How to clean my copper old coins.

I want to clean some copper coins in my collection without degrading the coin quality. One more thing to ask do we have a link where we can find all the list of only rare coins in World.

For the first question: Anything stronger than mild soap and water or (acetone for gunk) is going to degrade the coin. Nearly all discoloration or patination on copper coins is a result of chemical changes to the metal itself. The only way to remove it is to remove that part of the coin. This is essentially what acids and polishes do. This kind of harsh "cleaning" does remove unpleasant coloration, but it removes nearly all value with it.

For the second question: I don't know that such a link exists or even could exist. The term "rare" is extremely subjective, to the point where it doesn't have that much utility.

The problem with copper is that everything that "cleans" it also cleans away the copper itself.
There are chemical methods but they are not for laymen and most often not worth the effort.
There is also the firing method but that is dangerous and can also destroy the coin if not done properly or even when done properly.

Quote: "Rarity in the sense of minting can always be gathered as per my thinking. "Rarity in the sense of minting can always be gathered as per my thinking. i. e. how many coins has been minted in the same year and mint which is mostly not available here. So wanted link for that.

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Quote: "Idolenz"​The problem with copper is that everything that "cleans" it also cleans away the copper itself.
​There are chemical methods but they are not for laymen and most often not worth the effort.
​There is also the firing method but that is dangerous and can also destroy the coin if not done properly or even when done properly.

​Sir you think other as layman that does means you are an expert. Can you suggest a method to preserve your copper coin degrading due to green, black or brown platina on it. Which is causing corrosion of copper coin.

I only know of them I hardly ever work with metals other than catalysts and electrodes.

A general rule is keep away organic compounds like sweat, spit etc. from copper surfaces. They can be the starters for other chemical reactions.
Also like for most other coins try to store them in a low to medium humidity environment at a stable temperature (bonus: keep a way the air).
A brown patina is not bad for copper coins and many prefer it on older coins.
If you have brittle green crystalline growths on your coin try to get rid of them when they are still small by carefully using a tooth pic or something softer without touching the non green surface.
Try to keep the surface in a basic (pH wise) and dry state to keep it from forming new verdigris spots.