Shrink-Swell & Fixers
Using alkaline fixer should lead to shorter fixing times, which naturally leads to short washing times. The amount of soaked fix is thought to be lower because the paper is immersed for less time so the fixer can't penetrate deep into the paper. All seem logical...well, almost. The logic behind is that alkaline solutions cause swelling which helps with washing. But doesn't swelling already start during the fixing stage? Meaning that although there is less time for the fixer to penetrate, the gelatine already begins to swell, becoming softer so the alkaline fixer penetrates deeper especially if the acid stop bath is omitted from the process - which is often (but not always) advised.
I believe that the gelatine should shrink in a stop bath and stay this way during fixing in an acid fixer so that there is as little penetration as possible. It's only after fixing the the paper should be immersed in an alkaline solution (HCA) which swells the gelatine and promotes efficient washing.
What do you think?
p.s. I'm aware that fixer penetrates several media (gelatine, baryta, pulp) independently, and that not all are pH dependant.