Dick Johnson submitted this essay on the differences between bronze and brass. Thanks!
The Manhattan Beach California struck piece mentioned in the last two issues of E-Sylum is an attractive numismatic item. It is called a "coin" which does not bother me -- it is not a coin by numismatic definitions because it does not bear a denomination -- but it is struck in a coining press so the term can be considered appropriate because it squeaks in under the umbrella of "coining."
What does bother me, however, is calling the bronze version "brass." Granted, the boundary line between bronze and brass is not finite. Both are alloys of copper. I once wrote that copper is the word's most popular coinage metal. Mixed with a portion of zinc and or tin it is bronze, it is alloyed in coinage nickel, with silver it forms sterling or .900 fine silver. Copper is even alloyed with gold to lessen its karat content.
So what is the difference between bronze and brass? If the zinc is less than 10% it is bronze. But numismatists are not satisfied with the term at this precise formulation.
For numismatists -- who can best describe an item by inspection -- the term is determined by color. If the piece is brown it is bronze. If it is golden yellow it is brass. But the color of the metal alloy doesn't change until the zinc content is above 15%, or as expressed in the metalworking trades, copper 850 zinc 150. This adds to 1000, but sometimes expressed .850 and .150 to add to 1 -- the total amount.
Technically that area between 10% zinc and 15% zinc alloyed with 90% to 85% copper is called red brass. At zinc 160 copper 840, one percent more zinc you find a solid yellow-brass color. This continues as the amount of zinc increases. However red brass is not permanent. Like a freshly struck U.S. cent it is copper-red color that after about six month's time harsh exposure or much handling in circulation has turned brown. It is the copper content that causes the color change.
All of these copper alloys have been used for coins under a variety of terms for the various compositions. These include French bronze, tombac, Dutch metal, Mannheim gold, copper-nickel, and ultimately oroide or goldene. The latter is at 33% zinc content with an obvious brass-gold color.
In medal rank, brass is beneath bronze: Gold, Silver, Bronze, Brass. Thus bronze is a tad bit more éclat with a higher esteem. respect, repute, it is more desirable.
This wide diversity of zinc content in copper alloys also has another popular use -- foundry casting of statues. Statues can be made from the same metal as copper, bronze or brass alloys used for coins. The standard alloy for bronze casting is 900 copper, 030 zinc, 070 tin. Makes the best for casting and the patina afterwards for both indoor and outdoor statues.
When the zinc is entirely replaced by tin it can be used for bell manufacture. However, after centuries of bell manufacture, bell foundries like to get as close as possible to 78 to 80% copper and replacing the zinc entirely with tin content at 20 to 22%. I guess this is best for the sound quality.
Impurities can be found in all these compositions by spectrographic analysis. Other metal elements are often found in these alloys. A trace of phosphor is sometimes beneficial (up to 0.2%). A trace of lead is undesirable. However, even lead in a copper-zinc composition is permissible for making cartridge casings for ammunition. Since these encase lead projectiles, lead will be found in spent cartridges, particularly when reused over and over, or melted and made into new cartridges.
We could not have all the world's coins if we did not have copper. The alloys of copper for numismatic items have been called many things. But it's okay to call brown coins or medals "bronze" and golden yellow coins and medals "brass." One variety of the Manhattan Beach Centennial Medal is brown. Let's call it bronze.