Two-bath fixing is still the most effective way to fix film. Combined with rotation processing it is also very efficient.
Two-bath fixing is still the most effective way to fix film. Combined with rotation processing it is also very efficient.
Even a lightly used fix can test positive for exhaustion to a novice who misinterprets the density or even the formation of the cloudy precipitate.
Besides which, the KI solution does not last forever. It goes bad over about 6 - 12 months.
... May I ask, just out of curiosity, how two bath fixing is more effective than single bath, assuming a film strip test is done the way I describe above? ...
Thomas
The film-strip test is practical an acceptable, but nothing is as effective in removing silver and silver complexes as fresh fixer.
During the fixing process, residual silver halide is converted to silver thiosulfate without damaging the metallic silver of the image. The first fixing bath does most of the work, but it is quickly contaminated by the now soluble silver thiosulfate and its complexes. Soon the entire chain of complex chemical reactions can not be completed successfully, and the capacity limit of the first fixing bath is reached. A fresh second bath ensures that all silver halides and any remaining silver thiosulfate complexes are rendered soluble.
While talking about it, is there an equivalent of the clear time test for paper fixer ?
As iodide solutions age, they release iodine. If I remember right, iodine in solution will combine with iodide to form the I3- ion (that is, the tri-iodide ion, I (sub) 3 ion with 1 negative charge).
How does free iodine, or really it's the triiodide ion, affect this test?
Well, oxidation forms Iodates and maybe even Periodates which then go on to decompose. It generally turns into a brownish mess with a strong halogen odor. It depends on concentration. Nitrogen Triiodide may even form if there are impurities and if the pH is alkaline (with ammonia), so watch for a purple color or a purple precipitate. If it looks reddish, brownish or like grapejuice do not use it. If it smells like chlorox, do not use it.
Just as an aside, NaI is so unstable it is not routinely sold nor used.
OK, so that is what you mean by using the word 'effective'. It is basically bullet proof and always insures total removal of the residual halide.
Do you switch the second bath to become the first bath, once the original first bath is spent, (and mix a fresh second one)? This is how I do it for prints.
- Thomas
However, as you know, TMax films exhaust your fixer a lot faster than others. I usually count a roll of TMax as 2 or even 3 rolls against my capacity, which I conservatively rate and .....
Ron (PE), I've just come across a film fixer specifically designed for high Iodide film emulsions, it appears there was an issue with these & fixing back in the late 1920's. The fixer contained Thiocarbamide (Thiourea), I'll find it and convert the weights & volumes to Metric, the books at hand so I'll post the formulae later or more likely tomorrow.
Ian
I have re-posted them here.
[is Photo Engineer long gone from Photrio?]
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