Bronze decease, an agressive form of corrosion that attacks copper and bronze coins, often manifesting itself as a green or blue green deposit that is soft and powdery. It will eat into a coin if not treated immediately.
If Clavdiv's experience of RenWax works for him, that's great. However, if moisture can cause real problems, then that is a disadvantage to be taken seriously. Admittedly, I have no first-hand knowledge in these matters.
I knew what you were talking about. Ipana had a funny commercial back then that had a cameo in the movie "Grease".