The terms brass and bronze have become so muddied that they don't mean much if anything specific anymore. I would call all those medals copper with trace amounts of alloy with the one exception that was 2% zinc which is a true copper-alloy.

The same question was nagging me when I was researching medals from my collection. In one catalog a medal can be described as copper, in the other - as bronze. What proof does the author have to choose one name over the other if he did not test the alloy? (I do not think that either Freeman or Storer examined the chemical content of each medal when they were compiling their great works). So I came to a very simple conclusion - that numismatists use the metal name in a common sense; they describe more the look of it than the content. For a chemist it may matter that the brass is an alloy of copper and zinc, while bronze is a mix of copper and tin, but for a numismatist (especially a newbie like myself) it may be OK to go with a common sense and a duck test for those few medals I could not find authoritative reference. I will call a copper anything that looks like a copper, a bronze - any shades of brown, a brass – anything with hues of yellow. After all, I am looking at the medals and describing them as objects of art.

I read the brass & bronze definitions in last week’s E-Sylum, and thought I might clarify it from a metallurgist’s point of view.

The problem comes about in the origin of the names, from tradition dating back hundreds of years for some specific alloys, vs. modern definitions for general groups. The modern metallurgical definitions I was taught in my courses for a Master's degree in metallurgy reveal a confusing difference between alloy groups and specific alloys.

For the general categories, the definition of a brass is copper alloyed with less than 40% zinc, and no other elements. Copper with over 40% zinc is Muntz metal. Copper alloyed with anything other than zinc, (especially tin, but also aluminum, nickel, etc, and it may also include zinc along with these other elements) is considered a bronze alloy. An aluminum bronze is copper with aluminum plus possibly other elements, nickel bronze is copper with nickel plus possibly other elements, etc.

The confusing problem is the overlapping traditional naming for the very specific alloys, which go back hundreds of years, and which are not fully consistent with the above modern system. “Commercial Bronze”, composed of 90 copper and 10 zinc, is really a brass alloy by modern definition. “Aluminum brass”, at 76 copper, 22 zinc, and 2 aluminum, is really in the bronze series.

The situation creates more confusion than it alleviates. Specifically for coinage, I believe that most of the copper zinc alloys that are used have a more golden color, and the copper tin alloys have a lighter color. For coinage, it may be more practical to use the modern category definitions which are more consistent with the colors we see in coinage, and ignore the specific traditional names like “Commercial Bronze”. Reference for most of the above is “Physical Metallurgy for Engineers”, Donald S Clark and Wilbur R Varney, Van Nostrand 1962, pp 392-393.

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.

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."

Anyone who wishes to continue the conversation can contact me at dave@lovetttokensmedals.com . And John Kraljevich said bronze was "any non-red copper alloy". That's pretty simple!