Glass in the Middle East and Western Europe at the End of the First Millennium CE, Transition from Natron to Plant Ash Soda or Forest Glasses

The production of natron glass started at the beginning of the first millennium BCE and prevailed in the Mediterranean world for almost two thousand years. This production seems to cease progressively from the end of the eighth century CE onwards, with a different timing based on the region (e.g. Syria, Egypt). A recent study of Islamic glass weights and stamps, which provide a fairly continuous chronology of glass compositions from the reign of Abd al-Malik (685–705 CE) to the reign of the Fatimid caliph al-Hakim (996–1020 CE), shows that natron glass was produced in Egypt at least until the middle of the ninth century. Thus, in the Mediterranean world, a radical change is observed in glass recipes between the end of the eighth century and the tenth century CE resulting in the systematic use of soda plant ashes instead of natron. This recipe was then adopted all around the Mediterranean and became predominant in that area by the end of the twelfth century.