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MEXICAN REVOLUTION - 2 Centavos Hidalgo del Parral - BRASS OR COPPER ?

Started by MORGENSTERNN, May 07, 2017, 01:29:01 PM

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I recently bought a 2 Centavos from Hidalgo del Parral - Chihuahua, with a weight variation, see here,35839.0.html

I'd like to have your opinion about the composition of that coin because it's colour seems closer to brass than copper.
The red oxidation of that coin is also similar to a red oxidation that I can observe on a Belgian Congo brass coin (2 francs 1943).

To have your opinion I took a picture of that coin among Mexican copper coins from the revolution era (picture 1) and among brass African coins showing a similar red oxidation (and a bronze-alu coin from Guatemala, I don't get any brass coin from Central America).

If that coin is well made in brass instead of copper it should be a KM-607a scarcer than the KM-607

Thank you !


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.

An unidentified coin is a piece of metal. An identified coin is a piece of history.


Quote from: Figleaf on May 08, 2017, 08:08:45 PM
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.

Thank you Peter !
If I only judge by colour my coin should be in brass : the copper ones are from red/pink (UNC) to dark brown almost black while brass coins are yellow with sometime red/brown oxidation


Flans for this type were made from salvaged scrap metal.  The larger part of them are electrical grade copper.   Brass is copper + zinc.   The commonly encountered kind is gold colored, about 30% zinc, in non-technical parlance called "cartridge brass".   At 30% brass is at its maximum "elongation", meaning it is best for forging, making die-struck shapes, and coins.  Maximum hardness is at 43%.  Cast coins have been made as high as 50%. 

Brass tends to become enriched with copper on its surface.  That is extreme with wet conditions, but also occurs completely dry.  It is accelerated by higher zinc content.  Coin brass will redden both from surface copper, and formation of cuprite.  The way to distinguish brass would be scratch the edge.   Chances are this coin has previously been cleaned.