Glassmaking using natron from el-Barnugi (Egypt); Pliny and the Roman glass industry

Abstract

Pliny the Elder describes the discovery of a process for making natron glass, which was widely used for much of the first millennium BC and AD. His account of glassmaking with natron has since been corroborated by analyses of archaeological glass and the discovery of large-scale glass production sites where natron glass was made and then exported. Analyses of Egyptian natron have shown it to be a complex mixture of different sodium compounds, and previous experiments to make glass with Egyptian natron have been unsuccessful. Here, natron from el-Barnugi in the Egyptian Nile delta, a site which also probably supplied Roman glassmakers, is used to produce glass. The experiments show that highquality glass, free of unreacted batch or bubbles, could have been produced from natron in its unprocessed form in a single stage, that larger quantities of natron would be required than has previously been anticipated, that the presence of different sodium-containing compounds in the deposit aided melting, and that negligible waste is produced. The implications for the identification of glass production sites, for the organisation of trade and for the supply of natron within and outside Egypt are discussed in the light of Pliny's accounts.

Glass import and production in Hispania during the early medieval period: The glass from Ciudad de Vascos (Toledo)

“…These lead glasses have exceptionally high chlorine values (1.7%–2.5%), negatively correlated with calcium. It has been shown that the chlorine content decreases with increasing temperature and calcium oxide content [ 66 ]. This could explain the high chlorine level, because the lime concentrations are very low and the melting temperature of glass with high lead content (PbO > 40%) is drastically reduced.…”

Geochemistry of Byzantine and Early Islamic glass from Jerash, Jordan: Typology, recycling, and provenance

“…Jackson, Paynter, Nenna, and Degryse () have recently suggested that a negative correlation between CaO and Cl among Roman glass groups and experimental glass synthesized using Egyptian natron is a signature of primary glass production. The lack of a similar correlation among the Byzantine glasses of Jerash ( R 2 = 0.2) does not exclude this possibility, but does suggest that additional factors affect Cl and Ca in Levantine glasses.…”

“…Moreover, the strong negative K-Cl correlation (R 2 = 0.63) compared to other sites in the region (Umm el-Jimal at 0.25 and Petra at 0.24), in addition to even stronger positive K-P correlation (R 2 = 0.88; Figure 12), suggests that glass recycling was more intensive at Jerash. Jackson, Paynter, Nenna, and Degryse (2016) have recently suggested that a negative correlation between CaO and Cl among Roman glass groups and experimental glass synthesized using Egyptian natron is a signature of primary glass production. The lack of a similar cor- (Carroll, 2005;Metrich & Rutherford, 1992;Veksler et al, 2012).…”

An Archaeometric Investigation of Gems and Glass Beads Decorating the Double-Arm Reliquary Cross from Liège, Belgium

“…The pXRF analyses also reveal the presence of other chemical elements, such as aluminium, titanium, iron, or antimony (Table 2). As natron contains very low amounts of impurities, minor and trace elements certainly originate from sand (Ti, Al, and Fe), decolouring (Mn and Sb) or colouring (Co, Cu, Fe, and Sb) agents (see below), and/or sometimes from recycling processes (Sb, Sn, Pb, Ni, and Cu) [19,33]. Sodalime glasses with natron were exclusively used until the beginning of the Middle Age, before being gradually replaced by wood and plant ashes to almost disappear during the 13th century [20,25,27,28].…”