regions, and later ones (dating to LBA
and Early Iron Age) all over the Spanish territory (Gómez Ramos,
1999; Rovira, 2007). Studies on these slags and associated metallurgical debris (e.g. reduction vessels) has conducted to the
proposal that bronze was initially obtained by co-smelting (option
1), a technique that was still in use during LBA and Early Iron Age in
many settlements. They also showed some possible evidences of
smelting cassiterite (tin oxide, as it appears in nature) with metallic
copper (option 2) during the transition from LBA to EIA, being the
earliest evidences of copper and tin alloying (option 3) dated to
0305-4403/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jas.2010.01.023
Please cite this article in press as: Figueiredo, E., et al., Smelting and recycling evidences from the Late Bronze Age habitat site of Baiões (Viseu,
Portugal), J. Archaeol. Sci. (2010), doi:10.1016/j.jas.2010.01.023
ARTICLE IN PRESS
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E. Figueiredo et al. / Journal of Archaeological Science xxx (2010) 1–12
VIII–VII century B.C., probably as a result of Mediterranean contacts
(Rovira, 2002).
In the Iberian Peninsula, the adoption of bronze did not seem to
change the extractive technology; bronze was obtained in a similar
way as was previously done in Chalcolithic times for copper, with
a direct smelting of ores in reducing vessels (Gómez Ramos, 1999).
Such primitive smelting process involved a very simple infrastructure, as those composed by a small pit excavated in the soil
where a vessel containing the ores was placed, with charcoal, being
heated from above. The resulting smelt was completely fragmented
to recover the metallic lumps and prills (also called smelting
droplets) (Hauptmann, 2007) leaving scarce evidences (e.g. slags)
in the archaeological record.
Significant changes in extractive metallurgy in the Iberian
Peninsula just happened at the beginning of Iron Age in those
regions better connected with the Eastern Mediterranean
(frequently called the Orientalising period) as has been indicated by
the content of iron in copper-based metals which increased to
values >0.05 wt.% (iron is most dependent on the smelting process
and primitive relatively mild reducing conditions prevented iron
minerals to be reduced to metal) (Craddock and Meeks, 1987).
The employ of a primitive and simple method for smelting for
such a long period of time in the Iberian Peninsula (about 3
millennia) has been related to its adequacy to the kind of minerals
being worked – rich minerals, such as copper carbonates, achieving
acceptable efficient rates of metal recovery – and to the social
adequacy – serving the metal requirements of the immediate local
community (Rovira, 2002).
A different reality existed in most Eastern regions, as in Central
and Alpine regions of Europe, Eastern Mediterranean and Middle
East, that experienced important developments in technological
knowledge and skills between Chalcolithic and LBA, i.e. a transition
from simple primitive, crucible based, small scale domestic
production to mass production involving slag heaps and complex
furnaces, the existence of large smelting sites distributing ingots,
sites specialized in producing copper and sites specialized in
producing tin (Adriaens et al., 1999; Burger et al., 2007; Rothenberg,
1985).
These differences may rely mostly in the Iberian Peninsula (and
generally Western Europe) social landscape, which was very
different from the one in the Eastern Mediterranean, which saw the
development of early states which controlled large territories and
populations (Whittaker, 2008).
In the Iberian Peninsula almost all the recently excavated habitat
sites, including some of very small size, from Chalcolithic in most
southern regions to LBA sites in Northwest regions record metallurgical activities (Bettencourt, 2000; Rovira, 2002; SennaMartinez and Pedro, 2000a; Vilaça, 2004). This reality indicates
disseminated metallurgical knowledge since early times, and
substantiates absence of any monopoly controlling production. It
also suggests regular supply of ores and metals for a long period of
time, probably a reflection of the exploration of the Iberian
minerals.
The Iberian Peninsula is very rich in both copper and tin ores,
having one of the major tin deposits of the European Old World.
The geographical distribution of the copper and tin deposits is
different, with a general dispersion of the former ones and
a concentration of the latter ones mainly in the northwestern
region. During the last quarter of the second millennium B.C., with
the advent of full adoption of bronze and the increase in metallic
artefacts production, the Central Portuguese Beiras witnessed an
emergence of many sites, most of them with vestiges of metallurgical activities. This emergence has been suggested to be related to
the control and exploitation of gold and cassiterite (SennaMartinez and Pedro, 2000a), the latest an essential ore for bronze
fabrication. The collapse of most of those sites in the middle of the
1st millennium B.C. (Vilaça, 1995a) has been explained as a possible
result of the rupture on metal circulation, which happened with the
crisis of the Phoenician settlements in Iberian coastal areas (SennaMartinez, 1998).
The development of local elites during the LBA has been linked
to the role of metallurgy in producing status enhancing artefacts
(archaeologically expressed by the higher number of metallic
artefact productions, their more complex shapes as well as and new
techniques of production). So an easy access to the minerals must
have been seen as an advantage, and can also be taken into account
in the positioning of some emerging sites (Senna-Martinez, 1996;
Vilaça, 1995b).
While the exploitation of Iberian copper resources seems to be
widely accepted, the exploitation of the local tin resources is more
discussed, and rather difficult to prove due to the scarcity of
evidence. Old mines can be difficult to find due to posterior mining
works and due to the possibility that most of the tin explorations
would occur in alluvial placers. Nevertheless, in the Central
Portuguese Beiras – a region with abundant tin and gold resources
(Garcia, 1963) – during the reopening of the ancient gallery of the S.
Martinho mine (Orgens, Viseu), during the World War Two,
a bronze dagger of ‘‘Porto de Mós’’ type was found at the bottom of
the rubble which filled its shaft, proving its original opening and
posterior infilling during the Late Bronze Age, probably for cassiterite exploration (Correia et al., 1979). Other Iberian evidences of tin
exploration come from the Spanish area of Cáceres, from the LBA
settlement of Cerro de Logrosan (Caceres, Spain) (Merideth, 1998;
Rovira, 2002).
An LBA Iberian production of bronze, based on the exploitation
of the local ores and independent of the most Atlantic and Mediterranean areas has been previously suggested based on the
composition of many Iberian bronzes. While comparing the
composition of bronzes from the Ria de Huelva LBA hoard with
contemporaneous bronzes from external peninsular regions, Rovira
and Gómez-Ramos (1998) have stressed the low impurity pattern
(namely of Pb) and the slightly higher Sn content that seem to
differentiate the Huelva bronzes from other bronzes in Atlantic and
Eastern Mediterranean areas (Fig. 1). Analysis of bronzes from
various emerging sites in the Central Portuguese Beiras has also
showed compositions similar to the Ria de Huelva hoard, mostly
w8–15 wt.% Sn and <1 wt.% Pb (Figueiredo et al., in press; Valério
et al., 2007; Vilaça, 1997). If these bronzes were made just by
recycling imported bronzes, lower contents in tin were to be
expected since tin is lost preferentially to copper after remelting
(Rovira and Montero, 2003).
In the present work we will discuss the analytical results of
a study made on selected items – that include a slag fragment –
recovered at the Castro de Nossa Senhora da Guia de Baiões LBA
archaeological site, situated in the Central Portuguese Beiras.
2. Baiões site and its artefact collection
The Castro de Nossa Senhora da Guia de Baiões (CSG) site is
placed on a granitic hilltop in the county of S. Pedro do Sul, Viseu,
in central Portugal, part of a series of residual reliefs which
dominate the Vouga river valley (Fig. 2A and B). In modern times,
a sanctuary (Senhora da Guia Sanctuary) has been constructed
which provoked the destruction of most of the archaeological site
(Fig. 2C).
The site has a great domain over the involving landscape and
controls the old road going west through the passes of the Gralheira
massif, alongside the northern margin of the Vouga river that was
navigable just some 20 km ahead (until middle of XIX century),
allowing a good access to the Atlantic waters (Fig. 2B). Its
Please cite this article in press as: Figueiredo, E., et al., Smelting and recycling evidences from the Late Bronze Age habitat site of Baiões (Viseu,
Portugal), J. Archaeol. Sci. (2010), doi:10.1016/j.jas.2010.01.023
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3
Fig. 1. Approximate location of the Central Portuguese Beiras and the Ria de Huelva hoard in Iberian Peninsula; location of tin deposits (grey areas) in European areas based on
illustrated in Merideth (1998); and average of bronze compositions in different regions (indicative of general trends) based on Rovira and Gómez-Ramos (1998). A decrease in Sn
and an increase in Pb content occur when moving from Iberian Peninsula towards Atlantic and Mediterranean territories.
prehistoric occupation is estimated to lay in between the 13th and
the 8th centuries B.C. (Senna-Martinez and Pedro, 2000a).
The site’s archaeological interest was first acknowledged in the
XVIII century when Friar Agostinho de Santa Maria mentioned that
‘‘.digging in the same place, worked gold has been found such as
bracelets and similar things.’’ (Santa Maria, 1716).
In 1947 during some road construction to improve the access to
the sanctuary the so called ‘‘treasure of Baiões’’, comprising two
gold torcs and a bracelet, was found. Later works in 1971 revealed
an important group of pottery and bronze artefacts (Silva, 1979).
The first archaeological excavations took place in 1973 conducted by Celso Tavares da Silva (Silva, 1979) followed in 1977 by
a campaign directed by Kalb (1978). All these interventions
confirmed the concentration of metal findings in the general area of
the old ones. Although most of those interventions are poorly
published, Kalb (1995) describes that numerous metallic nodules
were found in the surroundings of a fireplace, interpreting this area
as a melting place (being the nodules a result of some spilled metal
during a pouring operation), and Baiões as a habitat site.
In 1983, when the construction of the actual layout surrounding
the chapel of Senhora da Guia began, the finding of a series of
bronze artefacts lead to an urgent archaeological excavation
resulting in the finding of the so called ‘‘Baiões Hoard’’ (Silva et al.,
1984). Since then, the gold and bronze artefacts from the Castro da
Senhora da Guia de Baiões have been presented as a ‘‘hoard’’ or
‘‘foundry deposit’’.
The majority of the metal finds of Baiões comprise bronze
foundry leftovers, scrap, bits of wire and bars to forge, as well as
moulds in clay, stone and bronze together with brand new artefacts
still with casting seams. All the collection – c. 400 pieces – was
made public, for the first time, at the 2000–2001 exhibition
‘‘Walking along Viriato’s land: The Archaeology of Viseu’s Region’’,
Fig. 2. (A) Approximate location of Senhora da Guia de Baiões and other LBA sites in the proximities – the Baiões/Santa Luzia cultural group (Senna-Martinez and Pedro, 2000a); the
sea level and palaeo-estuarine systems during Bronze Age are depicted. (B) Google Earth image (http://earth.google.com) showing the hilltop of Baiões and surroundings. (C)
Modern sanctuary on the archaeological site.
Please cite this article in press as: Figueiredo, E., et al., Smelting and recycling evidences from the Late Bronze Age habitat site of Baiões (Viseu,
Portugal), J. Archaeol. Sci. (2010), doi:10.1016/j.jas.2010.01.023
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presented at the National Museum of Archaeology, Lisbon (SennaMartinez and Pedro, 2000a). Since then, the existence of a metalworking area at Baiões site (and not a ‘‘hoard’’ or ‘‘foundry deposit’’)
similarly to what had been recently exposed through excavation in
other sites at the proximities, namely the sites of S. Romão and
Outeiro dos Castelos de Beijós (Senna-Martinez and Pedro, 2000b),
was strengthened.
Although the widespread metallurgical evidences in LBA sites,
including those in the proximities of Baiões which compose the
Baiões/Santa Luzia cultural group (Fig. 2A), the Baiões collection,
with its metal and metallurgy related artefacts, has a strong
expression amongst the latest as well as amongst other
contemporaneous sites from the Iberian Peninsula. Its collection
has been reported in several studies, related with typological (e.g.
Atlantic and Mediterranean features) and production issues
(Ambruster, 2004; Coffyn, 1985; Giardino, 1995; Senna-Martinez
and Pedro, 2000a; Ruiz-Gálvez, 1998). Despite the richness and
importance of the collection, analytical studies are very scarce.
The most significant investigation carried out until now were the
energy dispersive x-ray fluorescence (EDXRF) analyses recently
performed by Valério et al. (2006) over 54 bronze artefacts
(complete or semi-complete), which showed that the alloy
employed was a bronze, occasionally with lead and arsenic as
impurities. Once this study was performed in artefacts with
museological interest the analyses were performed over noncleaned patinated surfaces, not allowing the determination of the
bulk composition.
For the present study a multi-method approach was adopted
and other items were selected, most of them metallurgical debris.
The items include one vitrified fragment, later recognized as a slag
fragment, sixteen artefacts and artefact fragments and twelve
minute roundish or irregular fragments of metal named ‘‘metallic
nodules’’, for the sake of simplicity (Fig. 3). The latest were selected
owing their high number amongst the collection and since their
study could provide information about processing techniques.
Some of the selected artefact fragments showed partially heatdistorted areas. Accordingly, the microstructure examination could
help in their classification as faulty castings or partial melting of
artefacts, e.g. during an incomplete recycling operation. Overall, the
main purposes of the present study were to: attain the metal
compositions; describe the thermomechanical sequences
performed on the artefacts; and infer about the metallurgical
processes undergoing at the site, to which a significant contribution
of the slag fragment was expected.
3. Experimental
In order to cause the minimum damage in the collection, all the
metallic items were analysed by micro-energy dispersive x-ray
fluorescence spectrometry (micro-EDXRF) for elemental composition determination in a small area (frequently <25 mm2), which
had been cleaned (by removing the superficial corrosion patina)
and polished (until 1 mm diamond paste). These prepared areas
were afterwards observed under an optical microscope (OM) for
Fig. 3. The twenty-nine items selected for analyses: (A) metallic nodules; (B) slag fragment; and (C) fragments of artefacts and artefacts.
Please cite this article in press as: Figueiredo, E., et al., Smelting and recycling evidences from the Late Bronze Age habitat site of Baiões (Viseu,
Portugal), J. Archaeol. Sci. (2010), doi:10.1016/j.jas.2010.01.023
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microstructure examination, under bright field (BF) and polarized
light (Pol) illumination, in unetched and etched conditions. Etching
was performed with an aqueous ferric chloride solution.
The slag fragment was sectioned into two parts that were
analysed by scanning electron microscope (SEM–EDS) without
a conductive coating (metallic oxides were conductive enough
for backscattering electron observations and elemental analysis) and one of the parts was analysed by x-ray diffraction
(XRD).
The OM observations were conducted in a Leica DMI5000M
microscope, coupled to a computer with the LAS V2.6 software.
The micro-EDXRF analyses were performed in an ArtTAX Pro
spectrometer, with a low-power X-ray tube (30 W), a molybdenium
anode and a set of polycapillary lens that generate a microspot of
primary radiation, of w70 mm in diameter. The quantification
analyses involved the WinAxil software. Details on quantification
procedures have been recently described (Figueiredo et al., 2007;
Valério et al., 2007). Three analyses were made on different spots
of the prepared area of the artefacts, being considered the average
values.
The SEM analyses were performed in Zeiss model DSM 962,
with a backscattered electrons detector (BSE) and an energy
dispersive spectrometer (EDS) from Oxford Instruments model
INCAx-sight with an ultra thin window which extends the detection to light elements, as oxygen and carbon. Semi-quantifications
were made using ZAF correction procedure.
The XRD analyses were conducted in a Siemens D5000 diffractometer, with Cu Ka radiation. This analysis has been carried out on
the cross section of the slag part.
5
4. Results and discussion
Results are presented in the following sections, accordingly to
the nature of the analysed items.
4.1. Slag fragment
In Fig. 4 are presented the main results from the SEM–EDS
analyses made on the cross-sections of the fragment (1.28 g). These
revealed a heterogeneous structure, essentially composed by:
a vitreous matrix (aluminium silicate) with the regular presence of
O, Cu, Al, Si and irregular presences of K, Fe, Pb, Mg and Ti; large
globular inclusions of malachite (surrounded by cuprite) (Fig. 4A),
cuprite and metallic copper (surrounded by cuprite) (Fig. 4B);
occasionally some small inclusions of metallic lead (Fig. 4B); cuprite
in coarse dendritic (image embedded in Fig. 4A) or small globular
form (Fig. 5B); and the presence of cassiterite, frequently in needle
like crystals with a rombohedric form enclosing cuprite (Fig. 5A, B
and C). The morphologies of the cassiterite and dendritic cuprite
among the vitreous matrix suggest that they formed during the
solidification process.
Many of these features have been described previously for Bronze
Age and Early Iron Age slags from the neighbouring Spanish territory
and regarding some particularities, they have been related with cosmelting processes, ‘‘cementation’’ of copper with cassiterite or an
alloying of copper with metallic tin (in later times) (Rovira, 2007).
The XRD analyses showed peaks related to cassiterite, cuprite
and magnetite (Supplementary online material). The formation of
magnetite (Fe [II/III]) instead of fayalite (Fe [II]) is frequent in early
Fig. 4. SEM (BSE) images (A–B) of CSG-315 slag fragment at lower magnifications (Mal – malachite; Vit – vitreous matrix; Cup – cuprite; Cas – cassiterite). At right some
representative examples of EDS spectra of different compounds present in the slag.
Please cite this article in press as: Figueiredo, E., et al., Smelting and recycling evidences from the Late Bronze Age habitat site of Baiões (Viseu,
Portugal), J. Archaeol. Sci. (2010), doi:10.1016/j.jas.2010.01.023
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The studied fragment is most likely only one small part of the
whole product that resulted from a metallurgical operation. The
weak reducing atmosphere that this particular fragment experienced, at least in the last stage before solidification, was only
enough to keep some Cu in metallic form, but clearly not enough to
allow Sn exist in the metallic solid solution (Sn is preferentially
oxidised in respect to Cu). The interpretation of such a microstructure is rather difficult, more over since we lack other vitrified
fragments and any ceramic body that served as reaction vessel,
which could give additional information. This fragment could be
a result of an oxidation process, e.g. during a bronze recycling or an
alloying of metallic copper and metallic tin, or it could be a result of
an extractive operation, such as a smelting operation to reduce
copper and tin ores. All these possibilities can be considered since
ancient firing techniques, as using blow pipes, did not create
constant or uniform conditions inside the reaction vessel
(Hauptmann, 2007). Thus, this fragment does most probably not
represent the thermodynamic conditions reached in other parts of
the reaction vessel, sufficient to retain or produce bronze. It has
been shown that in a recycling or alloying operation some oxidation could occur (e.g. Klein and Hauptmann, 1999) and in ancient
smelting operations all the transitional stages between thermal
decomposition of the original material up to the formation of
proper melts can be present in the slag (e.g. Hauptmann, 2007).
These heterogeneities might even explain why this fragment stayed
behind in the archaeographic record: it was probably recognized as
‘‘waste’’ part that enclosed no metallic bronze.
Regardless all the possibilities, some particularities in the
microstructure may suggest that the fragment is a slag resulting
from a reduction operation. The presence of malachite inclusions in
areas without external corrosion evidences, as the malachite
inclusion (Cu [II]) that is totally surrounded by cuprite (Cu [I])
(Fig. 4A top right) suggests that this malachite is not a secondary
corrosion product. Most likely, it was originally present in the
mixture, and was partially decomposed at some stage of the
process into CuO, CO2 and H2O (decomposition of malachite can
continue to temperatures greater than 600 C (Simpson et al.,
1964)), and the resultant tenorite was reduced into cuprite.
Although copper may initially been present as ore, the initial
state of tin is more difficult to accomplish. In the fragment, tin is
only present as cassiterite that resulted from the slag’s solidification process. Thus, it is impossible to determine if tin was added as
metal or ore. Additionally, the lack of archaeological evidences of
metallic tin items or cassiterite fragments in Baiões and other local
LBA sites, does not provide additional information on the subject –
both can be very difficult to recognize in the archaeographic
records, due to ‘‘tin pest’’ in the first case, and due to the not
expressive colour of cassiterite when compared with copper ores in
the second case. So, future studies on other materials and sites are
needed to help answering this last question.
4.2. Nodules
Fig. 5. SEM (BSE) images (A–C) of CSG-315 slag fragment at higher magnifications
(Vit – vitreous matrix; Cup – cuprite; Cas – cassiterite).
Iberian smelting slags (before the Iron Age). This is a consequence
of the smelting being normally conducted in open shape reaction
vessels with heat from above (Rovira, 2004), producing very
heterogeneous conditions inside the vessels, and thus frequently
weak reducing atmospheres in many parts.
The main results on the elemental composition and microstructural features of the nodules are summarized in Table 1.
Relative standard deviations (RSD) calculated for alloying elements
and impurities (RSD ¼ SD 100/average) show disperse values: in
the alloying element Sn, RSD is mainly <10%, except for 3 items; in
minor elements, RSD is mainly <50%, except for Pb in one item.
These values are expected due to micro-heterogeneities on the
analysed areas (Northover and Rychner, 1998), namely different
metallic phases and some intergranular corrosion (Figueiredo et al.,
2010). Fig. 6 comprises micrographs of the microstructures of the
items examined in this section with the exception of the nodule
CSG-327 that is described later in more detail.
Please cite this article in press as: Figueiredo, E., et al., Smelting and recycling evidences from the Late Bronze Age habitat site of Baiões (Viseu,
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Table 1
Summary of the experimental results on the copper-base metallic nodules.
Composition for each nodule is given by average of three micro-EDXRF analyses
one standard deviation (SD).
No.
CSG-153
CSG-154
CSG-159
CSG-186
CSG-187
CSG-210
CSG-227
CSG-317
CSG-320
CSG-325
CSG-327
CSG-329
Total
Weight
(g)
0.99
0.90
1.02
1.50
1.03
2.73
0.54
3.73
2.93
2.91
1.93
0.42
21.7
Composition (wt.%)
Sn
Pb
As
Fe
12.0 1.0
12.9 1.2
13.6 0.6
12.9 0.9
10.9 0.6
12.6 0.1
12.5 2.8
14.2 2.2
9.7 0.2
14.3 2.8
14.3 0.5
15.5 4.6
n.d.
n.d.
0.44 0.21
n.d.
0.11 0.08
n.d.
n.d.
n.d.
n.d.
<0.1
n.d.
n.d.
<0.1
0.13 0.05
0.21 0.02
0.18 0.02
<0.1
<0.1
<0.1
0.10 0.01
<0.1
<0.1
n.d.
0.11 0.03
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
0.08
<0.05
0.05
<0.05
<0.05
13.0 1.6
–
–
–
Phases
present
a
a
a, d
a, d Y
a, d
a, d [
a, d
a
a
a, d
a, d, 3, h
a, d Y
n.d., not detected; Y, low amount; [, high amount.
The micro-EDXRF analyses indicated that all the nodules are
made of bronze with Sn in the range of 9.7–15.5% and Pb and As
frequently present in low contents.
The microstructures of the nodules CSG-154, 186 and 320 (with
Sn contents between 9.7 and 12.9%) are composed by twinned
equiaxed grains, a result from a mechanical deformation followed
by annealing, and exhibit deep intergranular corrosion. Among
these, the CSG-186 nodule shows the smallest recrystallized grains
which are superimposed in an earlier dendritic structure, pictured
by the corrosion along preferential paths. These paths are given by
the interdendritic regions that show a concentration of Cu–S
inclusions and (a þ d) eutectoid. Their microstructures suggest that
they are probably remains of artefacts.
The other nodules, show coarse microstructures with grain
twinning absent or very low (CSG-153, 187, 317, 325 and 329) or
cored dendrites with (a þ d) eutectoid in the interdendritic areas
(CSG-159, 210 and 227). Cu–S inclusions are frequently observed.
The nodules with coarse microstructures suggest a very slow
cooling rate or a heat-treatment after solidification (it is difficult to
distinguish between both) and the nodules with cored dendrites
suggest faster cooling and absence of a heat-treatment. It can be
proposed that some of those with coarse (more homogenised)
microstructures and rounded shapes (CSG-317, 325, 187, 327 and
329, with Sn contents between 10.9 and 15.5%) are smelting
droplets. Smelting droplets are expected to show coarse microstructures due to the rather slow cooling of the smelt. Nevertheless,
if this is so, one has to question their narrow range of Sn content,
since dispersed Sn contents among lumps and prills recovered from
a smelt are expected (Rodrı́guez Diaz et al., 2001; Rovira, 2007). The
existence of some melting droplets, as suggested by Kalb (1995),
cannot be rejected within those that show a faster cooling
microstructure.
The CSG-327 nodule has a distinct microstructure of the
previous nodules and was thus also analysed in SEM–EDS. The bulk
is composed by primary a phase grains and (a þ d) eutectoid. Near
to the nodule surface two clear layers of the intermetallic
compounds d and 3 were observed, followed by an irregular outer
layer of h phase which had small amounts of a tin rich constituent
amongst it (Fig. 7). These features suggest two independent events:
one at higher temperatures (>520 C), to allow the formation of
(a þ d) eutectoid from g decomposition in the bronze bulk; and
another, at lower temperatures (<415 C), to allow a thermally
activated solid interdiffusion of Sn from metallic tin and Cu from
the pre-existing bronze. For this last stage the system temperature
should be between 350 and 415 C, since only at this temperature
7
range, and accordingly with the Cu–Sn equilibrium phase diagram,
all the three monophasic layers (d, 3, h) could coexist, without an
(a þ d) eutectoid layer resulting from g decomposition during
cooling.
The archaeometallurgical explanation of this nodule is not
simple. The absence of conventional tinned artefacts during Bronze
Age – tinned artefacts have a eutectoid or delta (Rovira, 2005) layer
formed by in situ cassiterite reduction or by inverse segregation
during solidification (Meeks, 1986) – seems to rule out the possibility of this being a fragment of a tinned artefact. As a result, the
nodule might have been formed during a smelting or alloying
operation, where at a stage of cooling of the reaction vessel some
metallic Sn (formed over strong reduction conditions if cassiterite
was initially added), still in a liquid state, moved through fissures
and cracks ending up in contact with a bronze nodule already in
a solid state, starting the interdiffusion process. On the other hand,
if this nodule is a result of some recycling operation, then one can
only suppose that metallic tin or cassiterite was intentionally added
to balance the loss in tin due to its preferential oxidation in respect
to copper. Either way, the presence of metallic tin adds the information that the local metallurgists were capable of creating
reducing conditions sufficient to preserve tin in a metallic state or
reduce cassiterite into metallic tin in the course of their metallurgical operations. This should bear no surprise, since Timberlake
(2007) was successful in reducing cassiterite to tin, by smelting
high grade ores within small, low-temperature, poorly reducing
open hearths, and thus in a comparable way as bronze could have
been produced in LBA Iberian Peninsula.
4.3. Artefacts and fragments
The main results on the elemental composition, microstructural
features as well as possible thermomechanical treatments applied
are summarized in Table 2. Fig. 8 comprises micrographs with the
microstructures of all the items examined in this section.
The micro-EDXRF analyses indicated that the artefacts and
fragments are made of bronze, except for the bar CSG-293 that is
made of unalloyed copper. Pb, As and Fe are frequently present,
although in low contents – sometimes in concentrations lower than
the quantification limits (Pb and As <0.1 and Fe <0.05%). The
presence of Cu–S inclusions is also recurrent, similarly to the
nodules.
The copper bar CSG-293 has equiaxed twinned grains and
numerous Cu–S inclusions. Its microstructure indicates that it has
been shaped through thermomechanical work to the final semiquadrangular section. The composition and typology of this artefact
suggests that it might be a semi-finished product. It could have
served to provide small amounts of metal, that were cut-off, to
manufacture small simple copper items, such as rivets, cramps, etc.,
or to melt to produce more complex shaped copper artefacts. The
thermomechanical work detected can be explained as a result of
shaping and softening it for easier transport, handling and posterior
cutting. There are evidences for use of copper during LBA to the
manufacture of specific objects such as two rivets in Ria de Huelva
(Rovira, 1995), a belt hook fragment from Fraga dos Corvos
(Figueiredo et al., 2009), a cramp (possibly another belt hook
fragment?) from Canedotes (Valério et al., 2007) and a gilded nail in
Castro de São Romão (Figueiredo et al., in press). Another hypothesis could be that the copper bar was used for bronze production, to
be joined to cassiterite in a partial smelting operation (option 2 in
introduction), as a copper ingot. Some copper ingots attributed to
LBA have been found in the Iberian territory. However, these are
scarce, and a clear connection to metallurgical activities is lacking
since most of them were found in hoards with finished palstaves
and not among metallurgical debris (Gómez Ramos, 1993).
Please cite this article in press as: Figueiredo, E., et al., Smelting and recycling evidences from the Late Bronze Age habitat site of Baiões (Viseu,
Portugal), J. Archaeol. Sci. (2010), doi:10.1016/j.jas.2010.01.023
ARTICLE IN PRESS
Fig. 6. OM (BF) images of some nodules, showing various microstructures. All images were taken at the same magnification (200) except 186 which has a second image taken at
500. All surfaces are etched except for CSG-187, 317, and 210.
Please cite this article in press as: Figueiredo, E., et al., Smelting and recycling evidences from the Late Bronze Age habitat site of Baiões (Viseu,
Portugal), J. Archaeol. Sci. (2010), doi:10.1016/j.jas.2010.01.023
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E. Figueiredo et al. / Journal of Archaeological Science xxx (2010) 1–12
9
Fig. 7. OM (BF) (left) and SEM (BSE) (centre and right) images of CSG-327 nodule. The table shows the results of the EDS analyses on the different Cu–Sn intermetallic compounds.
Among the bronzes, tin contents are in the range of 9.6–15.4%,
except for two items: socket fragment CSG-139 and pin head CSG162, which have >15% (17.1 and 18.8%, respectively). These two
items show as-cast microstructures, with the formation of cored
dendrites and a high amount of interdendritic (a þ d) eutectoid.
Increasing Sn content in bronze increases the hardness but
decreases its ductility. Therefore, it seems reasonable that these
artefacts were not subjected to mechanical works.
The use of a w10–15% Sn bronze on all the other items suggests
that its optimum mechanical properties were appreciated. Besides,
the absence of low tin bronzes suggest that some ‘‘control’’ in the
bronze composition was accomplished.
The microstructures of the heat-distorted blade fragments CSG318 and CSG-335 and the sickle fragment CSG-400 show equiaxed
a-grains, with varying (although low) amount of twinning and low
amount of (a þ d) eutectoid taking into account the Sn contents.
These features represent a typical recrystallized microstructure,
indicating a post-casting work, which suggests that they were not
faulty castings. If they were faulty castings a dendritic microstructure composed by a-cored dendrites with interdendritic
(a þ d) eutectoid would be expected. They are most likely artefacts
that suffered high temperatures, perhaps during a recycling operation interrupted at an initial stage or during a larger fire involving
the settlement. However, the occurrence of artefacts in the collection with microstructures that show absence of a final heat-treatment, as well as the relatively small number or artefacts showing
heat-distorted shapes, does rather point out to some intentional
metallurgical operation, such as a recycling operation.
The amalgam of four bar fragments, CSG-312, joined by corrosion products or partially melted together, also suggests recycling
operations at the site since they appear to be scrap fragments
gathered for melt. Microstructures of two analysed bar fragments
are similar to the sickle (CSG-400).
The microstructures of the artefact fragments CSG-314 and CSG316, scabbard chape fragment CSG-346, buckle element CSG-407
and bracelet fragment CSG-408 show absence of high deformations. They have a dendritic (CSG-314) or an annealed microstructure with large grains (CSG-316, 346, 407 and 408), without
annealing twins, and presenting various amounts of (a þ d) eutectoid. They have only been subjected to a annealing and/or to a slight
final cold work – evidenced by corrosion along slip bands (CSG-314
and 407). Their shapes were most probably obtained by cast, with
some posterior mechanical work applied for surface finishing.
The unifacial palstave butt fragment CSG-308 has a microstructure composed by large equiaxed grains with a small amount of
twinning. Its primary shape was most likely obtained by cast
Table 2
Summary of the experimental results on the copper-base artefacts and fragments of artefacts. Composition for each artefact is given by average of three micro-EDXRF analyses one standard deviation (SD).
No.
Item
Weight (g)
CSG-139
CSG-162
CSG-179
CSG-293
CSG-308
CSG-312
Socket fragment
Pin head
Spatula fragment
Bar
Unifacial palstave butt fragment
Amalgam of 4 bar fragments
4.12
2.29
1.10
83.0
57.1
12.3
CSG-314
CSG-316
CSG-318
CSG-330
CSG-335
CSG-383
CSG-346
CSG-400
CSG-407
CSG-408
Fragment
Fragment
Blade fragment partially remelted?
Spatula fragment
Blade fragment partially remelted?
Double spatula
Scabbard chape fragment
Sickle fragment partially remelted?
Buckle element
Bracelet fragment
8.47
16.8
20.7
0.64
20.7
3.29
6.02
44.1
9.98
11.1
Total
301.7
Composition (wt.%)
Sn
Pb
As
Fe
17.1 1.8
18.8 2.1
10.9 0.1
n.d.
13.6 1.7
13.2 3.2
9.9 1.7
13.7 2.9
14.8 0.7
9.7 2.3
11.7 0.9
11.1 0.6
10.8 3.0
15.4 1.0
14.4 2.0
9.6 1.7
10.6 0.7
<0.1
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
<0.1
n.d.
n.d.
n.d.
n.d.
n.d.
<0.1
n.d.
n.d.
n.d.
0.17 0.06
0.16 0.03
0.12 0.06
0.16 0.02
<0.1
0.12 0.04
0.11 0.01
0.13 0.01
0.18 0.01
n.d.
<0.1
<0.1
<0.1
0.15 0.02
0.15 0.03
<0.1
<0.1
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
12.8 2.8
–
–
–
Method of fabrication
Phases present
C
C
CþFþA
CþFþA
C þ FY? þ A
CþA
C þ FY? þ A
C þ FY?
C þ AY
C þ FY þ A
C þ FþA þ F
C þ FY þ A
C þ FþA þ FY?
CþA
CþA
CþAþF
C þ A þ FY?
a, d [
a, d [
a
a-copper
a
a
a
a, d
a, d
a, d Y
a
a
a
a, d Y
a, d Y
a
a
n.d., not detected; C, cast; F, forged/deformed; A, annealed; Y, low amount; [, high amount.
Please cite this article in press as: Figueiredo, E., et al., Smelting and recycling evidences from the Late Bronze Age habitat site of Baiões (Viseu,
Portugal), J. Archaeol. Sci. (2010), doi:10.1016/j.jas.2010.01.023
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10
E. Figueiredo et al. / Journal of Archaeological Science xxx (2010) 1–12
Fig. 8. OM (BF) images of the artefacts and fragments of artefacts. All images were taken with a magnification of 200 except CSG-293, 314 (500) and 383 (1000). All surfaces are
etched except CSG-139, 162 and 316.
(a mould to produce such a palstave was found at the site). Its
microstructure suggests that after casting it was subjected to some
cycles of deformation and annealing possibly for the cutting of the
casting sprue and finishing of the surface.
The two spatula fragments CSG-179 and CSG-330 and the
double spatula CSG-383 are those which show the most
pronounced thermomechanical worked microstructures. They are
composed by equiaxed grains totally twinned and CSG-383 show
clear elongated Cu–S inclusions. They also have slip bands indicative of a final cold work, probably performed to provide a strain
hardening effect. The shape and microstructure of these artefacts is
thus consistent with a cast bar fragment that was subject to thermomechanical cycles until its final shape.
5. Final discussion
Baiões collection has showed that there is more about the
archaeological site than just an LBA foundry place with good
examples of Late Bronze Age artefacts with Atlantic or Mediterranean typological features. The presence of a slag fragment gives
evidences for the local production of bronze – and this happens for
the first time in the studied region – offering new expectations to
the early proposals of a local exploration of ores, as cassiterite. Also,
it suggests that smelting was still performed inside the settlement,
similarly to what happened in earlier periods in the Iberian
Peninsula, and differing from what happened in many contemporaneous LBA metallurgical sites in more Eastern/Mediterranean
territories where smelting was done exclusively at the vicinity of
the mine. The analysis of the slag fragment suggests smelting of
copper ores with cassiterite or metallic tin by a rather primitive
smelting process (as in a reaction vessel/crucible) leading to
incomplete ore reduction and resulting in a heterogeneous microstructure with fine grained mixture of different phases. The low Fe
content (<0.05%) in the analysed bronze artefacts does also point
out to their fabrication in this kind of primitive smelting
technology.
The metal worked in the site was mainly bronze – just a copper
bar being identified – with an average composition of 13% Sn, with
Pb and As absent or present as impurity. This alloy shows closest
resemblances with other bronzes from the Central Portuguese
Beiras and the bronzes from the Ria de Huelva hoard, rather than
with bronzes from external Iberian regions (that show generally
lower Sn contents and higher impurity patterns, specifically Pb).
The extension of the area where this bronze is present, from Huelva
to the cassiterite-rich areas of the Iberian Peninsula, might give
some clues to LBA interactions among different regions of Iberian
Peninsula, as well as give further support to the early proposals of
a peninsular origin of the Huelva bronzes.
Please cite this article in press as: Figueiredo, E., et al., Smelting and recycling evidences from the Late Bronze Age habitat site of Baiões (Viseu,
Portugal), J. Archaeol. Sci. (2010), doi:10.1016/j.jas.2010.01.023
ARTICLE IN PRESS
E. Figueiredo et al. / Journal of Archaeological Science xxx (2010) 1–12
The presence of partially heat-distorted fragments of artefacts
with equiaxed grain microstructure suggests recycling operations
rather than faulty castings. Also, the assemblage of metallic
nodules with worked microstructures and tin contents similar to
the artefacts suggests that these might be parts of artefacts or
other metallurgical remains (e.g. seams and splashing droplets)
gathered for recycling. The coarse microstructure of some nodules
suggests the presence of smelting droplets, or, due to their narrow
Sn content range comparable to the Sn contents in the artefacts,
heat altered fragments of artefact. If they were smelting droplets,
their narrow Sn content can only be explained by previously
selected prills that were being gathered with the aim of melting
them together, perhaps with fragments of artefacts (recycling) to
produce new artefacts with the proper Sn content. If the second
hypothesis is to be true, these nodules might be, similarly to the
partially heat-distorted fragments of artefacts, a result of a recycling operation. All these evidences pointing out to recycling
operations, suggests that recycling was a normal procedure, even
in sites where smelting, and thus production of new bronze, was
performed.
The absence of low tin bronzes suggests that the loss in tin that
occurs in regular recycling operations must have been compensated. Possibly, recycling was conducted with the addition of tin
metal or tin ores, being the nodule CSG-327 an evidence of such an
operation.
The ‘‘control’’ over Sn content in the artefacts, could possibly be
achieved by the awareness of the colour (and hardness?) of the
metals. The Sn content range of w10–15% (most of the artefacts)
produces a metal with a yellowish ‘‘gold like’’ colour that was
probably appreciated, besides its good thermomechanical properties. The manufacture of two items with a higher Sn content (17–
19%) could be intentional, to produce a more ‘‘silver like’’ colour, or,
if unintentional, these artefacts could just be waiting for recycling.
Most probably, among these LBA communities, ‘‘control’’ must be
understood in the basis of a trial and error practical experience,
which nevertheless, led to an empirical deep understanding of the
materials behaviours and characteristics. This can somewhat be
reflected in the various thermomechanical works that were applied
in the artefacts, regarding their shape and composition. Long cycles
of forging and annealing were more evident in the spatula fragments, suggesting the shaping of cast bars. Others, of larger size and
more complex shapes, such as the scabbard chape, buckle element
and bracelet fragment, were shaped by casting being needed just
some final works. On the other hand, the socket fragment and the
pin head, with the higher Sn compositions, were not subjected to
any mechanical treatment.
The presence in Baiões of some items that can be a result of
more than one operation, e.g. the nodule CSG-327 (smelting or
recycling of bronze with addition of tin metal or cassiterite?),
or items that could have had more than one function, e.g. the
copper bar (to produce copper items or to be alloyed with tin metal
or cassiterite in a partial smelting operation?), points out to the
possibility of bronze being produced by various methods, regarding
the needs and materials available. Certainly, more studies on
metallurgical remains from other LBA sites of the region and from
the Portuguese territory will be needed to fully understand the
variety of the metallurgical operations that could have been
undertaken at these small size LBA settlements.
Generally, the Baiões evidences suggest that smelting and
metalworking could have been a commonplace activity requiring
no special facilities (as complex furnaces and large infrastructures),
no task specialization (various metallurgical procedures could be
performed in one place possibly by the same people), being thus
perfectly adequate to be performed inside the settlements, at
a domestic part-time(?) level.
11
The relatively high Sn content among the studied items
(w13 3%) and absence of low tin bronzes may suggest that the
exploitation of local tin ores was a reality (although in a relative low
scale), resulting in an constant tin supply, and thus enforcing the
role of metallurgy and associated activities in the site/region.
Finally, the present study suggests that the neat separation
among smelting and melting sites, mostly based on Mediterranean
models, does not seem to be adequate to the central Portuguese
LBA reality, namely to the Baiões/Santa Luzia cultural group.
Sharing the problem of slags scarcity, as generally happens for the
Atlantic areas, this study suggests that the problem might rely
mostly in the different archaeological visibilities that exist between
large, specialized smelting sites (as those present in many Eastern/
Mediterranean areas) and small bronze producing settlements
(maybe with simple smelting processes), whose activities are not so
perceptible in the archaeographic records. Perhaps, the increase in
bronze circulation during the LBA in Western Europe could have
had a significant contribution from (numerous?) small habitat sites
like Baiões that were also smelting to produce bronze.
Acknowledgements
The authors are thankful to Prof. Thilo Rehren and the anonymous reviewers for their valuable comments and suggestions to an
early version of the manuscript. This work has been carried out in
the framework of the project METABRONZE (Metallurgy and
Society in Central Portugal Late Bronze Age) financed by the
Portuguese Science Foundation (FCT) (POCTI/HAR/58678/2004).
The first author acknowledges the FCT for the SFRH/BD/27358/2006
grant. CENIMAT/I3N funding by FCT/MCTES is acknowledged by
RJCS and FMBF.
Appendix A. Supplementary material
Supplementary data associated with this article can be found in
the on-line version, at doi:10.1016/j.jas.2010.01.023.
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Please cite this article in press as: Figueiredo, E., et al., Smelting and recycling evidences from the Late Bronze Age habitat site of Baiões (Viseu,
Portugal), J. Archaeol. Sci. (2010), doi:10.1016/j.jas.2010.01.023