Coin Cleaning

First, Dan, welcome to the forum! We're a friendly group and the collective expertise is tremendous!

You mentioned a four-letter word here, "cleaning", so you're likely to receive a LOT of responses. The most important comment will be the same as mine: do NOT clean these coins! A cleaned coin is an altered coin which then loses virtually all its collector value. Your two Columbian Exposition halves are definitely collector items no matter what their condition or color. Cleaning would ruin them from a numismatic viewpoint.

That said, National Conservation Service (NCS) http://www.ncscoin.com/ professionally conserves (cleans) and encapsulates coins. There are very few of us (I'm not one of them) who have the expertise to clean a coin and get away with it.

Fred

So much depends on if your interested in those coins as a hobby, investment, for resale, display or what. If you don't care about the value and plan on keeping them, then the type of cleaning doesn't matter. Once you clean those coins the value will drop substantially. Part of the reason is any cleaning will take away some of the original material as well as any dirt, toning, discoloration, etc. If you ever watched that TV show called Antique Road Show you have noticed any tampering with any old item reduces it's value to a collector.
However, if you feel the urge to really clean those coins, you may as well use Tarn-X, Lemon Juice, battery acid or any of the jewlry cleaners on the market. Many solvents will make the coin worse and some will damage the material that is left. Some will further darken the coins. If it is really a necessity to clean them, try going to just about any coin web site and type in cleaning coins for a search of what has already been discussed. Really common question about coins.