Fernandes et al. Heritage Science 2013, 1:30
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RESEARCH ARTICLE
Open Access
The use of Hand-Held XRF for investigating the
composition and corrosion of Roman
copper-alloyed artefacts
Ricardo Fernandes1,2*, Bertil JH van Os3 and Hans DJ Huisman3,4
Abstract
The study of archaeological artefacts using deployed in situ analytical instruments presents some obvious
advantages. Including, obtaining an immediate feedback that can be used to redefine in real-time fieldwork
strategies. Ideally analytical field instruments should also have characteristics that limit damage to the studied
artefact.
Here, we present a case study on the use of a Hand Held XRF (HH XRF) device employed to define the
composition of copper-alloyed artefacts retrieved from the Roman military site of Fectio in the vicinity of Vechten
(The Netherlands). The goals of the study were to establish artefact preservation status, to investigate artefact
elemental composition, and to compare the composition of artefact corrosion layer and uncorroded core.
The results showed that the objects were in an overall good preservation state. Decuprification and dezincification
represented the probable main corrosion processes resulting in the formation of smooth corrosion layers or patinas.
The major elemental composition of the artefacts’ uncorroded cores showed a wide-range variability most likely
associated with recycling practices of scrap metal during the 3rd century CE.
Keywords: Roman, Copper-alloyed artefacts, Hand Held XRF, Vechten, Fectio, Metal corrosion
Introduction
Hand Held X-ray fluorescence devices (HH-XRF) and
other portable XRF (pXRF) devices are regularly used in
industry and are gradually being introduced also for
archaeological/historical applications [1-5]. Within archaeometric research, previous studies have also employed
pXRF devices in the measurement of the elemental composition of bulk and corrosion layers of copper-alloyed
artefacts [1,4]. Given that this technique has the potential to provide high precision and fast results, allowing
for non-destructive measurements to be made in situ, it
becomes ideal for many archaeological applications.
In this study, a set of copper-alloyed archaeological artefacts from the Roman Limes military fort of Fectio, in
the vicinity of Vechten (The Netherlands), were analysed
using a HH-XRF device. The artefacts were recovered
* Correspondence: rfernandes@gshdl.uni-kiel.de
1
Leibniz-Laboratory for Radiometric Dating and Isotope Research, Christian
Albrechts Universität, Max-Eyth-Str. 11-13, 24118 Kiel, Germany
2
Graduate School “Human development in landscapes”, Christian Albrechts
Universität, Kiel, Germany
Full list of author information is available at the end of the article
during a metal detector survey. The preservation status
of the artefacts was established in two ways; macroscopically, by describing and classifying visible evidence for
surface damage, and chemically by comparing elemental
content (Cu, Pb, Sn, Zn) of each object’s corroded surface and uncorroded core. These criteria provide information on two different corrosion effects. The first,
surface damage represents a semi-qualitative criterion
but that provides relevant information for archaeological
research. The second, elemental variability is a quantitative criterion although not necessarily linked with loss of
archaeological information.
The main goal of the present study was to provide an
illustrative application of the use of a HH-XRF device in
an archaeological context. The material selected for
analysis contributes to the existing knowledge on the
composition of Roman artefacts from a military Limes
site occupied between the 1st and 3rd centuries CE. Finally, a simple assessment was made of the relationship
between the preservation status of collected artefacts
© 2013 Fernandes et al.; licensee Chemistry Central Ltd. This is an Open Access article distributed under the terms of the
Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use,
distribution, and reproduction in any medium, provided the original work is properly cited.
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and observed variations in elemental composition due to
the formation of corrosion layers.
Materials and methods
Artefacts
Metallic artefacts, located using a metal detector, were
collected from the top 30 cm of soil at the ancient site
of Fectio; a Roman military settlement in the vicinity of
modern day Vechten located approximately 5 km to the
southeast of the city of Utrecht in The Netherlands [6-8].
The settlement was established during the Augustan
period on the southern bank of a former Rhine bed, probably close to the spot where the river Vecht diverged from
it [7,9]. The site was abandoned in the 3rd century CE
when the river channel silted up [10].
The site had previously been the target of a baseline
study to establish the preservation of copper-alloyed artefacts and its relationship with soil aggressiveness parameters [11]. The soil at the site is a thick and fairly
impermeable clayey anthropogenic soil rich in lime and
organic matter known in the Dutch soil classification as
a “tuineerdgrond” (loosely translatable as garden plaggen
soil). The topsoil consists of loam and sandy or silty clay.
Due to intensive bioturbation and anthropogenic mixing,
the profile is fairly homogeneous, with a black to black
brown colour [11].
A total of 61 copper-alloyed artefacts were collected
from the site (Additional file 1). The majority of the collected artefacts were assigned to the Roman period (44).
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However, some more recent objects (e.g. brass buckshot
shell casings) were also collected. Although some easily
recognizable artefacts were found (Figure 1), most of
collected objects were in a fragmentary state. The results
here presented refer only to the archaeological artefacts
assigned to the Roman period.
Removal of corrosion layer
To limit damage to each artefact the corrosion layer was
removed only on a small area using a drill and a metal
scalpel (Figure 2). The procedure in some cases was
made difficult due to the thickness of the corroded layer
and the small size of some of the artefacts.
HH-XRF measurements
For elemental measurements (Cu, Pb, Zn, Sn, and Fe) a
HH-XRF device was used. The HH-XRF device was a
Thermo Scientific Niton XL3t with a GOLDD (Geometrically Optimised Large area Silicon Drift Detector)
detector equipped with a silver anode operating at a
maximum of 50 kV and 40 μA. The device was factory
calibrated and additional elemental standards were also
measured.
Measurements were performed in a portable test stand
with a lead liner and a helium purge was applied. Metal
samples were placed over the exit of the detector and
were measured in “mining mode” on their corrosion/patina layer (untreated surface), and on a treated spot. In
this way, the compositional differences between the
Figure 1 Examples of metallic artefacts located at Vechten. Sheet fragment (A), likely part of a key (B), ring (C), modern button (D), trident
shaped artefact (E), unknown artefact (F).
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Figure 2 Examples of untreated and treated objects’ surfaces. Sample 128 with untreated (A) and treated (B) surfaces. Sample 52 (C) with
untreated upper part and treated lower part. Sample 12 (D) with untreated (right side) and treated (left side) surfaces.
corroded surface and the uncorroded core could be
determined.
Artefact preservation status
The preservation status of each artefact was defined in
accordance with the classification system described in
Table 1. This classification system considers the presence
of pitting, overall preservation of artefact surface and
shape, and the presence or not of corrosion scale.
Results and discussion
Assessment of artefact preservation status
Most of the objects, albeit fragmented, were relatively
well preserved from corrosion attack (Table 2). The artefacts presented low amounts of pitting, with 82% having
a score of 1 while the remaining 18% had a score of 2.
The surface of the majority of objects was also relatively
well preserved with 48% having a score of 1, 45% a score
of 2, and only 7% presenting a partially degraded surface
(score 3). Defining preservation of shape was often difficult due to the fragmentary state of many of the objects.
Table 1 Parameters, and corresponding scores, used to
define artefacts’ preservation status
Parameter
Values
Individual scores
Pitting
No pits
1
Visible pitting
2
Completely pitted
3
Preservation of surface
Preservation of shape
Corrosion scale
All details visible
1
Details visible
2
Surface partly degraded
3
No original surface left
4
Object is complete
1
Some damage is observed
2
Object is partly deformed
3
Object not recognizable
4
Not present
0
Present
1
However, no heavy degradation of shape was observed,
with 27% of the objects presenting small amounts of
damage (score 2) and 73% a good shape preservation
(score 1). The presence of corrosion scales was observed
in only 30% of the objects.
Elemental composition
Figure 3 shows box and whisker plots of the elemental
composition (Cu, Pb, Zn, Sn, and Fe) measured on the
treated artefact surface of the copper-alloyed artefacts
recovered from Vechten and assigned to the Roman
period. The full list of measured artefacts is provided in
Additional file 1.
The results show that all major elements are present
in significant amounts and that these have wide ranges
in concentration. This is especially evident for Cu and
Pb. The artefacts were classified according to their composition using Riederer’s [12] classification to which was
added the category of gunmetal (objects containing both
zinc and tin). In accordance with this classification system the Vechten’s artefacts are classified as tin bronzes
(18%), brasses (6%), lead bronzes (2%), lead tin brasses
(26%), and gunmetals (48%) (Figure 4).
The mechanical properties of bronze make it an ideal
choice for the fabrication of different objects including
weapons. The use of tin bronze became almost universal
in Europe by the end of the second millennium BCE
[13]. The Romans employed great quantities of both low
tin and high tin bronzes, especially prior to the large
scale introduction of brass during the late 1st century
BCE [14].
The production of metallic zinc is problematic since
zinc evaporates at 950°C while it requires a temperature
of around 1000°C to be reduced from zinc ores. Thus in
a smelting process metallic zinc is evaporated and
quickly converted into an oxide. During the 1st century
BCE brass was produced through the direct mix of copper and zinc ores in a closed crucible at 1000°C, this
process is referred as co-smelting or cementation [15].
The Romans were the first to produce brass on a large
scale, with brass representing one third of the copper
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Table 2 Distribution of preservation scores for Roman objects found at Vechten
Criterion
Score 0 (%)
Score 1 (%)
Score 2 (%)
Score 3 (%)
Score 4 (%)
Pitting
-
82
18
0
-
Preservation of surface
-
48
45
7
0
Preservation of shape
-
73
27
0
0
Corrosion scale
70
30
-
-
-
alloys used during the Roman Imperial period. Zinc content for early Roman brasses is typically in the 18-24%
range [16].
During the Roman period lead was cheaper and more
easily obtainable than zinc or other metals, and high lead
contents are often observed in casted objects. When up
to 2% lead is added to an alloy there is a significant increase in the mobility of the molten metal [15]. Further
increases in lead content (3-4%) does not increase significantly the fluidity of the alloy but there is a lowering
in melting point. This makes leaded bronzes easier to
cast, but also easier to drill, file or grind [15]. Metallic
lead oxidizes very quickly and forms a passive oxide
layer within seconds and is therefore very corrosion resistant. Furthermore, lead is very malleable and was
widely used by the Romans in the making of a large variety of objects, including, the making of funerary urns,
inscribed tablets, pipes, coins, etc [17-19].
Over 60% of the measured artefacts had iron contents
above 5%. These high iron levels may, in part, originate
from impurities in the copper ore. High concentrations
of iron in Roman alloyed artefacts have been previously
reported [20]. For instance, dupondi and sestertii, early
Roman brass coinage, had higher iron content than contemporary bronzes [15]. However, compared with the results here presented (Figure 3) the study by Dungworth
showed, for Roman artefacts, a lower maximum iron
content of 2% [21]. Therefore, the observed high levels
of iron probably result from post depositional processes
with the applied surface treatment not completely removing iron containing clay minerals such as illite. Additionally, given the small sizes of some of the artefacts
and the need to limit the removal of the corrosion layer
it is possible that portions of untreated surface were also
targeted by the primary X-ray beam.
Compositional differences are expected for artefacts
depending on their functional characteristics. However,
observed wide variations in elemental concentrations are
most likely attributable to common and time extended
recycling practices of scrap metal. Similar compositional
ranges have been previously reported on Roman British
objects from the 3rd and 4th centuries CE [21]. This
contrasted with previous centuries where lower amounts
of leaded bronze or leaded brass were observed and unleaded brasses and bronzes were more prevalent. Increased alloying with lead during the later stages of the
Roman Empire has also been reported for objects having
a unique function (e.g. statuary) [22]. Given that the majority of retrieved objects are most likely reflecting the
later phases of site occupation it can be hypothesized
that rather than the specific physical properties of leaded
alloys determining the choice of their use, the large
Figure 3 Box and whisker plot showing the distribution of Cu, Pb, Zn, Sn, and Fe weight content of the Roman objects found at
Vechten. Asterisks indentify compositional outliers, while circles with cross within identify mean values. The measurements refer to treated
artefacts, that is, surface measurements for which the corrosion layer was removed.
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Page 5 of 7
Figure 4 Compositional distribution of Roman artefacts according to Riederer’s (1984) classification with the added category
of gunmetal.
compositional variation resulted from difficulties in
accessing alternative metals during the 3rd century CE.
This hypothesis is framed within the unstable political
and economic situation of the Roman Empire during the
3rd century CE.
Differences in composition of treated and untreated
artefact surfaces
The composition of untreated metal surfaces, for all collected objects and measured elements, is reported in
Additional file 1. Table 3 shows, for artefacts assigned to
the Roman period, the relative enrichment or depletion
in the concentration of major elements (Cu, Pb, Zn, and
Sn) determined by comparing the elemental contents of
the corroded surface and the uncorroded core.
In 82% of the objects the results showed depletion in
copper content when comparing the corrosion layer with
bulk alloy composition (Table 3). Standard tin bronzes
present a microstructure consisting of a delta phase (tin
rich) interspersed by dendritic arms of a copper rich alpha
Table 3 Percentages of elemental enrichment or
depletion for metal objects retrieved at Vechten
established by comparing the composition of treated and
untreated artefact surface
Element
Enrichment (%)
Cu
18
Depletion (%)
82
Pb
57
43
Zn
36
64
Sn
63
37
phase [23]. In an oxygenated environment the delta phase
is more resistant to corrosion than the alpha phase
resulting in the selective dissolution of copper (decuprification). Tin remains in the alloy surface as oxide and the
values for tin in Table 3 show that tin enrichment occurs
in 63% of all samples. In a decuprification process even
surfaces (Type I surfaces) or patinas consisting of copper
oxides and copper carbonates are usually formed [24].
Thus, corrosion mechanisms in which decuprification predominates are consistent with surface preservation results
that indicated low amounts of pitting and limited formation of corrosion scales (Figure 2, Table 2).
Brass artefacts are well known for being less hard and
less corrosion resistant than bronze artefacts [25]. Brass
alloys are subject to dezincification in which zinc is selectively leached. Zinc is either deposited as an insoluble
compound or carried away as a soluble salt, while copper is re-deposited at the alloy surface in a porous form
[26]. Objects showing zinc depletion represent the majority (64%) although there is still a significant percentage of
objects showing zinc enrichment (36%). Corrosion studies
on Roman coins have previously shown that the presence
of alloy tin limits dezincification [27]. This may also explain the significant percentage of Vechten objects showing zinc enrichment.
Alloy lead is immiscible in the copper matrix forming
discrete globules. Buried lead objects generally do not
corrode severely [28]. However, high concentrations of
lead might lead to the aggregation of dispersed globules
causing a weakening of the mechanical properties of
the alloy [15]. The Vechten objects exhibited similar
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percentages of relative lead depletion (43%) and enrichment (57%).
Conclusions
A Hand-Held XRF (HH XRF) device is an analytical tool
well suited for investigating major elemental composition
of metallic archaeological artefacts. It can be deployed for
measurements in situ ensuring limited or no damage to
measured artefacts. A HH XRF device was used to provide
an insight into the composition of copper-alloyed artefacts
from the Roman site of Fectio in the vicinity of Vechten
(The Netherlands).
Retrieved copper-alloyed artefacts were in an overall
good preservation status owing to the local characteristics
of the clayey carbonate containing soil that limited access
to atmospheric oxygen and assured a neutral to slightly alkaline pH. The objects, albeit fragmented, showed a good
surface preservation through the formation of smooth
corrosion layers. The formation of such smooth layers is
consistent with comparison of the elemental composition
of the corrosion layer and uncorroded core that indicate
that decuprification and dezincification were the main
corrosion processes.
The artefacts presented wide compositional ranges of
major elements (Cu, Sn, Zn, and Pb). These are probably
associated with recycling practices of scrap metal, and a
time-related increase in lead content. Compositional results offer a scenario similar with other locations within
the Roman Empire during the 3rd century (time of abandonment of the site), a period well-known for its political and financial instability.
Additional file
Additional file 1: Chemical composition and preservation status of
copper-alloyed artefacts collected at Vechten.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
RF wrote the manuscript revised by BJHO and HDJH. RF and BJHO collected
objects during fieldwork. RF, BJHO, and HDJH performed analytical
measurements. All authors read and approved the final manuscript.
Acknowledgments
This study was carried out within the scope of an internship made possible
by the Cultural Heritage Agency of the Netherlands. The authors would like
to thank Prof. Henk Kars (Vrije Universiteit Amsterdam) for introducing
Ricardo Fernandes to the Dutch archaeometric community and for
supervising the internship. The authors would like also to thank Jo
Kempkens and Ton Lupak from Restaura (Haelen, The Netherlands) for
assisting in the cleaning and restoration of the artefacts, and for providing
access to a micro camera. Finally, two anonymous reviewers are thanked for
their helpful comments.
Author details
1
Leibniz-Laboratory for Radiometric Dating and Isotope Research, Christian
Albrechts Universität, Max-Eyth-Str. 11-13, 24118 Kiel, Germany. 2Graduate
Page 6 of 7
School “Human development in landscapes”, Christian Albrechts Universität,
Kiel, Germany. 3Cultural Heritage Agency, P.O. Box 1600, 3800, BP Amersfoort,
The Netherlands. 4Faculty of Archaeology, Leiden University, Leiden, The
Netherlands.
Received: 31 March 2013 Accepted: 9 September 2013
Published: 16 September 2013
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Cite this article as: Fernandes et al.: The use of Hand-Held XRF for
investigating the composition and corrosion of Roman
copper-alloyed artefacts. Heritage Science 2013 1:30.
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