Journal of Archaeological Science: Reports 16 (2017) 248–257
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Journal of Archaeological Science: Reports
journal homepage: www.elsevier.com/locate/jasrep
Bronze Age Caucasian metalwork: Alloy choice and combination
a,⁎
Marianne Mödlinger , Benjamin Sabatini
a
b
b
MARK
IRAMAT-CRP2A - UMR 5060 CNRS, Université Bordeaux Montaigne, Maison de l'archéologie, Esplanade des Antilles, 33607 Pessac, France
Department of Materials Science & Engineering, Massachusetts Institute of Technology, 13-5065, 77 Massachusetts Avenue, Cambridge, MA 02139-4307, USA
A R T I C L E I N F O
A B S T R A C T
Keywords:
Bronze Age
Greater Caucasus
Metallurgy
Daggers
Lead isotope analyses
Chemical composition
The chemical composition and microstructure of eleven Bronze Age Caucasian daggers from North OssetiaAlana, Russia were studied in order to establish a baseline for metallurgy and alloy production in the region.
They have been housed in the Natural History Museum, Vienna since the 1880′s. The assemblage comprises
arsenical bronzes characterized by high concentrations of arsenic (2–10 wt%), tin bronzes with high tin
(10–17 wt%), and several ternary Cu-As-Sn dagger blades. The chemical composition of the dagger blades was
analysed with EDXS and XRF. Furthermore, metallographic analyses and lead isotope analyses were carried out.
Two of the arsenical bronze blades showed extreme γ-phase segregation along their surfaces and grain
boundaries. Two tin-bronze dagger blades, containing high amounts of eutectoid, prevented the measurements
of the hardness of the eutectoid. One dagger combined a tin bronze blade and arsenical bronze hilt. Lead isotope
analyses of selected daggers indicate a close relation to copper ore sources in the Greater Caucasus and Armenia.
1. Introduction
The aim of this study is to document the microstructure, chemical
composition, and lead isotopic signatures of several copper-based
daggers from North Ossetia Alana, Russia. These artefacts are listed as
having belonged to the Koban culture (phase I) by the Stuttgart-based
Studien zu den Anfängen der Metallurgie (SAM) project (Junghans et al.
1968–1974; Krause, 2003), but have no other extant information. Until
now, no detailed characterisation of metal objects from the eponymous
find spot of Koban has been produced. Those chosen for study were
reported by the SAM project as having high As content, ranging between 2 and 5 wt% As.
Presented at the 5th Allrussian Congress of Archaeology, September
8–11, 1881 in Tbilisi, Georgia, these daggers and other bronzes from
Koban (Fig. 1) were sold to the Naturhistorisches Hofmuseum in Vienna,
and other museums, including the Berlin museum and MAN in St.
Germain-en-Laye. The daggers studied originated from the Natural
History Museum, Vienna, Austria, where they have been housed since
the late 19th century, having been purchased by F. Heger, the director
of the anthropological and ethnographic department between 1881 and
1893 (Fig. 2).
Although purchased, the daggers are known to have been plundered
by landowner C. D. Kanukov beginning in 1869 from the Verchni Koban
and Chmi cemeteries, both located in the Republic of North OssetiaAlania, Russia. Of the more than 1000 graves (see Heinrich 2006/7,
126), most of the metal artefacts were sold to various museums
throughout Europe devoid of context and detailed description. The
grave goods associated with the daggers, and gender of the interred,
are, however, listed in Table 1 as they appeared on the parcel listing
that accompanied the daggers to the museum. Record of the parcel
listing comes from the museum inventory book.
As a result of their uncertain procurement, much archaeological
evidence of the grave sites has been lost, however, several excavations
were undertaken by G. D. Filimonov in 1869, V. B. Antonovič in 1871,
E. Chantre in 1881, and F. Heger himself during his last visit to the site
in 1891. Artefacts sent to the Natural History Museum, Vienna, including those studied in this work, arrived in several parcels between
1883 and 1888 with the following information (after Heinrich 2006/7,
139):
1) Parcel XVIII, 1883: prehistoric finds from Koban and Chmi, ‘excavated’ by C. D. Kanukov; the acquisition of the finds was paid by
the consul general of Peru, L. Schiffmann (inv.no.s 41.226–41.441).
2) Parcel XIX, 1883: prehistoric finds from Koban and Chmi, ‘excavated’ by C. D. Kanukov; the acquisition of the finds was paid by
the consul general of Peru, L. Schiffmann (inv.no.s 41.442–42.154).
3) Parcel I, 1884: prehistoric finds from Koban (inv.no.s
42.155–42.361).
4) Parcel VI, 1884: prehistoric finds from Koban (inv.no.s
42.362–42.465).
5) Parcel XVIII, 1884: finds from Chmi, excavated by I. Dolbežev in
Wladikawkas in 1883. The content of seven graves is a donation
Corresponding author.
E-mail addresses: marianne.modlinger@u-bordeaux-montaigne.fr (M. Mödlinger), bsabatin@mit.edu (B. Sabatini).
⁎⁎
http://dx.doi.org/10.1016/j.jasrep.2017.10.018
Received 21 March 2017; Received in revised form 21 September 2017; Accepted 7 October 2017
2352-409X/ © 2017 Elsevier Ltd. All rights reserved.
Journal of Archaeological Science: Reports 16 (2017) 248–257
M. Mödlinger, B. Sabatini
Fig. 1. – Verchni Koban and Chmi cemeteries
located in the Republic of North Ossetia-Alania,
Russia.
Fig. 2. – Studied Bronze Age daggers. Daggers A
– I likely originated from the Koban cemetery,
and J and K from Chmi. Samples were taken from
the locations indicated with an arrow. The OES
analyses from the SAM database are indicated by
circles. However, the sampling location of the
OES analyses could not be identified on daggers E
and I. The samples taken from the blade of dagger
J for OES analyses were not published in the SAM
database.
Despite their insecure find associations, the daggers can be approximately dated. Dagger B is dated to the Early Bronze Age, while
dagger J is associated with the Meskhetian Culture of southwestern
Georgia. Dagger J and K are dated to the beginning of the Late Bronze
from the Anthropologische Gesellschaft (F. Zwicklitz) (inv.no.s
42.466–42.553).
6) Parcel I, 1888: old finds from the Caucasus, which were bought from
S. Kulov in Wladikawkas, February 1888 (inv.no.s 42.554–42.637).
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Journal of Archaeological Science: Reports 16 (2017) 248–257
Microstructural characterisation of the daggers, and chemical analyses, were performed on cross-sections taken at the locations shown in
Fig. 2. Further chemical analyses were carried out on drilling samples
taken with a 1 mm drill bit. Each sample was mounted in cold epoxy
resin and polished using 400-1200 SiC papers, and then by diamond
suspension paste of up to 0.25 μm granulometry. The samples were
characterized using optical microscopy in both bright and dark field,
chemically analysed using EDXS, and then etched for metallographic
examination using NH4OH + H2O2 (according to the ASTM E407 no.
44 recipe).
Chemical analyses of the polished cross-sections were also conducted using X-ray fluorescence (XRF). These analyses were compared
to past results by Optical Emission Spectrometry (OES) given in the
SAM database, and current ones obtained by EDXS. The analytical
methodology employed by the SAM study, and the condition of the
samples are unknown. In order to completely characterize the daggers,
micro-hardness measurements and Pb-isotope analyses were carried out
on select daggers.
Chemical analyses were performed using a JEOL JSM-6460LV SEM
with an Oxford Instruments SDD XMax 20 under high vacuum, and an
ARL Quant'X (Thermo Fisher Scientific) XRF at 28 kV (with Pd filter),
and 50 kV (with Cu filter). The SEM was calibrated using the internally
provided software database standards library, as well as certified pure
standards of Si, Ca, etc. for the quantitative analyses. The results shown
are the mathematical average of 6–10 spectra of approximately
200 × 600 μm taken for 60 s each. The element concentrations for each
averaged analytical campaign were classified as follows: alloying (wt
% > 1), minor (1 > wt% > 0.3), and trace (wt% < 0.3).
Compositional analyses by SEM and XRF were taken at the same locations. The XRF results are the average of two measurements of the
whole surface of the sample, which were quantified using the manufacturer's software.
Micro-hardness of the daggers, as well as Pb-isotope concentrations,
were also measured. Micro-hardness was taken at 10 g for 10 s
(μHV10,10) for daggers B and E. Lead isotope analyses were conducted
on the hilt of dagger A, and several of the dagger's blades (A–D, F, and
J). One sample from each dagger, samples that were first studied metallographically, were later analysed for isotopes at the Curt-EngelhornZentrum Archäometrie GmbH (CEZA), Mannheim, Germany using a
Neptune Plus HR-MC-ICP-MS. These results were compared to scantly
available lead isotopic signatures for the region.
The hilt of dagger A and several blades (daggers A–D, F, and J) were
selected for isotopic analysis based on their chemical composition.
Artefacts of different composition were chosen in order to identify and
document possible differences in their signatures, and any signs of
metal recycling and mixing. One should note that Cu-As-Sn alloys are
generally considered the result of recycling in this region (Kunze,
2012), and, consequently, arsenical bronzes with no or small amounts
of Sn (the hilt of dagger A, blades of daggers B and C, and blade of
dagger D) were selected for analysis. Tin bronzes with no detected As
(the blades of daggers A and J) and a ternary bronze (blade of dagger F)
were also selected.
Lead isotopes give indication of the age of the ore used in the
manufacture of a copper-based artifact. Knowing the age of the ore, this
information can aid in identifying its geographic origin and thus the
source of the metal used to manufacture the daggers. This methodological approach to provenancing metal finds is well-recognized and
powerful, however is often more useful in eliminating possible ore
sources than definitively identifying them (e.g. Pernicka, 1987).
Though significant copper bearing minerals exist in the Greater Caucasus', the ones presented by Kunze et al. (2017), and here by the
1
2
X
1
1
1
1
Belt buckle, mace head (quartzite)
bronze button, 4 short, zylindric
bronze spirals
Tweezers
Knife, 2× jewellery, bronze sheets
Neck ring, tweezers
Earring, neckring, 2 finger rings,
bronze sheets
1
X
2
2
2
1
3
1
1
2
1
31
9
1
2
1
X
2
1
1
3
3
(C)
(D)
(E)
(F)
(G)
(H)
(I)
(J)
41.389
41.631
41.788
41.803
41.927
41.928
42.186
42.466
42.623 (K)
Koban, grave XI (adult, male)
Koban, grave XVI (juvenil male)
Koban, grave XXIX (adult, male)
Koban, grave XXX (juvenil,
male?)
Koban (?)
Koban (?)
Koban, grave III (adult, male)
Chmi (grave I)
Chmi (?)
1 (toy)
1
1
1
1
41.268 (A)
41.283 (B)
Koban, grave IV (juvenil, male?)
Koban, grave V (juvenil)
1
Further finds
Ceramics
Necklace
Spirals
Temple ring
Bracelet
Appliques
Beads
Pin
Fibula
Pendant
Belt plate
Axe
2. Methodology
Dagger inv. no. (in brackets
letter for identification)
Associated finds
Age at the middle of the 2nd mill. BC. All other daggers are dated to the
Middle and Late Bronze Age.
Find spot
Table 1
– Alleged associated finds and find spots of the studied daggers. Both the sex and age of the interred are uncertain. ‘X’ indicates the presence of specific types of objects where the exact number is unknown (information as from the inventory book of
the Natural History Museum Vienna).
M. Mödlinger, B. Sabatini
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Journal of Archaeological Science: Reports 16 (2017) 248–257
M. Mödlinger, B. Sabatini
Table 2
– Chemical composition of the analysed Koban- and Chmi-daggers. Apart from three drilling samples (dagger A hilt, dagger E hilt and rivet), all EDXS analyses were carried out on freshly
polished and un-etched metal surfaces. Corrosion zones were avoided throughout, which prevented the analysis of dagger K. The reported OES analyses were retrieved from Krause
(2003).
Dagger
Source
Detail
Cu
A
SAM
EDXS
XRFa
EDXS
XRF
SAM
EDXS
XRFa
SAM
EDXS
XRF
SAM
EDXS
XRF
SAM
Hilt
Hilt
Hilt
Blade
Blade
Blade
Blade
Blade
Blade
Blade
Blade
Blade
Blade
Blade
Blade
(upper part)
Blade
(lower part)
Rivet
Hilt
Blade
Blade
Blade
blade
blade
Blade
Blade
Blade
Blade
Blade
Rivet
Blade
Blade
Blade
Blade
94.34
90.15
88
89.31
91.02
96.11
93.98
86.85
94.79
93.23
90.34
94.64
93.33
93.11
92.03
B
C
D
E
EDXS
F
G
H
I
J
K
a
b
SAM
EDXS
XRFa
SAM
EDXS
XRFa
SAM
EDXS
SAM
EDXS
SAM
EDXS
XRFb
SAM
EDXS
82.09
Mn
S
Fe
Co
Ni
Zn
As
5
9.85
11.2
0
< 0.005
< 0.05
< 0.01
0.06
< 0.1
< 0.005
< 0.05
< 0.01
0.03
0.01
< 0.1
< 0.005
< 0.05
< 0.01
0.04
0.01
< 0.1
< 0.005
< 0.05
< 0.01
0.02
0.02
< 0.1
< 0.05
< 0.01
0.05
0.03
< 0.1
###
< 0.005
0.08
3.80
6.02
12.37
5.00
6.77
9.13
3.50
4.78
5.05
3.70
Se
Ag
Cd
0.08
0.10
0.10
0.02
< 0.1
0.03
0.08
< 0.1
0.03
0.03
0.04
0.01
< 0.1
4.15
4.48
3.00
4.45
3.82
3.00
5.82
5.50
2.60
2.90
2.20
1.75
2.70
0.50
2.50
Sb
0.07
0.3
tr.
0.16
0.55
0.07
0.06
< 0.005
####
< 0.005
< 0.005
0.09
0.02
< 0.01
< 0.005
0.36
0.01
< 0.005
0.06
0.04
< 0.005
0.19
0.04
tr.
0.30
0.11
< 0.005
0.08
0.06
tr.
0.08
2.50
0.34
0.14
tr.
0.23
1.40
1.30
1.13
1.00
16.94
0.97
2.72
2.54
0.82
0.91
0.82
0.38
0.70
0.43
4.00
4.63
3.80
5.17
1.15
8.72
8.76
0.03
0.91
0.67
0.28
tr.
0.25
0.55
0.93
0.58
0.19
0.40
1.95
1.83
0.04
0.57
0.13
0.03
< 0.005
< 0.005
tr.
89.00
### 1.53
89.38
### 1.53
95.23
93.99
tr.
93.90 < 0.005
< 0.05 < 0.01
95.57
91.86
92.54 < 0.005
< 0.05 < 0.01
92.63
91.91
###
90.99
90.38
###
95.58
90.52
###
89.98 < 0.005
< 0.05 < 0.01
97.29
Too corroded for chemical analyses
Sn
0.03
< 0.005
0.25
0.05
< 0.005
< 0.005
0.22
0.07
< 0.005
0.08
0.03
< 0.005
0.24
0.07
< 0.01
0.053
10.13
8.66
n.d.
Te
Pb
Bi
0.1
n.d.
< 0.005
0.15
< 0.01
< 0.005
0.07
n.d.
< 0.01
n.d.
< 0.005
0.05
0.01
< 0.01
n.d.
< 0.005
0.09
0.34
tr.
0.42
0.62
< 0.01
n.d.
< 0.005
< 0.005
< 0.005
< 0.005
tr.
0.53
0.64
0.97
0.42
0.69
0.79
0.42
tr.
0.95
0.72
0.46
0.42
0.04
< 0.01
0.01
0.01
< 0.01
0.01
< 0.01
0.01
n.d.
0.01
< 0.01
0.03
Low intensity.
Presence of corrosion.
blades. Consequently, their analyses may have showed higher amounts
of Sb, Ni, Bi, and Pb than by EDXS, since these elements are usually
enriched on the surface. Interestingly, the amounts of As are usually
higher according to EDXS, except for dagger I because As was not enriched in the corrosion layer (see also Fig. 3c).
In most of the cases, the EDXS and XRF analyses are in good
agreement for alloying elements (e.g. As, Sn, Sb, and Pb), except for the
amount of As in the blades of daggers B and C, and in general for dagger
E. The difference can be explained by the presence of γ-phase close to
the surface, and especially along the edges of the blades of daggers B
and C. The OES analyses of the same daggers were taken from the
center of the blade where there is less γ-phase present. Coupled together, these methodological differences led to higher amounts of As
reported by XRF compared to either EDXS or OES. Dagger B′s blade, for
example, is reported by OES to contain 3.8 wt% As, 6 wt% with EDXS,
and 12.4 wt% with XRF.
Differences in sample preparation and analytical method aside, a
vast discrepancy exists between the analyses for the blade of dagger E.
While EDXS did not show any significant amounts of As, OES showed
almost 4 wt%. The SAM data also showed about 2.5 wt% of Sn, which is
low compared to the EDXS analyses at almost 17 wt%. The latter results
are confirmed by the microstructure of the dagger's blade, which is
indeed full of Cu-Sn eutectoid. The discrepancy in composition is the
result of a common ‘restoration’ practice in the 19th and early 20th
century of combining parts of artefacts if they seemingly belonged together (or fit together). The part of the blade analysed by OES was at
the upper portion of the blade, and by EDXS at the lower. From the
current authors, are the only ones reported in the southeast. As a result,
the only geographically relevant dataset is the one recently reported for
Armenian copper ores (Meliksetyan and Pernicka, 2010). The results of
our lead isotope analyses are compared to these data.
In addition to the scarcity of comparable ore sources, the applicability of artifact lead isotopic signatures must be considered in light of
both pre- and post- metal production activities. To be useful they ideally
should not have been the product of recycling and mixing of differently
sourced metal, nor the mixing of several ores pre- metal production.
The chemical and lead isotopic signatures of potential ore sources
should also not be common to several others, and an ore source should
ideally have a homogenous lead isotopic signature across the entire ore
body (e.g. Pernicka, 1987; Sabatini, 2015).
3. Chemical composition
The chemical composition of the daggers, according to the analytical methods mentioned above, is reported in Table 2. The relative
purity of the alloys, having few reported elements when measured using
EDXS, is due to the detection limit of the instrument (0.1 wt%); however low amounts of Ni in Late Bronze Age Caucasian copper alloys are
typical (Japaridze et al., 2007; Kunze, 2012). The same limitation of
EDXS also accounts for the lack of reported Bi and Ag, which are often
present in the SAM data (Krause, 2003).
Comparatively higher concentrations of trace elements in the SAM
data are also likely due to their sampling strategy. Each 2 mm sample
drilling included the corrosion layer on both sides of the dagger's
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Journal of Archaeological Science: Reports 16 (2017) 248–257
M. Mödlinger, B. Sabatini
Fig. 3. – Selected SEM images of dagger blades B,
C, D, E, and F. a) Dagger B (arsenical bronze): the
light grey γ-phase precipitated on the surface in a
thick band (partly covered by corrosion), and at
the grain boundaries in thinner bands. At the
grain boundaries growing corrosion was noted
(small to big black zones). b) Dagger B (arsenical
bronze): the darker α-phase contains about
4.5 wt% As, and the light grey γ-phase about
30 wt%. Sb is enriched in the corrosion. c)
Dagger C (arsenical bronze): the light grey band
between sound metal and corrosion (dark grey)
consists of γ-phase. There was no As detected in
the outer, darker zone of corrosion. d) Dagger D
(arsenical bronze): dark inclusions consist of CuS
with c. 21 wt% S. White inclusions consist mainly
of Cu-Pb with c. 20–22 wt% Pb, and other elements such as Sb, Sn, and Ag with each up to
1.5 wt%. e) Dagger F (ternary bronze): 1 and 2
are Sn crystals with c. 90 wt% Sn, 3.7 wt% Sb,
0.9 wt% Ta, and 7 wt% Cu; 3 is a Pb-inclusion
with c. 65 wt% Pb, 19 wt% As, 15 wt% Cu, and
1 wt% Sn; 4 is γ-phase (As-Cu system) with c.
3 wt% Sb. f) Dagger E: soldered on tin bronze top
with eutectoid up to 3.4 wt% Sb. The Sb tends to
enrich more in the δ-phase.
present in either minor or trace amounts (0.01–0.95 wt%) according to
OES and XRF analysis.
soldering, and the vast differences in chemical composition between the
top and bottom halves, it is clear that two different blades were soldered together. The microstructure of the adjoined dagger top reveals
significant amounts of (α + δ) Cu-Sn eutectoid, where Sb is enriched,
and no signs of Pb, which is typically seen as white spots (Fig. 3f).
Furthermore, some analytical discrepancies between analytical
campaigns may have arisen due to sample preparation. Drilling samples
taken for analysis in the SAM project from the hilts of the daggers may
have contained small amounts of the blades, as was certainly the case
for dagger A (this resulted in significantly lower amounts of As measured by OES, since the blade of dagger A contains almost no As).
Interestingly, none of the reported OES analyses contain Fe or S. These
elements were detected by EDXS, and S was detected in half of the
daggers (D, E, F, H, I, and J). Iron, meanwhile, was only detected in the
three drilling samples of one rivet and the hilt of dagger E (that also
contain up to 1.7 wt% S), which were taken for EDXS analyses. It
should be noted that Fe likely did not derive from the drill bit, since the
drilling sample from dagger A contains no Fe. Low concentrations of Fe
were also noted by XRF (< 0.05 wt%), however this analytical method
is typically imprecise. It is also not uncommon for ancient copper alloys
to contain low amounts of Fe. In all but one dagger (dagger B), Pb is
4. Microstructure
The microstructure of all of the daggers, whether arsenical or tin
bronze, or a mixture (Cu-As-Sn), show corrosion and inhomogeneous αsolid solution within their dendritic structures (so-called ‘ghost-structure’) that are visible through differences in their copper concentrations. The blade of dagger K also shows cracking, which was likely
caused by tension during deformation (Fig. 4d), indicating not enough
or too late annealing. Significant deformation was also noted in the
blades of daggers A, F, H, J, K, and the soldered-on top of dagger E (see
also Fig. 4b–c). Deformed equiaxed grains with twins and strain lines
are visible. The corrosion usually followed the Cu-rich areas of the αsolid solution. Minor and trace elements were mainly found in inclusions and along the grain boundaries. Deformed equiaxed grains with
twins and strain lines are visible. The corrosion usually followed the Curich areas of the α-solid solution. Minor and trace elements were mainly
found in inclusions and along the grain boundaries.
Due to greater electrochemical potential, corrosion preferentially
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Journal of Archaeological Science: Reports 16 (2017) 248–257
M. Mödlinger, B. Sabatini
Fig. 4. – Microstructure of the blades of daggers
G, H, J, and K (all ternary Cu-As-Sn bronzes). a)
Dagger G: corrosion outlines the grain boundaries
of the inhomogeneous α-solid solution, and is
significantly increased at the grain boundaries. b)
Dagger H: etched with NH4OH + H2O2. The Curich zones of the inhomogeneous α-solid solution
are corroded. In the Cu-poor zones severely deformed grains with strain lines and twins can be
seen. c) Dagger J: the microstructure is clearly
visible even without etching. Corrosion outlines
not only the grain boundaries, but also twins and
strain lines. d) Dagger K: the dagger was too
corroded to carry out chemical analyses. A fragile
fracture is shown in the picture. It was caused
during deformation of the blade that increased its
fragility due to the many CuO-inclusions.
Fig. 5. – Microstructure of the blade of dagger B (arsenical
bronze). Note the vast amount of light grey γ-phase, which
precipitates all along the surface (thicker bands) and along the
grain boundaries (thinner bands). The dark spots are corrosion,
which start at grain boundaries and especially at their crossing.
Inclusions in all of the daggers showed low amounts of deformation,
which is unusual. However, since most of the inclusions contain significant amounts of Pb, and are not of the more common variety of
Cu2 − xFexS known from Central European Fe- and S-rich tin-bronzes
(Mödlinger and Piccardo, 2013), they cannot be used to interpret the
total amount of deformation applied to the blade. After each annealing
process the inclusions would have returned to a globular form, so only
information about the last annealing was preserved.
The advantage of SEM-EDXS analyses is that they allow one to see
how, and in which form, minor and trace elements and different phases
are distributed in the microstructure. The composition of the inclusions
varied widely between each blade: the blade of dagger D showed both
Cu-S and Cu-Pb inclusions (the latter containing also Ag, Sn, and Sb)
(Fig. 3d); dagger G showed Pb-inclusions containing about 2.6 wt% Sn
(2 wt% more than in the α-solid solution), 18 wt% As, and only 14.5 wt
% Cu; dagger H, Cu-Pb-inclusions with slightly more Sn and Sb, and
slightly less As than in the α-solid solution. The blade of dagger I
showed a variety of vastly different inclusions, including: Cu-Pb-
begins at the intersection of grain boundaries. On the surface, azurite
and malachite were visually identified as the main corrosion products
with copper oxides such as tenorite and cuprite between them and close
to the surface. The blade cores showed indications of the original surface metal in the form of thin layers of copper carbonates. The corrosion
layer was especially thick on dagger K. Some of the alloying elements,
but also minor elements, are significantly enriched in the corrosion, as
was observed for Sb and Sn on the blade of dagger I.
Two arsenical bronze daggers, daggers B and C, showed significant
amounts of γ-phase, which precipitated along the grain boundaries and
formed thin band-like structures starting from the edge of the blade and
extending to their centers (Fig. 5). These γ-phase bands are also found
on the surface of the daggers in thicker bands, and are covered by
corrosion in some zones (Fig. 3a–c). They are not, however, evidence of
the inverse segregation of arsenic (Mödlinger and Sabatini, 2016).
Dagger C showed blotted γ-phase around the intersection of the grain
boundaries. It contained about 1 wt% Sb in the bands of γ-phase as
measured by EDXS, which was comparatively 0.2 wt% by XRF.
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M. Mödlinger, B. Sabatini
Fig. 6. – Microstructure of dagger blade D (arsenical bronze blade) and the soldered on top of
dagger E (tin bronze blade), and its micro-hardness values. a) Dagger D: The grain boundaries
are outlined by corrosion. Moreover, corrosion is
severe around the inclusions and where grain
boundaries cross. b) Dagger E: Even without
etching the microstructure is clearly visible.
Corrosion outlines not only the grain boundaries,
but also twins and strain lines. c) Dagger E: The
(α + δ) eutectoid of the Cu-Sn system is clearly
visible. d) Dagger E: micro-hardness measurements (μHV10,10). The imprints were made in
zones with different amounts of alloying elements in the inhomogeneous α-solid solution and
on the eutectoid.
Fig. 7. – Microstructure of the blade of dagger I
(ternary Cu-As-Sn bronze) after etching with
NH4OH + H2O2. a) and b) Remnants of the
dendritic structure are still visible, as well as inclusions of different compositions. c) The dendritic structure is clearly visible and not significantly deformed. The alloy did not receive
much deformation in the sampled area. d)
Hardness measurements (μHV10,10). The imprints were made in zones with different amounts
of alloying elements in the inhomogeneous alpha
solid solution.
showing various types of inclusions, such as Pb-Cu-As (c. 60 wt% Pb
and small amounts of Sb, Sn, and Cl), the blade also contains small
amounts of Cu and Sn crystals (Fig. 3e). These crystals are of particular
importance since they show that the Sn was not completely molten
when the alloy was cast and may be the result of the last-minute addition of cassiterite or another Sn mineral to molten copper or a recycled tin bronze (e.g. Rovira et al., 2009; Farci et al., 2017). There are
inclusions with about 85 wt% Pb; Cu-Pb-inclusions with c. 18 wt% Pb,
and slightly less As, Sn, and Sb than in the α-solid solution; Cu-Sninclusions with almost 10 wt% Sn, 4 wt% Sb, and 2 wt% As; CuS-inclusions; and finally, Cu-S-inclusions with Sb and Sn. The blade of
dagger J showed two types of inclusions: one with Cu-Pb and some Sn;
and, the other with Cu-Pb with Sn and Fe.
The most intriguing inclusions were visible in dagger F. Apart from
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M. Mödlinger, B. Sabatini
Fig. 8. – Lead isotope ratios of the analysed daggers, and of copper ores from the south-eastern Great Caucasus (Kunze et al., 2017). The data from Armenia is taken from Meliksetyan and
Pernicka, 2010, 51–52, Tab. 5–6. c) shows details of a), while d shows details of b).
also small Cu crystals still visible in the matrix, pointing more likely to a
last-minute addition of Cu to the melt rather than a recrystallisation of
Cu afterwards.
Finally, the temperature that the daggers were annealed was not
consistent nor necessarily very high, since there is eutectoid in daggers
A and E (tin bronze), and F (ternary bronze). The blade of dagger A and
the top of dagger E show (α + δ) eutectoid of the Cu-Sn system. Of
particular importance is that the δ-phase contains significant amounts
of Sb of up to 3.4 wt% (dagger A). The corrosion is concentrated on the
α-solid solution, and sparsely on the δ-phase as well as zones inside the
eutectoid that seem to be pure copper (dagger E; see Fig. 6c–d). One can
also clearly see the progression of corrosion around the more corrosionresistant inclusions and grain boundaries (Fig. 6a), as well as the
copper-rich zones of the α-solid solution, twins, and strain lines
(Fig. 6b). Interestingly, Cu or Cu-rich zones were often found as ‘bands’
inside the eutectoid (Fig. 6c).
5. Micro-hardness
Several micro-hardness measurements (μHV10,10) were carried out
in different Cu-rich and Cu-poor zones, and on the (α + γ) eutectic of
dagger's B and (α + δ) eutectoid of dagger E (i.e. the top of dagger E)
(Fig. 6d). Daggers B is considerably higher in arsenic than the rest of the
studied set (c. 6 wt%). Micro-hardness measurements of dagger B
showed higher values for the γ- than α-phase; however, these values
should be considered relative since the bands of γ-phase were too thin
to be certain that only the bands themselves were tested and not the
underlying α-phase. The measurements on dagger E showed lower
hardness values in the Cu-rich than in the Cu-poor zones, and much
higher in the eutectoid (about 450 ± 30 μHV). Fig. 7d clearly shows
the impact the amount of As and Sn has on the hardness of the alloy
(dagger I; ternary bronze). Even though the blade of dagger I was annealed and cold hardened several times, the alloy did not homogenize,
indicating that annealing times were rather short at lower temperatures. The micro-hardness measurements were around 140–170 μHV
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M. Mödlinger, B. Sabatini
The Sn crystals in dagger F can provide valuable information regarding the origin of the metal through the identification of their minor
and trace elements. Significant to dagger F, and its Sn crystals, is the
detection of c. 1 wt% Ta, which was not found in any other dagger.
Hosking (1982) notes that ‘intensely red-pale coloured cassiterites containing Ta and possibly Nb in the lattice, are restricted to the west [Southeastern Asian Tin] belt and are paramagnetic, whilst those that are brownpale colour pleochroic, a phenomenon probably also due to Nb/Ta or W in
the lattice, occur in both belts and may be ferromagnetic’. One of the two
crystals also contains 0.4 wt% Fe, and both of them contain 3.5–4 wt%
Sb (dagger F; see Fig. 3e). However, no Zr or Nb was detected, as one
might expect to find if the Sn originated from cassiterite or pegmatite
minerals.
Finally, the lead isotope signatures of all but one dagger match well
with those from Georgian copper ore sources overlapping with those
from Armenia. The daggers were, apart from dagger J, which only
overlaps with the Armenian copper ores, most likely made of copper ore
from the Greater Caucasus'. According to the prior and produced chemical, microstructural, and isotopic data, there is no indication of recycling with non-localized copper ores.
Table 3
- Measured lead isotope ratios. The analyses were carried out with a Neptune Plus HRMC-ICP-MS at the Curt-Engelhorn-Zentrum Archäometrie GmbH (CEZA), Mannheim,
Germany. The precision of measurement is less than ± 0.001% for ratios with 208Pb and
206Pb in the denominator and for 207Pb/204Pb, and up to ± 0.02% for 207Pb/206Pb.
For 208Pb/204 Pb it is up to ± 0.06%. Sample weight: 100 ppb.
Dagger Object
208Pb/
206Pb
207Pb/
206Pb
208Pb/
204Pb
207Pb/
204Pb
206Pb/
204Pb
A
A
B
C
D
F
G
J
2.0900
2.0821
2.0857
2.0847
2.0839
2.0856
2.0860
2.0659
0.84957
0.84470
0.84574
0.84577
0.84518
0.84608
0.84630
0.83425
38.414
38.499
38.543
38.486
38.504
38.504
38.513
38.818
15.615
15.619
15.629
15.614
15.616
15.620
15.625
15.675
18.380
18.490
18.480
18.462
18.477
18.462
18.463
18.790
Hilt (CuAs)
Blade (CuSn)
Blade (CuAs)
Blade (CuAs)
Blade (CuAs + tr. Sn)
Blade (CuAsSn)
Blade (CuAs + 0.7% Sn)
Blade (CuSn)
for Cu-rich zones, and above 200 μHV for Cu-poor zones (i.e. zones with
higher amounts of As and Sn).
6. Lead isotope analyses
8. Conclusion
As shown in Fig. 8, the isotopic signatures for Georgian ores and the
daggers overlap well with the Armenian ore sources. Apart from the
blade of dagger J, the ratios for the daggers are concentrated in a very
narrow field at 208Pb/204Pb vs. 206Pb/204Pb at 38.5 and 18.5, respectively (Table 3). The same is true for the 208Pb/206Pb vs. 207Pb/
206Pb at 2.85 and 0.845, respectively. The ratios for the ores are instead concentrated at 208Pb/204Pb vs. 206Pb/204Pb at 38.40–38.45
and 18.40, respectively, and for 208Pb/206Pb vs. 207Pb/206Pb at 2.95
and 0.850. The isotopic signature of dagger A overlaps with the Georgian isotopic values from the Stori valley (Kunze et al., 2017). The other
daggers, apart from dagger J, however, are very close to the Georgian
ore signatures.
Until disproven by additional isotopic analyses of ores in the region,
all daggers, apart from dagger J, which seems to only overlap with the
Armenian copper isotopic ratios, were likely made from Caucasian
copper ore. Due to the lack of ore analyses from the Greater Caucasus',
no further relationship between the daggers and the source for their
metal can be postulated. Also, according to the available data, there
were no indications of recycling of differently sourced metal or ore.
Eleven Bronze Age dagger blades from Koban and Chmi, North
Ossetia-Alana, Russia, were chemically analysed by EDXS, and their
microstructures characterized. The dagger blades were made of either
arsenical bronze with up to ~7 wt% As (daggers B-D), of tin bronze
with 10 or 17 wt% Sn (dagger A, and soldered on top of dagger E), or of
a ternary Cu-As-Sn alloy (upper part of the blade of dagger E, and
daggers F–K). The alloys characteristic have low amounts of Ni, Ag, Pb,
S, and Fe. It should be noted that Ni and Ag were usually present in
amounts below the detection limit of EDXS. Trace elements were
mainly detected in the inclusions or along grain boundaries. Antimony
is in ten out of eleven of the blades, and in four daggers (daggers D, E,
G, and I) at around 1–2 wt%. The blades were analysed by the SAM
project, however the current analyses showed several discrepancies in
chemical composition. These differences can be explained by the inclusion of corrosion products in the OES analyses, and the presence of γphase on the surfaces of the daggers (blades of daggers B and D).
In two instances the chemical composition of the dagger hilts were
analysed and found to contain almost 10 wt% As (dagger A) with a
blade containing 10 wt% Sn, while the hilt of dagger F was made of a
ternary Cu-As-Sn alloy. These material choice applications suggest that
differences in the alloys were recognized, and that each was used intentionally during the manufacture of the daggers.
All of the dagger blades have been annealed and cold worked. Two
dagger blades (dagger A, and the top of dagger E) show Cu-Sn (α + δ)
eutectoid, indicating low temperature or short-term annealing. The
amount of deformation applied during working is not connected to the
chemical composition and none of the blades are homogenous. Their
dendritic structures differ visibly throughout based on the amount of
alloying elements present in the α-solid solution. This difference in
composition also results in different micro-hardness values in Cu-rich
and Cu-poor zones in the alloys.
The blade of dagger F showed Sn crystals, indicating that tin was
added when the copper was not completely molten. These untouched
Sn crystals can help identify the metals origin, since they contain significant amounts of Ta (c. 1 wt%). One of the two analysed crystals also
contained 0.4 wt% Fe, and both have 3.5–4 wt% Sb.
Due to scarcity of lead isotope analyses of copper minerals from the
Greater Caucasus', no relationship between the daggers and ore sources,
other than from the Greater Caucasus', can be drawn. However, a close
relationship with Armenian ores is likely. According to the available
data, no indication of recycling with non-local ore seemed to have occurred. These results support the interpretation that Sn and As, in some
form, was intentionally added to the local copper.
7. Discussion
Only four of the eleven Bronze Age dagger blades are not ternary
Cu-As-Sn alloys (daggers A, B, C, and D). These blades consist of arsenical (daggers B, C, and D) or tin (dagger A) bronze. Dagger A is
unique in the assemblage in that the hilt contains ~9.8 wt% As and no
Sn, while the blade contains 10.1 wt% Sn and no As. The selection and
use of these alloys, especially for dagger A, suggests intentionality in
metal use. Apart from dagger E, which comprises two different alloys
soldered together in the modern era, all of the others studied are consistently Cu-As, Cu-Sn, or Cu-As-Sn. The overall chemical composition,
corrosion structure, and identified inclusions of dagger E indicate that
the soldered on piece is ancient. As for more precise dating of the
daggers and their relationship to the graves they originated, no interpretation can be made at this time due to the circumstances of their
procurement.
Objects made of ternary Cu-As-Sn alloys with > 1 wt% Sn and As
are known from the Late Bronze Age site of Udabno, Georgia (one pin)
(Kunze, 2012), the Middle Bronze Age objects from Atskuri, Georgia
(three daggers and one ring), and the Late Bronze Age Colkhian bronzes
reported by Japaridze et al. (2007) (one dagger, one axe). The finds
from Udabno, which contain ≤1 wt% Sn and As, suggest heavy recycling of old arsenical bronzes with tin bronzes, resulting in ternary
alloys (Kunze 2012, 96, Fig. 5.6).
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M. Mödlinger, B. Sabatini
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Acknowledgments
The authors would like to acknowledge the financial support provided by the European Union's Horizon 2020 research and innovation
programme under the Marie Skłodowska-Curie Actions, grant agreement no. 656244. The XRF and lead isotope analyses were funded by
the Fritz Thyssen Stiftung (project number Az. 20.15.0.084AA) as part
of a bigger project on copper mineral study in Eastern Georgia by René
Kunze, Tübingen, and Marianne Mödlinger. The authors are very
grateful to Armanda Barbangelo, Università degli Studi di Genova,
Italy, for the micro-hardness measurements and fruitful discussions
regarding microstructure.
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