The earliest forms of glasses were made from sand, fluxed (melted together) with either soda or potash. Adding a flux material to quartzite sand as it is melted controls both the heat and the viscosity of the glass as its formed. Natron, sodium carbonate 10-hydrate, (best known as an aid to mummification) was used as a flux for the production of faience and glazed steatite beads beginning at least in the early 4th millennium BC.
But, before about 500 BC, soda glasses in the Mediterranean area were primarily based on plant ash, produced in specialized locations in Egypt and Mesopotamia. During the 5th century BC, natron glass--glass made with soda-rich salt called natron combined with quartz sand--became dominant in the Mediterranean and Europe, and remained dominant until between AD 833 and 848, when an abrupt end came to the use of natron as a flux and glass makers in the Islamic and European markets switched back to plant ash.
What happened? In a 2006 article, Shortland and colleagues argue convincingly that the end of natron as a resource for glass making occurred when shifting politics in the region cut off the nearly universal access to Wadi Natrun.
Sources
Degryse P, and Schneider J. 2008. Pliny the Elder and Sr-Nd isotopes: tracing the provenance of raw materials for Roman glass production. Journal of Archaeological Science 35(7):1993-2000.
Kato N, Nakai I, and Shindo Y. 2009. Change in chemical composition of early Islamic glass excavated in Raya,Sinai Peninsula, Egypt: on-site analyses using a portable X-ray fluorescence spectrometer. Journal of Archaeological Science 36(8):1698-1707.
Kato N, Nakai I, and Shindo Y. 2010. Transitions in Islamic plant-ash glass vessels: on-site chemical analyses conducted at the Raya/al-Tur area on the Sinai Peninsula in Egypt. Journal of Archaeological Science 37(7):1381-1395.
Shortland A, Schachner L, Freestone I, and Tite M. 2006. Natron as a flux in the early vitreous materials industry: sources, beginnings and reasons for decline. Journal of Archaeological Science 33(4):521-530.
