Western Mediterranean sand deposits as a raw material for Roman glass production

During the Late Roman and Byzantine period, natron glass was made from its raw materials in a limited number of primary production centres in Egypt and Syro-Palestine. For the earlier Hellenistic and Roman period, no primary furnaces have been found and the location of primary production during this era remains unclear. Ancient authors such as Strabo and Pliny the Elder suggest that glassmaking sands were found near the River Belus (Israel), in Egypt, near the mouth of the Volturno River (Italy) and also in Spain and France. However, primary production in the western part of the Mediterranean is not supported by any direct archaeological evidence and possible sand raw materials from these regions have never been evaluated for their suitability to produce glass. In this study 178 modern beach sands from Spain, France and Italy were analysed for their major and minor elemental compositions. By calculating the composition of the glasses that can be produced with these sediments after the addition of pure natron, and comparison with the composition of typical Roman natron glass, we were able to judge whether or not these sands are suitable for Roman glass production. The results indicate that good glassmaking sands are rather rare. Only a very limited number of the 178 analysed beach sands would produce a glass with major and minor elemental compositions within the ranges of Roman imperial natron glass. The rest of the analysed sands are unsuitable for glass production in their present form due to their insufficient SiO2, high Al2O3 and Fe2O3 and either too low or too high CaO contents. If the sand raw material was too low in CaO, extra lime could be added to the glass batch in the form of shell or limestone. This was taken into account in a second calculation. Overall we were able to define six limited areas where suitable sand raw materials would have been available to the Roman glassmaker. Good glassmaking sands occur in the Basilicata and Puglia regions (SE Italy), and Tuscany (W Italy). After the addition of an extra source of lime also sands from the Huelva province (SW Spain), the Murcia region (SE Spain) and from the Provence (SE France) would produce glasses with a typical Roman composition.