This is the detail of a collage with many cut-out photographs attached to paper. The entire collage was laminated, and over time the adhesive yellowed and the plastic from the lamination became rubbery and wrinkled.
Photo credit: Alaska State Museum collection 2002-22-2
Photographs often curl as the emulsion layer shrinks but the backing material does not shrink at the same rate. If you try to force these flat, the emulsion is likely to crack.
Photo credit: Alaska State Museum collection III-O-560
This is an example of the emulsion flaking off a glass substrate. This kind of instability is a critical condition issue.