Quote Originally Posted by dancqu View Post
It is that uncertainty with the usual sulfite based
HCAs on the market that has me ready to switch to
Agfa's recommended sodium carbonate based HCA.

A study quoted in a post to rec.photo. darkroom
recently told that sodium sulfite was, IIRC the exact
words, "as good as any other". That is, not any better
than some others. I suspect Agfa's recommended
sodium carbonate is as good as sulfite and it
does not oxidize. Agfa's instructions may
still be on the WWW. Dan
However there are many posts on rec.photo.darkroom stating that sulphite is better than carbonate. I agree that carbonate is tempting since it is cheaper and used at a lower concentration and lasts longer in solution. It would be better than nothing.

The Agfa pdfs might not be all findable on the web. I have some of them. FWIW, this text is cut from the most recent pdf on fibre paper:

<start quote>
Soda intermediate bath

A soda bath (1 % sodium carbonate solution) should be included
for fibre-base paper, between fixer and final wash (time: 3
minutes). This ensures that the fixer is washed off the paper
surface faster and more thoroughly.
This not only cuts down the final washing time by about 30 %,
and in particular it increases the prints' durability.
If a hardener-fixer is used, the soda intermediate bath is not
recommended.
<end quote>

In the unlikely event that hardening fixer is used, the carbonate is not recommended because its alkalinity would negate the hardening which is pH dependent. I wonder if the alkalinity would leave the paper emulsion softer which might make it vulnerable to some toning processes.