Metal rusted to coin

I've heard to never clean your coins, but I think this might be the exception. One side of the coin has the remains of another coin stuck to it with rust. Any ideas how to expose the coin underneath?

thx

I think it came out pretty well. I ended up putting it a solution of citric acid, 2 parts water to 1 part of citric acid powder from the specialty kitchen store. I think I soaked it for about 6 hours total, gently removing the loose rust with a soft toothbrush. I stopped with some of the extra metal still on the coin, mostly because I wasn't seeming any change over the last few hours and I didn't want to press my luck.

I found a lot of good info about cleaning silver here.  https://www.numisforums.com/topic/7284-cleaning-silver-coins/

Shout out to user roerbakmix for the chemistry skills and for sharing.

Revealing the obverse side made it easy to identify it as Hamelin, City, which is cool because the 1578 1/24th Thaler is not yet on here. I'll enter it once I can get my hands on a copy of Kalv/Schr “Münzen der Stadt Hameln” and confirm my identification.

Well done, you have restored it not cleaned it. The old adage „never clean your coins“ comes from people with no knowledge of coin restoration - and thus an almighty f§€% occurs! It’s like saying „never drive a car“ to people who don’t know how to drive - it’s obvious, but with training they are able to do it.

Any coin dealership / auction house / experienced coin collector will emphasise the point so that value isn’t being wiped off  higher value and or higher grade coins, and now it has become a commonly repeated phrase, but Jesus if you have a bloody great crust on a coin or it’s covered in muck you are going to need to clean it (now called restoration) because the value and beauty can be increased, like yours. Thousands and thousands of coins have been restored, sometimes they turn into a train wreck and people jump on their high horse about cleaning - but no one ever says a word when it was done expertly and no damage was done. Like no one compliments anyone for not having a car crash!

So to you, well done for making you coin better 👍