ph a measure of exhaustion???

[RalphLambrecht]

i noticed a change in ph in developer fixer and other working solutions over time. is there any rule of tmub at which ph these solutions are no longer usable?

[johnielvis]

probably--I've noticed that when I started using stop bath (used to water rinse afer development--now I use the same water rinses but also add a short stop bath step)....the fixer last CONSIDERABLY longer...I use very powerful developers for reversals and even with a LOT of water rinsing, the fixer was getting weak very quickly--this is just for the final "cleanup" fixing step when there's hardly anything left to fix--now with the stop bath after the second deveoplment, the fixer lasts and lasts and lasts---as it should since it's hardly getting used.

[markbarendt]

I've often wondered why there isn't an "indicator" fix like there is with stop.

[Photo Engineer]

It depends strongly on the initial pH value of each solution. A change of 0.5 units may be big or small depending on the starting value, so at 8.5 a change to 8.0 might be critical for a developer but at 10.5 it might be minor and then again it might not. Sometimes only trial and error can teach us these things.

PE

[anikin]

I've often wondered why there isn't an "indicator" fix like there is with stop.

What a great idea! If it's possible, it would make a great product. I also wish there was an indicator for the wash water as I wash my prints. I love the way pot. ferri bleach washes off. You can always tell whether you washed enough. What I noticed that it takes much longer for the water to lose that yellow tint than I would have expected. Somehow it makes me feel that the recommended wash times for RC papers are just a hair too short. Especially when doing large prints.

[Photo Engineer]

There are indicator solutions. Use the retained hypo and the retained silver test solutions. The problem is that the test solutions cannot be added to the wash or the hypo in the same way or they do bad things. But, they do work.

Also, the hypo exhaustion test solution is quite good but very qualitative.

PE

[anikin]

Yes, I have the HT and silver test solutions. I'm just too lazy to use them on a regular basis. It would have been so much more convenient to add a drop of indicator to the wash basin and wait for the water to clear again. Then I would know that I'm done with the wash. I guess I'm just dreaming here.

[Photo Engineer]

Unfortunately, the test solution stains prints.

And a pH indicator is useful, but you would have to have one for every fixer there is. There is no real indicator for hypo other than the test solution which is Silver Nitrate itself.

PE

[Gerald C Koch]

Since pH can change due to other factors I really don't think that this is a practical approach at least for fixer. Hypo test solutions like FT-1 aren't very good. They only give a positive reaction long after the fixer is really exhausted.

I have found that the best way to determine whether a solution is good or not is to keep track of its usage and age. HCA and stop bath are so cheap that I never make an attempt to keep them past a darkroom session.

[johnielvis]

I just have junk film ruined by accidents and not developed laying around in a coffee can...before I want to use the fix...I check the clearing time first by using a teeny strip of film in the fix and timing it.


OH...be sure to soak the film in hot water for 5-10 minutes to remove the dyes/backings so you don't color and foul yor fixer