About Acetone

First, thank you for saying this. You are an example for others just beginning to think about acetone.

Acetone is an excellent solvent of organic substances on a coin. It is not an all-conquering solution to any numismatic problem. Fingerprints are usually permanent unless removed immediately; no known method short of a wire wheel exists to remove them. Acetone will not do it.

On the other hand, it might be the solution for the 2x2 problem you mention. Some silver coins develop this effect as a result of the washing process at the mint - ASE's are a notable example - and this is not a reversible situation. Give acetone a shot; it will not do damage, it just might not do good.

If it does happen to fix the problem, it is time for you to repackage your stored coins because the 2x2's you have are unworthy of long-term use. No guarantee that the actual problem is the 2x2; it might be something in the atmosphere of the area where you store them, but that's a less-likely cause for what you would describe as a "milky" substance. Atmospheric contamination should lead to something you'd describe as "toning" or "tarnish."

Thank you very much Dave & biokemist6, I'll try that right away.
Where I live is humid and hot in the summer, and humidity level is high throughout the year. We had a record breaking hot summer in 2010. The room I keep my coins is in the first floor of the house, and there si another floor on top of it. The said room doesn't get direct sunlight and I keep the door shut at all times. It is one of the coolest and less humid rooms in the house.
I use Lighthouse brand 2x2's and keep them in Lighthouse brand album pages, and Lighthouse binders with outside protectors (Like an old casette).
I only spot the said milky substance on the %50 silver coins. The sterling silver coins that had stayed longer in the 2x2's are free of that substance. (they're British Half Crowns). Weirdly enough, when I check my cupro-nickel world coins (US and Canada quarters, nickels, Turkey coins, etc. etc.) I keep seeing that substance. Only gold and sterling silver coins seem to stayed pretty well inside same brand 2x2's. Most probably because they are nobler metals.
However, what I am going through with cupro-nickel and %50 silvers is very frustrating. I can not take a proper photo of what I describe as "milky substance" properly but it is like the water that stick to a cold surface from our breaths (sort of). I am moving to acrylic capsules (direct-fits) slowly but based on what I see, my upgrade will haste.
Any ideas what is happening with my cupro-nickel and %50 silvers?

There is a lot of different manufacturers of 2x2's. I would first of all suggest changing brands of those. IF for some reason the ones you are using are the cause of any problems, that well could be from the ones you are using. For one thing those may have been made a long time ago and include substances that cause problems, New ones, even fron the same company may not have that problem. Also, you may try a test on the air tightness of your 2x2's. If you use staples, pick one that is already stapled shut and put your mouth to one of the ends that would mormally open and blow. If your breath goes through, so does air, gasses and humidity from your general area.Myself I use a clear tape like 3M's clear tapes to seal the ends of my 2x2's.
As to Acetone, it will seldom remove fingerprints unless they are recent. As already noted your fingers contain acids that etch your prints onto the coin and that is there forever. It is now as much a part of a coin as if you took a knife and scratched your initials on them. Acetone has very little effects on coins except if there is a contaminate on the coins that is soluable in Acetone.
Contrary to that though I've done some really long testing on Acetone with coins. I've found that for some reason long term exposures with a coin soaking in Acetone does effect some coins appearances. I've had some Copper coins turn a real Red from long term esposures in Acetone and not normally explainable.

thanks Gary and JustCarl. You are teaching me stuff I didn't know before. This is why it is so great to be here.
is pure acetone safe to try on cupro-nickel coins? Does it affect their original lustre?

Acetone should not affect metal at all* so it won't affect the luster on the coppernickel.

* Acetone has been shown to have a slight effect on copper if kept in contact for a LONG period and under intense sunlight. Long period as in days.

As already noted Acetone has little to no effect on the metal of a coin regardless of the type of metal. And seldom would be considered cleaning a coin.
HOWEVER, in some instances a coin could be covered with organic types of dirt and a dip or bath in Acetone would remove that and leave the coin appearing as if cleaned. If too a coin had been cleaned in the past and dirt had accumulated, removing that dirt with Acetone would leave the original cleaned coin appearing cleaned. So although Acetone may not be considered a cleaning agent for coins, the dipping or soaking could end up making a coin APPEAR as if cleaned to a TPGS. And again, there is that HOWEVER. A dealer I know has sent cleaned coins to some TPGS's and had them slabbed and graded with no mention of cleaning. May or may not be just the TPGS.
One really important item is to remember that Acetone dissolves a large variety of STUFF. If you allow it to just evaporate on a coin, that STUFF will be redeposited on the coin.
As always it really pays to do a search on thie forum for all the information on Acetone.