I've got fifteen early 20th century Chinese coins that come in two varieties: copper or brass. I'm trying to tell them apart. That ought to be simple (brass should be yellow), but in these cases I'm not sure - they are maverick. Copper or bronze coins can occasionally turn partly yellowish when exposed to the elements. (The brass versions are the scarce ones, by the way).
Here's what I did: I grinded a tiny part of the edge to see what they were like under the patination. They were all sparkling peach-coloured. I figured they would turn darker through regular oxidation. So I exposed them to hydrogen-peroxide, with minimal effect. Then I rubbed them in my armpit, which had an effect (
) - but I still can't say that they are clearly one thing or the other.
I refuse to give up (considering that this issue will arise again). So do any of you have a bright idea?
I should add that there probably were no officially prescribed compositions - or if there were, they probably weren't implemented. I suppose it boils down to testing for the presence of zinc. I'm a non-chemist.