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The Bronze age amber industry in northern Italy in light of high-resolution 3D imaging

L’industrie de l’ambre à l’âge du Bronze dans le nord de l’Italie à la lumière de l’imagerie 3D haute résolution
Ivana Angelini et Massimo Vidale
p. 237-249

Résumés

Nous résumons ici les résultats préliminaires de l’utilisation expérimentale de l’imagerie 3D haute résolution dans l’étude et la reconstruction de la chaîne opératoire du façonnage des perles d’ambre dans la péninsule du nord de l’Italie au 2e millénaire avant J.-C. L’ambre, étant une matière première exceptionnellement tendre et très sensible à tout type de changement physique et chimique, enregistre un large éventail d’informations archéologiques, presque inimaginable jusqu’à une époque récente. Nous montrons comment l’application du microscope optique-numérique et du microscope confocal laser (LSCM) sur les déchets de fabrication et les perles finies, en tenant compte des interactions avec les traces d’usage post-fabrication, révèle des preuves inattendues sur les phases de l’histoire de vie de la perle, mettant en évidence surtout le rôle important des traitements thermiques de l’ambre avec des outils en métal.

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Notes de la rédaction

rec. juillet 2019; acc. avr. 2021

Texte intégral

The authors would like to thank M. Cupitò (Dep. of Cultural Heritage, University of Padova), N. Carrara (Museum of Anthropology, University of Padova) and E. Bianchin (Archaeological Superintendency of the Veneto Region) for the permission to study the amber beads from Fondo Paviani, Ledro and Este Borgo Canevedo discussed in this paper. Many thanks are also due to S. Buson who cleaned and restored the collection from Este Borgo Canevedo. The authors are indebted with G. Artioli (Dep. of Geosciences, University of Padova) for the access to the LSCM instrument. Conceptualization of the work, data analysis, writing of the paper and revisions are due to both the authors; optical and LSCM analysis were done by I. Angelini, ESEM analysis and palaeotechnological study were made by M. Vidale.

1. Introduction

1Amber is a fossilized tree resin from forests that thrived millions of years ago that can be found in primary or secondary deposits dated from the Carboniferous to the Quaternary period (Langenheim, 1969; Rice, 2006; Kosmowska-Ceramowicz, 2017; Angelini, 2010). Thanks to its extensive use amber provides crucial evidence for trade and contact in European prehistory and later chronological horizons as far back as Neolithic times. To date, the trade of amber ornaments and the relative socio-economic implications of this trade have been intensively studied in terms of typology as well as through chemical characterization, focusing on provenience and long-distance distribution (Angelini, 2010; Beck, 1966, 1970, 1986; Beck et al., 1964, 1965; Angelini et Bellintani, 2005, 2006, 2017; Boon et al., 1993; Maish et al., 2018; Negroni Catacchio et Guerreschi, 1970; Negroni Catacchio, 1972; Bergonzi, 1997; Bellintani et al., 2015; Devoto, 2002; Álvarez-Fernández et al., 2005; Murillo-Barroso et al., 2018; Néraudeau et al., 2011; Teodor et al., 2010; Langenheim, 2005). Archaeometric analysis proved that even if succinite (often simply named Baltic amber) was the major type traded in the past, other sources of amber, such as simetite from South Italy, rumenite from the Coltzi Mountains (Romania) and several varieties of Iberian amber (among others, Beck, 1970, 1986; Álvarez-Fernández et al., 2005; Angelini et Bellintani, 2005, 2017; Peñalver et al., 2007, 2018; Mukherjee et al., 2008; Teodor et al., 2010; Kaur et al., 2012; Odriozola et al., 2019) were also exploited and their products exchanged.

2Today, high-tech investigations of plants and animal remains preserved in amber are a prominent line of paleontological research. However, at present there is no archaeological or literary evidence that reduction of amber lumps was dictated by the presence of such inner fossil inclusions.

3Studies specifically focused on the ancient technologies of amber processing in the study areas and periods are much rarer and still lag behind. In fact, very little is yet known or reported about the chaînes opératoires of the earliest amber beads. In spite of interesting details provided by ancient classical authors, primarily Pliny the Elder (see below), well known Roman amber industrial and craft locations were not studied in great detail to our knowledge.

4Late antique amber beads in the Baltic region were manufactured by combining handmade reduction with cutting and scraping operations and with some form of turning or lathing, while drilling was performed with an “extended bowstring” (Bliujiene, 2011: 92). More information is available for medieval amber and bone bead workshops excavated in England and dated to the 13th-15th centuries AD, when the mass production of amber beads for rosaries supported the economic investments of important craft guilds (Blair & Ramsway, 1991: 270; Mackinney, 2007); lathing was also used for making buttons and ring-like beads (Mead, 1977), while a horizontal device used for drilling was endowed with sharp conical metallic bits (Gottschall, 2008).

5On the Italian peninsula, too, the technologies of pre- and protohistoric amber bead-making have been long neglected in spite of the discovery, in the last decades, of some important amber processing sites dated to the Late Bronze and early Iron ages (summary in Strafella et al., 2017; original reports in Cicirelli, 2007; Salzani, 2011; Bellintani, 2013). In the above-mentioned reports, manufacturing waste and debitage are superficially described and grouped into wide categories, without detailed documentation and observation. The study of important assemblages of industrial amber refuse (Thun Hohenstein et al., 2018), as well as crucial experimental archaeology projects (Lovino, 2015) are still in their infancy.

6A recent paper by the authors (Strafella et al., 2017), in contrast, proposed a comprehensive study of the lifecycle of Bronze age amber beads. By examining the surface of the objects and the use-wear caused by the interaction of strings, cloth and human fingernails, even the level of simple gestures, the study moves backwards to record the original traces of manufacturing (both the negative interfaces left by reductive processes, like grinding/polishing and perforation, and the material residues of other bodies applied to the amber bead).

7Another recent study that follows a similar line of inquiry (Butrimas et al., 2016) reveals the real complexity of amber manufacturing in Europe since its earliest steps: for example, a Neolithic amber disk from the site of Daktariške 5, Lithuania, which was studied chemically (by infrared and Raman spectroscopy) and in traceological terms, revealed that, below the use-wear, its fine decoration had been traced with two different tools, and that its incised patterns had been filled with a mixture of coniferous tree resin, beeswax, and fat, colored with red ochre. It is expected that the application of the same detailed observations to other finds and contexts will reveal comparable technical complexity. Amber is, in fact, a highly sensitive material, capable of retaining important evidence of its manufacturing technologies, but also subject to radical taphonomic transformations. It can be affected by heat and UV radiation, by exposure to saline solution, as well as by cycles of high and low relative humidity. The main chemical degradation in amber is related to the oxidation processes, and particularly to the oxidation of terpenoid components, since oxygen causes de-polymerization, breakdown of terminal unsaturated carbon-carbon bonds, and transformation in acid groups. Mechanical actions such as grinding, cutting, sawing, filing, and drilling on the surface of amber finds are believed to have a further impact. Both acidic and alkaline pH conditions are active factors that can cause aggressive chemical processes and surface deterioration, particularly when micro-environmental niches change from strongly basic to slightly acidic conditions, as normally happens with the decomposition of buried human bodies. A summary of the decay processes affecting amber finds includes acidic hydrolysis, saponification of ester in alkaline conditions, thermal- and photo-oxidation of terpenoids, depolymerization of surfaces and cores, decomposition of terpenoids, and production of volatile organic acids (Beck, 1986; Beck et al., 1965; Pastorelli, 2009; Urbanski, 1971; Thickett et al., 1995; Pastorelli et al., 2012; Bisulca et al., 2012).

8After such processes, the surface of amber finds may be affected by bleaching, micro-cracking, swelling and detachment. Discontinuous and diversely altered patches may occur across the same surfaces, and react differently under the various types and sources of light we may apply for direct observation. “[…] In general, deterioration manifests itself as a thick ‘corrosion’ crust that not only obscures the translucent quality of amber but may also lead to flaking and loss of the carved surface. In the worst-case scenarios, the carved surface completely flakes off, leaving an ambiguously shaped amber core” (Maish et al., 2018, Technical Essay).

9This latter description is quite appropriate, because such damaged “cores”, thus transformed, bear little or no interest for the paleo-technological investigation of ancient amber industries: the loss of the original surface, in fact, destroys any possible residual evidence of manufacturing traces (i.e. reduction, abrasion, polishing and perforation) which may have survived on the original amber waste fragments.

10This contribution focuses on the study of manufacturing traces (or tracéologie) for the reconstruction of amber bead production by means of techniques commonly used in this kind of research, such as optical microscopy and silicone casts, observation with Environmental Scanning Electron Microscopy (ESEM), but also by new applications of an advanced technique: Laser Scanning Confocal Microscopy (LSCM). ESEM microscopy is widely used for investigating the surface micromorphology of various classes of materials, but rarely, so far, for amber (Strafella et al., 2017). On this material, secondary electron (SE) images are useful for observing manufacturing evidence in limited areas, but they can hardly be used for a general 3D mapping of the whole object. Moreover, they don’t provide the means to link morphology to the actual physical features of the material (color, opacity, transparency, inclusions). This potential, in contrast, is fully granted by LSCM. Moreover, LSCM increases the resolution to 10-100 nm (see below) whereas other techniques potentially applicable to the study of both bulk and micro-archaeological surfaces (i.e. X-ray tomography) need to be performed with lower resolutions, generally in the order of 10-50 µm, in order to be applied to entire objects. This last technique, or other advanced imaging techniques performed with synchrotron sources, however, are very useful for the study of inclusions in amber, as is currently done in paleontological studies (Coty et al., 2014; Georgiu et al., 2019). Moreover, to be meaningful, the study of manufacturing traces on the surface of amber objects needs to be carried out on significant numbers of items, therefore with fast and lower cost laboratory techniques.

2. Materials and methods

11For the first steps of this research, we studied three small collections of amber finds coming from different sites (Figure 1) and chronological periods. The first, and oldest, collection includes only finished beads recovered from the uppermost levels (IV-I) of the pile-dwelling site of Lake Ledro, in the Trentino mountain region of northern Italy. These are dated from the middle of the Early Bronze to the beginning of the middle Bronze age (c. 2000-1700 BC). The artifacts are currently stored at the Museum of Anthropology of the University of Padua. Secondly, we studied a small group of beads from Fondo Paviani, in the Basso Veronese plains, the central place of the so-called Valli Grandi Veronesi polity, which is datable to the middle of the Late Bronze age (c. 1300-1200 BC) (Strafella et al., 2017).

Figure 1: A map of northern Italy, showing the location of the three sites (Ledro, Fondo Paviani, and Este Borgo Canevedo) where the amber beads and manufacturing waste discussed in this work were found / Figure 1 : Carte du nord de l’Italie, montrant l’emplacement des trois sites (Ledro, Fondo Paviani et Este Borgo Canevedo) où les perles d’ambre et les déchets de fabrication objet de ce travail ont été trouvés

Figure 1: A map of northern Italy, showing the location of the three sites (Ledro, Fondo Paviani, and Este Borgo Canevedo) where the amber beads and manufacturing waste discussed in this work were found / Figure 1 : Carte du nord de l’Italie, montrant l’emplacement des trois sites (Ledro, Fondo Paviani et Este Borgo Canevedo) où les perles d’ambre et les déchets de fabrication objet de ce travail ont été trouvés

12The third collection, at the National Archaeological Museum of Este (Padova, Italy), is formed by 12 amber finds, all manufacturing waste fragments, that come from a small test trench dug in the site of Borgo Canevedo, the most ancient settlement core of the ancient Venetic center of Este. The site is preliminarily dated to late Bronze/early Iron age, i.e. c. to the 11th-10th centuries BC. The assemblages we examined thus opened three windows, discontinuous but meaningful, on the processing technology of amber beads in the northern Italian peninsula through the 2nd millennium BC.

13For the sites of Ledro and Fondo Paviani, provenience analysis by Infrared Spectroscopy performed on coeval amber specimens revealed a Baltic origin (Angelini & Bellintani, 2005, 2006; Strafella et al., 2015). The analysis for Borgo Canevedo is currently ongoing.

14The amber surfaces of the three collections were first observed with a binocular microscope, carefully cleaned, and restored. Thanks to the very good state of preservation of the amber, it was possible to obtain silicone casts of the holes of the beads of the first collection by coating the holes’ surface with a water solution with a low percentage surfactant. Then, the silicone casts were examined with an Environmental Scanning Electron Microscope (ESEM), at the Istituto Superiore per la Conservazione e il Restauro (ISCR) labs in Rome. A set of secondary electron (SE) images were collected at low magnification (20-60X) with a Zeiss EBO 60 instrument using a 15-20 mm working distance and 20 kV. This technique, originally adapted from silicone casting in dentistry, has a long history in archaeological bead studies (among others, Gwinnet & Gorelick, 1981, 1991, 2008; Kenoyer & Vidale, 1992; de Mille et al., 2008; Kenoyer, 2011; Lume Pereira, 2017; Uesugi et al., 2018).

15The artifacts were observed in detail at the Departments of Cultural Heritage and Geosciences, University of Padua, with two different type of microscopies in order to record high resolution 3D images:

  • an opto-digital Olympus DSX500, with magnification in the range of 5-40× (images and results in Strafella et al., 2017);

  • a laser scanning confocal microscope (LSCM) Lext OLS4000, by Olympus, that is also coupled with the conventional opto-digital system, working with reflected light and always with a confocal system (see Sheppard & Shotton, 1997; Stemp & Chung, 2011; Stemp et al., 2013; Pitzalis et al., 2008). The instrument is equipped with a 405 nm laser, 4 lenses (5×, 10×, 20×, 50×) and is capable of resolving features 10 nm in size in the Z direction and 120 nm in the x-y plane. This allowed us to combine to the images and 3D models obtained by laser scanning with the optical images of the amber surfaces, in their real colors. We thus overcame great part of the problems caused by the various states of conservation of the amber finds, often co-present in the same objects, and the related incidence of transparency and reflections.

3. Results: visualizing surface conservation, reduction and use-wear traces

16Confocal 3D digital microscopy is a powerful tool for observing micromorphological features due to reduction processes, both in the course of manufacturing and in the subsequent wear and post-depositional alteration phases of the beads’ biography; integrated by LSCM imagery in a very effective way, as an alternative and often determinant source of information.

17In Figure 2, we show the optical image of the surface of one of the lumps from Borgo Canevedo from the confocal 3D microscope. Figure 2b is a laser LSCM image of the same find. When compared with Figure 2a, it immediately reveals the advanced state of decay of the surface of the amber lump, which, as a consequence, is practically worthless for paleo-technological study. The original surface is present only in a narrow strip in the center of the find (b), and due to the corrosion of the surface, and the high reflectivity of the amber, this is hardly recognizable with optical observation (a).

Figure 2: Digital 3D optical image (A) compared to a laser LSCM image (B) of an amber lump from the workshop site of Este Borgo Canevedo (Padova, Italy, 11th-10th century BC). A) enhances the fall of great part of the original surface of the object, now useless for the study of ancient manufacturing traces / Figure 2 : L’image optique 3D numérique (A) comparée à l’image laser LSCM (B) d’un morceau d’ambre de l’atelier d’Este Borgo Canevedo (Padoue, Italie, xie-xe siècle av. J.-C.). A) Perte d’une grande partie de la surface d’origine de l’objet, désormais inutile pour l’étude de traces de fabrication anciennes

Figure 2: Digital 3D optical image (A) compared to a laser LSCM image (B) of an amber lump from the workshop site of Este Borgo Canevedo (Padova, Italy, 11th-10th century BC). A) enhances the fall of great part of the original surface of the object, now useless for the study of ancient manufacturing traces / Figure 2 : L’image optique 3D numérique (A) comparée à l’image laser LSCM (B) d’un morceau d’ambre de l’atelier d’Este Borgo Canevedo (Padoue, Italie, xie-xe siècle av. J.-C.). A) Perte d’une grande partie de la surface d’origine de l’objet, désormais inutile pour l’étude de traces de fabrication anciennes

18In Figure 3, one sees a manufacturing flake (actually, a residue of the cortex of the original amber nodule) from the same Borgo Canevedo workshop assemblage, as it appears in the optical image from the confocal 3D microscope. The photo in Figure 3b shows the same flake as it appears in the laser LSCM recording. This latter image, which fully eliminates the effects of reflection and transparency, enhances the features of a conchoidal fracture, namely the concentric waves produced by the impact of a hard punch, and the direction of the blow. This flake was detached by what in prehistoric lithic technology is called indirect or pressure flaking by the means of a hard punch, which was evidently applied as a primary forming process. The hypothesis that this technique played a major role in the preliminary reduction of Bronze age amber lumps needs to be carefully considered with the available evidence from known ancient craft areas.

Figure 3: Digital 3D optical image (A) matched with a laser LSCM image (B) of the ventral side of an amber cortical flake from the workshop area of Este Borgo Canevedo (Padova, Italy, 11th-10th century BC). The concentric percussion waves typical of knapped flint flakes and blades show the direction of the blows. This and similar flakes, apparently abundant in Bronze age amber beads production contexts, seem to have been detached by the means of indirect percussion or pressure flaking, perhaps using a hard-pointed punch in copper, antler or bone / Figure 3 : Image optique 3D numérique (A) associée à une image laser LSCM (B) de la face ventrale d’une lamelle corticale d’ambre de l’atelier d’Este Borgo Canevedo (Padoue, Italie, xie-xe siècle av. J.-C.). Les ondes concentriques typiques des lamelles de silex taillées indiquent la direction des coups. Ces lamelles et autres similaires, apparemment abondantes dans la production de perles d’ambre de l’âge du bronze, semblent avoir été détachés par percussion indirecte ou écaillage sous pression, avec un poinçon à pointe dure en cuivre, velours de bois ou os

Figure 3: Digital 3D optical image (A) matched with a laser LSCM image (B) of the ventral side of an amber cortical flake from the workshop area of Este Borgo Canevedo (Padova, Italy, 11th-10th century BC). The concentric percussion waves typical of knapped flint flakes and blades show the direction of the blows. This and similar flakes, apparently abundant in Bronze age amber beads production contexts, seem to have been detached by the means of indirect percussion or pressure flaking, perhaps using a hard-pointed punch in copper, antler or bone / Figure 3 : Image optique 3D numérique (A) associée à une image laser LSCM (B) de la face ventrale d’une lamelle corticale d’ambre de l’atelier d’Este Borgo Canevedo (Padoue, Italie, xie-xe siècle av. J.-C.). Les ondes concentriques typiques des lamelles de silex taillées indiquent la direction des coups. Ces lamelles et autres similaires, apparemment abondantes dans la production de perles d’ambre de l’âge du bronze, semblent avoir été détachés par percussion indirecte ou écaillage sous pression, avec un poinçon à pointe dure en cuivre, velours de bois ou os

19The study of wear patterns (particularly those concerning the interaction between the beads with strings, and among strung beads) currently represent an important matter of study in the biography of ancient beads (Guzzo Falci, 2015; Guzzo Falci et al., 2019). The high-resolution 3D images in Figure 4a, recorded by the opto-digital microscope, show wear traces on an amber button from Fondo Paviani. The perfectly preserved surface retained easily recognizable traces of the asymmetrical friction of the string at the point of contact between the holes and the flat lower surface of the ornament, compatible with its use as button (Strafella et al., 2017). On the edge of the same button, the details of Figures 4b and 4c, a scar made by multiple microscopic conchoidal fractures, continuously worn by the contact with a soft medium (probably cloth), suggests a repeated contact between the button and another hard object with which the amber item was in prolonged contact.

Figure 4: Digital 3D optical image of a well preserved amber conical button from the site of Fondo Paviani (Verona, Italy, c. 1300-1200 BC), viewed from the basal side. Note in A) the eccentric wear left by the string on the edge of both holes, when the button was levered from a side. In B) and C), digital 3D optical images shows details of a multiple micro-flaked scar on the edge of the same button. The conchoidal microfractures are due to repeated impacts in the same position, while uniform wear shows that this happened while the button was also interacting with a soft surface (cloth or leather) / Figure 4 : Image optique 3D numérique d’un bouton d’ambre conique bien conservé provenant du site du Fonds Paviani (Vérone, Italie, vers 1300-1200 av. J.-C.), vu de la base. A) Montre l’usure excentrique lorsque le bouton a été travaillé latéralement. En B) et C), les images optiques 3D numériques montrent les détails d’une cicatrice à écaillages multiples sur le bord. Les micro-fractures conchoïdales sont dues aux impacts répétés dans la même position, tandis que l’usure uniforme montre que cela s’est produit alors que le bouton interagissait également avec une surface douce (tissu ou cuir)

Figure 4: Digital 3D optical image of a well preserved amber conical button from the site of Fondo Paviani (Verona, Italy, c. 1300-1200 BC), viewed from the basal side. Note in A) the eccentric wear left by the string on the edge of both holes, when the button was levered from a side. In B) and C), digital 3D optical images shows details of a multiple micro-flaked scar on the edge of the same button. The conchoidal microfractures are due to repeated impacts in the same position, while uniform wear shows that this happened while the button was also interacting with a soft surface (cloth or leather) / Figure 4 : Image optique 3D numérique d’un bouton d’ambre conique bien conservé provenant du site du Fonds Paviani (Vérone, Italie, vers 1300-1200 av. J.-C.), vu de la base. A) Montre l’usure excentrique lorsque le bouton a été travaillé latéralement. En B) et C), les images optiques 3D numériques montrent les détails d’une cicatrice à écaillages multiples sur le bord. Les micro-fractures conchoïdales sont dues aux impacts répétés dans la même position, tandis que l’usure uniforme montre que cela s’est produit alors que le bouton interagissait également avec une surface douce (tissu ou cuir)

4. Prehistoric heat treatments of polymers

20An important result in the samples that we analyzed was the discovery that amber beads that circulated in the Po river plains (northern Italy) during the 2nd millennium BC were not only perforated with stone or metallic drills-heads, as commonly assumed, but also with red-hot copper punches. Figure 5 offers a detail of the perforation of a bead from Fondo Paviani: in the hole, the optical 3D digital image distinctively shows a burnt orthogonal grid of cracks made by a red-hot punch, while Figure 6 shows an ESEM image of the positive silicon cast of a similar hole in an amber bead from Ledro, spared by the lateral friction of the string on which the bead was fixed. The same perforation technique was also identified in the amber bow of a brooch from the Iron age cemetery of Vace, Slovenia (at present at the Museum of Anthropology, University of Padua) (Figures 7 and 8). This suggests that, after its introduction, hot copper punch perforation of amber was applied for more than a millennium (and probably up to Roman times).

Figure 5: Detail of the split perforation canal of a bead from Fondo Paviani, in a digital 3D optical image (Verona, Italy, c. 1300-1200 BC). Note the partially burnt inner surface, where the use of a red hot copper punch created a distinctive orthogonal grid of carbonized cracks / Figure 5 : Détail du canal de perforation divisé de la perle du Fondo Paviani, dans une image optique 3D numérique (Vérone, Italie, vers 1300-1200 av. J.-C.). Notez la surface interne partiellement brûlée, où l’utilisation d’un poinçon en cuivre chauffé au rouge a créé une grille orthogonale distincte de fissures carbonisées

Figure 5: Detail of the split perforation canal of a bead from Fondo Paviani, in a digital 3D optical image (Verona, Italy, c. 1300-1200 BC). Note the partially burnt inner surface, where the use of a red hot copper punch created a distinctive orthogonal grid of carbonized cracks / Figure 5 : Détail du canal de perforation divisé de la perle du Fondo Paviani, dans une image optique 3D numérique (Vérone, Italie, vers 1300-1200 av. J.-C.). Notez la surface interne partiellement brûlée, où l’utilisation d’un poinçon en cuivre chauffé au rouge a créé une grille orthogonale distincte de fissures carbonisées

Figure 6: SE-SEM image of a silicon cast of an amber bead from the pile-dwelling site of Ledro (c. 2000-1700 BC). Because of the eccentric bipolar perforation, the intensive wearing-off of the hole due to the string on which the bead was fixed spared the trace left by the hot copper punch. Note the identity (although in positive) of the grid-like trace of this cast with the pattern visible on the later amber bead from Fondo Paviani (in Figure 5) / Figure 6 : Image SE-SEM d’un moulage en silicone d’une perle d’ambre provenant de Ledro (vers 2000-1700 av. J.-C.). En raison de la perforation bipolaire excentrique, l’usure intensive du trou, due à la corde sur laquelle la perle a été fixée, n’a pas modifié la trace, faite à l’origine par la perforation du poinçon de cuivre chaud. Notez l’identité (bien qu’en positif) de la trace en forme de grille de ce moulage avec le motif visible sur la dernière perle d’ambre du Fondo Paviani (dans la figure 5)

Figure 6: SE-SEM image of a silicon cast of an amber bead from the pile-dwelling site of Ledro (c. 2000-1700 BC). Because of the eccentric bipolar perforation, the intensive wearing-off of the hole due to the string on which the bead was fixed spared the trace left by the hot copper punch. Note the identity (although in positive) of the grid-like trace of this cast with the pattern visible on the later amber bead from Fondo Paviani (in Figure 5) / Figure 6 : Image SE-SEM d’un moulage en silicone d’une perle d’ambre provenant de Ledro (vers 2000-1700 av. J.-C.). En raison de la perforation bipolaire excentrique, l’usure intensive du trou, due à la corde sur laquelle la perle a été fixée, n’a pas modifié la trace, faite à l’origine par la perforation du poinçon de cuivre chaud. Notez l’identité (bien qu’en positif) de la trace en forme de grille de ce moulage avec le motif visible sur la dernière perle d’ambre du Fondo Paviani (dans la figure 5)

Figure 7: A large amber bead originally fixed on the bow of a large brooch from the Iron age cemetery of Vace in Slovenia (7th-6th century BC) / Figure 7 : Une grosse perle d’ambre à l’origine fixée sur l’arc d’une grande broche dans le cimetière de l’âge de fer de Vace en Slovénie (viie-vie siècle avant J.-C.)

Figure 7: A large amber bead originally fixed on the bow of a large brooch from the Iron age cemetery of Vace in Slovenia (7th-6th century BC) / Figure 7 : Une grosse perle d’ambre à l’origine fixée sur l’arc d’une grande broche dans le cimetière de l’âge de fer de Vace en Slovénie (viie-vie siècle avant J.-C.)

Figure 8: SE-SEM detail of a silicone cast of the hole in the amber ornament of Figure 7. Note the presence of a orthogonal grid of heat-produced cracks similar to those discussed in the Bronze age amber beads of Figures 5 and 6. The long hole within this large bead was made by pressing the hot punch with minor axial deviations, resulting in the winding structure visible in the image / Figure 8 : Détail SE-SEM d’un moulage en silicone du trou dans l’ornement en ambre de la figure 10. Noter la présence d’une grille orthogonale de fissures thermiques similaires à celles décrites dans les perles d’ambre de l’âge de Bronze des figures 5 et 6. Le long trou dans cette grosse perle a été réalisé en appuyant sur le poinçon chaud avec des déviations axiales mineures, ce qui a pour effet de rendre la structure tortueuse visible sur l’image

Figure 8: SE-SEM detail of a silicone cast of the hole in the amber ornament of Figure 7. Note the presence of a orthogonal grid of heat-produced cracks similar to those discussed in the Bronze age amber beads of Figures 5 and 6. The long hole within this large bead was made by pressing the hot punch with minor axial deviations, resulting in the winding structure visible in the image / Figure 8 : Détail SE-SEM d’un moulage en silicone du trou dans l’ornement en ambre de la figure 10. Noter la présence d’une grille orthogonale de fissures thermiques similaires à celles décrites dans les perles d’ambre de l’âge de Bronze des figures 5 et 6. Le long trou dans cette grosse perle a été réalisé en appuyant sur le poinçon chaud avec des déviations axiales mineures, ce qui a pour effet de rendre la structure tortueuse visible sur l’image

21When exactly did the use of stone drills on amber, coexist with or get replaced by the use of red-hot copper punches, a prehistoric example of advanced heat treatment of polymers that made the perforation of amber beads a faster and more “industrial” process in Europe (Mainman & Rogers, 2000; definitions and contemporary scenarios in Aly, 2015)? Another issue is that the partial burning of the beads’ holes had as the side effect an unpleasant darkening of the core of the beads (as for example in Figure 5). We suspect that this condition might have required other kinds of amber pyro-technological treatments, namely boiling the beads in the fat of piglets along with dye plants, a technique mentioned by Pliny the Elder in his Naturalis Historia, Book XXXVII, 46 and 48 (Strafella et al., 2017: 154). In our preliminary experiments, four pieces of succinite with different degrees of translucency were plunged in solid pig fat and heated in a metal container on a bonfire. The temperature was slowly increased up to the melting point of the fat (about in the range of 40-50 °C) and then boiled for 7-8 minutes. The amber pieces were then extracted and cleaned. The results clearly show that simple boiling in fat may give light orange, transparent amber reddish shadows, diminishing its transparency (and thus concealing any possible inner darker phase). In this light, a defect brought on by an important pyro-technical innovation may have promoted the intensification of heat-treatment experiments, and the discovery of new solutions.

22Finally, another open question is the possible use of red-hot copper or iron blades for preliminarily shaping the amber nodules and lumps, a hypothesis currently emerging from our paleo-technological case studies. Knives were certainly used to cut amber in the medieval workshops of England, where they might have been particularly suitable to carve truncated-pyramidal pendants, crosses and other items with flat faces (Mainman & Rogers, 2000: 2501). Once the principle of hot-working had been successfully practiced with the intensifying the use of copper punches, red-hot copper blades might also have been tested. In fact, some of the amber lumps from Borgo Canevedo show parallel flat faces that are compatible with the uses of copper knives in reduction. Figure 9 shows the combined use of laser (9b) and optical (9a) images recorded by LSCM on a lump found at Borgo Canevedo, Este (Padova). The parallel, longitudinal faces may be due to knife reduction, but are distinguished by a heavy surface decay. However, the laser LSCM image (Figure 9b) not only has a much greater resolution than the optical 3D one (Figure 9a), but also reveals some unexpected features.

Figure 9: An amber lump from the workshop area of Este Borgo Canevedo (Padova, Italy, 11th-10th century BC). A) a Digital 3D optical image, showing a series of parallel flat reduction planes, possibly obtained by the means of a blade. B) Laser LSCM image of the same amber lump / Figure 9 : Un morceau d’ambre de la zone d’atelier de Este Borgo Canevedo (Padoue, Italie, xie-xe siècle av. J.-C.). A) Image optique 3D numérique, montrant quatre plans de réduction plats parallèles, éventuellement obtenus au moyen d’une lame. B) Image Laser LSCM du même morceau d’ambre

Figure 9: An amber lump from the workshop area of Este Borgo Canevedo (Padova, Italy, 11th-10th century BC). A) a Digital 3D optical image, showing a series of parallel flat reduction planes, possibly obtained by the means of a blade. B) Laser LSCM image of the same amber lump / Figure 9 : Un morceau d’ambre de la zone d’atelier de Este Borgo Canevedo (Padoue, Italie, xie-xe siècle av. J.-C.). A) Image optique 3D numérique, montrant quatre plans de réduction plats parallèles, éventuellement obtenus au moyen d’une lame. B) Image Laser LSCM du même morceau d’ambre

23In fact, its surfaces are studded with microscopic flecks of charcoal, up to c. 0.5 × 2 mm wide (Figure 10a-10b) that seem to have been pressed into the amber lump’s surfaces while these latter were exposed to heat and in a locally softened state, possibly while the lump was shaped by the means of a red-hot blade. The false colors picture of Figure 10c confirms that the carbon particle impressions on the amber surfaces are preserved in undercuts (blue areas), and an optical image recorded at high magnification shows the impression of the cellular structure of charcoal in the amber (Figure 10d, in the red square). However, this observation is preliminary, and we will need more case studies, and a better understanding of the physical transformations of amber in similar burial microenvironments, to substantiate the proposed interpretation.

Figure 10: The Laser LSCM image of the same amber lump (A). The detail in B) enhances one of the micro-fragments of charcoal included on surface, apparently while this latter was in a state of partial viscosity. The evidence is interpreted as supporting the use of a red-hot copper blade in the stages of the lump’s reduction. C) is a deep profile image of another side of the same amber lump, in fake colors, representing the relative depth (left) aside E, a laser LSCM image of the same view. In the red rectangle, D) is a magnification of some charcoal prints / Figure 10 : A) L’image Laser LSCM du même morceau d’ambre. Le détail en B) fait ressortir l’un des micro-fragments de charbon sur la surface, apparemment quand elle était dans un état de viscosité partielle. Ces éléments sont interprétés comme preuve de l’utilisation d’une lame de cuivre chauffé au rouge dans les phases de la réduction du morceau. C) Une image de profil profond d’un autre côté du même morceau d’ambre, dans de fausses couleurs, représentant la profondeur relative (à gauche) du côté E. Une image au laser LSCM de la même vue. Dans le rectangle rouge, D) montre un agrandissement de traces de charbon

Figure 10: The Laser LSCM image of the same amber lump (A). The detail in B) enhances one of the micro-fragments of charcoal included on surface, apparently while this latter was in a state of partial viscosity. The evidence is interpreted as supporting the use of a red-hot copper blade in the stages of the lump’s reduction. C) is a deep profile image of another side of the same amber lump, in fake colors, representing the relative depth (left) aside E, a laser LSCM image of the same view. In the red rectangle, D) is a magnification of some charcoal prints / Figure 10 : A) L’image Laser LSCM du même morceau d’ambre. Le détail en B) fait ressortir l’un des micro-fragments de charbon sur la surface, apparemment quand elle était dans un état de viscosité partielle. Ces éléments sont interprétés comme preuve de l’utilisation d’une lame de cuivre chauffé au rouge dans les phases de la réduction du morceau. C) Une image de profil profond d’un autre côté du même morceau d’ambre, dans de fausses couleurs, représentant la profondeur relative (à gauche) du côté E. Une image au laser LSCM de la même vue. Dans le rectangle rouge, D) montre un agrandissement de traces de charbon

5. Conclusions

24The combination of optical digital and laser scanning confocal microscopy (LSCM) techniques to amber manufacturing waste and unfinished and/or discarded beads is a quite valid and promising approach to the study of the chaîne opératoire of amber ornaments’ processing, a topic that has been rather neglected in Italy to date. These two independent analytical techniques counteract the problems caused by the transparency and reflectivity of amber finds, and thus integrate with more traditional and consolidated techniques, such as observation at the stereoscopic microscope (eventually followed by manual drawing at a larger scale) and scanning electron microscopy (SEM, ESEM). The hypothesis that prehistoric heat treatments of amber were applied in Europe as early as the end of the Neolithic (c. 4000-3000 BC) is one of the intriguing fields of research that may emerge from this study.

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Table des illustrations

Titre Figure 1: A map of northern Italy, showing the location of the three sites (Ledro, Fondo Paviani, and Este Borgo Canevedo) where the amber beads and manufacturing waste discussed in this work were found / Figure 1 : Carte du nord de l’Italie, montrant l’emplacement des trois sites (Ledro, Fondo Paviani et Este Borgo Canevedo) où les perles d’ambre et les déchets de fabrication objet de ce travail ont été trouvés
URL http://journals.openedition.org/archeosciences/docannexe/image/8024/img-1.jpg
Fichier image/jpeg, 506k
Titre Figure 2: Digital 3D optical image (A) compared to a laser LSCM image (B) of an amber lump from the workshop site of Este Borgo Canevedo (Padova, Italy, 11th-10th century BC). A) enhances the fall of great part of the original surface of the object, now useless for the study of ancient manufacturing traces / Figure 2 : L’image optique 3D numérique (A) comparée à l’image laser LSCM (B) d’un morceau d’ambre de l’atelier d’Este Borgo Canevedo (Padoue, Italie, xie-xe siècle av. J.-C.). A) Perte d’une grande partie de la surface d’origine de l’objet, désormais inutile pour l’étude de traces de fabrication anciennes
URL http://journals.openedition.org/archeosciences/docannexe/image/8024/img-2.jpg
Fichier image/jpeg, 903k
Titre Figure 3: Digital 3D optical image (A) matched with a laser LSCM image (B) of the ventral side of an amber cortical flake from the workshop area of Este Borgo Canevedo (Padova, Italy, 11th-10th century BC). The concentric percussion waves typical of knapped flint flakes and blades show the direction of the blows. This and similar flakes, apparently abundant in Bronze age amber beads production contexts, seem to have been detached by the means of indirect percussion or pressure flaking, perhaps using a hard-pointed punch in copper, antler or bone / Figure 3 : Image optique 3D numérique (A) associée à une image laser LSCM (B) de la face ventrale d’une lamelle corticale d’ambre de l’atelier d’Este Borgo Canevedo (Padoue, Italie, xie-xe siècle av. J.-C.). Les ondes concentriques typiques des lamelles de silex taillées indiquent la direction des coups. Ces lamelles et autres similaires, apparemment abondantes dans la production de perles d’ambre de l’âge du bronze, semblent avoir été détachés par percussion indirecte ou écaillage sous pression, avec un poinçon à pointe dure en cuivre, velours de bois ou os
URL http://journals.openedition.org/archeosciences/docannexe/image/8024/img-3.jpg
Fichier image/jpeg, 963k
Titre Figure 4: Digital 3D optical image of a well preserved amber conical button from the site of Fondo Paviani (Verona, Italy, c. 1300-1200 BC), viewed from the basal side. Note in A) the eccentric wear left by the string on the edge of both holes, when the button was levered from a side. In B) and C), digital 3D optical images shows details of a multiple micro-flaked scar on the edge of the same button. The conchoidal microfractures are due to repeated impacts in the same position, while uniform wear shows that this happened while the button was also interacting with a soft surface (cloth or leather) / Figure 4 : Image optique 3D numérique d’un bouton d’ambre conique bien conservé provenant du site du Fonds Paviani (Vérone, Italie, vers 1300-1200 av. J.-C.), vu de la base. A) Montre l’usure excentrique lorsque le bouton a été travaillé latéralement. En B) et C), les images optiques 3D numériques montrent les détails d’une cicatrice à écaillages multiples sur le bord. Les micro-fractures conchoïdales sont dues aux impacts répétés dans la même position, tandis que l’usure uniforme montre que cela s’est produit alors que le bouton interagissait également avec une surface douce (tissu ou cuir)
URL http://journals.openedition.org/archeosciences/docannexe/image/8024/img-4.jpg
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Titre Figure 5: Detail of the split perforation canal of a bead from Fondo Paviani, in a digital 3D optical image (Verona, Italy, c. 1300-1200 BC). Note the partially burnt inner surface, where the use of a red hot copper punch created a distinctive orthogonal grid of carbonized cracks / Figure 5 : Détail du canal de perforation divisé de la perle du Fondo Paviani, dans une image optique 3D numérique (Vérone, Italie, vers 1300-1200 av. J.-C.). Notez la surface interne partiellement brûlée, où l’utilisation d’un poinçon en cuivre chauffé au rouge a créé une grille orthogonale distincte de fissures carbonisées
URL http://journals.openedition.org/archeosciences/docannexe/image/8024/img-5.jpg
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Titre Figure 6: SE-SEM image of a silicon cast of an amber bead from the pile-dwelling site of Ledro (c. 2000-1700 BC). Because of the eccentric bipolar perforation, the intensive wearing-off of the hole due to the string on which the bead was fixed spared the trace left by the hot copper punch. Note the identity (although in positive) of the grid-like trace of this cast with the pattern visible on the later amber bead from Fondo Paviani (in Figure 5) / Figure 6 : Image SE-SEM d’un moulage en silicone d’une perle d’ambre provenant de Ledro (vers 2000-1700 av. J.-C.). En raison de la perforation bipolaire excentrique, l’usure intensive du trou, due à la corde sur laquelle la perle a été fixée, n’a pas modifié la trace, faite à l’origine par la perforation du poinçon de cuivre chaud. Notez l’identité (bien qu’en positif) de la trace en forme de grille de ce moulage avec le motif visible sur la dernière perle d’ambre du Fondo Paviani (dans la figure 5)
URL http://journals.openedition.org/archeosciences/docannexe/image/8024/img-6.jpg
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Titre Figure 7: A large amber bead originally fixed on the bow of a large brooch from the Iron age cemetery of Vace in Slovenia (7th-6th century BC) / Figure 7 : Une grosse perle d’ambre à l’origine fixée sur l’arc d’une grande broche dans le cimetière de l’âge de fer de Vace en Slovénie (viie-vie siècle avant J.-C.)
URL http://journals.openedition.org/archeosciences/docannexe/image/8024/img-7.jpg
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Titre Figure 8: SE-SEM detail of a silicone cast of the hole in the amber ornament of Figure 7. Note the presence of a orthogonal grid of heat-produced cracks similar to those discussed in the Bronze age amber beads of Figures 5 and 6. The long hole within this large bead was made by pressing the hot punch with minor axial deviations, resulting in the winding structure visible in the image / Figure 8 : Détail SE-SEM d’un moulage en silicone du trou dans l’ornement en ambre de la figure 10. Noter la présence d’une grille orthogonale de fissures thermiques similaires à celles décrites dans les perles d’ambre de l’âge de Bronze des figures 5 et 6. Le long trou dans cette grosse perle a été réalisé en appuyant sur le poinçon chaud avec des déviations axiales mineures, ce qui a pour effet de rendre la structure tortueuse visible sur l’image
URL http://journals.openedition.org/archeosciences/docannexe/image/8024/img-8.jpg
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Titre Figure 9: An amber lump from the workshop area of Este Borgo Canevedo (Padova, Italy, 11th-10th century BC). A) a Digital 3D optical image, showing a series of parallel flat reduction planes, possibly obtained by the means of a blade. B) Laser LSCM image of the same amber lump / Figure 9 : Un morceau d’ambre de la zone d’atelier de Este Borgo Canevedo (Padoue, Italie, xie-xe siècle av. J.-C.). A) Image optique 3D numérique, montrant quatre plans de réduction plats parallèles, éventuellement obtenus au moyen d’une lame. B) Image Laser LSCM du même morceau d’ambre
URL http://journals.openedition.org/archeosciences/docannexe/image/8024/img-9.jpg
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Titre Figure 10: The Laser LSCM image of the same amber lump (A). The detail in B) enhances one of the micro-fragments of charcoal included on surface, apparently while this latter was in a state of partial viscosity. The evidence is interpreted as supporting the use of a red-hot copper blade in the stages of the lump’s reduction. C) is a deep profile image of another side of the same amber lump, in fake colors, representing the relative depth (left) aside E, a laser LSCM image of the same view. In the red rectangle, D) is a magnification of some charcoal prints / Figure 10 : A) L’image Laser LSCM du même morceau d’ambre. Le détail en B) fait ressortir l’un des micro-fragments de charbon sur la surface, apparemment quand elle était dans un état de viscosité partielle. Ces éléments sont interprétés comme preuve de l’utilisation d’une lame de cuivre chauffé au rouge dans les phases de la réduction du morceau. C) Une image de profil profond d’un autre côté du même morceau d’ambre, dans de fausses couleurs, représentant la profondeur relative (à gauche) du côté E. Une image au laser LSCM de la même vue. Dans le rectangle rouge, D) montre un agrandissement de traces de charbon
URL http://journals.openedition.org/archeosciences/docannexe/image/8024/img-10.jpg
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Ivana Angelini et Massimo Vidale, « The Bronze age amber industry in northern Italy in light of high-resolution 3D imaging »ArcheoSciences, 44-2 | 2020, 237-249.

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Ivana Angelini et Massimo Vidale, « The Bronze age amber industry in northern Italy in light of high-resolution 3D imaging »ArcheoSciences [En ligne], 44-2 | 2020, mis en ligne le 03 janvier 2023, consulté le 07 décembre 2023. URL : http://journals.openedition.org/archeosciences/8024 ; DOI : https://doi.org/10.4000/archeosciences.8024

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Auteurs

Ivana Angelini

Department of Cultural Heritage, University of Padova, Italy (ivana.angelini@unipd.it)

Massimo Vidale

Department of Cultural Heritage, University of Padova, Italy (mass.vidale@gmail.com)

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