the all-seeingeyeThreats to Photographs: Water

Fairly typical water damage. This photograph was in a glass-faced frame. The missing section is where the photograph stuck to the glass after drying.

Water presents two hazards to photographs-high humidity, and flooding (too much water and way too much water). Chemical reactions, in general, require liquid in which to occur. Some chemicals which would freely combine when dissolved in water are almost completely inert without it. The presence of high humidity tends to accelerate the chemical processes of deterioration.

Flooding, of course, is another problem altogether. Good paper and waterproof inks will actually survive lengthy immersion, provide they are treated by professional conservators immediately after being removed from the water. (the aftermath of the 1966 flood of Venice, Italy, is still being worked on) Photographs don't do nearly as well. The image layers will usually separate from the backing fairly quickly. Another problem even for brief immersions is that photographic paper tends to stick together permanently when it starts to dry out-a process that is usually irreversible.

Disclaimer: I'm neither a chemist nor physicist, I only play one on the web.