Nuclear Instruments and Methods in Physics Research B 213 (2004) 741–746
www.elsevier.com/locate/nimb
EDXRF study of Prehistoric artefacts from Quinta do
Almaraz (Cacilhas, Portugal)
M. F
atima Ara
ujo
a,*
, Luıs de Barros b, Ana Cristina Teixeira a,
vila de Melo c
Ana A
a
Departamento de Quımica, ITN – Instituto Tecnol
ogico e Nuclear, E.N. 10, 2686-953 Sacav
em, Portugal
b
Museu Municipal de Almada, Olho de Boi, 2800 Almada, Portugal
c
Museu Nacional de Arqueologia, Mosteiro dos Jer
onimos, Pracßa do Imp
erio, 1400-206 Lisbon, Portugal
Abstract
This paper presents a non-destructive analytical study by secondary target energy-dispersive X-ray fluorescence
spectrometry of selected artefacts found during excavations carried out since 1988, at the archaeological site of ‘‘Quinta
do Almaraz’’, Estremadura, West Portugal. The analysed collection was composed by metallic artefacts (fibulae, fishhooks, needles, buckle, tweezers, knives, arrowheads), crucibles, slags and metallurgical residues.
The chemical composition of the metallic artefacts have made possible to identify different groups belonging to
distinct Prehistoric periods, from the Bronze (bronzes) till the Iron (iron-based alloys) Age. Variation in the Sn and Pb
percentages in the bronzes pointed out to the existence of three different metallurgical processes, although they did not
present different typological characteristics.
Semi-quantitative analysis on fragments of crucibles have permitted to identify particular metallurgical operations,
namely the preparation of gold alloys and the remains of the silver cupellation process, which was introduced in the
Iberian Peninsula by the Phoenician [Early Metal Mining and Production, Smithsonian Institution Press, Washington,
DC, 1995].
Ó 2003 Elsevier B.V. All rights reserved.
PACS: 07.85.)m
Keywords: EDXRF; Archaeometallurgy; Bronzes; Prehistoric artefacts
1. Introduction
The ‘‘Quinta do Almaraz’’ archaeological site is
located in Cacilhas (Almada), in front of Lisbon in
the Tagus estuary at the western Portuguese Coast.
*
Corresponding author. Tel.: +351-21-994-6204; fax: +35121-994-1455.
E-mail address: faraujo@itn.mces.pt (M.F. Ara
ujo).
Excavations carried out since 1988 by the Museu
Municipal de Almada have demonstrated that this
particular location has favoured human occupation since an early age, and archaeologists have
found remains (thousands) from the Neolithic till
the Roman period. The set of the studied artefacts
is varied (Fig. 1) and the typological characteristics
point out to an exceptional collection in the context of the Late Bronze and Iron Age in the
Portuguese territory. Energy-dispersive X-ray
0168-583X/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0168-583X(03)01696-3
742
M.F. Araujo et al. / Nucl. Instr. and Meth. in Phys. Res. B 213 (2004) 741–746
surfaces and the shape of the artefacts are serious
factors that affect the analytical results. In fact, the
penetration depth of the incident X-ray beam for
copper and iron-based alloys is within the order of
not more than several tenths of micra, being the
dominant contribution of the detected characteristic X-rays from the corroded/patinated surface
[2]. However, the Prehistoric metallurgical evolution can be associated with the emerging of particular types of metals/alloys is easily identified
even in the presence of such restrains. Typological
characteristics are not sufficient to infer about the
recurrent questions: when and by whom an artefact was made. Styles were often copied at different
times and distinct locations from their origin, and
in such cases, the chemical composition of a given
artefact has a primordial role in allocating it to a
particular Prehistoric context and in the attribution of a specific technology used in its manufacture. For instance, copper-based metal artefacts
with variable percentages of As, Sn, or Pb, that
could be intentional, varied with the region
(available raw materials) and with the time (evolution of technology).
This work demonstrates the importance of the
chemical composition in the archaeometallurgical
field. Analysed artefacts could be grouped according to their composition. Analysis of bronze
artefacts having the same style evidenced the
presence of distinct technologies of manufacturing
and a probable distinct origin. Nevertheless, this
archaeological site located at the Portuguese coast
at the Tagus estuary, was easily accessed by different seafaring travellers and traders. The metal
residues in crucible fragments indicated local
smelting furnaces and the extraction of silver by
cupellation.
2. Experimental
Fig. 1. Examples of metallic artefacts from Quinta do Almaraz.
fluorescence spectrometry (EDXRF) is extremely
widely used in archaeometry as a basic method of
non-destructive characterisation of metal artefacts.
The presence of corroded and patinated metal
The elemental composition of the metallic artefacts was determined by EDXRF analysis using
a commercially available Kevex EDX-771 Analyst
System, with a rotating 16-position sample tray. A
computer running the WinXRF/ToolBox applications software, which commands the X-ray
generator, the detection system and the multi-
743
M.F. Araujo et al. / Nucl. Instr. and Meth. in Phys. Res. B 213 (2004) 741–746
fundamental parameter method that uses calibration coefficients and accounts for matrix effects.
Calibration was performed with standard bronze
materials certified by the Bureau of Analysed
Samples, Ltd., by using a single calibration coefficient for each element. Crucible fragments were
also irradiated in their external and internal surface by using the same excitation conditions to
infer about their use in archaeological operations.
channel analyser, controls the spectrometer. A
rhodium anode X-ray tube with six secondary
targets and filters produces the primary photon
beam. The characteristic X-rays emitted by the
samples are collimated at 90° and measured with a
Si(Li) detector with a 165 eV resolution and an
active area of 30 mm2 . Artefacts were irradiated in
different areas using a monochromatic X-ray beam
generated by a Gd secondary target and filter,
using a voltage of 57 kV and 1 mA current intensity, during 300 s. Spectra were processed using
a Gaussian deconvolution that assumes a theoretical relationship among the intensities of X-ray
lines within each elemental line series [3]. Elemental concentrations were determined through
the EXACT computer program [4], based upon a
3. Results and discussion
3.1. Metallic artefacts
The chemical composition of the analysed
artefacts are listed in Table 1 (copper-based
Table 1
Chemical composition of the copper-based metallic artefacts from Quinta do Almaraz
Artefact no.
Description
Cu
Pb
Fe
Sb
Ni
MMA9605-ALZ1790
MMA9605-ALZ1790C
Bracelet
94.2
89.7
5.21
9.56
n.d.
n.d.
0.55
0.79
n.d.
n.d.
n.d.
n.d.
QA12S-B12NPL5C24D
QA12S-B12NPL5C24DC
Fish-hook
98.3
97.4
1.24
1.92
n.d.
n.d.
0.50
0.67
n.d.
n.d.
n.d.
n.d.
MMA9621-ALZ1798
MMA9621-ALZ1798C
Fibulae
92.9
94.3
3.33
2.69
0.88
0.51
2.74
2.37
n.d.
n.d.
0.13
0.13
MMA9622-ALZ1799
Fibulae
fragments
Fibulae
95.9
2.87
0.73
0.23
0.14
0.11
89.0
9.33
0.40
1.02
0.16
0.11
MMA4404-ALZ437
MMA4404-ALZ437C
Fish-hook
93.3
92.8
4.45
5.0
1.48
1.34
0.66
0.73
n.d.
n.d.
0.12
0.13
MMA9456-ALZ1765
MMA9456-ALZ1765C
Arrowhead
94.1
87.0
5.34
11.75
0.20
0.52
0.11
0.56
n.d.
n.d.
0.27
0.16
QA12S-B12NPL6C26A
QA12S-B12NPL6C26AC
Fibulae
91.2
91.0
5.19
4.54
0.84
1.37
2.64
2.93
n.d.
n.d.
0.11
0.15
QA12S-B12NPL6C26B
QA12S-B12NPL6C26BC
Buckle fragment
91.1
91.8
7.62
7.08
0.42
0.30
0.92
0.86
n.d.
n.d.
n.d.
n.d.
MMA4411-ALZ444
MMA4411-ALZ444C
Tweezers
80.4
80.5
9.08
9.52
9.87
9.37
0.33
0.33
0.16
0.18
0.13
0.11
MMA4410-ALZ443
MMA4410-ALZ443C
Small fish-hook
77.2
76.8
15.91
16.76
6.30
5.85
0.62
0.63
n.d.
n.d.
n.d.
n.d.
MMA9445-ALZ1753
MMA9445-ALZ1753C
Fish-hook
71.6
69.9
14.89
16.47
11.96
11.85
1.55
1.80
n.d.
n.d.
n.d.
n.d.
MMA9446-ALZ1755
MMA9446-ALZ1755C
Fish-hook
82.0
82.6
7.64
7.89
9.04
8.03
1.14
1.32
0.19
0.21
n.d.
n.d.
MMA9622-ALZ1799C
n.d. – not detected.
Sn
744
M.F. Araujo et al. / Nucl. Instr. and Meth. in Phys. Res. B 213 (2004) 741–746
Table 2
Chemical composition of the iron-based metallic artefacts from Quinta do Almaraz
Artefact no.
Description
Cu
Fe
As
QA12S-B12NPL6C26D
QA12S-B12NPL6C26DC
Knife edge
0.26
0.56
99.5
99.1
0.22
0.33
QA12S-B12NPL6C26E
QA12S-B12NPL6C26EC
Knife hand
0.33
0.78
99.4
98.6
0.26
0.59
QA12S-B12NPL5C24A
QA12S-B12NPL5C24AC
Knife edge
0.17
0.33
99.7
99.5
0.11
0.20
QA12S-B12NPL5C24B
QA12S-B12NPL5C24BC
Ball
0.22
0.44
99.5
99.2
0.33
0.37
MMA9601ALZ1788
MMA9601ALZ1788C
Knife edge
0.54
0.41
99.2
99.4
0.23
0.18
MMA9437-CACII5
Knife with bronze
nails
1.45
98.4
0.20
Codes (A, B, D and E) were attributed to different artefacts with the same number. Code C refers to a second analysis in a different area
of the same artefact.
artefacts) and Table 2 (iron-based artefacts). The
copper-based artefacts (bronzes) can be gathered
in three groups according to their composition. In
Table 1 the three different groups of bronze artefacts are separated by lines. Objects of the first
group (bracelet and fish-hook) have unexpected
low percentages of Sn, in spite of the usual Sn
surface enrichment measured in the patina of
bronzes [2].
The second group is composed by bronze artefacts with rather different stylistic characteristics
(fibulae, fish-hook and an arrowhead) also having
low Sn percentages, although small percentages of
Pb (<1.5%) were measured. During Bronze Age,
the addition of Pb was initialised in order to lower
the melting point resulting in a more malleable
alloy. However, the low contents in Pb indicate
that its presence might be due to the type of ore
used in the smelting process rather than an intentional addition. This is the case of bronze artefacts
of the third group (fish-hook and tweezers) which
exhibit significant amounts of lead. The Pb addition could be in this case related to the stylistic
specifies of these artefacts, since the addition of Pb
can produce breakable alloys.
These different groups correspond to technological productions characteristic of the transition
period Chalcolithic to Bronze Age (third to the
second millennium) for the first group and Late
Bronze Age for the remaining artefacts (XII to
VIII century BC).
Iron-based artefacts (Table 2) are more recent
and were manufactured during Iron Age, which
was introduced in the region by the Phoenician
during the VIII century BC.
3.2. Crucible fragments
Comparison of the characteristic X-rays emitted
by the irradiation of two crucible fragments (Fig.
2(a) and (b)) in their internal and external surfaces
demonstrated that they have been used in smelting.
Spectra displayed in Fig. 2(a) shows that the internal surface present significant amounts of Cu,
Br, Ag, Bi and Pb. The presence of Ag, together
with Bi and Pb points out to a similar extraction
process of Ag from jarosites. The most famous
ancient mine where jarosites were exploited in the
Iberian Peninsula was Rio Tinto, as previously
reported [1] and Ag could only be smelted by the
addition of Pb (or lead ores). Those minerals have a
wide variety of metals, such as the Bi, which on
smelting goes off with the silver into the lead. Enrichment in Br is explainable by the high stability of
the silver halogenides. Elements like Fe and Zr are
due to the crucible raw material composition.
Spectra obtained with the irradiation of the
second crucible (Fig. 2(b)) shows the presence on
M.F. Araujo et al. / Nucl. Instr. and Meth. in Phys. Res. B 213 (2004) 741–746
745
Fig. 2. X- ray spectra emitted by the irradiation of crucible fragments.
its internal surface of Cu, Ag and Au, suggesting
that it should has been used for the refining of
gold. The ability to refine the gold by separating
the silver has very ancient records, namely in
Sumeria and Egypt dating back to the third millenium BC, although in Western Europe it has
been safely attributed to occur during the first
millenium BC [5].
4. Conclusion
EDXRF analysis has demonstrated once more
its potential in the answering of relevant questions
in the archaeological field. The non-destructive
analysis of this unique collection has considerably
contributed to the advance of the knowledge in the
archaeometallurgy at the Iberian Peninsula. Apparently, two stylistically identical groups of artefacts (groups 2 and 3) co-exist in the same
chronological period – Late Bronze Age, but they
seem to have been produced with different metallurgical technologies, which may be an indication
of their different origins. The semi-quantitative
analysis of crucible fragments proved the existence
of local furnaces and identified specific smelting
processes, particularly the cupellation of Ag not
previously testified in Portuguese territory before
746
M.F. Araujo et al. / Nucl. Instr. and Meth. in Phys. Res. B 213 (2004) 741–746
the Roman period. Iron technology was introduced with the Phoenician settlements during the
VIII century BC, amongst them ‘‘Quinta do
Almaraz’’.
Acknowledgements
This work was partially financed by the IPA
(Instituto Portugu^es de Arqueologia), in the
framework of the protocol ITN/IPA, theme
‘‘Characterisation of Prehistoric Metals and Alloys’’.
References
[1] P.T. Craddock, Early Metal Mining and Production,
Smithsonian Institution Press, Washington, DC, 1995.
[2] J. Tate, Nucl. Instr. and Meth. B 14 (1986) 20.
[3] T.P. Schreiber, A.M. Wins, X-ray Spectrom. 11 (1982) 42.
[4] R.A. Vane, Adv. X-ray Anal. 26 (1983) 369.
[5] R.E. Tylecote, The Prehistory of Metallurgy in the British
Isles, The Institute of Metals, London, 1990.