About a month ago I bought a few rolls of cents. I took out the ones worth keeping and dumped the rest in a metal container, and forgot about them. Yesterday when I opened them I found that some of the cents had developed a white, crusty like quality to them. It does not appear to be PVC staining because some of the patterns created by this mystery substance appear to have been fluid-like. Some coins that have browned also appear to have also regained some of their luster. Also there is minor toning that has appeared in most of the coins. Some of the coins toned are also cents that have been recently minted (2010). Another thing is that some of the coins have developed black spots, some small others almost covering the whole design. What is this stuff? Does it make the coins worthless or does it raise their value because of the toning/regeneration of luster? Anything will be useful.
Examples of Substance: http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Stained/?action=view¤t=2004.jpg http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Stained/?action=view¤t=2004.jpg#!oZZ2QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FStained%2F%3Faction%3Dview%26current%3D2001.jpg%26 http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Stained/?action=view¤t=2004.jpg#!oZZ3QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FStained%2F%3Faction%3Dview%26current%3D2000.jpg%26 http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Stained/?action=view¤t=2004.jpg#!oZZ4QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FStained%2F%3Faction%3Dview%26current%3D1994.jpg%26 http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Stained/?action=view¤t=2004.jpg#!oZZ5QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FStained%2F%3Faction%3Dview%26current%3D1987.jpg%26 http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Stained/?action=view¤t=2004.jpg#!oZZ6QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FStained%2F%3Faction%3Dview%26current%3D1985.jpg%26 http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Stained/?action=view¤t=2004.jpg#!oZZ7QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FStained%2F%3Faction%3Dview%26current%3D1977_Reverse.jpg%26 http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Stained/?action=view¤t=2004.jpg#!oZZ8QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FStained%2F%3Faction%3Dview%26current%3D1973.jpg%26 Sorry, pics are didn't reorient themselves.
They're still worth 1 cent. Similar things happen to coins that fall in my night stand. They then get wet (spilled coke or water) surrounded by the fumes of all the various medicines and ointments. They make great test material for conservation practice.
Renewal of Luster: http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Renewal%20of%20Luster/?action=view¤t=2001_AngledView.jpg#!oZZ2QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FRenewal%2520of%2520Luster%2F%3Faction%3Dview%26current%3D2001.jpg%26 http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Renewal%20of%20Luster/?action=view¤t=2001_AngledView.jpg#!oZZ3QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FRenewal%2520of%2520Luster%2F%3Faction%3Dview%26current%3D1982.jpg%26 http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Renewal%20of%20Luster/?action=view¤t=2001_AngledView.jpg#!oZZ5QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FRenewal%2520of%2520Luster%2F%3Faction%3Dview%26current%3D1973.jpg%26 http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Renewal%20of%20Luster/?action=view¤t=2001_AngledView.jpg#!oZZ4QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FRenewal%2520of%2520Luster%2F%3Faction%3Dview%26current%3D1973_AngledView.jpg%26
Spots: http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Spots/?action=view¤t=2009_FewSpots.jpg#!oZZ3QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FSpots%2F%3Faction%3Dview%26current%3D2004_SingleSpot.jpg%26 http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Spots/?action=view¤t=2009_FewSpots.jpg#!oZZ4QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FSpots%2F%3Faction%3Dview%26current%3D2003_SingleSpot.jpg%26 http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Spots/?action=view¤t=2009_FewSpots.jpg#!oZZ5QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FSpots%2F%3Faction%3Dview%26current%3D1990_CocentratedSpots.jpg%26 http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/Spots/?action=view¤t=2009_FewSpots.jpg#!oZZ2QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FSpots%2F%3Faction%3Dview%26current%3D2007_LotsofSpots.jpg%26
New Toned Coins: http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/New%20Toned%20Coins/?action=view¤t=2000.jpg&t=1289448245320 http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/New%20Toned%20Coins/?action=view¤t=2000.jpg&t=1289448245320#!oZZ5QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FNew%2520Toned%2520Coins%2F%3Faction%3Dview%26current%3D2005_CloseUp.jpg%26 http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/New%20Toned%20Coins/?action=view¤t=2000.jpg&t=1289448245320#!oZZ4QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FNew%2520Toned%2520Coins%2F%3Faction%3Dview%26current%3D2006_CloseUp.jpg%26 http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/New%20Toned%20Coins/?action=view¤t=2000.jpg&t=1289448245320#!oZZ3QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FNew%2520Toned%2520Coins%2F%3Faction%3Dview%26current%3D2007.jpg%26 Near Rim. http://s1102.photobucket.com/albums/g457/sirlupinus/Pennies/Stained%20Pennies/New%20Toned%20Coins/?action=view¤t=2000.jpg&t=1289448245320#!oZZ2QQcurrentZZhttp%3A%2F%2Fs1102.photobucket.com%2Falbums%2Fg457%2Fsirlupinus%2FPennies%2FStained%2520Pennies%2FNew%2520Toned%2520Coins%2F%3Faction%3Dview%26current%3D2007D.jpg%26
It is corrosion. You have several things going on, You have cents that have oils and salts on them from handling, probably moisture trapped inside the metal container, and dissimilar metals in contact with each other in the presence of an electrolyte. Water vapr condensing on the coins or can can allow the salts to begin corroding the coins, and it can also set up electrolytic corrosion from the dissimilar metals.