While watching the Superbowl (well, while the commercials are muted
), I came across this youtube video, interviewing a gentleman named Victor Castillo. He works for JM Restorations, in Oceanside, CA (Jaime Mendez' studio).
A nice interview and informative, but what caught my ear was his comment at about 3:08, where he states that after the touch up work has been completed, the entire poster is "sprayed and sealed." I am assuming this would be a water-based type of sealer, as anything else would make the touch ups permanent and non-removable (or much more difficult to do so).
What i did like, too, was the way the camera captured the touch ups to the fold lines at :56. From this angle, the retouched folds are still visible; the idea being that when looking at it straight on and in the proper lighting, fold lines can be rendered *almost* invisible, (since folds can result in breaks in the paper fibers and ink).
http://www.youtube.com/v/LpIPGVRxyqY