I just developed a sheet of 4x5 Portra 160 using solution I had mixed up a couple of weeks ago then put in a plastic bottle and filled the space with butane gas to keep it fresh and sealed it. Now the film has come out completely blank not a sign of any image at all. My processing times follow the standard recommended widely of 3.15 dev, 5 blix, 2 stab.

I don't know if it is the old solutions that is the problem, or does it sound likel I have inadvertantly tried to develop a blank film? I use the Tetanol Colortec kit.