Pennys Destroyed?

I agree. Unless you see discoloration, I wouldn't even bother to remove it. You find this a lot with the old large coppers, also.

then again it could be toning setting in which some people will pay extra for if it fits the look they desire then some people are against toning.... if its just clear tho it prolly is varnish

"Powdery substance" sounds like the zinc is reacting with something - oxide, carbonate or sulfide; my guess would be sulfide in the paper. It's white in colour, I presume - most zinc compounds are white.

Either way, the coins are probably ruined as collectables.

Be careful, the coating that you see may be PVC, if the coins are in an old plastic slip album, it may be the plastic residue that you are looking at.
It should be removed, carefully. Acetone (also sold as AFTA) would be the best to remove it, just be careful.

As to the steel cents I am a steel cent collector. I have about 40 to 50 rolls of the things. I just like them from when I was a kid and they were new. Now as to the stuff on them. What you have is just a roll that someone put together of those oxided coins. That was just one of the problems with them. Don't try to remove that Oxidation. It acutally is preserving the coin. If you tried to remove the Zinc Oxide, and it can easily be removed, you will expose the raw steel under and that will begin to rust as fast as the air will let it and you will end up with just rust. You can check this out in a chem web site on Zinc Oxides or in any chem book. If you want put them in a plastic roll or 2x2's and the Oxidation process will stop. If not the ones I've been hoarding for well over 60 years should be a mess by now. As to the copper coins here is something to try. Take one that is not worth a fortune and feel it. Back when I was a kid we all used to put motor oil on coins to make them shine. Some kids used the castor oil their moms tried to make them take. If that coin feels like oil it is probably from an old keezer like me that thought all coins should shine. As already noted try a dip in Acetone. However, remember the stuff is flamable and can really be a not to good thing to get in your eyes. If you can find a glass spoon, fork or something to place one of the coins on and try dipping it in Acetone. You can use standard Acetone from Walmart. Don't be fooled about going out to buy the expensive stuff that is more pure because your going to rinse the coin anyway. After dipping in Actone, dip in Distilled water and again in another separate glass of distilled water. Now don't try to wipe it dry. Put on a soft towel and blow dry with a hair blow dryer. If the glaze is now gone you've done it. Now put the coins in either a new Album or separate 2x2's. Do not use the same album they are now in. Spend a few $ and get a new one. Also, to help preserve the coins, once in an album, put the entire album in a freezer bag and push as much air out as possible. I've been doing this for well ofer 60 years now and it things don't work out this way for the next hundred years I'll let you know.