Coins will tarnish over time when in books. Even Dansco books do not protect the coins as well as they should. I have bought complete dansco books in the past and looked with disgust at the tarnished coins that I know were in superb condition when they were put in the book to begin with. I use 2 x 2 flips but your best bet is airtight capsulation and tubes for long term storage. Sincerely, John Leckrone