Late Roman archaeology and art-historical sources. ⢠Not much was known about its production organization, nor its connection to the changes in the Roman ...
Evaluation of handheld X-ray fluorescence spectroscopy results of Roman copper alloy brooches by using archaeological typology Vince Van Thienen(1,3), Sylvia Lycke(1,2) and Peter Vandenabeele(1)
(1) Department of Archaeology, Ghent University, Sint-Pietersnieuwstraat 35, UFO, Ghent, Belgium (2) Department of Analytical Chemistry, Ghent University, Krijgslaan 281, S12, Ghent, Belgium (3) Department of Anthropology, Yale University, 51 Hillhouse Avenue, New Haven, CT, USA
INTRODUCTION
METHODOLOGY
• This study is part of the research on the northern periphery of the Late Roman Empire that studied the developements between the 3rd to 5th century in this region1 • The crossbow brooch is a well-known artifact, frequently found in Late Roman archaeology and art-historical sources. • Not much was known about its production organization, nor its connection to the changes in the Roman world2 • The aim was to investigate the composition of these brooches to explore how this could inform us on changes in metal production that reflect the larger socio-cultural changes in the Late Roman world
• Handheld XRF was chosen because the artifacts belong to invaluable collections and a non-destructive, fast, and mobile technique was required • Olympus InnovX Delta handheld X-Ray Fluorescence instrument, spot size 5x5 mm², Rh-anode, silicon-drift detector, air in shielded chamber, 40kV, 79mA, 300 sec live time.
• There are known issues with surface XRF on copper alloy artefacts, including positioning difficulties due to multidimensionality: • Measurements with noticeable effects from corrosion, surface enrichments, and soil contaminations were discarded; • Flat surfaces were located on the underside of the foot (catch) and arms (crossbar with hinge mechanism) and sides of the bow (arch);
MATERIALS
• Multiple measurements per brooch (2-5, depending on fragmentation) to account for the heterogeneity.
• The crossbow brooch has its origin in the 3rd century as a military item, gains status with the rise of the military elites in the 4th century, and becomes a symbol of Roman power and state authority in the 5th century3 • A total of 187 brooches were collected from 12 different sites in Belgium and the Netherlands • The sample population covers the complete typological and stylistic variability between ca. AD 250 and 450 in this region
• Semi-quantitative method4: • No focus on exact compositional information: uncertain how reliable that information would be and uncertain what the actual value is in reconstructing choices made in Antiquity; • Questions are not about exact technological differences, techniques or skills, but about how changes in production relate to changes in the social transformations of Roman life.
Type ‘0’
Type 2
Detail from the Great Hunt mosaic (Villa del Casale, Sicily): Roman soldier or military officer (AD310-340).a
• 3rd century • Cast in mold, possible batch production
• Little decoration and dimensional variation • Part of soldier’s uniform
Detail from the consular diptych depicting the Roman state official Rufius Probianus (ca. AD400).e
Detail from the Sabinus (also Lateran) Sarcophagus (Rome, Italy): Roman military officer with a Pannonian hat (AD315-325).c
• Ca. AD 350-415 decoration types • Mainly working of sheet metal • Production on commission • Continuity of standardized • Symbol for military elite and dimensionality, appearance of new administrative state officials
• Ca. AD 300-365 dimensional variation • Combination casting and working • Military officer’s brooches and • Further increase in decoration and civilian imitations
Type 1 • Ca. AD 280-320 • Increase in decoration and • Casting, working or a combination dimensional variation that was assembled • Common military brooch
Type 5
Type 3/4
Type 6
• Ca. AD 325-410 standardization • Combination casting and working • High-output craft production • Diminished decorative variability • Marker for military and and increased dimensional administrative officers (insignia)
Detail from the Arch of Constantine (Rome, Italy) : Roman military officers with Pannonian hats (AD312-315).b
Detail from the Projecta Casket: Roman official Secundus and his wife (AD350-380).d
RESULTS
• Typological information can be used to move beyond a black box approach of the compositional data:
• The socio-historical changes3 linked to the typological model provides explanations for the compostitional data: • Type 0 and 1 are local and regional productions, possibly batchproduced and intended for the general military class (soldiers and officers); • Type 2 brooches increase in number and variation as the brooch type becomes more frequent and is imitated in non-military productions with larger regional distributions; • Type 3/4 is a (state) controlled large-scale production supplying to the entire Roman army. Despite its larger numbers is this type an outlier to the rest of the typological population by the clearly different role of Zn. It has been suggested that brass production was a monopoly of the Roman state6; • Despite the shift to military elites and high state officials, type 5 and 6 do not appear to have altered in composition, nothwitstanding the increased use of gilding and excessive decoration.
Number of brooches
60 50 40 30
6
• All brooches are made from copper alloys;
4 2
• Minority have precious metal decoration (gilding or silvering);
0 0
1
2
3/4
5
6
• One silver alloy brooch was found;
Type Silver
20
Silvered
Leaf Gilded
Mercury Gilded
• The continuous variation in Zn, Sn, Pb makes it useless to try to allocate modern alloy labels and fails to deliver distinct groupings based on the XRF data alone.
10 0
• A typology is a collection of variables that reflects differences in the material. The distinction between types means that at least one variable is significantly different.
DISCUSSION
70
Number of brooches (n=187)
• Typology is an archaeological tool that contains information about both regionality and chronology
• General compositional results:
Precious metal
80
• Ideally provenance and dating are used to make significant groupings; but often with old finds or museum collections, these are uncertain
• Typological models reflect aspects from both the production and consumption of that material.5 By using typology to clarify analytical data, we insert a number of variables that are most likely to represent conscious or unconscious choices by the producers.
standardized dimensionality • Production on commission • Symbol of state authority and highest elites
Detail from the San Gennaro fresco (Naples, Italy) depicting senator Theotecnus (AD400-500).f
TYPOLOGY AS A VARIABLE
• A single typological variable represents a number of related variables that have a significant meaning about the material.
• Ca. AD 390-460 • Working of sheet metal • Frequent use of precious metal, highly decorated, continuity of
type 0 (n=22)
type 1 (n=34)
type 2 (n=37)
type 3/4 (n=73)
type 5 (n=6)
type 6 (n=7)
INDET (n=8)
Silver alloy
0
1
0
0
0
0
0
Silvered
0
0
0
0
1
0
0
Mercury Gilded
0
1
2
0
0
0
0
Leaf Gilded
1
0
4
4
1
4
0
Copper alloy
21
32
31
69
4
3
8
• Trends and patterns visible with the typological separation (use of net peak intensities): • XRF-spectra indicate a difference in Zn and Sn between types 0-1 and 2-3/4-5-6; • Ternary plot confirms this difference and indicates a general increase in Zn and decrease of Sn between types 0-1 and 2-3/4-5-6. However, a significant overlap remains.
Cu-K1
Cu-K2 Zn-K1
• PCA illustrates a shared general trend that persists through all types, mainly influenced by fluctuations in Sn and Pb, less so of Zn. Only part of the type ¾ population deviates from this main pattern by the increased significance of Zn, although this shift is already visible in type 2. Additionally, to few samples of types 5 and 6 are available to make any statements.
Sn-Ka
Zn-K2
Zn-Ka
Pb-Ka
CONCLUSION • Using typology to interpret compositional data: • Investigates diachronic change and persistence; • Explores regional diversity and similarities; • Adds socio-historical information from archaeological, iconographical and historical sources.
• Ideal method when it is not possible to obtain exact compositional data:
REFERENCES 1.
2.
3.
• Focus on patterns and trends; • Supported by additional layers of information which are object or context related.
• For the Late Roman crossbow brooches, the compositional analysis informed us on7:
4.
• Production organization; • Changes in the producer-consumer relations; • Production choices as the result of changes in the Late Roman society. 5.
This research is part of the project “Decline and Fall? Social and cultural dynamics in the Low Countries in the Late Roman Empire (AD270450)”, financed by the Netherlands Organisation for Scientific Research (NWO) and the Research Foundation – Flanders (FWO) (GA04612N).
6.
Dungworth D., 1997. Roman Copper Alloys: Analysis of Artefacts from Northern Britain, Journal of Archaeological Science 24, 901-910.
7.
Van Thienen V. and Lycke S. (in press) From commodity to singularity: the production of crossbow brooches and the rise of the Late Roman military elite.
Swift E. 2000. Regionality in Dress Accessories in the Late Roman West, Editions Monique Mergoil, Montagnac.
Artwork
Van Thienen V. 2017. A symbol of Late Roman authority revised: a sociohistorical understanding of the crossbow brooch. In: Royamns, Heeren, De Clercq (eds.) 2017. Social dynamics in the northwest frontiers of the Late Roman Empire: beyond decline or transformation, Amsterdam Archaeological Studies, Amsterdam University Press, Amsterdam.
a.
Pensabene P. and Gallocchio E. 2011: The Villa del Casale of Piazza Armerina, in: The magazine of the University of Pennsylvania 53,p. 32.
b.
Photo taken by V. Van Thienen.
c.
Art in the Christian Tradition, a project of the Vanderbilt Divinity Library, Nashville, TN. http://diglib.library.vanderbilt.edu/actimagelink.pl?RC=46406 [retrieved April 21, 2017]
d.
Courtesy of the British Museum, number 1866, 1229,1 AN493408001
e.
Parani M.2007: Defining personal space. Dress and accessories in Late Antiquity. In: Lavan, Swift, Putzeys (eds.) Objects in context. Objects in use (Late Antique Archaeology 5), p. 503.
f.
Courtesy of Getty Images (# 158644825, credit: DEA / A. Dagli Orti)
Asinelli M. G. and Martinón-Torres M. 2016, Copper-alloy use in a Tyrrhenian medieval town: The case of Leopoli-Cencelle (Italy), Journal of Archaeological Science: Reports 7, 597-608; Orfanou and Rehren 2015. A (not so) dangerous method: pXRF vs. EPMA-WDS analyses of copper-based artefacts, Archaeological and Anthropological Sciences 7, 387-397. Caple C. 2006. Objects: reluctant witnesses to the past, Routledge, London/New York.
ACKNOWLEDGEMENTS We would like to thank the following museums and institutes for granting us access to their collections: Gallo-Roman Museum Tongeren; Roman Archaeological Museum, Oudenburg; Flemish Heritage Agency; RAAKVLAK, Brugge; National Museum of Antiquities, Leiden; G.M. Kam Museum, Nijmegen; Archaeological service, Nijmegen
