It doesn't go bad, but if in a bottle that was capped in an environment where contaminants were present, it could mix with solution...
PF solutions are usually mixed very strong, leaving remains as haze or tracks of liquid remains on materials, so the use of as little as possible is required... I experimented with this long ago and found the proper solution for the PF 200 stock (from bottle)... First, go to a pharmacy to get a small glass dropper bottle, and add stock 1:2 (1/3 of the dropper bottle) into it and fill the rest with distilled water... For working solutions, use 1 drop per liter in distilled water... Only allow film to bathe in solution for 30 second, as it will start penetrating emulsion and can dry with a haze once solution starts coming to surface when dry...
This can be used for prints also at half the dilution as above...
The other trick for haze free drying of materials is after washing is a final soak for at least 10 minutes in distilled or deionized water before PF bath to soak out minerals from the wash water that are deep in materials...
My experience is from using the hard water of the SW that tends to leave a mineral haze on materials...
Steve K
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