one shot fixer - again!

[wcwiseman]

This question has come up before, but I’ve never seen it actually answered properly. The replies usually go off into never-never land on one tangent or another, concerning the environmental concerns of dumping fix, or the attributes of 2 fixer baths, or detailed descriptions of how “I” process film, but never have I seen an actual answer for the question.

Here it is:

How does one make a one-shot fixer – just strong enough to do the job, and then be discarded?

For example, I use Kodak Rapid Fixer, so how much solution “A” is minimum (diluted with enough water to cover 120 roll film) to effectively fix the film – only used one-shot and then dumped? Or how much solution “A” (diluted to sufficient volume) is required to fix one 8x10 sheet of film?

This would be economical for those of us who process just occasionally and prevent worrying about deterioration of stored working solutions. It seems prepared working solutions do not last very long per the data sheets.

I figured about 10cc of solution “A” SHOULD fix one roll of 120 film, but it would be diluted to 400cc to cover the film (in my tank), so it is a 1:39 dilution. WOULD this work as long as enough TIME is given in the bath? Or is the actual CONCENTRATION too weak to do a proper job?

So does the chemistry of fixation change because of the weak dilution, and is a full strength working solution necessary?

Surely someone has worked out this problem and has experiences to relate.

[Nick_3536]

http://groups.google.ca/group/rec.photo.darkroom/browse_thread/thread/9c36760dbcb2360b/c03df72f80fac142?q=single+use+fixer&rnum=1&hl=en#c03df72f80fac142

Search for various other threads by Dan Quinn.

Personally if I was worried about working solutions I'd scrap the commerical stuff and mix my own.

[Bruce Watson]

Yea, my thread on photo.net went right down the tubes didn't it?

I dug around and found an old instruction sheet that comes with Kodak's Rapid Fixer. It says, if you mix for film use (makes one gallon), that the gallon is good for 120 8x10 sheets or equivalents.

That means, I think, that if I use 250ml in my Jobo 3010 drum, I've got enough for 30 sheets of 4x5 film. If I use 125ml of straight fixer and dilute that with 125ml of water, I would have enough for 15 sheets of 4x5 which would easily let me use it as a one shot. My assumption (oh, I hate that) that I could then fix for 4 minutes and toss the fix into the recycle bucket.

So... why won't that work?

[Donald Qualls]

I think there's a problem with your arithmetic there. 250 ml is just over a cup, or 1/16 of a gallon, and will be good for something close to 8 sheets at the rate of 120 per gallon. Your Jobo holds, what, six sheets? That amount should be fine, but you a) need some reserve, and b) don't need to dilute further.

[Bruce Watson]

Let's see.

[(120 sheets)/(3.8 liters)] * .25 liter = 7.89 sheets of 8x10. It seems that we are violently agreeing on this. Another way to look at it is 31.58 sheets of 4x5. If I cut that in half, that would be 15.8 sheets of 4x5 from 125ml of undiluted fixer, yes?

The 3010 drum holds 10 sheets of 4x5 film. So 125ml of uncut fixer should give me enough sodium thiosulfate to handle my 10 sheets, with 50% spare capacity.

This doesn't seem terribly wasteful to me to use as a one-shot, and there should be enough capacity to fix any normal negative. If my negatives are so thin that this isn't enough, it won't matter - they'll end up in the trash anyway ;-)

[Donald Qualls]

Ah, so.

Just under 8 "sheets" per 250 ml -- but that's 8x10. There's where I got crossed up in my mind.

In any case, my monobath formula used 10 ml of Ilford Rapid Fixer concentrate in 256 ml final working solution; usual film strength would be 1:4 with published capacity of 24 8x10 per liter, meaning I had capacity for something less than 4 rolls. Fixing was complete in less than ten minutes.

So, I wouldn't want to use less than your 1.5x safety factor on capacity (and I'd be happier with 2x), but based on Kodak's published capacity for their product, and correcting for four 4x5 instead of a single 8x10, you should have adequate margin, even for fixing blank sheets (which I recommend avoiding -- bad for your blood pressure).

Bottom line, *yes*, you can use higher dilutions if you leave the film in the solution long enough. I'd recommend a clearing test to determine correct time, of course -- using a scrap sheet of the same film in fixer at the dilution you'll use (in the light, doesn't matter), put a drop of fixer on the film, wait a few seconds, then immerse the film in the fixer and start time. When you can no longer distinguish the drop's clearer area from the rest of the sheet, stop time; with actual images, fix for twice this period.