Silveror0,
This is the first time I've heard that mixing selenium toner with a wash-aid "ensures better archival permanence." What doesn't seem to be addressed here is how toner+wash-aid compares with toner followed by wash-aid. Certainly, no wash-aid at all is not optimum practice. One interpretation of the above could simply be that one needs to use a wash-aid to ensure "better archival permanence," something I would not argue with.
I do, however, question the notion (not expressed in the Ilford correspondence you quote, by the way) that toning and then giving the print a bath in a wash-aid is somehow not as effective as doing it all in one step. I can't really imagine that the "archival permanence" would be negatively affected by waiting the few minutes that it takes for a print to tone before using the wash-aid. Certainly no more than just leaving the print sit in a water bath for the same time...
Until someone shows me otherwise, I'm going to believe that toner followed by wash-aid is just as effective (i.e., not any different than) mixing the wash-aid with the toner. Sure, it eliminates a step, but other considerations make dividing the processes more desirable.
The problem with mixing toner with wash-aid, as I see it, is that the wash-aid exhausts very, very much faster than the toner; it has both a smaller capacity and a shorter lifespan, since it cannot be kept more than 24 hours without it being destroyed by oxidation. That means, you have to discard a whole lot of still-active selenium toner when the wash-aid capacity has been reached, or when 24 hours is up, whichever comes first. I find this wasteful, uneconomical and environmentally irresponsible. I replenish and reuse my toner; none of it ever gets discarded - very economical and eco-friendly.
As for "archival permanence": a well-processed print, however processed, is one that contains very, very little residual hypo and very, very little residual silver. There are test for these (the most common being HT-2 and ST-1 respectively). I check the last print of every run with these tests and never have had anything but excellent results with my work flow (two-bath fix, toner, wash-aid for 10 minutes, running-water wash for minimum 60 minutes). Excellent results are excellent results and support my position that a wash-aid after the toner is equally effective for ensuring adequate washing of fiber-base prints.
It would be interesting to hear what the Ilford techs have to say specifically about toner+wash-aid vs. toner followed by wash-aid.
Best,
Doremus