I purchased this coin in a lot and wasn't intending on ever finding anything like this in it so it was a bonus to begin with. I soaked it in acetone and the appearance improved greatly. I tried 2 other overnight soaks and it didn't do anything to help or hurt it. I am wondering if there is anything else that can be done to remove this scale white on the coin or is it time to give up? The photo is a lot off color because I am using a USB scope to take this photo. The coin is a greyish color and the scale for lack of better term is white.
Those Zinc, Third Reich coins are notorious for real bad corrosion. And it can not be be reverse in any way. The corrosion eats into the surface, if you can remove the corrosion it will just leave pitting.
That one looks to be in a terminal state. What I've done with zinc coins that just have a white haze or spots is soak them in lemon juice. That has helped somewhat, but as alurid mentioned, this one is too far gone.
Unless it's a key date or it's worth a bit - I personally don't think it's worth spending that much time and effort.
Zinc coins always deteriorate this way. The damage has reached its last stage, it is almost impossible to reverse the same. If you are interested in German coins, you can rather look for some fresh ones here: [Spam link removed by moderator]
When I was stationed in Germany from 1974-1977 my metal detector finds were at best bleached out and hard to read the dates. We used chisel tip black magic markers to restore the color and make the details visible. This left a coin with a distinct odor but it was an improvement in appearance. I don't think you would lose any value.
I figured they would be reasonably priced however I like the challenge. Plus it allows you to experiment without having to worry about messing up anything good!