To Clean; Not To Clean: War Nickels?

I know I will get an ad from BadThad but....Never clean coins!

Littlemoney has it - vinegar contains acetic acid which will react with the surface of the coin. Altering the surface (chemically or mechanically) of a coin does significantly lower its numismatic value in most cases, so keep that in mind. Now, to be honest I've never soaked a War Nickel in vinegar so I couldn't tell you how long it could resist such a bath before being obvious. Regular nickels are obviously acid bathed within a few hours.

If you want to experiment with cleaning coins, I'd suggest starting with something with a higher silver content like Roosevelt dimes or Kennedy halves. You have a passable chance of making one look better with a dip in a cleaning solution like E-Zest or something like that. A circulated War Nickel will always look ugly no matter what you do to it. They just tone too ugly and too quickly.

Please keep in mind that a quick rinse of distilled water or acetone (quick, rinse, not 3 days) isn't considered "cleaning" in the pejorative sense by most collectors. You can call that conservation since neither distilled water nor acetone will generally react with the metal on the coin's surface. Vinegar will. EZest or jewelry cleaner will. Baking soda and toothpaste are even worse since they are abrasive and will mechanically damage the surface of the coin.

Go ahead and search the forum for info on cleaning coins - there are more opinions and more information from people who know more here than I.