How To Store And Display Awards.

[Bob]

Exactly right. Polyvinyl chloride - Wikipedia, the free encyclopedia

Anyone who's a coin collector here has seen the effects of PVC in coins. Plastic that contains PVC isn't stable, releases gas into its environment (usually a rule of thumb is, the harder and stiffer the plastic, the better), and tarnishes metal. Copper and copper alloys are most affected; silver is affected as well. The harmful effects include greenish film and tarnish, which can become permanent.

So thin ziplock bags are also not a good idea? It's how I have most of my items stored (before they're placed into old shoe boxes (and then in "the vault").