How to unclean coins?

Here's a question I didn't think I'd need to ask: how to unclean coins, if that is at all possible?

Recently I did a swap with a nice fellah from Qatar and although he was terribly slow in shipping (waited until he received my coins - I guess the 45 5-star ratings didn't convince him) everything did arrive eventually. However, and you'll guess it, they're not coins, they're 30 shiny polished discs.

The bronze, copper-plated and aluminum-bronze coins are probably beyond rescue, but can I do something with the copper-nickel and nickel-plated coins? Throw them in my garden for a week, for example?

PS What rating do you guys think I should give? I was thinking about deducting 1 star for the slow shipping, but in my opinion that guy has no business in a serious coin collecting community. At the very least he should put a big disclaimer in his profile.

3/4 depending on whether he said they were cleaned or not

You can't in- clean em although I have seen a toning product that stops coins looking new on that wizard coin supplies !

I must admit I have received coins in a swap that I was really disappointed in and wish I had been told about it. I'd talk to him first and see what he says. I gave 5 stars as I didn't want to stir up any trouble: but perhaps he wasn't at fault. ?.

Well, they're not valuable coins or so, just contemporary middle eastern coins. He never mentioned he cleaned coins, and I never bothered to ask. I also don't ask if a train ever ran over the coins  

When asked he immediately admitted he cleaned them.

I often ask for a hi-res scan of all the coins I picked and often the swap partner is able to do that. Though it depends on their scanning "skills" it may be a bit hard to recognize if a coin was cleaned or not.

If he cleaned them, tell him that's bad to all coin collectors around the world and he should send you some uncleaned coins, hopefully he learns not to clean anymore. But it will be OK, just enjoy them as they are, and time will help them.
 As for putting them in your garden, yes that would help, and also touching them.