The real issue here is if the silver levels in the fixer have risen with use then prolonging fixing will allow more of the semi-soluble silver thiosulphate complexes to bond weakly to the cellulose in the paper base and these may become very difficult to wash out even with a wash aid.
From experience 5 minutes in fresh Hypam or Ilford Rapid fixer is too long and definitely causes slight image bleaching (with warm tone papers), the recommend time is 1 minute at 1+4 and 2 minutes at 1+9
Ilford recommend a maximum silver level in a one bath fixer of 2g/litre for FB prints and say -you can go to 4-6g/litre with RC paper as the paper base is protected on both sides by an impervious polythene layer.
Ian
Ian,
I guess I should qualify and modify my earlier post. I don't want to mislead anyone or generalize where I shoudn't
Of course, when speaking of accidentally fixing too long, I'm assuming fixer that has not been used beyond capacity and, therefore, that there wouldn't be a lot of really complex insoluble compounds to wash out. "Unwashable" really only happens with overused fixer as far as I know.
As for bleaching at 5 minutes in Rapid Fix 1+4... I've never fixed a print that long in Hypam or Rapid Fix at 1+4. For the 1+9 dilution, four minutes total fixing time (2 min each bath, which is long for me) has never caused any loss in highlight detail; but then again, I use cold-tone papers. I guess I'll have to do some extended fixing tests to find out exactly where bleaching sets in.
However, even if the print is slightly bleached, if the fixer was relatively fresh and five minutes time was given, I'd still think one could wash the print to "archival" standards (for me, no stain with ST-1 and HT-2). But again, I haven't tried it. Nevertheless, Kodak recommends 5-10 minutes for its Rapid Fixer at the 1+7 dilution, which has similar composition to the Ilford products and should be roughly equivalent to the Ilford 1+9 dilution unless I'm mistaken...
But don't misunderstand me: I am not advocating anything but fixing for the optimum time for the product and dilution being used. Why people can't read the directions and use the manufacturers' recommendations as to fixing times and capacities is just beyond me (and the main reason for my earlier rant).
Whatever fixing method we end up with, either the Ilford sequence using stronger fixer and shorter times or the more traditional Kodak method with longer fixing and wash times, we should strive to optimize times and capacities. If we aren't testing our own workflow and establishing our own process limitations and optimizations, then at least we can read the directions and follow them.
Best,
Doremus