Ancient Romans recycled glass

A fragment of colorless Roman glass

The 21st century's three Rs -- Reduce, Reuse, Recycle -- were all the rage in Britain during the last century of Roman rule, a compositional analysis of ancient Roman glass tableware has revealed.

According to the study, published in the Journal of Archaeological Science, large quantities of glass were recycled in Britain during the 3rd and 4th centuries A.D. The reason wasn’t exactly a desire to go green, but a shortage of raw glass in the northern regions of the Roman Empire during the last centuries of Roman rule. “It appears much of the glass reaching Britain in the late Roman period was manufactured from recycled material,” Caroline Jackson, at the archaeology department of the University of Sheffield, U.K., told Discovery News.

Believed to have originated in Mesopotamia around 2500 B.C., the art of glass-making spread to Egypt, with the most significant technological revolution -- glass blowing employing a tube -- occurring in the 1st century B.C. in the area of Syria and Palestine.

The Romans exploited the technique, and glass-making spread throughout the empire, with glass becoming a common household material. Made out of sand, glass takes on the color of the chemical elements present in raw material. For example, sand containing iron produces blue-green glass, while iron and sulfur elements make a brownish glass. Skilled Roman craftsmen were able to control glass color through a careful selection of the raw materials, and produced colorless glass by adding a decolorizer, an element which oxidizes the chemicals in the sand to remove the color. “In the Roman period, this element would have been antimony or manganese,” said Jackson.

Resembling crystal, colorless glass was much valued. According to the Roman author, Pliny, the emperor Nero (37-68 A.D.) gave 6,000 sestertia (roughly $250,000) for two clear glass cups of ordinary size, with handles. A highly developed and successful industry, Roman glass-making still holds some mystery. It is unknown where colorless glass was produced, and scholars still debate how the glass industry was organized.

“Pliny suggests that sand for colorless glass was sourced in Italy and it has often been suggested that colorless glass manufacturing was centered in the Rhineland,” Jackson and colleague Harriet Foster from the Norfolk Museums and Archaeology Service wrote.

In order to understand more about the production and distribution of colorless glass in the late Roman period, the researchers used a spectroscopic technique called ICP-AES to analyze the chemical composition of 128 samples of glass tableware from 19 sites across Britain. It emerged that 46 samples had been decolored using antimony, 13 with manganese, while the remaining 69 contained both elements.

According to the researchers, recycling is the reason for the presence of both antimony and manganese in the 69 samples. They would have resulted from mixing various pieces of colorless broken vessel glass. The analysis also supported the theory of a centralized glass production at locations yet to be determined. “Indeed, further investigation using trace elements analysis and isotopes is necessary to identify potential manufacture regions,”Jackson said.