BAS Lecture – 15 February 2025
From Constantinople to Berkshire. Linking Roman copper-alloys across the empire through new chemical analysis at the University of Reading
Dr. Peter Bray, University of Reading
This lecture gave an insight into the REMADE (Roman and Early Medieval Alloys Defined) project, a national UK programme bringing together many partners across the heritage sector and hosted by the University of Reading. Currently two years into the seven-year project, REMADE uses new chemical analysis techniques to investigate the metallurgy of Romano-British artefacts found across the UK, to better understand how copper-alloys were used, valued and recycled, and how they were moved across the Roman empire.
The REMADE team at the University of Reading includes Roman and Medieval experts and partners with national museums, English Heritage and archaeological consultancies. It has currently analysed more than 60,000 artefacts with over 100 case studies across the UK, covering both regional and period divisions.
Analysis starts with a non-destructive method using the Niton XL5 Portable X-Ray Fluorescence (pXRF) analyser. This is followed by a destructive method of testing using a nitrogen plasma spectrometer in the dedicated MP-AES laboratory at the University of Reading. A tiny sample (10mg-20mg) of the metal object is removed using a 1mm drill bit, which is then dissolved in nitric acid and heated in the spectrometer, resulting in the type and percentage of each element present. This method requires a far smaller sample than previous methods, and the location from where the sample was removed can barely be seen, even from the most fragile of coins. This is in contrast to samples taken from the Bronze Age Knocknagree Hoard for example, where samples taken in the 1960s have left large, visible holes. Such methods caused too much damage to objects and were limited in the data they gave, hence the need for the REMADE collaboration.
The majority of the analyses has been carried out on Roman coins, giving us, for the first time, more detailed local stories from local empires. Analyses were carried out on finds from Bloomberg in London, most of which are from AD 43 – 95 and included both military and domestic objects such as horse brasses, jewellery, coins and hair pins. Analysis of the coins have given us much more information on the metal compositions than was previously known.
Archaeometallurgy is the discipline of the past production and use of metals by humans. For copper alloys, just 16 elements are needed to chemically describe several archaeological themes. These elements are grouped as:
- Copper.
- Tin, Lead, Zinc.
- Arsenic, Antinomy, Silver, Nickel, Iron.
- Bismuth, Chromium, Cobalt, Gold, Sulphur, Manganese, Mercury.
In literature, brass, an alloy of copper and zinc, is strongly associated with the military and there was none in the iron Age. It was therefore assumed to have been brought to Britain from Italy during the pre-conquest. However, this project has found that domestic as well as military brass, including core military equipment, coins, brooches etc, are all chemically the same, which was an unexpected result. Another collection shows scale armour worn by auxiliary troops as having a much higher percentage of zinc than the other objects within the assemblage, which would have been a deliberate action to make it easier to work and to exhibit a different colour.
One question to consider is how much knowledge was known of the properties of different copper-alloys by owners, producers and primary metal manufacturers? The colour differences we see now in corroded artefacts would have been very different when they were first produced.
The recycling of different copper alloys was commonplace, thought to be done purely when metals were scarce. However, from this project we can see deliberate patterns of mixing during recycling to obtain specific colours. Among the finds at Fishbourne Palace in West Sussex, from the 1st and 2nd centuries AD, was a large lump of solidified metal still in a crucible containing separate concentrations of copper, brass and bronze frozen in time part-way through the manufacturing process. There is a surprising longevity seen in recycling, illustrated in local contemporary coin copies produced in Berkshire. Another interesting discovery is that while we knew Roman mirrors were made of high-tin bronze, we now know that bells were made of the same metal composition.
The Cunetio Hoard from Wiltshire consists of approximately 55,000 Roman coins, dating from AD 250–275. So far, 1,500 have been non-destructively analysed. Between AD 262 and AD 271 the Western Roman Empire was in crisis. During this tumultuous period the chemical composition of the coins reflects the pattern of political changes by the ruling emperors, from the percentages of tin and silver present. Yearly changes can be seen in the metal mixes in mints in Britain and also in Milan, for example as silver supplies reduced, more tin was used. A higher percentage of tin in coins (i.e. less percentage silver) has been interpreted as reflecting a poor economy. However, this is now also seen as a positive economic indicator, because people were in need of large amounts of small change. Copies, or imitation coins, always have far less silver and more tin than the originals. They also have a higher percentage of zinc, where previously zinc was rare. Copies invariably used recycled coins.
The next steps of the project are to look at the additional elements listed above, such as antimony. The Romans had a unique signature in their deliberate addition of this element to their copper, and they also added it to their glass. This illustrates a surprising 1st century AD connected economy. Sampling will also continue of the 900 coin finds from Beedon in West Berkshire. Results from this assemblage have shown evidence of silvering as a surface treatment of coins. There is, however, the need for more data, especially from the UK, to see the scales of behaviour and choice in Roman metallurgy.
Further information can be found at: REMADE – Roman and Early Medieval Alloys Defined
report by Debbie Cousins