Even the Romans recycled glass
Even the Romans recycled glass
The Romans weren't just dab hands at making beautiful vessels, ornaments and plates from glass; they were also good at recycling the stuff. A new study has found that towards the end of their rule in Britain, the Romans were recycling vast amounts of glass.
But the researchers behind the study think this probably had less to do with their concern for the environment, and more to do with the fact that glass became scarcer in the northern fringes of the Roman Empire during the last century of their rule.
Glassmaking was a highly sophisticated and successful industry during Roman times. Not only did the Romans spend over 600 years making things out of glass; they also knew exactly how to colour or decolourise it.
When you make glass out of sand, it takes on the colour of the various chemical elements from the sand. Given the right furnace conditions, sand containing a minute amount of iron makes glass blue-green, whereas iron and sulphur make it brown. So, sand from different parts of the world gives glass its own distinctive colour. That is, if you don't add anything to it.
'We think this means the Romans were increasingly relying on recycling to produce the vessels they wanted, possibly because less glass was coming into that part of the Empire by that time.'
But the Romans already knew how to make colourless glass. If you add tiny amounts of a so-called decolouriser like antimony or manganese to the sand, it'll come out of the furnace nearly clear. 'Although if you look closely, this glass isn't always truly colourless,' explains Harriet Foster from the Norfolk Museums and Archaeology Service and co-author of the study.
'The Romans clearly had an understanding of how to colour or decolourise glass to their liking,' she adds.
But very little is known about exactly where the glass was made. Glass produced throughout the Roman world has a relatively uniform composition, suggesting it might have been made in a few small centres, and was shipped across the whole Empire before being reworked into different shapes in regional centres where necessary.
'We know a lot more about Roman glass now than we did 15 or 20 years ago but there's still a real vacuum in our understanding of the development of glass in the civilised world,' says Foster.
In an attempt to understand how colourless glass was made and distributed during the mid-third to fourth centuries, Foster and co-author Dr Caroline Jackson from the University of Sheffield decided to analyse the chemical composition of 128 samples of glass from 19 sites across Britain. They sourced samples from intact vessels, bowls, jugs or plates held in museums around the country.
'We used a technique that meant having to destroy the glass in question, so we had to make sure the information we were getting about each piece outweighed the fact that we'd be destroying a tiny piece of valuable archaeology,' says Foster.
The researchers used a sophisticated spectroscopic technique called ICP-AES, which can detect the the major and minor element present in the glass, including metals the Romans used to decolour it.
Of the 128 samples, 46 had been decoloured using antimony, 13 with manganese and the remaining 69 contained both. Dating evidence suggests the Romans may have increasingly relied on manganese over antimony by the mid-fourth century.
But the 69 samples that contain both metals point to recycling well into the fourth century.
'We think this means the Romans were increasingly relying on recycling to produce the vessels they wanted, possibly because less glass was coming into that part of the Empire by that time,' Foster explains. The Roman Empire may have started to fragment by the end of the fourth century. There's less evidence for investment in public buildings, statues and amenities. And trade seems to have slowed down.
But the researchers can say that their findings point to the Romans using three distinct sources of raw materials to make their glass. However, they're still no clearer about where this glass was produced.
'To get to the bottom of this, we need to analyse better dated colourless glass over a larger geographical range,' says Foster.
The research was published in the Journal of Archaeological Science.