Baseball Hall of Fame Says "No" to Slabs.

[David Atkatz]

Originally Posted by steve B

That check began degrading when the paper was made, before it even became a check. What Archival storage to high standards does is delay the inevitable as long as possible. In the best cases, as long as possible means a very long time.
Even without stuff like Mylar some things can last a long time, it's just less likely. Like King Tuts stuff, mostly preserved in good condition for thousands of years. Assuming the check was high rag content paper and not particularly acidic it's something you probably won't have to worry about.

It's also true that some things even stored up to standards - like many books from the 1890s-1920's- degrade to the point of being unsaveable in a fairly short time. Once the wood fibers in the paper begin creating acid it's just a matter of time.

True.
Ancient Egyptian material has lasted because it was stored at very low humidity, and in total darkness. It was also not in contact with other objects that could cause them to deteriorate.
Old books deteriorate because of the acid in wood pulp paper. (Rag paper has far, far, less acid, and some none at all.) In order to preserve those books, they must be deacidified.
Mylar keeps its contents safe from environmental hazards, and contact with dangerous things--like acidic wood pulp paper. It is also stable--chemicals do not leach out of mylar, as they do with other plastics.
What is worrisome about slabs is that they are not made of long-term stable plastic.