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Copper

Copper.  A metal element, the basis for many coinage and medal alloys, making it the most useful metal in the field. More numismatic items are made of copper than any other material, but most always in mixture with other metals, thus historically it is the world's most popular coinage metal. With zinc and/or tin it forms bronze, with nickel it forms copper nickel, with silver it forms coin silver or sterling, with zinc it forms brass, with zinc and nickel it forms German silver or nickel-silver. Whenever it is used alone it has a distinctive red color, when alloyed with other metals it takes on colors from brown to white to yellow.

Pure copper is most useful in the manufacture of metal patterns and shells, predominantly by electroforming and electrolysis. Electrotypes must be pure metal to effect an electrolytic circuit and copper is one of the best conductors of electricity (however, certain impurities markedly decrease its conductivity). Thus absolutely pure copper must be employed for anodes for use in electrolysis.

Copper is the least expensive metal of all the metal elements with electrolytic properties (nickel, silver, gold, chromium, rhodium, others). Thus the importance of copper in electroforming is so great that literally no coin or medal from three-dimensional models anywhere in the world could be made without copper. Also, obviously, it is the basis of all copper plating.

As a further, but less important point, copper is highly suitable for repoussé. Because of its malleability thin sheets of copper can be hammered from the back to form a design on the front (the process of creating the Statue of Liberty as well as small objects so made). As such beaten copper is a term for all repoussé work.

The first metal to be used by man, copper is universally distributed throughout the world. Copper is the most ductile and malleable of the common metals (along with silver and gold) ranking it very high in coinability. It readily combines with other metal elements to form useful alloys, its strength can be changed by varying the alloy, it has deep-drawing capabilities in machining, has resonant qualities when struck (or cast, like a bell), and has excellent anti-corrosion capability (even with salt water).

Copper becomes work hardened but is easily annealed making it particularly suitable for art medals that require multiple striking. Easily cast, easily machined and worked in all metalworking ways, copper is the ideal metal for all phases of the art medal field.

Copper tones brown, but also forms a green carbonate which will increase to cover the entire surfaceincrusted patina  – which then protects it from further corrosion. Copper is the basis for all bronze alloys which can be given a multitude of patina finishes, from browns and greens to many others. Thus the importance of copper extends from the process prior to making the dies to the end product and its permanent finish and coloration.

Copper is abbreviated cu (from Latin cuprum) for its use as a chemical element

and ae (from Latin aes) for use in numismatic work.

See bronze, composition (2).

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators

COMPILED AND WRITTEN BY D. WAYNE JOHNSON

Roger W. Burdette, Editor


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