Expert: Dmitry Livshits - 4/2/2010

Question
My friend has a ton of these really cool Nazi German coins. Including a ten pfennig zinc peice that would we worth quite a lot of money, however, it has a stain of this strange white non-mettalic substance that seems to plague those specific German coins. We don't know wether to clean them in water, whether this could damage them, lime? vinegar? what should we do? Whats the safest and best way to clean german coins and do you have any idea what the white substance is.

Answer
Hi Cameron,
These white spots plague all coins made of zinc, such as the 1940's Nazi coins that you have. This is simply oxidation from years of contact with air and moisture. Normally rust shows up as an orange color on most metals, but on zinc it's white.
There is no way to truly clean it off. And doing so would end up destroying any collector value that it has. A light rub with hand soap and warm water often removes some of the white, as does a soak in pure lemon juice. However, it will not remove the visible surface corrosion left over beneath the white spots. This is a major reason that old zinc coins that are free of spots or have original mint luster are so hard to find.
Even with white spots, some of the dates and mint marks can still have a good value. For example, you may want to look out for coins dated 1945 or later, as well as any of the military issues which will have a hole in the center and a different design from the other coins.
Thanks for the question! =)