I have been doing an exposure test and realized I was getting film fog. I assumed it was light leaks. To make a long story short I completely sealed up all light leaks and worked at night. I did a test with Ilford HP5 plus 4x5. I exposed the film just enough to get over the threshold and than placed the film on the counter in complete darkness. I put coins on the film and removed them one at a time every three minutes, than processed the film. I also moved my timer and covered it so that it would not fog the film. I do not have flourescent lights. At that point it was the darkest darkroom I have ever worked in. The result was that the coin that was not removed was clear but I could clearly see the image from the other coins. I have used this darkroom for many years for alt photography. could it be a chemical fog from chemicals in the air? Has any one experienced this?