I don't get how uniface errors occur - is it because one of the dies is just not there or I suppose you can sandblast one side and let it circulate for a while.

I've wondered about that too, but sandblasting isn't an option, because the weight would be influenced quite alot.

I think they are made by place 2 or more planchets between the dies, perfectly centered. But then you still will have some ghosting on the blanc side. The only other option is that there is a blanc die instead of the obverse or reverse die. Those wouldn't be errors, but trial strikes then.

Anyhow, it's strange how they end up in circulation...

Jos

Jos, I now have two South Korean coins that are uniface which is quite bizarre, considering that error coins from South Korea is extremely rare. Both of them seem to be circulated at one stage. The only other uniface "coin" that I have is a possible trial strike Russian 1992 100 ruble coin which no catalogues ever mention it.