What is the most likely cause of a brownish stain on radiographs taken several years ago?

A brownish stain on radiographs is commonly indicative of insufficient or improper washing of the film after it has been developed. During the processing of radiographic film, it is crucial that excess developer is thoroughly rinsed away; otherwise, it can lead to discoloration over time. This chemical residue can react with light or air, resulting in stains that may appear brown. Proper washing ensures that all developer chemicals are removed, preventing any potential staining or degradation of the image.

Other factors such as excessive exposure to light or using expired film typically produce different types of artifacts or degradation, usually manifesting as fogging or loss of image quality rather than a brownish stain specifically. Similarly, inadequate developer solution affects the quality of the image itself but does not typically cause a brown discoloration after years. Thus, the most likely reason for the brownish stain is indeed due to insufficient or improper washing of the film post-development.