Alloys of copper with tin, zinc and lead have been used for at least 2,000 years due to their ease of casting, good strength and corrosion resistance. Early uses were for brooches, mirror cases, church doors, fonts and statues. The use for cannon in Mediaeval times led to the term ‘gun metal’ being adopted; this use is now obsolete with the manufacture of steel ordnance.
Today, in the UK, the term ‘gunmetal’ is applied to a family of copper-based casting alloys containing between 2-11% tin and 1-10% zinc. Modified forms may contain, in addition, such elements as lead (up to 7%) and nickel (up to 6%) when the alloys are classified as ‘leaded gunmetal’ and ‘nickel gunmetal’.
Gunmetals are noted for the manufacture of intricate castings required to be pressure tight such as valves, pipe fittings and pumps. They are also frequently used for bearings where loads and speeds are moderate.
Gunmetals are the first choice for modern statues, an example being the 2.1 metre high sculpture of Sir John Betjeman by Martin Jennings in St Pancras International Station, London.
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