I like naturally toned coins. Coins naturally tarnish if left exposed to the elements. Corrosion is tarnish that has already damaged the surface of the coin. Fortunately under some conditions coins tone in beautiful colors.
Collectors have found many ways to store coins over the years. Successful collectors protect their coins from damage. One hundred years ago a collector might have a velvet lined wooden cabinet made especially for coins. Proof coins stored in this way sometimes developed uniform toning of a champagne color.
Cardboard coin albums and holders were developed in the 20’Th Century. There were several styles and brands. Often the chemicals in the cardboard worked with the environment to tone the coins.
This pattern is said to be specific to a bank promotion. I guess the holder exposed the fasces so that it alone remained untoned.
Mint Sets dated 1958 and earlier came packaged from the US Mint in cardboard between a folded piece of colored paper. The materials used sometimes caused super nice toning.
Be careful if you are buying these sets. Many high grade or super colorful coins have been removed and replaced with lesser coins.
Many Morgan dollars sat in bags in bank vaults undisturbed for more than one hundred years. A few of these coins developed very colorful toning. Some were so undisturbed that you can even make out the pattern of the fabric bags that they were stored in.
Some coins show up in hoards and not much is known about them. This nickel is from the Appalachian hoard.