I went through all of my sets this weekend. Some of them have been locked up for more than a decade. There is definitely some toning going on. I noticed it mostly on the dollars and pennies. Some of them look to clearly have been handled by fingers before sealing. I am developing a new appreciation for what uncirculated means. I am dissapointed, I've gotten better looking coins from banks.
I have had good luck with Intercept Shield (IS) holders and IS boxes to help delay toning of silver coins. TC
In fireproof boxes One theory is the coins reacted with something else in the box. Another item (perhaps something printed on paper) released a gas.
if there is paper in there, it could be a sulfer reaction especially if the temperature inside the boxes is warm or the environment is humid.
To stop it, simply place the coin away from any type of fabrics or paper products, as these materials *may* have some sulfur or chlorine traces (which will tone these polished metals). It's best to keep them in cool environments sealed tightly as possible in some type of sterile plastic or pre-treated coin albums, such as an Intercept Shield album.
