Quote Originally Posted by psvensson
The OF-1 formula looks interesting, but why is the alkali necessary? Doesn't it work if it's neutral (or becomes acidic through contamination)?
It works just fine. But I prefer to have a buffered solution of known pH, as it makes everything a lot more predictable. Both alternatives give a pH of about 8.5, which is just enough to be stable and wash out easily.

I know from experience that acidic ammonium fixers bleach highlights in prints, and I assume they also lose shadow detail in film. I have also established to my own satisfaction that this does not happen with alkaline fixers, at least not without ridiculously long fixing times or very sensitive processes (read: van Dyke).

That's why I put alkali in it.