Uncirculated Coins In Dansco Albums With Slipcase

Pretty sure the modern ones are inert plastic. IIRC, the old ones weren't. Lots of "interesting" toning is the result of crappy holders years ago. Whitman tri-folds are bad enough with their sulphur content, but the old ones put the glue on the paper and the paper on the codbod, where the new ones only put the glue on the codbod. That's what caused tarnish stripes on reverses of many coins. I've also seen tarnish letters on obverses, where they were up against the paper sheet with type.

I've got well over 100 Whitman Albums and all are in Zip Lock bags with as much air as possible pushed out. Prior to Zip Lock bags I just used any plastic bags for those albums and well into 60 years of collecting, no problems yet. When I firs started there was only Whitman. No such thing that I know of like Dansco, Littleton, etc. so all mine became Whitman. I've had several Dansco albums and sure wished they were around way, way back. They look more expensive, are a bit stronger, a little higher and deeper and appear better made than my Whitmans. However, most of mine are very, very old. For example my Lincoln Albums have so many blank cent pages added the only ones with dates for coins are in the 80's.
The primary thing is as already noted. How you store coins or anything. If you are in a high humidity area, Sulfur coal burning area, lots of air movement where you keep your coins, many problems could happen in any album.

Depends I guess. I've been doing this for well over 60 years now. Way back before Zip Lock bags I used just plastic bags. I push out as much air as possible. I live in an area of fantastic humidity most of the year. Today for example it is 84%. What ticks me off with the weather people is we never get 100% humidity even when it is raining. They are nuts. Yesterday it rained and the humidity was reported as 93%.
Meanwhile back to Zip Lock bags. So far I've never had coins in those albums tone, tarnish, corrode or anything but for a storage of several hundred years, it is a little difficult to know.
I'd really like to let you know though.