A non-destructive approach for the characterization of glass artifacts: The case of glass beads from the Iron Age Picene necropolises of Novilara and Crocefisso-Matelica (Italy)

Highlights:

• A total of 211 beads were recovered from two Picene necropolises.

• A non-invasive study was performed using XRF, XRD and spectroscopic techniques.

• Chromophores were found by FORS, and crystalline phases by XRD and Raman Spectra.

• The non invasive approach allowed a quite detailed e characterization of samples.

• Further investigations are needed to study crystalline phases.

Abstract

A totally non-destructive approach was employed to characterize beads from two Picene necropolises (Novilara-PU and Crocefisso-Matelica-MC) dating back to between 9th and 6th centuries B.C. Investigations were carried out principally by means of Reflectance Spectroscopy determining Co²⁺, Cu²⁺ and Fe³⁺ as the main chromophores, and by Raman Spectroscopy to distinguish samples realized with other materials, in particular bones and shells were recognized. Furthermore, Raman spectroscopy identified hematite as a coloring phase in the unique red bead discovered as unmelt crystals in blue and yellow beads. Additionally, X-Ray Diffractometry investigations indicated Ca-phosphates, bindhemite and the less common brizzite, as opacifiers in white and yellow beads, while chemical data collected through X-Ray Fluorescence evidenced differences between findings from the two localities and/or within the same site. Beads were found to belong to the Low Magnesium Glass (LMG) and High Magnesium Low Potassium (HMLK) classes with most blue beads being comprised of cobaltiferous alum salts and a relatively impure sand, and a calcareous sand having been used for all other analyzed beads. Finally, differentiations performed on the basis of MgO amounts tended to indicate the samples from Crocefisso as being more similar to Bronze Age compositions than the Novilara ones which are closer to typical Iron Age proportions. In addition, high amounts of lead have been detected in all the yellow beads, but they could be positively correlated to Sb₂O₃ only for samples recovered in the Novilara necropolis, thus indicating the use of lead antimonates as coloring agents.

Introduction

The earliest known glass production dates back to the second half of the 3rd millennium B.C. in Mesopotamia, mostly in the form of beads (Henderson, 2013). However, the occurrence of highly colored glassy objects only becomes common in Syria-Mesopotamian and Egyptian archaeological records from the Late Bronze Age (16th–15th century BCE) onwards. All such findings were fluxed with soda-based materials. In particular, plant-ash was used for the older fluxes, and glasses were normally obtained using quartz pebbles as silica source. The replacement of ashes derived from desert plants with mineral soda occurred at the beginning of the 1st millennium BC, when natron glasses started being produced. This later typology involved the use of quartz sand as its silica source instead. Many studies indicate that between the 2nd and the 1st millennium B.C. two main glass categories could be identified (e.g. Henderson, 2000, Towle et al., 2001, Gratuze and Billaud, 2003, Barkoudah and Henderson, 2006, Nikita and Henderson, 2006, Henderson et al., 2010, Henderson, 2013), the older of which (from the 15th to the 9th century BCE) mainly derives from Egypt and Mesopotamia and is characterized by high percentages of Na₂O and MgO (2–6 wt%), often correlated with high levels of K₂O (0.5–2 wt%). This composition was obtained by using plant ashes as flux, commonly known as High Magnesium Glass (HMG), and was widespread during the Bronze Age in the whole Mediterranean area and in Europe (imported by the Middle-East) (Hartmann et al., 1997, Santopadre and Verità, 2000).

During the Final Bronze Age, and particularly between 12th and 10th century BCE, another production source appeared in the Northern-Eastern Italy regions. Many finds come from excavations carried out in Frattesina (Biavati and Verità, 1989, Brill, 1992, Angelini et al., 2004, Angelini, 2008;), a relevant production site, especially for beads displaying both high Na₂O and K₂O content but low MgO concentrations. Scientific investigations identified that the glass composition could not be related to any other productions and was described as “mixed alkali glass” or “Low Magnesium High Potassium” (LMHK) (Henderson, 1988a). It was suggested to be a European production obtained by using leached wood ash as its source of alkali (Hartmann et al., 1997, Angelini et al., 2004). Consequently, these glasses can be considered as a typical European variety, showing clear similarities with coeval artifacts from other European countries such as Germany, Switzerland, France, England, Ireland and Greece (Henderson, 1988a, Henderson, 1988b, Guilaine et al., 1990, Henderson, 1993, Hartmann et al., 1997, Angelini et al., 2006, Arletti et al., 2010a), as well as from Italian sites (Mariconda, Citanal Bianco, Poviglio, Prato di Frambulino, Trinitapoli, Chiaromonte, Grotte Vittorio Vecchi and Vicofertile) (Henderson, 2013). The most recent LMHK glass artifact was a bead with high social and ritual value excavated in Rathgall (Ireland) dating back to the 8th century (Henderson, 2013).

A successive typology, mostly produced since the 8th century BCE, is characterized by a change in the alkali source and is natron-based, using the mineral trona (Na₂CO₃·NaHCO₃·2H₂O) which forms the main component of the evaporitic deposits such as that of Wadi-al-Natrun (Egypt). The use of calcareous sand also contributed to the peculiar composition of these materials, displaying high Na₂O content and low K₂O and MgO concentrations (“Low Magnesium Glass”, LMG). The earliest natron glass findings were vessels from the burial of Nesikhons (Egypt), dating back to the 10th century BCE (Henderson, 2013, Schlick-Nolte and Werthmann, 2003). The spread of this compositional class is well known even during the Iron Age from the Middle East, to Italy in Villanovian and Etruscan sites (Towle et al., 2001, Towle and Henderson, 2007, Arletti et al., 2011a). This natron-based glass substituted the plant ash one imported from the Near East and the local LMHK glass. Different models concerning the production of LMHK glass in the Roman period have been proposed, i.e. few primary production centers and many secondary workshops, or several sites coupling glassmaking and glassworking (Henderson, 1989, Reade et al., 2006, Degryse and Schneider, 2008, Wedepohl et al., 2011, Degryse, 2014). However, no definitive theory has been formulated for the period ranging between the introduction of natron as flux (10th–9th century BCE) and the Roman Empire (1st century BCE) (Henderson, 2013, Conte et al., 2018).

A transition period in glassmaking can be identified between the Bronze and the Iron Age, whose artifacts, although quite often found during excavations, have been rarely studied. Modifications of the glass chemistry are related to experimental changes in raw materials and resulted in the creation of new recipes providing typical chemical compositions, which often lead to materials less stable towards degradation phenomena, e.g, due to burial. Almost all findings datable back to the first centuries of the 1st millennium BCE therefore exhibit very variable chemical compositions, interpreted by researchers as due to a combination of recipes, proportions and techniques not yet well defined (Conte et al., 2016).

Studies carried out on protohistoric French beads dating back from the Bronze to the Iron Age allowed for recognition of a temporal evolution in their chemistry (Billaud and Gratuze, 2002, Gratuze and Picon, 2006). Glass beads from the Middle Bronze Age originating from the eastern Mediterranean basin (Mesopotamia), were plant ash-based materials, containing only copper as blue chromophore, while the presence of Co²⁺ can be related to an Egyptian origin. In the Late Bronze Age, the flux composition was slightly changed into a mixed alkali one, and an Italian origin was hypothesized for these samples, blue-colored by both copper and cobalt associated to arsenic and nickel. Glass samples from the beginning of the Iron Age (9th–7th century BCE) were found to be natron-based with peculiar compositions, which became more stable from the 6th century BCE (Billaud and Gratuze, 2002, Gratuze and Picon, 2006).

A large set of polychrome samples found in necropolises from Northern Italy (such as Spina and Bologna) dating back to the 6th–4th century BCE revealed a standardization of production process due to chemical homogeneity within the same color class and opacifying agents, thus indicating the existence of consolidated recipes (Arletti et al., 2010b). Analyses carried out on beads, vessels and spindle whorls displayed a quite high homogeneity of the main chemical components, suggesting a common origin of these findings, probably from an Eastern region and excluding a relationship with the Final Bronze Age productions from Northern Italy (Arletti et al., 2010b).

Glasses from the Spina necropolis were also studied taking into account that radical changes occurred in glass production during the Iron Age, since from the 7th century BCE natron glass became widespread in both eastern and western Mediterranean regions (Arletti et al., 2011a).

However, archaeometric studies on glassy materials recovered in the Italian peninsula exhibit a void of knowledge along the Adriatic coast. This research represents the first study of glassy findings dating back to the Iron Age period from this geographical area.

From the Early Iron Age (9–8th century BCE) onwards the ancient Italian populations exhibited growing regional diversity “as each center constructed its material culture by selecting, adjusting and incorporating explicit artefacts and habits from their neighbors and their interregional or overseas contacts. Thus, close study of most Iron Age centers in Italy demonstrates that they have certain aspects in common with nearby settlements but also that their archaeological record is unique in the sense that the cultural character of the settlements is the result of both a local and adopted repertoire of customs” (Nijboer, 2010).

It was a period of great change, with the adoption of new production technologies and important social changes: increasing mobility, centralization, early urbanization, growing population and a stronger definition of class distinctions. The economy, previously based on small-scale manufacturing, began to accommodate new classes of specialized craftsmen, thereby encouraging them by more extended trade routes (Bietti Sestire, 2010).

The first communities with strong and well-defined cultural identities appeared in this period (e.g. Etruscans, Picenes, Umbrians, Samnites).

While the Thyrrenian side is better known, and Etruria emerged as a complex territorial, political, and economic entity able to participate in an interregional network of trade, the Adriatic side is less well understood. “Picenes” is the conventional name used to indicate a civilization of the central Adriatic coast, living in an area roughly corresponding to the current Marche region. Based on archaeological data, this civilization developed from the 9th century BCE to the beginning of the 3rd century BCE, until the dominance of Rome. Picenes, in their whole distribution area, shared a common culture with some distinctive local features. Information about this civilization is mostly based on archaeological findings, largely coming from necropolises (Naso, 2000, Serventi et al., 2017).

The Novilara necropolis was recently excavated and has generated numerous data related to the Iron Age. The site is situated in the northern Marche region, about 4 km far from the Adriatic Sea coast. Novilara has been excavated since the late 19th century, initially by Edoardo Brizio in 1892 and 1893, in two different areas named “Molaroni” and “Servici”, with 263 burials discovered dating back to the 8th and 7th centuries BC (Delpino et al., 2016).

In 2012 new research began in the “Molaroni” area (10,000 m²) (Delpino et al., 2016). During 2012–2013 excavations, led by the Soprintendenza Archeologica delle Marche, 150 new burials, dating back to the second half of 8th century and 7th century BCE, were brought to light. All burials, except for one, consist of inhumations in simple trenches with bodies lying on the right side in fetal position, probably wrapped in a shroud, surrounded by personal belongings. There were specific “funerary roles” for both men and women: a distinction can be made between the idealized male identity of the warrior, symbolized by the weaponry, and the idealized female identity, adorned with ornaments (e.g. fibulas, pendants and amber earrings), among which complex garments embroidered with bronze, amber and glass beads stand ups (Delpino et al., 2016).

As a result of excavations carried out in the last 20 years, Matelica has become an important archaeological research site. It is located at the bottom of the Marchean sector of the Central Apennines, in the upper part of the Esimo river valley. During the 8th–6th centuries BC the village underwent an intense urbanization, leading to the occupation of all neighboring plains. The oldest site occupation dates back to the 9th century BCE, and archaeological data refer to the northern necropolis (Brecce locality), where several crematory and burial tombs were discovered, seemingly unconnected to an urban area. Funeral structures were typically grouped as 3–4 units, surrounded by a free area or delimited by a ring moat, mainly diffusing in the 7th century BCE. Parallel, the Crocefisso necropolis is placed on the South-West side of Matelica. At this location many pole holes related to coeval 20–25 m long straw-based structures were discovered and excavated, close to inhumation tombs dating back to the 8th century BCE. They generally exhibited elliptical and pseudo-rectangular perimeters with shorter curve sides.

In this historical period the most common burial rite featured the curled-up body, with male funeral goods usually to indicate the deceased as a warrior, in particular due to the presence of spears. The existence of higher rank warriors was demonstrated by male funerary goods containing swords and shields (tomb n. 77, Brecce). With regard to female funerary goods, the level of wealth achieved by these communities is clearly demonstrated through the discovery of sumptuous personal ornaments, often amber-based, together with spinning tools, bronze and, more frequently, clay pots (mostly cothon). During the 7th and at least up to the 6th century BCE, the urban area continued to grow and expand, leading to the development of the peripheral centers (Pian dell'Incrocca and Cavalieri on the Northern side of Matelica, Casette S. Domenico on the East side, and Crocefisso del Piano on the South-West side). In the same period local aristocracy evolved due to high economic wealth deriving from the agricultural exploitation of the territory. This new social class commonly imported refined imported artifacts and assimilated/re-elaborated cultural stimuli from the Adriatic and Aegean Greek environments as well as from the Etruscan (Lazio region) area. This centralization of wealth to a small number of people is expressed by the rich male and female funerary goods of these individuals. Deposit pits normally found close to the supine buried person or, as in the majority of excavated tombs, below the burial surface, contained wagons, finely crafted parade weapons embellished with ivory and amber inserts and metal and clay furnishings related to sumptuous tableware. Personal goods were generally represented by amber, ivory, or precious metal-based objects in addition to symbols of power such as “scepters”. Funerary structures were embedded in annular ditches of 10–40 m width, with the tomb located at the center of these configurations. The tomb itself comprises the deposit pit and the surface where the deceased was placed and covered by earth deriving by the moat excavation.

The cemetery space also contained burials in simple terrestrial graves, containing sub-adults or children, in some cases accompanied by rich outfits. These burials were typically located close to funerary circles.

In the 6th century BCE the population seemed to decrease compared to the previous period, with the planes surrounding the Matelica area becoming less occupied (AA. VV., 1999a, AA. VV., 1999b, Biocco, 2000, AA. VV., 2001, AA. VV., 2003, Silvestrini and Sabbatini, 2008, Camporeale, 2009, Biocco et al., 2010).