A question for all you seasoned B&W film developers

[Nick Zentena]

If you use a two bath fix you'll get more out of it then just a single. No different then prints.

[Roger Hicks]

You can also test with a clip of film leader and fix for twice the clearing time. If the clearing time becomes too long, then it's time to mix a new batch.

Dear David,

I am told by those who know more than I that 2x is merely a convenient number with a big safety margin: 3x should be OK too.

I add this only because there is often a temptation to 'gold plate' a rule of thumb like this, and say, "Well, if 2x is the safe limit, I'll go 1.5x" or whatever.

One more point worth making is that the easiest way to check clearing time is in two stages. Put a drop of fix on the film leader (or a piece of specially chopped up film for other formats); wait 20 seconds; chuck the film in the fixer, making sure it's covered. The time taken for the spot to vanish is much easier to gauge (and more reliable) than the time taken for the whole film to clear.

Normal fixing time, for clearing times determined like this, is 2x-3x clearing time. This has the further advantage of minimum necessary clearing time/minimum wet time; lengthening clearing times are automatically compensated for, because your fixing goes up in proportion.

This incidentally is why I don't use 2-bath, despite Nick's entirely accurate statement that you can get a bit more life out of your fixer that way: I find it easier and more predictable, because of the built in test, to start with 2x clearing time and then to chuck the fixer when the original clearing time (and therefore the total fixing time) is doubled.

Cheers,

R.

[David A. Goldfarb]

I'd go along with that, Roger. I'd even say 3x for T-max, new Tri-X and other films with the magenta dye.

[aldevo]

With Formulary TF-4 fix and conventional grain films I find that I can do about 24 36x exposure 35mm rolls before the clearing time becomes excessive and the fixer must be discarded.

With Tri-X, I find that starting my fix times at 3 minutes and incrementing the fix time by 30 seconds every 4 rolls keeps me on pace with exhaustion of the working solution.

I would definitely recommend the clearing time test be used instead of chemical fix tests. I find the chemical fixer tests (even the purpotedly excellent Edwal product) tend to give false negatives (i.e. insinuate your fixer is fine) even after the clearing time has become too great for my comfort.