Super Fix VIII?

[koraks]

It is also a very good buffer in the relevant pH range

Ah, then it's quite likely that its primary purpose is pH control.

 

[halfaman]

I checked msds file of Kodak Flexicolor RA fixer that I use and it list just ammonium thiosulfate and ammonium bisulfite (pH buffer?).

 

[Anon Ymous]

and ammonium bisulfite (pH buffer?)

And as a preservative. It likely also has ammonium sulfite, it's usually an ingredient of the ammonium thiosulfate solution and it's a precursor to it.

 

[Rudeofus]

I checked msds file of Kodak Flexicolor RA fixer that I use and it list just ammonium thiosulfate and ammonium bisulfite (pH buffer?).

Ammonium Thiosulfate plus Amminium Bisulfite in any meaningful ratio won't have the target pH of 6.5. Apparently Kodak was able to leave out some ingredients. I've seen Fuji MSDS for fixers, which listed only sulfite ...

 

[pentaxuser]

@pentaxuser, keep in mind the drawbacks of thiourea already mentioned (i.e. it's a powerful fogging agent as well), plus the ones not yet touched upon, in particular its somewhat suspect safety record. Compared to what you'd otherwise find in a typical rapid fixer (i.e. amm. thiosulfate and sulfite), it's not particularly benign (although it's not exactly a horror compound, either). I can imagine this, in combination with the by all means adequate effectiveness and speed of regular rapid fixers, precluded a widespread adoption of a 'better' alternative.

Indeed, my own interest in such a 'superfix' is more academic than practical; I don't really see how scraping a bit off the few minutes I usually spend fixing film will make my life all that much easier.

Yes you have introduced another reason why "Superfix VIII was not introduced by Kodak but by and large we seem to agree that good reasons exist

Maybe this thread was always born of academic interest only rather than practical reasons, although I suspect the OP was of the mind that it was a practical proposition. However he hasn't visited the site since 2018 so may have lost interest anyway

pentaxuser

 

[Rudeofus]

Yes you have introduced another reason why "Superfix VIII was not introduced by Kodak but by and large we seem to agree that good reasons exist

Kodak's C-41 RA fixer is pretty close to PE's Superfix 6, both in terms of composition and in terms of performance. What PE then did was introduce (and later remove) further development agents to the mix. DTOD would certainly help, but not at a price anyone is willing to pay for fixer. There are other compounds, which are even better (PE once mentioned this HTTT), but yet less available and likely extremely expensive at the quantities currently produced.

Fact is, that few people will spend half an hour mixing a fixer, which will then shave off 2 minutes of wash time. Been there, done that, now using cheap C-41 fixer concentrate, my stash of Ammonium Thiocyanate sits idly in the shelf.