Bronze / Copper Coin

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John1

Since copper alloy, brass, and bronze are names for different metals or alloys, ti comes down to what metals make up each of these material types, and that is really a matter of convention based on a loose specification for each material type.

Copper is generally accepted as having less than 2% tin and no zinc.
Bronze is generally accepted as having more than 2% tin and no zinc.
Brass is generally accepted as having more than 5% zinc and more usually, more than 25% zinc.

Naming problems arise when there are larger amounts than 5% tin and more than 10% zinc (the remainder copper) in the same alloy, but there is a tendency to class type of alloy as 'Brass'.

Further problems arise when aluminum is used for the alloy instead, but they are more commonly known as brasses due to their yellow color.

Australian yellow coinage metals are 92% copper, 6% aluminum (to give the alloy a yellow color, and increase corrosion resistance), and 2% Nickel (to increase wear resistance), with no Tin or Zinc at all. Has a very brassy color, yet is known as an 'Aluminum bronze'.

Hence, I can understand why the confusion in the naming the alloy of the 1949 Taiwan bronze? brass? copper? coin: - both could be right, and still be in disagreement !
The amount of tin and / or zinc in the alloy is on the borderline of a change in the naming of the alloy