Author Topic: not ancient but quite old  (Read 2075 times)

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Offline scottO

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not ancient but quite old
« on: October 27, 2010, 09:49:03 AM »

i know the dates of the emperor and mint, but i want o know why this is the only cash coin i have that looks this way (i have others with brasy looks on the outer rim areas but dark on the inside areas)

Offline badon

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Re: not ancient but quite old
« Reply #1 on: October 27, 2010, 12:37:55 PM »
I'm not familiar with the coin. Could you explain more? What's it made of? What about it's appearance are you asking about (I assume the yellow toning)?

Offline scottO

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Re: not ancient but quite old
« Reply #2 on: October 27, 2010, 02:45:27 PM »
yes the yellow colour
it is a cash from Shun Chih period (1661-1722) of the qing dynasty, all examples i have have the rim as a yellow colour but the inside area as black

Offline badon

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Re: not ancient but quite old
« Reply #3 on: October 27, 2010, 03:07:12 PM »
From this site:

http://wwwchem.uwimona.edu.jm/courses/copper.html

"The commonest [copper] ore is chalcopyrite, CuFeS2, a brass yellow ore that accounts for approximately 50% of the world's copper deposits."

My guess is that your copper (Cu) coin has natural iron (Fe) impurities, and it was exposed to sulfur (S) to produce a patina of chalcopyrite (CuFeS2). A google search for yellow copper compounds shows a variety of other possibilities, including copper chlorides, but the particular shade of your coin, combined with the likelihood of it being stored near or within objects containing sulfur, and the obviously easy way iron could be involved as a natural impurity, my first guess is chalcopyrite, which is famous for it's golden color.

I think it's quite a pretty coin. The black color on other coins is probably just a common form of copper oxide. Your coin was probably coated with a laquer or oil or something to preserve it at some time during its history, which prevented oxides from forming, but supplied an even coating of available sulfur for the copper and iron to grab.

All just guesses, but your coin sure looks golden. I can't think of anything more golden than pyrite (except brass, which is ruled out because that would take the fun out of it).

There are a few people on this forum with professional backgrounds in chemistry that might have more to say about this.