image/svg+xml
69
XII/1/2021
INTERDISCIPLINARIA ARCHAEOLOGICA
NATURAL SCIENCES IN ARCHAEOLOGY
homepage: http://www.iansa.eu
The Comparative Study of Tool Marks on Non-Ferrous Metalwork from
Archaeological Contexts: Methodological Considerations, Case Studies and
Experimental Archaeology
Birgit Bühler
1*
, Dávid Zsolt Schwarcz
2
1
Vienna Institute for Archaeological Science, University of Vienna, Franz-Klein Gasse 1, 1190 Vienna, Austria
2
Austrian Archaeological Institute, Austrian Academy of Sciences, Franz Klein-Gasse 1, 1190 Vienna, Austria
1. Introduction
The framework of technological necessities for creating
a particular efect in metalworking is defnable. Within this
framework, in many cases, the individual metalworker has a
number of choices. The technical decisions taken in each case
will depend on the craftsperson’s skills, personal preferences
and background, on smaller-scale “workshop traditions
”, on
larger-scale “cultural traditions
”, as well as on the demands of
the customer regarding motifs, style, material and technique in
the fnished product. Hence, the technological choices made
in the production process of a particular object are important
evidence, which may reveal its place of production, as well
as the cultural or even social background of the craftsperson
and the recipient of the product in question. The aim of this
paper is to give an overview of the methodology of tool mark
studies on gold and silver metalwork from archaeological
contexts, to demonstrate potential applications of this
approach with the help of a case study and to suggest
possible directions for future interdisciplinary research,
for example, using experimental archaeology. The frst
part of the paper (see chapter 2) discusses methodological
aspects of the comparative study of tool marks on precious
metalwork from archaeological contexts, including a case
study from the early medieval period. The second part of
the paper (see chapter 3) is a preliminary experimental study
of several types of punching tools, which commonly occur
in decorative techniques on early medieval non-ferrous
metalwork: The purpose of this section is to demonstrate the
potential of experimental archaeology for the interpretation
of tool marks on non-ferrous metalwork from archaeological
contexts.
Volume XII ● Issue 1/2021 ● Pages 69–81
*Corresponding author. E-mail: birgit.buehler@univie.ac.at
ARTICLE INFO
Article history:
Received: 9
th
September 2020
Accepted: 18
th
February 2021
DOI: http://dx.doi.org/10.24916/iansa.2021.1.5
Key words:
Avar archaeology
Byzantium
non-ferrous metalwork
technology transfer
experimental archaeology
ABSTRACT
The aim of this paper is to discuss methodological issues of comparative tool mark studies (with
special attention to decorative punched motifs), using a case study on sheet-gold metalwork from the
Middle and Late Avar Period (7
th
–8
th
centuries AD). The historical interpretation of tool marks on non-
ferrous metalwork
1
can take place at diferent levels of complexity. In some cases, the identifcation
of products from the same craftsperson is possible, via the identifcation of specifc tools. However,
when interpreting the results of comparative tool mark studies, many aspects are relevant, including
individual variations in tool usage. In this context, experimental archaeology can facilitate the
interpretation of tool marks, as is demonstrated in a preliminary study on two types of punches, which
are common on high-quality metalwork from the Avar Period.
1
The term “non-ferrous metals” encompasses all the metals and their alloys,
which do not contain iron. Hence, this denomination includes precious
metals (
e.g.
gold and silver) and non-precious metals, such as lead, tin, zinc,
copper and its alloys (
e.g.
bronze, brass,
etc.
), to mention the most relevant
concerning tool mark analyses on archaeological metal artefacts.
image/svg+xml
IANSA 2021 ● XII/1 ● 69–81
Birgit Bühler, Dávid Zsolt Schwarcz: The Comparative Study of Tool Marks on Non-Ferrous Metalwork from Archaeological Contexts: Methodological Considerations,
Case Studies and Experimental Archaeology
70
2. Tool mark studies on gold and silver metalwork from
archaeological contexts
2.1 Methodological considerations
The purpose of “basic tool mark studies
” on precious
metalwork from archaeological contexts is to identify the
techniques used in manufacturing and decorating a particular
artefact and to reconstruct its production process. In
contrast, the aim of “comparative tool mark studies
” on
precious metalwork from archaeological contexts is the
historical interpretation of the technological evidence.
Hence, “basic tool mark studies
” constitute a pre-requisite
for further, historical interpretation of the evidence, which
also requires the inclusion of additional criteria, derived
from other, related metalwork and the archaeological
context (“comparative tool mark studies
”
). As will be
illustrated below, in a case study, the process of historical
interpretation of tool marks can take place at diferent levels.
Starting at the lowest, most specifc level, this process can
involve the identifcation of individual tools, followed by
the identifcation of specifc types of tool, by technical
preferences and idiosyncrasies of individual metalworkers
and progressing to the higher-level aspects, such as the
identifcation of metalworking traditions characteristic for
individual workshops, as well as to larger-scale, local or
regional metalworking traditions.
Therefore, comparative tool mark studies may permit
researchers to identify artefacts produced by the same
Figure 1.
Gold belt-buckle from the
“Brestovac Hoard” (Croatia; end of eighth
– early ninth century AD). Kunsthistorisches
Museum Wien, Antikensammlung, inv. no.
VII B 70. Detail of sheet gold ftting: Highly
stylised plant motif (“
Stäbchenranke
”)
characteristic for the Late Avar Period III
in repoussé (“
Treibziselieren
”), worked
predominantly from the front; surface of
leaves decorated with “stippling punch”
(Photo: B. Bühler).
Figure 2.
Gold belt-buckle from the
“Brestovac Hoard” (Croatia; end of eighth
– early ninth century AD). Kunsthistorisches
Museum Wien, Antikensammlung, inv. no.
VII B 70. SEM-Detail of sheet gold ftting:
Repoussé (“
Treibziselieren
”), worked
predominantly from the front; surface of leaf
decorated with “stippling punch” (Photo:
M. Mehofer, VIAS).
image/svg+xml
IANSA 2021 ● XII/1 ● 69–81
Birgit Bühler, Dávid Zsolt Schwarcz: The Comparative Study of Tool Marks on Non-Ferrous Metalwork from Archaeological Contexts: Methodological Considerations,
Case Studies and Experimental Archaeology
71
craftsperson: The best way of verifying such an assumption
is to demonstrate the use of identical tools in the production
process of two or more particular metal products. The pre-
requisite for this, however, is the identifcation of individual
tools on the metal objects in question. Characteristic
irregularities on the surface of a tool’s working-edge (see,
for example, Figure 4, below) can facilitate the identifcation
of specifc, individual metalworking tools. In the absence of
such typical faults, exact measurements of the dimensions
of the tool-marks may assist in identifying a specifc tool.
Ideally, a Scanning Electron Microscope (SEM) is available
for precise measurements of tool mark dimensions, although
a variety of other measurement options exists (see other
comparative tool mark studies focusing on punching
especially as a decorative technique, Larsen, 1987; Mortimer,
Stoney, 1997 and Dal, 2017, pp.131–144).
However, when interpreting the results of comparative
tool mark studies, several aspects are relevant: Firstly, the
surface of a tool’s working-edge may change with time. This
could either be due to the natural process of use-wear or
to intentional re-shaping by a craftsperson. Secondly, tool
marks originating from the same tool may vary in size and
appearance (for examples, see chapter 2.2), due to variations
in the orientation of the tool to the metal surface and because
of variations in pressure when using the tool. As will be
demonstrated in chapter 3, experimental archaeology can
assist in the interpretation of tool marks on non-ferrous
metalwork from archaeological contexts. Thirdly, traces of
Figure 3.
Gold bowl number 13 from
the “Nagyszentmiklós (Sânnicolau Mare)
Hoard” (Romania; end of eighth – early
ninth century AD). Kunsthistorisches
Museum Wien, Antikensammlung, inv.
no. VII B 10. Detail of stylised plant
ornament (“
Stäbchenranke
”) in repoussé,
including leaves with “stippled surface” and
background flled with ring-shaped punch-
marks (Photo: Kunsthistorisches Museum
Wien).
Figure 4.
Gold bowl number 13 from
the “Nagyszentmiklós (Sânnicolau Mare)
Hoard” (Romania; end of eighth – early
ninth century AD). Kunsthistorisches
Museum Wien, Antikensammlung, inv.
no. VII B 10. SEM-Detail: Tool marks
of “stippling punch” with characteristic
irregularity (Photo: M. Mehofer, VIAS).
image/svg+xml
IANSA 2021 ● XII/1 ● 69–81
Birgit Bühler, Dávid Zsolt Schwarcz: The Comparative Study of Tool Marks on Non-Ferrous Metalwork from Archaeological Contexts: Methodological Considerations,
Case Studies and Experimental Archaeology
72
wear on the surface of a metal object may alter the original
shape and size of tool marks.
2.2 Case study: Interpreting decorative techniques on
sheet-gold metalwork from the Middle and Late
Avar Period (7
th
–8
th
centuries AD)
Interdisciplinary research on non-ferrous metalwork can be
helpful in identifying cultural traditions in archaeological
contexts. For example, there is ample evidence for a close
connection between “Byzantine
”
and “Avar
” culture in
the 7
th
and 8
th
centuries AD. However, the mechanisms of
cultural and technological transfer, as well as the regions
where such transfer processes may have taken place, are still
subject to debate. Comparative tool mark studies on precious
metalwork could contribute to resolving these questions, in
particular in conjunction with other criteria derived from
archaeological research. In this context, specifc variations
in decorative techniques for working precious metals are
relevant: True repoussé (= three-dimensional modelling of
sheet metal using individual tools, such as several diferent
types of punches;
“Treibziseliertechnik”
)
was an uncommon
technique in the Avar realm. However, it occurs within Avar
territory on a number of high-quality items of metalwork
(mainly gold objects; see Figures 1–5), which may be
associated – for typological, stylistic and/ or technological
reasons – with “Byzantine
”
culture. In the Early and Middle
Avar Period (7
th
century), the standard production method
for gold-, silver- and copper-alloy jewellery and dress
ornaments was pressing pieces of sheet metal over positive
models (“formers
”
). In the Late Avar Period (8
th
century), on
the other hand, the dominant technique for manufacturing
non-ferrous jewellery and dress ornaments was the casting
process. However, in the Mediterranean region, true
repoussé (
“Treibziseliertechnik”
) was a common technique
for producing three-dimensional decoration on high-
quality sheet metal (gold, silver and copper alloy) objects.
Although the import of top-quality gold metalwork with
repoussé ornament from the Byzantine Empire is a feasible
interpretation, an alternative hypothesis is that they are in
fact products of “Byzantine” type, produced in workshops
on the periphery of the Byzantine Empire with technical
expertise from Byzantium. In any case, it seems feasible
to associate the occurrence of these specifc decorative
techniques on metalwork found on Avar territory with
“Byzantine metalworking traditions”, although the specifc
workshops cannot yet be located (Bühler, 2014).
This case study summarizes the results of comparative
tool mark studies on high-quality sheet gold metalwork from
the Middle and Late Avar Period (7
th
–8
th
centuries AD), by
focusing on two key fnds from this period, both of which
are in the collection of the Kunsthistorisches Museum Wien,
Austria (Antikensammlung). Firstly, there are the 23 gold
vessels from the “Nagyszentmiklós (Sânnicolau Mare)
Treasure” (for an overview of archaeological research,
see Bálint, 2010; for the results of archaeometallurgical
research, see: Bühler, Freiberger, 2018), found in present-
day Romania in 1799. Secondly, there are four gold belt
ornaments from the so-called “Brestovac Hoard
”, found
in present-day Croatia in 1821. The plant ornament on
the youngest group of gold vessels (seven bowls with
“Stäbchenrankenzier”
= Nos. 13–16 and 19–21; late
8
th
century AD) from the “Nagyszentmiklós (Sânnicolau
Mare) Treasure” is closely related to the decoration of
the gold belt fttings from Brestovac (Bühler, 2014).
Similarly, comparative tool mark studies have revealed
that the repoussé work on the group of gold vessels with
“Stäbchenrankenzier”
from Nagyszentmiklós (Figures 3–5)
and on the gold belt fttings from Brestovac (Figures 1–2) is
strikingly similar (Bühler, 2014). In particular, the process of
modelling the three-dimensional plant ornament from sheet
gold was almost identical, although in terms of quality, the
repoussé ornament on the gold vessels is of a higher standard
than on the gold belt-fttings. For example, the tool marks on
the vessels represent a larger variety of diferent tool types,
Figure 5.
Gold bowl number 14 from
the “Nagyszentmiklós (Sânnicolau Mare)
Hoard” (Romania; end of eighth – early
ninth century AD). Kunsthistorisches
Museum Wien, Antikensammlung, inv.
no. VII B 11. Detail of stylised plant
ornament (“
Stäbchenranke
”) in repoussé,
including leaves with “stippled surface”
and background flled with ring-shaped
punch-marks; mistake in design of plant
ornament, refecting a diference in quality
to number 13 (Photo: Kunsthistorisches
Museum Wien).
image/svg+xml
IANSA 2021 ● XII/1 ● 69–81
Birgit Bühler, Dávid Zsolt Schwarcz: The Comparative Study of Tool Marks on Non-Ferrous Metalwork from Archaeological Contexts: Methodological Considerations,
Case Studies and Experimental Archaeology
73
as well as fner tools, than the tool marks detected on the
belt ornaments. The increased number of tools used on the
vessels could be explained by the diference in the size of the
objects under discussion. Hence, either limited or extended
possibilities are available for surface decoration, depending
on the dimensions of the given item. However, both on
the vessels and on the belt-fttings, the repoussé ornament
is characterised by a remarkably three-dimensional relief,
created mainly by working the sheet gold from the front (
i.e.
by pushing down the background of the ornament). It is not
surprising that the production of three-dimensional relief
ornament on sheet-gold vessels occurred predominantly by
working from the front (or outside) of the vessel, because
this is advantageous from a technical point of view. In the
case of the belt fttings, however, working from the front is
an unusual technique, for which technical advantages do not
sufce as an explanation. This observation, together with
other technical similarities, could support the hypothesis
that the production of gold vessels and gold belt fttings with
“Stäbchenrankenzier”
may have taken place in closely-
related workshops with similar metalworking traditions –
perhaps even in the same workshop (Bühler, 2014). However,
there was no evidence for the use of specifc, identical tools
on both the vessels and the belt fttings. Clearly, on the
vessels much fner tools were used, and more skilfully, than
on the belt fttings.
The use of “stippling punches
”
(see Figures 1–5)
within this typological group (= sheet-gold objects with
“Stäbchenrankenzier”
; see Bühler, 2014) provides evidence
for closely-related workshop traditions, but distinct variations
in skill and in the quality of metalworking technology.
“Stippling punches
”
served the purpose of creating a fnely-
textured surface, which occurs especially on decorative
elements of the stylised plant ornament characteristic for
this group. The shape of the tool marks suggests that the
“stippling punches
” used within this group of Late Avar
metalwork were all very fne tools with a conical working
edge. Although the same type of tool – a fne “stippling
punch”
– was used for creating the characteristic, fnely
“stippled
”
surface on both the plant and animal ornament of
all seven bowls with
“Stäbchenrankenzier”
(Numbers 13–16
and 19–21) from the “Nagyszentmiklós (Sânnicolau Mare)
Treasure”
, diferent tools were used to decorate each of
these vessels. This is clear from the dimensions of the tool
marks of the “stippling tools
”
, which were obtained from
measurements of the SEM
2
images: The fnest “stippling
punch”
was used on bowl number 13, with tool marks of
only 0.07–0.08 mm in diameter. The specifc tool used on
this vessel has a characteristic irregularity on the working
edge, which facilitates its identifcation (see Figure 4). In
contrast, the diameter of the tool marks of the stippling
punches on all the other six vessels is larger. This includes
2
All SEM research on archaeological metalwork mentioned in this paper
was carried out on a Zeiss EVO 60 XVP Scanning Electron Microscope
at Vienna Institute for Archaeological Science (supported by the Austrian
Research Fund as part of a research project on the Nagyszentmiklós
Treasure, 2004–2007).
the relevant tool marks (diameter = 0.16–0.21 mm) on
bowl number 14, which is similar to number 13 regarding
a number of formal, stylistic and technological aspects, but
of slightly lower quality in several aspects (Figures 3–5).
This provides support for the hypothesis that the pair of
bowls number 13 and 14 (Figures 3–5) was produced by
diferent metalworkers, but perhaps within one workshop
or associated workshops, with similar metalworking and
cultural traditions (see Bühler, Freiberger, 2018).
In addition, the results of comparative tool mark studies
show that the diameter of the stippling punch marks on the
other fve vessels of this group are in a similar range as those
on number 14. “Stippling tool
” marks of this type occur on
number 21 (diameter = 0.11–0.20 mm), number 19 (diameter
= 0.13–0.22 mm), number 20 (diameter = 0.12–0.19 mm),
number 16 (diameter = 0.15–0.28 mm) and number 15
(diameter = 0.16–0.26 mm). From this evidence, it is feasible
to conclude that “stippling tools
”
of similar fneness were
applied to six out of the seven gold vessels within this
typological group. However, in this case, due to the absence
of characteristic faults, it is impossible to identify specifc
tools. Hence, it is possible that more than one tool of this
type was used on a given vessel. Similarly, in this case, it
is impossible to verify the use of identical tools on two or
more of the gold vessels within this group. For example, for
the pair of bowls numbers 15 and 16, in this case, we can
only conclude that “stippling tools
” of the same type and
very similar diameter were used – thus suggesting (possible)
production in the same workshop. The problem of “normal
”
variation in the diameter of tool marks produced with the
same tool – which is apparent in the considerable variation in
diameter regarding the tool marks cited above – is addressed
by experimental research (see chapter 3). “Stippling
”
as a decorative technique for sheet-gold metalwork is
quite common in “Italo-Byzantine
” precious metalwork
from the 7
th
century, decorated with half-palmettes and
other types of stylised plant ornament (Ricci, 2012). This
provides support for the hypothesis that “Italo-Byzantine
”
goldsmith’s workshops may have represented a major factor
in the process of transmitting ideas, motifs and techniques
from the Mediterranean region to the Avar realm in the
Carpathian Basin (Bálint, 2010; Bühler, 2014). For example,
“Italo-Byzantine
” metalworking traditions may have played
a major role in the production of high quality, sheet-gold
repoussé with
“Stäbchenrankenzier”
, as discussed above.
Signifcantly, the evidence for a second decorative
technique common in Avar metalwork – flling the
background of chased or engraved ornament with ring-
shaped punch-marks (Figures 6–7) – appears to point in
the same direction (Bühler, 2014), which demonstrates that
comparative tool mark studies may be helpful in identifying
the process of transmission of metalworking traditions. On
Avar territory, the decorative technique with ring-punched
background frst occurs in the Middle Avar Period (middle
to late 7
th
century AD) and is most common towards the end
of the Late Avar Period (late 8
th
century AD), especially in
conjunction with diferent types of plant ornament
(Bühler,
image/svg+xml
IANSA 2021 ● XII/1 ● 69–81
Birgit Bühler, Dávid Zsolt Schwarcz: The Comparative Study of Tool Marks on Non-Ferrous Metalwork from Archaeological Contexts: Methodological Considerations,
Case Studies and Experimental Archaeology
74
2014). This decorative technique is also, for example,
common on belt buckles of Byzantine type with U-shaped
fttings from the 7
th
–8
th
century AD. Furthermore, the fact
that this decorative technique occurs on the reverse side of
a 6
th
–7
th
century AD gold cross reliquary from Monza (Italy;
see Bálint, 2010) may suggest that flling the background
of linear decoration, especially plant ornament, could be
characteristic for Italian precious metalwork production
in “Late Antique cultural tradition
”
, but still operating in
the 7
th
century AD. Hence, the evidence regarding this
decorative technique appears to support the hypothesis that
“Italo-Byzantine
” goldsmith workshops were crucial in the
process of transmitting metalworking techniques, but also
motifs and artistic conventions from the Mediterranean
region to the Avar realm in the Carpathian Basin. In the
“Nagyszentmiklós Treasure”, which could represent the
highest level of Avar non-ferrous metalwork in the 7
th
–8
th
century AD (Bálint, 2010; Bühler, Freiberger, 2018),
plant ornament with chased or engraved contours and the
background flled with ring punches occurs on four vessels
– three jugs (numbers 3, 6, 7) and one bowl (number 8); see
Figures 6 and 7. On three of these gold vessels, the diameter
of the tool marks recorded in the SEM is within a similar
range: On bowl number 8, the diameter of ring-shaped
punch-marks was 0.63 mm to 0.77 mm, on jug number 7 it
was 0.55 mm to 0.77 mm and on jug number 3, the diameter
was 0.52 mm to 0.70 mm. The dimensions of the tool marks
are sufciently similar to suggest that they could have been
produced using the same ring punch. In particular, the shape
of the ring-shaped punch-marks on vessels numbers 7 and
8 is strikingly similar, suggesting that the same tool may
indeed have been used when decorating these two vessels
(Figure 7). The ornament with ring-shaped punch-marks on
these three vessels is also linked by the fact that there is no
overlap of the punch-marks (as is the case on jug number 6,
for example): On vessels numbers 3, 7 and 8, there is
Figure 6.
Gold bowl number 8 from
the “Nagyszentmiklós (Sânnicolau
Mare) Hoard” (Romania; eighth century
AD). Kunsthistorisches Museum Wien,
Antikensammlung, inv. no. VII B 4. Detail of
handle: Plant ornament with chased contours
and background flled with ring-shaped
punch-marks (Photo: Kunsthistorisches
Museum Wien).
Figure 7.
Gold bowl number 8 from
the “Nagyszentmiklós (Sânnicolau
Mare) Hoard” (Romania; eighth century
AD). Kunsthistorisches Museum Wien,
Antikensammlung, inv. no. VII B 4. SEM-
Detail: Ring-shaped punch-marks of
characteristic shape (Photo: M. Mehofer;
VIAS).
image/svg+xml
IANSA 2021 ● XII/1 ● 69–81
Birgit Bühler, Dávid Zsolt Schwarcz: The Comparative Study of Tool Marks on Non-Ferrous Metalwork from Archaeological Contexts: Methodological Considerations,
Case Studies and Experimental Archaeology
75
a considerable distance between the ring-shaped punch-
marks, which constitute the background of the linear plant
ornament. This could be due to the metalworking traditions
of a particular workshop or to the preferences of a given
craftsperson. In addition, on several other gold vessels from
the “Nagyszentmiklós Treasure”, the background of plant
ornament in relief (repoussé) was also covered with ring-
shaped punch-marks. This includes repoussé scroll ornament
on jug number 2 (diameter of ring-shaped punch-marks =
0.83 mm to 0.93 mm) and repoussé stylized plant ornament
on three bowls from the
“Stäbchenranke”
group. These are
the pair of bowls number 13 (diameter of ring-shaped punch-
marks = 0.40 mm to 0.52 mm) and number 14 (diameter of
ring-shaped punch-marks = 0.40 mm to 0.47 mm), as well
as bowl number 21 (diameter of ring-shaped punch-marks
= 0.31 mm to 0.39 mm). It must be noted that the diameter
of the ring-punch marks suggests that diferent tools (one or
perhaps several per vessel) were used on the diferent vessels
with this type of decoration. For numbers 13 and 14, use
of the same ring-punch is possible, but cannot be verifed
with any degree of certainty (see Figures 3 and 5). On all
these vessels, there is a noticeable overlap of the ring-shaped
tool-marks, which contrasts with the background of the
linear ornament on vessels number 3, 7 and 8. Again, this
could be interpreted either as the preferences of individual
metalworkers or workshops, or even as larger-scale
“metalworking traditions”.
3. Experimental tool mark studies – a preliminary case
study focusing on ring punches and stippling punches
3.1 Introduction
Punching is a non-cutting, cold-working decorative technique
for non-ferrous metalwork, performed by tapping various
small “rod-shaped” iron pressure tools (= “punches”) with
a hammer to create geometric and ornamental decorations on
a metal surface. The punches have working edges of diferent
shapes and sizes with the required motive (Armbruster,
2000, pp.56–58). Accordingly, there are a variety of punch
types with pointed, fat, round or hollow heads in circular,
rectangular, triangular and a variety of other shapes;
those with a pre-prepared motive (
e.g.
fgural, foral or
a combination of geometrical shapes) are also called stamps
or patterned punches (Brepohl, 1978, pp.230–231,
cf.
Dal,
2017, pp.132–134). Hence, punching permits the creation
of diverse repetitive patterns based on dots, circles or rings,
as well as convex and concave hemispheres. In addition,
various types of punches are crucial for techniques aimed at
raising and shaping sheet metalwork (for example, repoussé,
see chapter 2, above and Bühler, 1998–1999, pp.430–433).
However, this experimental study focuses exclusively on the
punching techniques applied to the front side of the metal
surface, in order to compile decorative repetitive patterns.
Several factors infuence the negative imprint of the punches’
working edge and these are relevant in the examination of
such tool marks (see chapter 2, above). The pressed motives,
Figure 8.
Schematic illustration of punching technique. 1: Punches held in
a) 90 degrees on fat, b) 90–120 degrees on domed, and c) 45–60 degrees
on fat, metal surface. 2: Variations of tool marks left by the same punch
depending on the operating angle and the force of hammer blow. Red
line: the actual working edges of the tool (leaving sharp marks); Orange
interrupted line: the external convex side of the punch’s head (leaving blunt
marks). Illustration by D. Schwarcz.
even if they derive from the same tool, may vary greatly
depending on the following circumstances:
1. The hardness of the metal alloy to be decorated.
2. The force of hammer strike applied to the punch.
3. If annealing and intermediate annealing processes
have been carried out.
4. The operating angle of the punch.
5. The surface geometry of the area to be processed.
All these issues afect the appearance of the punch-marks,
individually as well as in combination. The hardness of
the metal alloy and the applied force defne the recess and
contours or even the basic shape of the motive, but these
could also afect the size of the punched decoration mainly on
a microscopic level. These efects are enhanced if the metal
is not recrystallized before the metalworking process or if the
piece is not annealed (several times) during the execution of
the given decoration technique. Recrystallization is essential
if pressing techniques are applied. Due to simultaneous
displacement and compression of the metal sheet, the
crystalline structure of the alloy is deformed and the
accumulated tension signifcantly decreases the malleability
of the material (Scott, 1991, pp.3–7). This problem can be
resolved by heating the product to an appropriate temperature
(for copper alloys: 500–800°C, according to Scott, 1991,
p.7) to induce the recrystallization of the grain structure, thus
restoring its malleability.
The force of the hammer strike on the punching tool defnes
the depth and even the size of the punched motive, if the
punching tool has a conical or domed head. The deeper the
head of the punch enters the metal, the larger the size of the
tool-mark. Figure 8.2 illustrates a ring-shaped punching tool
image/svg+xml
IANSA 2021 ● XII/1 ● 69–81
Birgit Bühler, Dávid Zsolt Schwarcz: The Comparative Study of Tool Marks on Non-Ferrous Metalwork from Archaeological Contexts: Methodological Considerations,
Case Studies and Experimental Archaeology
76
in practical use, showing that the tip of the punch (= “working
edge”) is responsible for forming the (constant) ring pattern
with sharp edges (Figure 8.2 – red markings). At the same
time, the slightly curved side of the punch´s head determines
the fnal size of the ring (including a concave “rim”; see
Figure 8.2 – yellow and orange markings) depending upon
how deep the head enters the surface of the metal. Basic
sharp-edged ring patterns without a rim would appear either
if the head of the punch has straight or slightly concave sides
or if the metal being worked on became rigid (Figure 14.5);
additionally, the lack of a solid support (
e.g.
a backing block)
could contribute to the formation of such a pattern.
The operating angle of the punch, described as the angle
between the punching tool and the (horizontal) surface of
the work piece, greatly infuences the shape of the punched
motive. In a normal operating state, the punch should be held
perpendicular to the surface. Even the slightest alteration of the
angle could result in a diferent pattern (
e.g.
in an interrupted
circle instead of a full circle,
cf.
Figures 8.1–2), especially
if any of the previous factors coincide. The distortion of the
original motive could be enhanced if the surface is three-
dimensional (
e.g.
domed), since the working edge could
hardly be placed on the surface and be at the correct angle
to the surface.
Due to the issues concerning the variability of patterns
created by the same tool, specialists of non-ferrous
metalworking techniques give special attention to reoccurring
irregularities of punched marks (Armbruster, 2000, p.116).
A characteristic faw appearing on several punched decorations
(see also chapter 2, above) suggests that those motives were
created by the same tool, which either had a fault in its original
design or its working edges had started to deteriorate (Larsen,
1987, pp.404–405, Mortimer, Stoney, 1997, p.121).
3.2 Experimental research on punched decoration
The purpose of this preliminary experimental research,
using diferent punches under controlled conditions, was to
expand our practical knowledge on punched decoration (see
the tools and the experimental sample in Figure 9). Our main
aim was to understand how the factors described above (see
chapter 3.1) may infuence the tool marks left on the surface
of metal objects and to gain comparative visual data for
future technological analyses. Based on the briefy outlined
technical process of punching, with particular attention to
the difculties of tool mark identifcation, the following
questions were of primary interest.
•
To what extent does the profle and especially the side
of the punching tool´s working edge infuence the tool
marks?
•
To what degree does the shape and size of the tool
marks change depending on the operating angle?
•
Are there diferences between the tool marks created
by the same tool?
Firstly,
sample 1
, a small rectangular metal strip
3
, was
3
Measurements of the metal strip: Length × Width 6.05 0215 × 1.53 cm,
Thickness 0.06 cm. Abbreviations used in the following: L. = length;
W. = width; THK. = thickness; DIA. = diameter.
Figure 9.
1: Photo and drawing of the
punches used in the experiment (from left
to right): nail with rhombic profled tip;
stippling punch number 33; ring punch
numbers 27 and 31. 2: The processed brass
sample. Photographs by D. Schwarcz,
R. Göttlich; edited by D. Schwarcz.
image/svg+xml
IANSA 2021 ● XII/1 ● 69–81
Birgit Bühler, Dávid Zsolt Schwarcz: The Comparative Study of Tool Marks on Non-Ferrous Metalwork from Archaeological Contexts: Methodological Considerations,
Case Studies and Experimental Archaeology
77
cut out of a brass sheet
4
and fattened using a rubber mallet.
A hardened steel block was placed under the sheet metal
strip. Subsequently, a small nail
5
(tip with rhombic profle),
an ad hoc ´stippling punch´ (
cf.
chapter 2.2) was used to
create a random pattern (Figure 10) in pointillé technique.
During the process, the orientation of the nail to the surface
was perpendicular. Secondly,
sample 2
, a piece of scrap
metal of adequate size, originally cut out of the same brass
sheet as sample 1, was selected from our inventory. First,
a dome was formed in the centre of the piece by embossing
(“
Formtreiben
”), for which a die (“
Anke
”) and a punch with
spherical head (“
Kugelpunze
”) was used
6
. The remaining
fat space between the edge of the metal sheet and the dome
was divided into four felds. On each feld, as well as on
the dome, diferent punches held at specifc angles were
applied, summarized in Table 1. (
cf.
Figure 8.1), to create
4
The brass sheet with appropriate cold working properties (zinc content:
less than 20%) was obtained from a commercial hardware store; however,
the exact alloy composition is not known.
5
Measurements of the nail: L. 3.80 cm, shaft DIA. 0.20 cm
6
The measurements of the fnal piece are L. × W. 4.18 × 4.26 cm,
THK.0.06 cm.
a random decoration, adequate for tool mark analysis. Two
ring-punches (number 27, and number 31) and a punch
with rounded pointed edge (“stippling punch” number 33)
7
were involved in the process. Neither of the samples was
recrystallized before, during or after the metalworking.
Finally, the samples were analysed and selected punch
marks were documented using a Zeiss EVO 60 XVP scanning
electron microscope in the laboratory of the Vienna Institute
for Archaeological Science.
3.3 Results and interpretation
The shape and size of the punched decorations permit several
important observations: The small nail with rhombic profled
pointed tip, an improvised punching tool, left elongated plum
seed-like marks with irregular contours on sample 1. Not
only the contours, but also the shape, size and even the inner
surface of the marks vary (Figures 10.1, 3–4). Although a nail
is suitable for preparing simple decorations, especially in
pointillé technique, the microscopic analyses reveal that the
7
Measurements of the punches: number 27, L. 9.24 cm; shaft DIA.
0.62 cm, working edge DIA. external 0.40 cm, internal 0.29 cm; number 31,
L. 9.38 cm, shaft DIA. 0.71 cm, working edge DIA. external 0.57 cm,
internal 0.50 cm; and number 33, L. 9.66 cm, shaft DIA. 0.50 cm
Table 1.
Summary of the experimental metalworking processes conducted on sample 1 and 2.
Processed areaSurfaceApplied tool Operating angleFigure number
Sample 1
FlatNail
90°10.
Sample 2
Field 1Flat
Ring-punch, no. 2790°11.
Field 2Flat
Ring-punch, no. 3190°12.
Field 3Flat
Punch, no. 3390°12.
Field 4
Flat
Ring-punch, no. 2745–60°11.
Domeconvex
Punches: no. 27, 31, 3390–120°13.
Figure 10.
Macroscopic photo of a metal strip decorated by punching with a rhombic-headed nail and the corresponding SEM-photos. Photographs by
D. Schwarcz, SEM-photographs by B. Bühler, D. Schwarcz; edited by D. Schwarcz.
image/svg+xml
IANSA 2021 ● XII/1 ● 69–81
Birgit Bühler, Dávid Zsolt Schwarcz: The Comparative Study of Tool Marks on Non-Ferrous Metalwork from Archaeological Contexts: Methodological Considerations,
Case Studies and Experimental Archaeology
78
patterns were created by a tool with a rudimentary working
edge. This statement is supported by the uneven surface of
the recesses, in contrast to the smooth concave impressions
made by proper punches (Figure 12.2). Most of the punched
dots and rings on sample 2 do not show irregularities in
their shape, but slight diferences in their size are apparent.
Although, the base ring-motive remains constant, the rim
(determined by the side of the tool´s head) is in several cases
wider or narrower depending on how deep the punch entered
the surface (
cf.
Figure 11.4, ring on top right).
Regarding our other research question concerning the
operating angle of the punches, besides individual pressed
patterns in feld 1 and 4, the tool marks on the dome show the
greatest diversity. On the reference feld number 4, where the
ring-punch number 27 was held at 45–60 degrees, regular
crescent-shaped motives can be seen (Figures 11.1–2).
Without knowing the exact tools and technique carried out,
one might conclude, based exclusively on the length of the
motives, that the punched decoration was executed by a ring-
tool and not with a punch having a crescent-shaped head.
One peculiar ring-decoration deserves our attention from the
feld 1 (Figure 11.3), where the same tool (number 27) was
applied. Even though the intention was to hold the punch
perpendicular to the surface, presumably, an error occurred,
resulting in a slightly diferent punching angle. This fault in
the working process must have also been supported by the
Figure 11.
Field 1 and 4 on the experimental sample and the corresponding SEM-photos. 1–2: Field 1; 3–4: Field 4 (white arrows mark the specifc
photographed punched motives). Photographs by D. Schwarcz, SEM-photographs by B. Bühler, D. Schwarcz; edited by D. Schwarcz.
Figure 12.
Field 2 and 3 on the experimental sample and the corresponding SEM-photos. 1–2: Field 3–4:
Field 2 (white arrows mark the specifc
photographed punched motives). 3: Tool marks deriving from die-forming in the area marked with green. Photographs by D. Schwarcz, SEM-Photographs
by B. Bühler, D. Schwarcz; edited by D. Schwarcz.
image/svg+xml
IANSA 2021 ● XII/1 ● 69–81
Birgit Bühler, Dávid Zsolt Schwarcz: The Comparative Study of Tool Marks on Non-Ferrous Metalwork from Archaeological Contexts: Methodological Considerations,
Case Studies and Experimental Archaeology
79
hardness of the unannealed sheet
8
resulting in an interrupted
circular pattern. On the dome, a slightly irregular crescent-
shaped punch prepared by ring tool number 27 (Figures 13.4
and 11.2) and other curved semi-circular lines made by the
latter tool (Figure 13.3) as well as number 31 (Figure 13.1)
are located. The striking diferences of the patterns is due to
8
Another indication of the metal sheet’s rigidity is apparent in the shallow
concentric lines at the conjunction point of the dome and the fat part of
sample 2 (Figure 5.2). These marks are the imprints of the die’s edge from
shaping the dome by embossing. In the case of a work piece regularly
recrystallized during processing, such tool marks are less likely to appear.
the three-dimensional surface geometry and the variations
of the punching angle (90–120°). Another peculiar motive,
compiled by ring-tool number 27, can be found on the dome,
consisting of two concentric semi-circular lines (Figure 13.2).
This must have formed due to the combination of several
factors: the non-annealed material, the lack of proper support
for the dome and the convex surface. All these prevented the
punch from entering deeper into the metal surface; hence, it
left only the outlines of the working edges behind.
If the punched decorations made by the same tool
(ring-punch number 27) are compared, a series of patterns
Figure 13.
The domed feld on the experimental sample and the corresponding scanning electron microscopic photos (white arrows mark the specifc
photographed punched motives). Photographs by D. Schwarcz, SEM-photographs by B. Bühler, D. Schwarcz; edited by D. Schwarcz.
Figure 14.
SEM-photos of dissimilar punch marks derived from the same tool (ring-punch number 27). SEM-photographs by B. Bühler and D. Schwarcz;
edited by D. Schwarcz.
image/svg+xml
IANSA 2021 ● XII/1 ● 69–81
Birgit Bühler, Dávid Zsolt Schwarcz: The Comparative Study of Tool Marks on Non-Ferrous Metalwork from Archaeological Contexts: Methodological Considerations,
Case Studies and Experimental Archaeology
80
with diferent features can be identifed. Regular ring
(Figure 14.1), interrupted circle (Figure 14.2), semi-circular
lines (Figure 14.3), crescent-shaped motive (Figure 14.4)
and concentric semi-circular lines (Figure 14.5) are the
patterns made by the very same tool. The operating angle of
the punch appears to be the main reason for the change (or
distortion) in the basic ring motive.
4. Conclusion
The technological choices made in the production process
of a particular gold or silver object can provide us with
valuable information not only on the level of metalworking
skill, but also on the background and afliations of the
goldsmith who created this particular product. The aim
of this paper is to present the methodological issues and
potential of comparative tool mark studies, using a case
study on high-quality sheet gold metalwork from the Middle
and Late Avar Period (7
th
–8
th
centuries AD). The process of
the comparative interpretation of tool marks can take place
at diferent levels. On the most specifc level, this process
can involve the identifcation of individual tools, followed
by the classifcation of specifc types of tool, by technical
preferences and idiosyncrasies of individual metalworkers
and progressing to the higher-level aspects, such as the
identifcation of metalworking traditions characteristic
of individual workshops, as well as to larger-scale, local
or regional metalworking traditions. In some cases,
comparative tool mark studies permit the identifcation of
artefacts produced by the same craftsperson: The best way
of verifying such a hypothesis is to demonstrate the use
of identical tools in the production process of two or more
particular metal products. The pre-requisite for this, however,
is the identifcation of individual tools on the metal objects
in question. Characteristic irregularities on the surface of
a tool’s working-edge can facilitate the identifcation of
specifc, individual metalworking tools. In the absence of
such typical faults, exact measurements of the dimensions
of the tool-marks may assist in identifying a specifc tool.
However, when interpreting the results of comparative
tool mark studies, several aspects are relevant, including
processes of wear and variations regarding tool orientation.
In this context, experimental archaeology may contribute
to the interpretation of tool marks, but further research is
required: for example, regarding questions of individual
variation.
In the current paper, we demonstrated how “basic” and
“comparative tool mark studies” can reveal far-reaching
cultural connections through the analyses of technological
details. The specifc choices the goldsmith made in the
production of non-ferrous metal objects provide us with
valuable information at various levels: ranging from the
metalworking skill (through the background and afliation) of
the craftsperson to micro- and macro-regional metalworking
traditions, which further highlight possible technological
transmissions between distant realms.
The group of gold vessels with “
Stäbchenrankenzier
”
from the “Nagyszentmiklós Treasure” and the gold belt
ornaments from the so-called “Brestovac Hoard” are both
outstanding examples of sheet-gold metalwork from the
Middle and Late Avar Period (7
th
–8
th
centuries AD). Although
qualitative diferences could be established between the
two groups of objects, the exceptionally executed repoussé
technique binds these high-quality gold items together under
the metalworking traditions of “Italo-Byzantine” goldsmith
workshops. Furthermore, other decorative techniques,
like “stippling” and the ring-shaped punch-marks used as
background ornaments, also point towards the important role
of the Mediterranean region in transmitting metalworking
techniques, including motifs and artistic conventions, to the
Avar realm in the Carpathian Basin.
Concerning the decoration technique of punching,
fundamental methodological questions were addressed.
Despite the limited number of punching tools used in this
experiment, the studied tool marks enriched our perspectives
on several aspects of this decorative technique. It was
successfully illustrated how diferent factors could have
an efect on the shape and size of the punched decorations.
In addition, the comparison of tool marks derived from the
same tool increases awareness of the methodological issues
associated with the identifcation of tool marks and their
technological interpretation. The current study, involving
comparative tool mark analyses combined with experimental
archaeology, was a preliminary attempt to expand our
knowledge on the metalworking process of punching.
Given the highly informative results, we aim to pursue well-
grounded research in the future, including experimental
methods on other metalworking techniques as well.
References
ARMBRUSTER, B.R., 2000.
Goldschmiedekunst und Bronzetechnik.
Studien zum Metallhandwerk der Atlantischen Bronzezeit auf der
Iberischen Halbinsel
. Montagnac.
BÁLINT, C., 2010.
Der Schatz von Nagyszentmiklós
. Varia Archaeologica
Hungarica XVIb, Budapest: Ungarische Akademie der Wissenschaften.
BÜHLER, B., 1998–1999. Untersuchungen zu Guß, Oberfächenbearbeitung
und Vergoldung an frühmittelalterlichen Bunt- und
Edelmetallgegenständen.
Archaeologia Austriaca
, 82–83, pp. 429–478.
BÜHLER, B., 2014.
Der „Schatz“ von Brestovac, Kroatien. Seine
kulturellen Beziehungen und technologischen Aspekte.
Monographien
des Römisch-Germanischen Zentralmuseums Mainz, 85, Mainz.
BÜHLER, B. and FREIBERGER, V., 2018. Die Ergebnisse der
goldschmiedetechnischen und chemischen Untersuchungen. In: F. Daim
ed.
Der Goldschatz von Sânnicolau Mare (ungarisch: Nagyszentmiklós).
Monographien des Römisch-Germanischen Zentralmuseums Mainz, 142,
Teil 1, Mainz, pp. 23–201.
BREPOHL, E., 1978.
Theorie und Praxis des Goldschmieds
. 5
th
ed. Leipzig.
DAL, L., 2017.
Scientifc analyses of Sösdala objects.
In: C. Fabech, and
U. Näsman eds.
The Sösdala horsemen – and the equestrian elite of ffth
century Europe.
Jutland Archaeological Publications, 99, Aarhus: Aarhus
University Press, pp. 131–152.
LARSEN, B., 1987.
SEM-Identifcation and Documentation of Tool Marks
and Surface Textures on the Gundestrup Cauldron
. In: J. Black, ed.
Recent Advances in the Conservation and Analysis of Artifacts
. London:
Londons University of London, Institute of Archaeology, pp. 393–408.
MORTIMER, C., STONEY, M., 1997.
A Methodology of Punchmark
image/svg+xml
IANSA 2021 ● XII/1 ● 69–81
Birgit Bühler, Dávid Zsolt Schwarcz: The Comparative Study of Tool Marks on Non-Ferrous Metalwork from Archaeological Contexts: Methodological Considerations,
Case Studies and Experimental Archaeology
81
Analysis Using Electron Microscopy.
In: A. Sinclair, E. Slater, J. Gowlett,
eds.
Archaeological Sciences 1995. Proceedings of a conference on the
application of scientifc techniques to the study of archaeology.
Oxbow
Monograph 64. Oxford (reprint 2017), pp. 119–122.
RICCI, M., 2012.
Rome-Byzantium Afnity and Diference in the Production
of Luxury Goods.
In: B. Böhlendorf, B. Arslan and A. Ricci, eds.
Byzantine Small Finds in Archaeological Contexts
. Byzas, 15, Istambul:
Deutsches Archäologisches Institut, Istanbul, pp. 1–16.
SCOTT, D.S., 1991.
Metallography and Microstructure of Ancient and
Historic Metals
. Singapore: Getty Conservation Institute, J. Paul Getty
Museum.
image/svg+xml