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Technological characterisation of early Medieval gilded copper hollow pendants (gombiky), from Mikulčice (Moravia) and Prague Castle (Bohemia)

DOI:10.1007/s12520-020-01084-4
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Estelle Ottenwelter at The Czech Academy of Sciences Institute of Archaeology Prague
Estelle Ottenwelter
  • The Czech Academy of Sciences Institute of Archaeology Prague
L. Barčáková
L. Barčáková
L. Barčáková
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Claudie Josse at Centre de Microcaractérisation Raimond Castaing
Claudie Josse
  • Centre de Microcaractérisation Raimond Castaing
L. Robbiola
L. Robbiola
L. Robbiola
  • This person is not on ResearchGate, or hasn't claimed this research yet.
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Abstract and Figures

Gilded copper hollow spherical pendants known as gombiky (s. gombik) were examined to identify the technology of gilding and the material chosen as the substrate. The examined ornaments dating from the ninth and tenth centuries AD were recovered from elite graves of two major political, ecclesiastical and economic centres of the Early Medieval period located in the territory of the present-day Czech Republic: Mikulčice and Prague Castle, major sites of Moravia and Bohemia, respectively. Taking into account the state of degradation and possible bias due to earlier restorations, surface and bulk characterisation of the gilded material has been performed combining optical observation, X-ray radiography, metallography, scanning electron microscopy with energy-dispersive spectrometry (SEM/EDS analysis) and focused ion beam (FIB) milling mounted on FEG-SEM. The manufacturing procedure was reproduced by experimental archaeology. A detailed investigation of the gilded artefacts revealed several types of gombik construction involving different mounted elements, including the main body parts and the suspension system elements joined by hard soldering. The different constitutive parts are made with almost pure copper or low-purity copper. The systematic use of fire gilding (mercury amalgam gilding) was documented. Differences in the materials that were used and technical quality show the coexistence of finely produced objects by highly skilled and knowledgeable jewellers alongside more coarsely manufactured imitations. These variations are discussed in terms of different workshops in a possible relationship with their origin of manufacture.
Ternary system Au-Ag-Cu (after Hauptmann and Klein 2016, Fig. 2 modified) indicating the composition of the gilding layer and the reference Byzantine coin
Ternary system Au-Ag-Cu (after Hauptmann and Klein 2016, Fig. 2 modified) indicating the composition of the gilding layer and the reference Byzantine coin
… 
Polished cross section of available fragments from hemispheres aGombik H115-8. b Smeared solder under the gilding layer, gombik H115-9. c Thick and porous gilding layer on gombik H104-3. d Thick and porous gilding layer, gombik H104-3. e Gilding layer on almost completely mineralised matrix, gombik H84-1. f Gilding layer on almost completely mineralised matrix , gombik H84-1. g Granular structure of the fire-gilded layer in a recess, gombik H108-2. h Polished and etched cross section, gombik 217/š
Polished cross section of available fragments from hemispheres aGombik H115-8. b Smeared solder under the gilding layer, gombik H115-9. c Thick and porous gilding layer on gombik H104-3. d Thick and porous gilding layer, gombik H104-3. e Gilding layer on almost completely mineralised matrix, gombik H84-1. f Gilding layer on almost completely mineralised matrix , gombik H84-1. g Granular structure of the fire-gilded layer in a recess, gombik H108-2. h Polished and etched cross section, gombik 217/š
… 
Detailed observation of fire-gilded layer from FIB cross sections obtained on FEG-SEM and X-ray linescan profiles. a–cGombik H115-9. b–dGombik H84-1
Detailed observation of fire-gilded layer from FIB cross sections obtained on FEG-SEM and X-ray linescan profiles. a–cGombik H115-9. b–dGombik H84-1
… 
Manufacture of a replica of gombik 217/š by the professional goldsmith Ludmila Barčáková. a Chasing of the palmette motive with a narrow chasing tool, note the smeared Ag-Cu hard solder around the joining area. b Working on the edge and plane surface with a planishing tool. c Making the dotted background with a dotting punch. d Removal of the chaser´s pitch. e Insertion of the suspension system in the pierced upper hemisphere. f Soldering of the suspension system on the upper hemisphere
Manufacture of a replica of gombik 217/š by the professional goldsmith Ludmila Barčáková. a Chasing of the palmette motive with a narrow chasing tool, note the smeared Ag-Cu hard solder around the joining area. b Working on the edge and plane surface with a planishing tool. c Making the dotted background with a dotting punch. d Removal of the chaser´s pitch. e Insertion of the suspension system in the pierced upper hemisphere. f Soldering of the suspension system on the upper hemisphere
… 
Studied gombiky. A From Mikulčice. B From Prague Castle, Lumbe´s garden cemetery. A a- gombik 76/š, grave 290-3rd church; b-gombik 129/š, grave 420b-2nd church; c-gombik 190/š, grave 550-3rd church; d-gombik 217/š, grave 625-3rd church; e-gombik 220/š, grave 662-3rd church; f-gombik 110/z, grave 498-3rd church; g-gombik 115/z, grave 508-3 rd church; h-gombik 117/z, grave 508-3 rd church; i-gombik 255/š, grave 43-6th church; j-gombik 26/z , grave 91-2nd church; k-gombik 45/z, grave 141-2nd church. B a-gombik H 104-4; b-gombik H 115-8; c-gombik H108-2; d-gombik H84-1; e-gombik H104-3; f-gombik H99-5; g-gombik H 74B-2; h- gombik H 53-14
+8
Studied gombiky. A From Mikulčice. B From Prague Castle, Lumbe´s garden cemetery. A a- gombik 76/š, grave 290-3rd church; b-gombik 129/š, grave 420b-2nd church; c-gombik 190/š, grave 550-3rd church; d-gombik 217/š, grave 625-3rd church; e-gombik 220/š, grave 662-3rd church; f-gombik 110/z, grave 498-3rd church; g-gombik 115/z, grave 508-3 rd church; h-gombik 117/z, grave 508-3 rd church; i-gombik 255/š, grave 43-6th church; j-gombik 26/z , grave 91-2nd church; k-gombik 45/z, grave 141-2nd church. B a-gombik H 104-4; b-gombik H 115-8; c-gombik H108-2; d-gombik H84-1; e-gombik H104-3; f-gombik H99-5; g-gombik H 74B-2; h- gombik H 53-14
… 
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FOR APPROVAL
ORIGINAL PAPER
Technological characterisation of early Medieval gilded copper
hollow pendants (gombiky), from Mikulčice (Moravia) and Prague
Castle (Bohemia)
E. Ottenwelter
1,2
&L. Barčáková
1
&C. Josse
3
&L. Robbiola
2
&Š.Krupičková
4
&J. Frolík
1
&L. Poláček
4
Received: 6 February 2020 /Accepted: 13 May 2020
#Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
Gilded copper hollow spherical pendants known as gombiky (s. gombik) were examinedto identify the technology of gilding and
the material chosen as the substrate. The examined ornaments dating from the ninth and tenth centuries AD were recovered from
elite graves of two major political, ecclesiastical and economic centres of the Early Medieval period located in the territory of the
present-day Czech Republic: Mikulčice and Prague Castle, major sites of Moravia and Bohemia, respectively. Taking into
account the state of degradation and possible bias due to earlier restorations, surface and bulk characterisation of the gilded
material has been performed combining optical observation, X-ray radiography, metallography, scanning electron microscopy
with energy-dispersive spectrometry (SEM/EDS analysis) and focused ion beam (FIB) milling mounted on FEG-SEM. The
manufacturing procedure was reproduced by experimental archaeology. A detailed investigation of the gilded artefacts revealed
several types of gombik construction involving different mounted elements, including the main body parts and the suspension
system elements joined by hard soldering. The different constitutive parts are made with almostpure copperor low-purity copper.
The systematic use of fire gilding (mercury amalgam gilding) was documented. Differences in the materials that were used and
technical quality show the coexistence of finely produced objects by highly skilled and knowledgeable jewellers alongside more
coarsely manufactured imitations. These variations are discussed in terms of different workshops in a possible relationship with
their origin of manufacture.
Keywords Fire gilding .Hard soldering .Jewellery .Gombik .Manufacturing process .Metallography .SEM/EDS .FIB
FEG-SEM
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s12520-020-01084-4) contains supplementary
material, which is available to authorized users.
*E. Ottenwelter
ottenwelter@arup.cas.cz
*L. Robbiola
robbiola@univ-tlse2.fr
L. Barčáková
barcakova@arup.cas.cz
C. Josse
claudie.josse@ums-castaing.fr
Š.Krupičková
krupickova@arub.cz
J. Frolík
frolik@arup.cas.cz
L. Poláček
polacek@arub.cz
1
Czech Academy of Sciences, Institute of Archaeology, Prague,
Letenská 4, 118 01 Praha 1, Czech Republic
2
TRACES laboratory (CNRS UMR5608), Université de Toulouse,
Maison de la Recherche, 31058 Toulouse Cedex 9, France
3
Centre de Microcaractérisation Raimond Castaing (CNRS UMS
3623), Espace Clement Ader, 3 rue Caroline Aigle,
31400 Toulouse, France
4
Czech Academy of Sciences, Institute of Archaeology, Brno,
Čechyňská 363/19, 602 00 Brno, Czech Republic
Archaeological and Anthropological Sciences _#####################_
https://doi.org/10.1007/s12520-020-01084-4
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... The study focuses on central European gilded copper jewellery, for which fire gilding was largely applied (Ottenwelter, in press). It concerns the fire gilding layers of specific archaeological artefacts found in Bohemia (Lumbe Garden cemetery at Prague Castle): gombiky (spherical hollow pendants) and medallions, characteristic pieces of the elite jewellery from the 9th and 10th centuries AD, detailed in previous studies (Ottenwelter et al., 2014;Ottenwelter et al., 2017;Ottenwelter et al., 2020;Ottenwelter, in press). The use of FIB FEG-SEM allows crosssections to be made and observations performed in situ within the SEM (Johnson et al., 2012;Chiavari et al., 2015;Masi et al., 2016, Masi et al., 2017. ...
... (i) The fragment of gombik H84-1 is a sample from a large gombik (total length: 55.6 mm, diameter: 44 mm - Fig. 1a) its construction is typical of Bohemian pieces, as shown from X-ray radiography (Fig. 1e): a two-hemisphere body and a suspension system made of three components (Ottenwelter et al., 2014;Ottenwelter et al., 2017;Ottenwelter et al., 2020): a loop, a clamp and a ring, in this case also including a small pellet inside the soldered hemispheres. The gombik was highly fragmented when excavated. ...
... In addition to the size of the artefact and the decoration type, which are the basic parameters of comparison, the technical consideration enables the identification of fine products produced by highly skilled and knowledgeable jewellers operating in a courtly environment, and coarse imitations produced by local and less experienced craftsmen (Ottenwelter et al., 2020;Ottenwelter, in press). This technical consideration is mainly linked to the mounting concept, the choice of material (base material, gilding layer, type of solder), the quality of the mounting, soldering, gilding, tool marks as well as the quality of the decoration. ...
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The study of ancient gilding is often problematic, as the gilding layers are soft and prone to deformation during sample preparation. In this respect, focused ion beam (FIB) milling on a field emission gun scanning electron microscope (FEG-SEM) provides poorly invasive in situ sampling. The operating process is here detailed and applied on gilded medieval copper-based elite jewellery (10th century) from Prague Castle. Obtained cross-sections and slices of gilded samples were investigated up to nanometer scale without gilding layer deformation. By coupling structural observation with elemental X-ray analysis (EDS) and electron beam diffraction (EBSD), FIB FEG-SEM provided new data on the physical–chemical characteristics of the gilded layer. The gilding has a two-layer metallurgical structure containing a quaternary Au (Hg, Cu, Ag) alloy corresponding to the gold solid solution fcc phase, and a submicrometric inner sublayer formed by a Au-Cu phase, relative to the interdiffusion of copper from the substrate during the fire gilding process. The applied temperature for gilding can be estimated at c. 400 °C. Sintering of the mercury-gold amalgam globules during the fire heating is highlighted. The precise characterisation of the gilding layers provided useful comparative parameters for identifying fire gilding skill levels and assessing the overall quality of the archaeological pieces.
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... Therefore, the study of unearthed cultural relics is no longer limited to the morphological observations or compositional analysis of the golden surface (Ingo et al. 2007). Instead, it goes deep into the interior of the cultural relics to study the compositional distribution and structural characteristics of the cross-section and the interface between the gold layer and the substrate (Ottenwelter et al. 2020), revealing the forming mechanism of the gold layer during the gilding process . It is worth mentioning that the heating causes phase change of Au-Hg amalgam during the gilding process, thereby forming a gold layer (Jin et al. 2017). ...
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