Quote Originally Posted by Michael R 1974 View Post
I didn't say the isoelectric point/pH had anything to do with gelatin swell. The discussion in Haist regarding the isoelectric point has to do with the affinity for thiosulfate and silver thiosulfate complexes.

Swell is discussed from a diffusion perspective.
Michael, in your introductory post to this thread you wrote "Given a non hardening Ammonium Thiosulfate fixer, my understanding is the most efficient washing will occur if the fixer pH is increased to the isoelectric point of the gelatin (~4.9), with no real benefits above that point. Am I wrong?". There is no reason I am aware of why the isoelectric point should the optimal, quite to the contrary. Looking at Ron's chart tells me that pH 8 is quite good and sure enough that's what TF-4 is set to according to their MSDS. I have no idea how they avoid the Ammonia smell at this pH, though.
Quote Originally Posted by Michael R 1974 View Post
But I can't agree everything they say about developers and fixers (developers in particular) is necessarily sound.
It is more sound and better tested than most of the data or info I gather from forum or news group threads by a wide margin. Fact is that film development and fixation is a huge topic that occupied dozens of the brightest minds in the chemistry world, and few of their findings were ever made public. Many pieces of information published in the FDC were gathered informally and could not be publicly attributed to their sources, it is well known (ask Ron) how furiously Kodak defended and still defends their trade secrets from becoming public.

Look at Mark Overton's heroic and ongoing effort in replicating Xtol to see how much work you can sink into one simple developer formula, and look at the sheer number of formulas in the FDC alone. It is quite plausible that Bill&Steve became so immersed in and overwhelmed by their effort that they drew some fast conclusions or let their opinion creep into their pile of accumulated facts. I still challenge everyone condemning the FDC and DCB to show me something better which is at least remotely up to date.