Evidence of early medieval soda ash glass in the archaeological site of San Genesio (Tuscany) S. Cagno a, * , L. Favaretto a , M. Mendera b , A. Izmer c , F. Vanhaecke c , K. Janssens a a University of Antwerp, Department of Chemistry, Universiteitsplein 1, 2610 Wilrijk, Belgium b University of Siena, Department of Archaeology, Via Roma 56, 53100 Siena, Italy c Ghent University, Department of Analytical Chemistry, Krijgslaan 281-S12, 9000 Gent, Belgium article info Article history: Received 15 September 2011 Received in revised form 5 December 2011 Accepted 27 December 2011 Keywords: Historical glass Glass composition Tuscany SEM-EDX LA-ICP-MS Raw materials abstract The early medieval period marks an important turning point in the history of glassmaking, since it comprises the transition period between the mineral-based silica-soda-lime glass of the Roman tradition and the plant ash-based glass. With the aim of expanding the knowledge on the glass recipes and technologies of this period, 37 glass samples were analyzed, originating from the archaeological exca- vations of San Genesio (Tuscany) and dated from the fourth to the eleventh century. The major and minor element concentrations were measured with SEM-EDX, while the trace elements were quantified with LA-ICP-MS. The results were compared with published compositions of glass samples of similar age in order to highlight differences and similarities. The results offer a very interesting view on the glass circulation in the religious/residential/manufacturing center of San Genesio in the early medieval period. Most of the glass has a typical late-Roman composition, but some glass fragments are identified as soda ash glass. These are among the earliest medieval ash-fluxed glasses ever found in the Italian peninsula. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction In this paper we present the analyses of 37 glass fragments dated from the fourth to the eleventh century and originating from archaeological site of San Genesio, located in Tuscany. The aim of this work is that of expanding the current knowledge on the glass recipes (glass raw materials, colorants, opacifiers) used in the early medieval period and to elaborate hypotheses on the possible commercial routes and transfers of knowledge at the time. 1.1. Glass production in Late Antiquity and Middle Age In Late Antiquity glass production has to be considered in close relation with the methods and the work organization of the Roman world, with a subdivision of primary and secondary glass work- shops (Foy, 2000). In this model, primary glassmaking centers located in the Eastern Mediterranean melted large batches of natron (a natural mixture of sodium salts) and lime-rich sand in order to produce large quantities of raw glass, to be shipped to the secondary centers located near the glass consumption areas, where raw glass was remelted and worked. Glass fluxed by natron has been named mineral soda-lime-silica glass (Gratuze, 2004), natron- based glass (Freestone et al., 2003), natron glass (Brill, 1992), soda- lime glass (Wedepohl et al., 2011) or Low Magnesium Glass (LMG) (Henderson, 1985). In this paper we will refer to this type of glass as natron glass. This type of market organization has been alternatively reported to be maintained during the late Roman and post Roman period (Foy et al., 2000; Freestone et al., 2005), or discontinued. In the latter case, according to Wedepohl and Baumann (2000) and Shortland et al., 2006, primary glassmaking centers started the production of glass from raw materials in Western Europe by retaining the pre-existing recipes. It is a fact that primary glass- making, with the use of new starting materials (e.g. plant ash in place of natron) was established throughout Europe by the end of the first millennium AD (Shortland et al., 2006; Verità and Zecchin, 2009; Wedepohl and Baumann, 2000). The Roman primary glass production being concentrated in a limited number of centers in the Levant, the glass compositions in this period are reported to be quite constant (e.g. Geilmann, 1955; Jackson et al., 1991). Early Roman glass (1e3rd century) shows a blue-green color due to the iron impurities and is often referred to as Roman blue-green glass (Foster and Jackson, 2009). However, clear differences in sand source and the type of decolorizer employed (Mn or Sb) have been evidenced (Silvestri et al., 2008), suggesting a multi-center primary production at least from the 3rd * Corresponding author. Tel.: þ32 3265 2363. E-mail address: simone.cagno@ua.ac.be (S. Cagno). Contents lists available at SciVerse ScienceDirect Journal of Archaeological Science journal homepage: http://www.elsevier.com/locate/jas 0305-4403/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2011.12.031 Journal of Archaeological Science 39 (2012) 1540e1552