Hafnium isotopes reveal origin of ancient Roman glass

Ancient Romans used glass to make everything from dining ware to colorful mosaics. But the Romans particularly prized a colorless, translucent glass they called “Alexandrian.” Its origin was an archaeological mystery, but research led by Gry Barfod, a geochemist at Aarhus University, shows that hafnium isotopes in Alexandrian samples reveal their ancient origin: Egypt (Sci. Rep. 2020, DOI: 10.1038/s41598-020-68089-w). Glass shards of different types collected from Gerasa—an ancient Roman city near modern-day Amman, Jordan—were analyzed by dissolution and ion-exchange chromatography for elemental analysis of strontium, neodymium, and hafnium. Though Sr and Nd isotopes have previously been used to study glass artifacts, their elemental signatures fail to distinguish Egyptian glass shards from those produced in other regions of the Mediterranean. But glass produced in Egypt shows a distinct 176Hf/177Hf signature because of minerals found in the sands of Nile sediments. This signature groups Alexandrian samples squarely among other glass types produced in Egypt. This research not only sheds light on ancient Roman trade practices but also shows that Hf could be useful for analyzing other human artifacts.