Seleukid Kingdom, Demetrios I Soter, 162-150 BC. AR Tetradrachm Antioch

Potin coin, a type of ancient coinage primarily associated with Celtic civilizations, particularly those in Gaul (ancient France) and Britain.
Key characteristics and facts about Potin coins:
Composition: Potin is a base metal alloy, typically a mixture of copper, tin, and lead, with varying proportions. Unlike billon coins, potin does not contain significant amounts of silver.
Manufacturing: Potin coins are distinctive because they were cast in molds rather than being struck like most other ancient coins. This casting process often resulted in an irregular, somewhat rough appearance and sometimes leaves evidence of casting sprues (remnants of the channels that connected the coin to the mold during casting).
Appearance: When new, potin coins would have appeared shiny and silvery. However, due to the high tin content, they commonly develop a characteristic dark, often black, patina due to tin oxidation when excavated.