Just stretched a painting on canvas (about 38 x 50") that a couple brought back from abroad. The thick paint was already cracked in quite a few places, which didn't worsen during stretching, but are still there. In some of them, the cracks are so deep that they extend into the thick gesso layer, which doesn't really show up unless you scrutinized the painting, but is still there. I've told them that if they want it touched up, we can have it done, but here's my question. They're pretty fine with how it looks now; if they choose to not have it touched up, will the exposed gesso ever cause a problem? For example, could it absorb moisture from the air that eventually causes it to flake, or the cracks to worsen? Thanks for any replies.