The Romans Called it ‘Alexandrian Glass.’ Where Was It Really From? - The New York Times

But the source of this coveted material — known as Alexandrian glass — has long remained a mystery.

Now, by studying trace quantities of the element hafnium within the glass, researchers have shown that this prized commodity really did originate in ancient Egypt.

The manganese-treated glass still retained a bit of color, however, said Gry Hoffmann Barfod, a geoscientist at Aarhus University in Denmark who led the study, which was published this month in Scientific Reports.

refers to this colorless glass as “Alexandrian” and values it at nearly double the price of manganese-treated glass.

The sherds, each no longer than a finger, included Alexandrian glass and manganese-treated glass from the first through the fourth centuries A.D.

The sample also included other specimens of glass known to have been produced more recently in either Egypt or the Levant.

Egyptian glass consistently contained more hafnium and had lower isotopic ratios than glass produced in the Levant, the team found.

That explains why glass forged in Egyptian furnaces tends to contain more hafnium than Levantine glass, the researchers suggest.

When researchers analyzed the sherds of Alexandrian and manganese-treated glass, they again found distinct differences in hafnium.

The manganese-treated glass had hafnium properties consistent with being produced in the Levant, as expected.

And Alexandrian glass, the clearest of the clear when it came to transparent glass, chemically resembled Egyptian glass.