Cleaning includes, soap and water, wiping, rubbing, alcohol, acetone, commercial cleaners, and jewelry cleaners. Any form of cleaning will remove the original luster the coin had, leaving a dull appearance. Cleaning is easily spotted by dealers and most collectors. Cleaned coins usually lose 30% or more of their wholesale/retail value. Conservation: This is a relatively new proceedure introduced to the coin hobby. Many became aware of the conservation services after the last couple of shipwrecked recovered coins. This process is becoming widely accepted throughout the hobby. The coins when conserved by a professional service do not harm the coins surfaces. A good article written here by NCS. Recommended reading. http://www.ncscoin.com/ Accepted cleaning: There are a few times when cleaning should be considered. (should only be done by a professional). PVC damage, tape residue, very ugly toning. If you have coins that do not warrant the costs of professional cleaning, yet fall under the conditions of needing cleaned, do so only with proper coin cleaning chemicals. Home made cleaners should never ever be used. Remember that any cleaned coin will substantially lose any value it had while original.