You would have to be more specific. Rust is a really general term and usually associated with Oxydation on Iron. Again though Rust is rather a vague term and you should either supply a photo or very carefull description. Example would be the metal of the coin, the color of the rust, how much is on the coin, etc. Other wise it is like calling a doctor and telling him your stomach hurts so should you cut it open to see what is wrong?
He probably means rust. Most notgeld cons are made of one of two metals, zinc, and iron. Rust tends to be a problem. Unfortunately if the coin has actually rusted there isn't a lot that can be done short of abrasive cleaning to remove it. You might try navel jelly and a softer bristle brush but it will still show evidence of the harsh cleaning. (Before the purists start squawking, this is almost a fact of life for notgeld collectors. The metals used were so reactive and the people who used the coins often resulted to such abrasive cleaning so that abrasively cleaned pieces are pretty much the norm for most issues.) After the rust has been removed and the coin rinsed well, use an acetone rinse to thoroughly dry the coin. Then you have the choice of applying a thin oil film or storage in a very low humidity environment to prevent further rusting. I'm not advocating you do this, just saying that that is really probably the only way to get rid of it and/or stop it.
Yeah, thanks, it is rust on what looks like some iron-based metal. I've got the same problem with a small fragment of an iron meteorite.
EDTA might work, but where do you get it? The only price quote I can find, other than for EDTA as a nutrition suppliment at $59 per oz for a product of unknown concentration (The figures they give don't add up.) is $19 for 2 ml of a .5M solution.
