Ruined pennies

I found this in Mother's hoard. A good illustration of what happens when coins are stored in non-archival materials. I pulled out the undamaged coins.

True, but still worth three cents. Dump them back into circulation please.

Interesting that the pure copper surface reacted but the bronze did not.

I expect it was the underlying zinc reacting through the copper. I also expect the bronze would also react, it would just take longer. 

I plan to keep them in the case as a stark reminder. I wonder what they will look like in 50 years.

The zinc could only react if the copper was breached.  To me it looks greenish which would be copper corrosion.

rsirian1, the evidence might suggest otherwise. A layer of copper measured in microns doesn't offer much of an impenetrable barrier over long contact. 

However, there is an anomaly. There should be four corroded coins, not three.

All true (~13 microns) but zinc doesn't have green corrosion byproducts and copper does.  Also I have 40 plus year old pennies that the copper protected the zinc just fine.  Regardless, the observation is still very interesting.