Knives that I don't use? I don't have many of those. I own a bunch, but I'm not a collector.

As said, don't store a knife long-term in a leather sheath. One thing I found out the hard was to not store anything metal near a bottle of iodine water treatment tabs. I had one in a kit. The iodine tabs ate throught the metal cap on the bottle, then started eating through the stainless steel knife also stored in the kit.

I just keep the knives I don't have on me either in a drawer, in the box they came in, or in a plastic fishing tackle box. I've never heard of storing folders opened. That would be tricky for me. I keep them clean, but I don't wax or oil them. 'Course, I live in SoCal. No humidity to speak of.

Kevin B.