Copper and
brass are not separate metals, but two point on a continuum. It is hard to separate them. The colour depends on the amount of zinc added to the copper.
In an emergency, including a revolution, copper tends to come from whatever is at hand. Worn guns tend to be bronze or copper, while pots and pans are more likely to be brass. One day, the metal mixture may look yellow, the next day brown.
A similar thing happened in the early years of the French revolution. The anti-clerical revolutionaries melted church bells, some bronze, some brass and struck sols and double sols that may look yellow or brown. The coin in the picture was described as bronze by its owner, presumably because it is listed in KM as bronze.
If you want to follow the catalogues strictly, it may be best to judge the coin by its colour. Brown is copper or bronze, yellow is brass. The shade of yellow is not really important.
Peter
