billon

Billon is a term used in numismatics to describe a debased alloy used in coinage, consisting primarily of a base metal such as copper (or a copper alloy) with a minority portion of a precious metal, typically silver or gold. The precious-metal content is generally small and varies by time and place, with the aim of reducing minting costs while producing coins that resembled higher-value currency.

Historically, billon coins appeared in the later Roman and Byzantine periods and continued into medieval and early modern Europe. They were common for small denominations and sometimes used for larger issues, depending on local metallurgy and economic needs. The exact composition could differ widely between regions and over time, and debasement could occur gradually as metallic content shifted.

Etymology-wise, the term billon is used by numismatists and is linked to historical practices of debasing coinage; the word is often associated with French linguistic origins. In English-language scholarship, the coins are frequently described as billon coins rather than by a specific base-metal or silver content.

Billon should not be confused with bullion, which refers to refined, valuable metal held for value or trade rather than for use in coinage. In contemporary minting, debasement practices like those implied by billon have largely ceased, replaced by standardized alloys and monetary policies that specify fixed metal content.

See also: bullion, electrum.