OTOH, blix is a well proven method over many years. No, commercial labs don't use it because they monitor and replenish, replacing just the solutions necessary. Not necessary for home use. There was a thread a few years ago, and even PE said that the benefit of separate chemicals was more hypothetical that real world difference. And as we all know, he's a stickler for doing it right.
I'm skeptical about blix, as opposed to separate bleach and fix, being a well-proven method for C-41 film processing. That said, I have never tried it, as IT DOES NOT MAKE SENSE FOR A COMMERCIAL FILM PROCESSOR. As a note, blix DOES make a lot of sense for PAPER processing.
(I'm gonna get pretty wordy, so this is a good place to quit if you don't wanna know about the technical details.)
I'll explain about this, but first a bit of background. I spent a number of years at a large photo lab in the U.S., overseeing the QC of chemical mixing (including regeneration, etc.), "process control," and meeting effluent standards. To put some perspective on it, during peak times we ran upwards of 5,000 gallons of replenished chemicals per day, albeit the vast majority for paper processing. At one time, back before the coming of RA-4, I oversaw the installation and operation of a developer regeneration system ("operation" consisted of 1) run the used developer through an ion-change column optimized for removal of bromide ion, 2) in our existing chem lab do a full analysis of the treated developer, 3) calculate the chemical additions for the chem-mix department, and 4) screen the regenerated developer for basic parameters, plus an actual processing test before clearing the mix for use). In my department we also worked out and oversaw the processing effluent control schemes, including the most glamorous aspect - monitoring of the sewer effluent for the mandated parameters.
I give this background to counter a common view of internet forums - the syndrome of, "I don't know that much about the topic of xyz, but I DO KNOW who the expert here is, it's so and so..." Forum members should recognize that other expertise sometimes exists.
Ok, regarding C-41 BLIX in the commercial processing world (bear with me, it's a long explanation):
if you run a SEPARATE bleach and fix, the expensive components of the bleach last a long time. It gets "worn out" in three main ways: 1) it gets diluted by the incoming wet film, 2) it gradually loses its ability to bleach (it becomes "reduced" as it "oxidizes" metallic silver, and 3) the bleach's surplus of bromide ion is gradually depleted. Item 2 can be dealt with simply by aerating the bleach. Items 1 and 3 are counteracted by replenishment with a more-concentrated replenisher. (The added replenisher volume means that you will have surplus volume, which will "overflow" from your system; it is possible to collect, and by adding the missing chemicals turn this back into replenisher to be used again.) It is possible to really stretch out the usage of bleach. (You really need squeegees between tanks for the most benefit and minimal effluent load).
Now to the separate fixer: the C-41 fixer, although relatively inexpensive, is more limited in its useable life. We see fixer as "exhausted" when its silver concentration reaches some specific amount - this can be controlled in the process by adding replenisher. Again this will cause a surplus of fixer "overflow," which contains silver. You might think, "hey, I could desilver the fixer, restore it chemically, then reuse it as replenisher. Same as the bleach!" But you cannot. Other byproducts, primarily iodide ion, "poison" the fixer's ability to remove silver. For all practical purposes, the fixer is done - nothing you can do economically to reuse it. (Your best bet, for cheapest fixer and minimum silver lost in the effluent, is to use multistage fixing tanks with "countercurrent flow" replenishment. (And you would ideally squeegee the film as it leaves each tank.) But the bottom line is that the C-41 fixer is very limited in its ability to be reused.
Ok, finally to C-41 combined bleach and fix, aka blix, which again, I have never used. The same situations should exist as for the separate bleach and fix. Except that now, combined, the ability to reuse is limited by the build-up of both silver and iodide (due to the poisoning effect on fixing rate). So, essentially you are not able to extend usage of the expensive bleach because you are limited by the fixer component. If you aerate the blix to restore bleaching power, you will also destroy sulfite ion (it will be oxidized to sulfate), which is essential to protect the fixer, so this is not a desirable thing to do (unless you are monitoring sulfite levels).
If you are a one-time use, then throw it away sort of person, then perhaps C-41 BLIX might be a good way to go; I dunno. I wouldn't want to store it too long, but I don't know what too long is.
A related question comes up with using blix for PAPER (not film). In this case yes, it works great. Two big differences: 1) the bleaching requirement is much smaller (paper has much less silver than film does), and 2) the standard color papers don't seem to have any appreciable iodide content - the fixing rate doesn't seem to be "poisoned." So with paper blix it is possible, in a replenished system, to collect the excess volume (overflow), electrolytically desilver it, aerate it, then "regenerate" so it can be reused as a replenisher. (Don't reuse more than about 80 or 90% of overflow; the build-up of oxidized sulfite (into sulfate) will eventually slow down the fixing rate.) Yeah, I have a great deal of experience with this.
Does anyone who read this far need a summary?
