Potin (also known as billon) is a base metal silver-like alloy used in coins. It is typically a mixture of bronze, tin and lead (in varying proportions) and it is debated whether any actual silver needs to be present. While the term billon is more commonly applied to ancient Roman coinage, potin is usually used for Greek or Celtic coinage.
Use in Celtic coinage
In 1890, so-called Potin lumps were found, whose largest weights 59.2 kilograms (131 lb) at the Prehistoric pile dwelling settlement Alpenquai in Zürich (Vicus Turicum) in Switzerland. The pieces consist of a large number of fused Celtic coins, which are mixed with charcoal remnants. Some of the about 18,000 coins originate from the Eastern Gaul, others are of the Zürich type, that were assigned to the local Helvetii, which date to around 100 BC. The find is so far unique, and the scientific research assumes that the melting down of the lump was not completed, therefore the aim was to form cult offerings. The site of the find was at that time at least 50 metres (164 ft) from the lake shore, and probably 1 metre (3 ft) to 3 metres (10 ft) deep in the water.
Kentish cast bronzes (historically referred to as Thurrock potins) appear to have been the first coins made in Britain dating from the end of the second century BC. They appear to have circulated mainly in Kent and were based on coins issued by Massalia (now Marseille).
Potin is traditionally an alloy of bronze, tin and lead, with varying quantities of each possible.