Abstract of a potentially-interesting article behind a payfer wall:
One hundred and twenty-eight colourless glass tablewares from settlement contexts throughout the British Isles, dating from the mid-3rd to 4th century AD, were analysed by ICP-AES spectrometry. Three distinct compositional groups were identified based upon the use of different decolourisers and primary raw materials, with possible sub-groups within these. These compositions have distinct, but overlapping chronological ranges, suggesting colourless glass production in at least three, possibly more, centres in the late Roman period. The compositional analysis highlights the high degree to which recycling of glass was taking place during this late period. The chronological distribution of some of these compositions is more restricted within the British assemblages than is observed in other published assemblages from Western Europe. This distinction may indicate different supply patterns of glass to the Western provinces.
A few more details can be had from an item over at Planet Earth Online … here’s a bit from the end:
‘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.