Cardinal Rule. Do Not Clean?

That dime looks like it's worth a dime so clean it all you want and it will still be worth a dime.

Let it be your learning coin and see what a difference acetone makes. You can use a dip if you have one to see the effect as well. What hurts is when someone dips a 100+ year old coin removing the old skin that time has put on it.

The case that modern coins should not be cleaned is perhaps right,
but
almost all ancient coins and modern detector finds that have been recovered from burial need to be cleaned.

It is probable that the pictured coin may have spent a small amount of time in an aggressive soil environment.
Acetone will not help this coin.
It could have already been cleaned with good old soap 'n water to get thus far.

I have seen ancient silver and bronze coins cleaned with a soft bristle toothbrush with success, but a good alcohol soak after this treatment would help to dry out the water in the porous surface of such coins, to avoid the possibility of verdigris in bronze and billon (silver / copper alloy) coins later on.

Soap 'n water and a gentle rub with softened skin on the tips of the fingers works wonders on most gold coins (ancient and modern), in lower AU grades or less.
Every such gold coin that I have, has had this treatment before enclosing in a 2x2.

To see how museum professionals clean and preserve their coins, refer to Youtube videos.

Never touch any proof coin, irrespective of the metal, except, perhaps with acetone, and then only if required.

generally, yes, cleaning should not be done to coins - it will hurt the value of them.

Cleaning coins is often necessary but you must know how to do it and which ones can benefit. Some coins will look worse after cleaning and if you do it wrong you can eliminate the value of formerly valuable coins. It's mostly of experience and knowledge so you want to practice on coins you don't want.

The coin above looks like it might profit from a "thumbing". Only do this on circulated coins. There is relatively little danger of wrecking a coins this way though many either can't be saved or can look worse. I can't really tell from a picture that this coin is even a candidate with certainty. Uncirculated coins should not be thumbed and if you do it anyway they must be soaked in alcohol or acetone afterward.

Once you have a good candidate for thumbing it is performed by pushing olive oil or body oil into the surface. Start on the smoother side. If it is improved do the opposite side as well. If there are any accumulations they can be gently worked with a black locust thorn or a toothpick. This is a very dirty process so plan on washing afterward.

Some circulated coins can be improved by washing or soaking in solvent but this tends to be ineffective on the the things found on circulated coins. These involve things they encounter in circulation as well as layers and layers of ancient tobacco smoke.

Uncirculated coins require a far lighter touch and no abrasives of any sort. Strong chemicals can impair or strip the luster.

The key is experience. If you want to keep the '08-D dime then find another coin that looks like it and practice on it.

It's a great hobby and the longer you're in it the more you'll know. You can even collect coins in such a way as to lead you to the type of education you want. The friendships you make in the hobby are great and coin collectors are a fascinating group of individuals.

Hi All!!

I purchased an entire roll of 1$ 90% silver West Point commemorative coins. Many of the coins have this REALLY UGLY brown gunk on the coins. This does not look like pleasant toning, more like gross tarnish. Should I really leave these coins alone and not try to clean them? I personally would not buy a coin in this condition. If I did try to clean them what is my safest bet?

OK I will shortly...

Also these were all in a roll and I purchased them in an online auction so I didn't see all the coins