I'm working with a curator from our local military museum. We have an old fibre based photo that is stuck to the glass along one edge. It looks like some liquid got in at some point. If there is a conservator on board, maybe you can help out. If we get no professional advice, we will do nothing. It might help to mention that the museum has a 'rehydrator' that will add moisture to a dry cracking print but we're not sure that method will work in this.