Geelkoper of messing is 'n legering van koper (Cu) en sink (Zn), in verhoudings wat gevarieer kan word om verskillende kleure en meganiese, elektriese en chemiese eienskappe te verkry, maar koper het tipies die groter verhouding.[1][2] Dit is sedert prehistoriese tye in gebruik.
Dit is 'n substitusionele legering: atome van die twee bestanddele kan mekaar binne dieselfde kristalstruktuur vervang.
Geelkoper is soortgelyk aan Brons, 'n ander koperlegering wat tin in plaas van sink gebruik.[3] Beide brons en geelkoper kan klein proporsies van 'n reeks ander elemente insluit, insluitend arseen (As), lood (Pb), fosfor (P), aluminium (Al), mangaan (Mn), en silikon (Si). Histories was die onderskeid tussen die twee legerings minder konsekwent en duidelik, en toenemend gebruik museums die meer algemene term "koperlegering".[4][5]
The term copper alloy should be searched for full retrievals on objects made of bronze or brass. This is because bronze and brass have at times been used interchangeably in the old documentation, and copper alloy is the Broad Term of both. In addition, the public may refer to certain collections by their popular name, such as 'The Benin Bronzes' most of which are actually made of brass