If a 6-year-old film shows yellow-brown staining, what is the likely cause?

The staining of a 6-year-old film that appears yellow-brown is most likely due to incomplete washing of the film. After a photographic film has been developed, it must go through a thorough washing process to remove any residual chemicals, particularly the developer and fixer. If this step is not adequately performed, these leftover chemicals can react over time, leading to discoloration, which can manifest as a yellow-brown stain.

The age of the film is also relevant; over time, any residual chemicals that were not properly washed away can further deteriorate or oxidize, contributing to the yellow-brown staining observed. Proper washing is crucial for ensuring that films remain clear and free from discoloration, particularly over extended periods of storage.

While other options also deal with common issues in film processing and storage, they do not specifically account for the yellow-brown staining that is tied to leftover chemicals. Storing film at a hot temperature or leaving it in the developer too long would likely cause different issues (like fogging or development defects) that do not match the specific discoloration described. Incomplete drying may create a different appearance and is less likely to produce the yellow-brown stain. Therefore, incomplete washing is the most plausible cause in this scenario.