I think technically it is oxidation or chemical reaction, but it is very acceptable and some people seek out toned coins. Look for some posts by Lehigh96 for some great examples of toned coins.
Some people like blast white coins some like coins that have subtle toning and some like crazy rainbow toning.
I'm a little confused. Are you using FOLDERS OR ALBUMS. Folders are the ones where you can not see the reverses of the coins. Albums usually refer to the ones with plastic slides where you can see both sides of the coins. Folers are OK for kids, amateurs and/or people that really just want to have fun. If your planning on keeping those coins for a long time, hopefully you mean Albums. From the dates it sounds like your using Whitman Folders though. Most modern day Albums are from 1909 to present or almost present pending manufacturer. That shinny stuff in the back of the slots for coins is the glue from the manufacturing process and not really great for coins for long periods of time. And if that was in fact a Zip Lock plastic bag, don't let people scare you with the old PVC stuff. I checked with the organization that makes Zip Lock Bags and they said NO PVC in thier products. Just more of what is usually known as old wives tales.
Sorry, you're right... I'm talking about Folders. In fact, the coin guy said if I ever found "this coin, that coin, or this other coin" referring to old pennies... he said don't you DARE put them in here. So yeah, I'm not planning on putting anything fancy in them. Just used, circulated common stuff. I did get thinking though, that it would be fun to start at a logical point (2000 on up? I'd have to see what albums are available) and begin collecting brand-spankin' new coins of the different denominations as they are issued (once I catch up). But to put those in the real nice albums so they never get tarnished and stuff. I need to get educated on what is out there, and what ones are really good. As for the PVC comment, maybe I took this wrong, but I thought the poster was referring to little 2x2 plastic baggies that the coins I bought came in. I do plan to get the other ones out of the zip locs and into the little 2x2 cardboard deals. Well, some will go in a folder.
That is cool Farns! Glad to see you all enjoying it. I love golden toned nickels just like you pictured. Very cool. Nice liberty nickel also - time for another book???
I have heard this before but don't know the facts.Are you referring zip lock bags? to How about the plastic cello that comes in the special mint sets? I have heard that flips can also be bad.