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Old 5th September 2009, 01:37 PM
Giuseppe Giuseppe is offline
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Default Correct time fixing

An issue that has always puzzled me is the correct time of fixing a print.
For the negative there is a clear clue: measuring the time occurred for clearing the film and then doubling (or tripling) is enough. But such luxury is not available for prints, and the suggestions by manufacturers or practitioners vary extensively. For instance for the formula F24, a traditional sodium hyposulfite fixer, it is recommended fixing for 5'+5' in a two bath setting.
With that fixer one day I made a test suggested by David Vestal which consisted in first fixing for a variable time a well exposed strip of paper, and then, after appropriate washing, developing it to reveal any halide left. Well, the segment fixed for 30" got a medium gray density, the segment fixed for 1' showed almost no density, above 1' the strip was all white.
With such result I am inclined to fix for 1'+1' in a two bath setting.
Has anybody made a similar test, and what conclusion should be drawn from it?
Giuseppe
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Old 5th September 2009, 03:56 PM
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Bob Bob is offline
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Yes, I do a similar test every time I use a new make of fibre paper (don't know why: it's always approx 40 seconds - except Fomatone warm for some reason which is fixed in only 20s). I don't bother testing RC paper as that will always be fixed in about 20-30s and does not soak up the fixer like fibre paper so leaving it in for 60s is not a problem.

I expose a strip of paper to room light and cut it into pieces and use a pencil on the back to mark the time it will be in the fixer. I don't wash it before dumping it in the developer as that may extend the fixing time by some unknown amount (and soaking the paper before the fixer does not seem to make any appreciable difference: perhaps a few seconds). I drop the pieces straight out of the fixer into the developer. I leave them in the developer for 10-15 minutes; if you only leave it for the normal developing time of 2-3 minutes you might find it will start to darken after 5 minutes or so, so I leave it longer - if it hasn't darkened after 10 minutes, I think you can safely say that it's fixed. I dump the contaminated developer afterwards.

In practice I tend to go with 90 seconds as leaving the paper in the fixer too long makes it harder to wash out. I wash fixed prints for at least 30 minutes. I used to use 10 min wash, 10 min soak in hypo-clear and 10 min final wash but no longer bother with the hypo-clear as I use a neutral fixer.

Note that these times are found in my darkroom... I use a neutral fixer rather than an acid one which is inherently easier to wash out. I use a single fixer bath at film strength (usually 1+4) that clears 120 FP4+ in about 10 seconds when fresh. I test it as I go along with Ag+ test strips and dump it when the silver content reaches 1g/l. I also do the same FP4+ film clearing time tests as a belt-and-braces approach, but 1g/l of silver always comes along before the clearing time has increased more than approx 30%. This ensures that my 90s is still well within safety limits. All that testing is a bit techy, but I would rather test a single fixer bath and know where I am than rely on untested two-bath fixing.

As always the disclaimer is that this works for me: I do not guarantee this will work for anyone else .
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Old 8th September 2009, 09:28 AM
Giuseppe Giuseppe is offline
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Thank you Bob, your reply is exhaustive. Next time I will develop longer the test strip, your advice on this point is very wise and I did not think about it before.

The fixer F24 I made reference to was the one where the difference between suggested time of fixing and my test results were very striking. But unless I print lith I normally use as first fixer the TF2 alkaline formula because it saves time in the washing stage. As a second fixer I use plain hypo immediately before selenium toning.

I have a question now about mixing TF2 in a stronger concentration similar to your 1+4 but I am going to submit this question under the "Chemical Formulas" thread to avoid off topics.
Giuseppe
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