Unsticking Stuck Envelopes

[horseshoes]

I have a stack of first day covers and presentations packs (stamps) and they've been stored away for years. It's apparent that there must have been damp because all the envelopes are glued down, so if you can picture the gummed part of the envelope is tucked into the pack and has now become glued to the card inside the envelope. I hope this makes sense. How do I unstick them all without damaging a) the envelope and b) the card inside.
T.I.A.

[gingejbee]

Perhaps a very damp atmosphere (like a sauna!) would soften and unstick the adhesive, eventually.

[woofgang]

might be worth asking this on a specialist philately site?

[Cloverjo]

I was going to suggest steaming them as well. Try a kettle rather than taking them into a sauna.

[horseshoes]

Thanks all. Sorry I'm late in replying to your answers. x