What might be the cause of a radiographic image appearing completely black?

A radiographic image appearing completely black is most likely due to exposure to light. When film is improperly stored or handled in conditions where it is exposed to light before being developed, the light can cause the emulsion on the film to be fully exposed. In such cases, the development process cannot reverse this exposure, resulting in a film that appears entirely black.

Over-exposure to radiation can darken a radiographic image, but it typically results in a gray or overly dense image rather than a completely black one. Insufficient developer solution might cause underdevelopment, which usually results in a lighter image rather than one that is completely black. Improper washing after development can cause residue to remain, but it does not lead to a black image; instead, it may cause stains or other artifacts.

Thus, light exposure is the definitive cause for a radiographic image to appear completely black, as it directly affects the film's ability to produce a latent image that can be developed.