Mold and fungus can form on slides and other photographic materials.
Fungus spores and bacteria are in the air regardless of air
temperature and humidity. Moisture, darkness, and
stagnant air foster fungus growth on the gelatin emulsions of film.
If photographic films are stored for any length of time in an area having
a relative humidity of 60% or above, there is a tendency for fungus to grow either on the emulsion surface or base side of the film.
Photographs are meant to freeze time on images. But, what happens when images are alive?