A characteristic I have come across when processing out-of-date sheet film is that sometimes the edges of the image tend to process with more density than the center of the sheet. This does not appear to be fog, as the unexposed film base (hidden behind the slots in the film holder) is still clear after processing. I'm thinking that the emulsion is not taking the developer evenly. Should I do a longer pre-soak? Right now I am doing a water presoak of 2 minutes before tray processing in D-76 straight. Any advice or comments appreciated.