500 yen coins change color (a.k.a. Behold the wonders of oxidization, kids.)

http://www.japanprobe.com/?p=11904

See if this was happening in the USA, it'll be a "SUPAH RARE MINT GENUINE ERROR COIN!! ONLY $79.95!!"

And SGS would've graded it WD-40 or something like that.

 

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Nice pictures of the Osaka Mint at the end of that piece.

 

That is actually pretty interesting, cupro-nickel shouldn't oxidise that quickly. I would like to know the exact cause for this.

 

Very interesting. Japan Mint rarely makes any errors but oxidization? Might be something to do when the mint was washing the planchet and it was washed with wrong chemicals.

 

More photos released from the Japan mint:

http://www.mint.go.jp/topics/new/pdf/59_photo.pdf

 

I have a bunch of 500 Yen coins sitting in un ideal conditions waiting for my next trip to Japan and they all look just like the day I got them. I'd be curious on what they find in their investigation. I'm betting someone just got a box of these and cooked them before spending.

 

Having cashed in a bunch on my last trip, I don't have any ¥500 coins that aren't part of my collection, but I must confess that since the current nickel-brass composition was adopted in Heisei 12 (2000), I have never personally seen a tarnished or discolored one.