Copper alloys are widely used for striking coins and medals. Even those items struck in silver and gold are alloyed with copper. I once wrote that copper is the world’s most popular coinage metal. Certainly before the 21st century when we had coins struck in bronze, silver and gold they were alloyed with copper. That holds true for medals as well.
Both bronze and brass are copper alloys. Both have the secondary metal of zinc. The two elements are found merged in nature. The Bronze Age existed since 4,000 BC. So not only is copper one of man’s most useful metals, it has been so for a very long time.
Technically any copper-zinc alloy with a zinc content of ten percent or less is bronze (it can also have some of the zinc replaced with tin and still be bronze). A content of ten to 15 percent zinc is red brass. When the zinc content reaches 16 percent not only is it brass, often called medal brass, it displays the golden hue we all recognize as brass.
Coinability – the ease of striking – and malleability increase with greater zinc content. Copper is harder than zinc. More zinc content the alloy is less hard and easier to work with.
Color also changes with the increase percentage of zinc. Adding additional amounts of zinc in the alloy changes copper-red to brass-yellow. At that 16 percent – 84 copper 16 zinc – the gold brass color is firmly entrenched.
Toning of the final alloy also changes. Copper tones slowly. A freshly struck cent even in bronze will tone in time, about six month’s time in normal handling, from one hand to another, from copper-red to brown. (It can also tone in harsh atmosphere conditions.) In contrast brass does not tone like bronze, it is fairly permanent in its golden tone.
Numismatists – and certainly the public — who cannot determine any precise formulation of copper-zinc by inspection alone, must describe a coin or medal by its color. If the piece is brown, it is bronze. If the piece is golden yellow, it is brass. (If it is heavy and golden color could be gold, of course.) Brass is widely used because it does closely resemble gold.
In medal rank, brass is beneath bronze: Gold, Silver, Bronze, Brass. If there were four platforms at Olympic Games, the lowest one would be brass. Bronze is more important than brass in the public’s mind. Bronze is more expensive than brass. Zinc is cheaper than copper. The greater the zinc content the less the cost, and certain bronze alloys are four times more expensive than certain brass alloys.
Thus bronze has the perception of greater value than brass. Bronze is more éclat, it has a higher esteem, respect, repute, and is more desirable to everyone.
The chart below is a study of bronze and brass alloys, not from a metallurgical viewpoint, but from a numismatic viewpoint. Coins and medals have been made of virtually every one of these alloys.
Types of Bronze and Brass Alloys
|Copper %||Zinc %||Tin %|
|Bronze or Brass Alloy||Cu||Zn||Sn||Other||Notes|
|Medal bronze||92-97||0-2||1-8||—||Exact formulations not exclusive for medals.|
|Coinage bronze||95||1||4||—||Also called French bronze.|
|Modern coinage bronze||95||5||—||—||Most malleable bronze.|
|Phosphor bronze||90-95.5||—||4.3-10 T-0.2P||Trace phosphor.|
|Statuary bronze (standard)||90||3||7||—||Best alloy for fine castings.|
|Commercial bronze||90||10||—||—||Easily available.|
|Gun metal||90||—||10||—||Strongest bronze alloy.|
|Red brass||85-90||10-15||—||—||Rich low brass, pinchbeck.|
|Jeweler’s bronze||88||12||—||—||Actually red brass.|
|Engraver’s brass||85||15||—||—||Red brass; ideal for engraving.|
|Medal brass||84||16||—||—||For brass “gold” color.|
|Oriental “bronze”||84||1||5||10 Pb||High lead content.|
|Tombac||82-99||1-18||—||—||Also called Mannheim gold, Dutch metal.|
|Gilding metal||80-90||10-20||—||—||Not unattractive in natural state, but usually plated.|
|Tin brass||79||20||1||—||One percent tin content.|
|Nickel brass||79||20||—||1 NI||One percent nickel content.|
|Bell metal||78-80||—||20-22||—||For bell casting.|
|Copper nickel||75-80||—||—||20-25 Ni||British cupro-nickel; also called nickel bronze or coinage nickel metal.|
|Bath metal||75||24.7||—||0.3 Ag||Wood’s metal; very soft, poor wearing quality.|
|Cartridge brass||67-70||30-33||—||Pb, Fe||Trace of lead; iron 0.07% max.|
|Yellow brass||67||33||—||—||Widely called OROIDE or goldene.|
|Speculum metal||67||—||33||—||Takes a high polish. Sometimes found with minute arsenic, antimony or zinc to improve whiteness and reflectiveness.|
|Nickel-silver||66-72||10-24||—||10-18 Ni||Formerly German-silver; expensive, high nickel cost.|
|Muntz metal||59-62||38-41||—||Pb||Lead 0.6% maximum.|
|White brass||51||49-65||—||—||Gray-to-white color.|