Chemical composition of medieval glass from excavations in West Germany

Abstract

Investigations of excavated glass fragments from the Roman-Frankish cemetery at Krefeld-Gellep, the Carolingian imperial palace with glassworks at Paderborn, the monasteries and towns of Corvey, Höxter and Brunshausen-Gandersheim and several glassworks in the Bramwald, Hils, Spessart and Eichsfeld areas allow conclusions on the sequence of major medieval glass types. Exhaustion of Imports of trona-soda or soda raw glass and increased needs caused the introduction of woodash as domestic alkali and earth alkali source for glass manufacture at about 800 AC. Early woodash glass from 800 to 1000, woodash glass from about 1000 to 1400 and woodash-lime glass from about 1400 to post-medieval times were the major glass types. They were accompanied by minor Imports of soda-lime and soda-ash glass objects, the latter since about 1300. From about 1100 to 1400 woodash-lead and lead glass have been produced from the P bO byproducts of the silver metallurgy. Galena from the Harz Mountains was a major source of lead for lead glass in northwestern Europe. The average production of a medieval glassworks was in the order of 15 t glass per year and its requirements for ash and fuel about 30001 wood. The number of glassworks in Germany during the late medieval period (moving after 5 to 30 years from one to another location) is tentatively estimated to be in the order of 40. Their main furnaces were constructed for about 1400 C working temperature. The occurrence of the medieval chemical glass types in a sequence allows some rough dating of glass fragments.