All kinds of interesting suggestions for the fogging. If the fogging is more or less uniform over the entire film, inappropriate storage (such as the heat in a car) is most likely the culprit. I have been developing all my HIEs in plastic tanks, and I have never had a problem (though many books state there might be problems). I would advise one precaution, however: If you develop in a plastic tank do so under fluorescent light (which is low in IR), in semi-darkness or, if you have to do it close to a IR rich light source, rather than buying a new tank, warp the tank in aluminium foil.(posted 8821 days ago)But one possibility has not been addressed yet: If plastic tanks are unsafe for IR, so are plastic cameras, and I guess some bellows cameras might be, too. And sunlight is surely rich in IR (or we couldn't make IR shots).