I recently found my 2nd silver war nickel and shined it up with baking soda and water. It not worth much more than melt value, if any at all, so I'm not affecting its value. After shining it up, it really needed cleaned due to some stuck on junk near Jeffersons chin, I decided I wanted a rainbow tone or something near to that affect. I learned about a method using egg yokes due to their sulfur content and this is what I did...
Separate the yoke from an egg and discard the whites. Put the egg yoke in a tupperware with a lid and microwave just long enough to cook through. In my microwave this only took about 15 seconds for one egg yoke. Once it is cooked through, stir up the yoke and break into very small pieces. Place the clean shiny silver on top of the yoke and cover with the lid. Monitor and flip the coin every few hours and remove when you get the desired tone. Here is my war nickel after cleaning with baking soda and then again after placing in with the egg yoke for about 30 hours or so. I would assume 90% silver coins will acquire a tone at a different rate than this 30% silver nickel. This is the only time I have tried this and could only recommend it for similar scenarios where the coin has no room to drop in value. Don't mess around with coins that have a value beyond their silver content unless you really know what your doing and assume your own responsibility for any loss in value afterwards.
Also, I don't know how resilient this toning will be. Its possible it may not hold up to handling and might just smear off if rubbed. If you're going to put it in a placeholder right away it would be fine. If you don't like the toning you can easily remove it with the same method you cleaned the silver to begin with.
You have to click the image below to animate the before/after toning GIF.
http://upload-pics.org/images/40155399472650585306.gif
Separate the yoke from an egg and discard the whites. Put the egg yoke in a tupperware with a lid and microwave just long enough to cook through. In my microwave this only took about 15 seconds for one egg yoke. Once it is cooked through, stir up the yoke and break into very small pieces. Place the clean shiny silver on top of the yoke and cover with the lid. Monitor and flip the coin every few hours and remove when you get the desired tone. Here is my war nickel after cleaning with baking soda and then again after placing in with the egg yoke for about 30 hours or so. I would assume 90% silver coins will acquire a tone at a different rate than this 30% silver nickel. This is the only time I have tried this and could only recommend it for similar scenarios where the coin has no room to drop in value. Don't mess around with coins that have a value beyond their silver content unless you really know what your doing and assume your own responsibility for any loss in value afterwards.
Also, I don't know how resilient this toning will be. Its possible it may not hold up to handling and might just smear off if rubbed. If you're going to put it in a placeholder right away it would be fine. If you don't like the toning you can easily remove it with the same method you cleaned the silver to begin with.
You have to click the image below to animate the before/after toning GIF.
http://upload-pics.org/images/40155399472650585306.gif