Turning on lights after developer

bdial said:

Not all of us routinely have film leader for checking clearing time.

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Well, it doesn't have to be film leader and it only takes a sliver. Even if you only shoot large format, you can buy one roll of the cheapest 135mm film you can find, and it will last you a very long time. It's a cheap way to test your fixer and determine clearing time.

I test with film leader myself, most of the time since I use a Jobo. But I do check in the tank, because it's easy to do, when I develop with an inversion tank (usually that means I'm using Diafine.) You don't have to of course, but I'm just defending the people who do from the cries of heresy and the crowd trying to erect the stake and gather firewood. It won't hurt a thing to expose to light half way (or even less) through the fix.

SkipA said:

It's a cheap way to test your fixer and determine clearing time.

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Why do you care?

Follow the manufacturer's instructions. I guarantee they've done more extensive testing than you have.

- Leigh

bdial said:

if you leave it in the dark for your expected fix time without inspecting it, you don't know if it cleared at 1/4, 1/2, 3/4 or 90% of that time.

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Why do you care?

- Leigh

Leigh B said:

Why do you care?

Follow the manufacturer's instructions. I guarantee they've done more extensive testing than you have.

- Leigh

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Last I looked, they said it was ok to expose film to light after 1/2 the fixing time.

Hi Roger,

Yes, I believe that's the recommendation that I've seen on commercial fixers.

- Leigh

I've enjoyed reading everyone's comments on this post. I'll continue to do as I always have done; refrain from showing film light until it's at least halfway through fixer. I recently switched from using a water stop to an acid stop for my film after I saw how much developer I was carrying over, specifically when tray processing.

A couple of comments to the above discussion:

First, developer will not work in an acid environment, even if it is present. The danger of exposing film to light after it has been in the stop for a while, but not yet in the fixer, is that the light itself will reduce some of the unfixed silver halide to silver, causing overall fog. This is usually very slow and weak, so often has no practical implication. It will, however, happen. I wouldn't expose my film to light while in the stop.

Second, if you use an alkaline fixer, regardless of whether you use an acid stop or not, the developer carried over in the film's emulsion will be reactivated. It actually does some more developing of the exposed part of the negative till the fixing process catches up with it and removes the undeveloped silver halides (this is a little bit of compensating development going on. There's another thread on PMK testing that I just posted to with this exact phenomenon). If you expose the film to white light in this scenario, you can (and likely will) get overall fog to some extent. Don't ask me how I know this... I use acid fixers for film now.

However, if you use an acid stop and an acid fixer, the film is in an acid environment and developer will not be re-activated in the fixer. Once the film has cleared, so has the danger of fogging from the light itself reducing the undeveloped halides. That is the thinking behind manufacturers' saying that it is safe to turn on the light after half the fixing time (in which time the film will have cleared, at least in fresh fixer).

So, I would, and do, turn on the white light after half or a little more of my fixing time has elapsed. I agitate my sheet film just a bit more securely with the light on.

And, doing film clip tests has more than one purpose. It is not useless at all. It is primarily useful for determining when your fixer is exhausted; when the clearing time is double that in fresh fix, it's time to toss the fixer. It is also useful for determining fixing time in partially-used fixer. I do clip tests before each batch to a) determine my fixing time for my fixer in whatever state of exhaustion it is in and b) determine when to toss it and mix fresh fix.

Plus, I usually figure in a 15% fudge factor after doubling or tripling the clip-test time to account for exhaustion of the fixer as it's being used. Try this: do a clip-test before fixing a batch of film and one immediately after. The time after will be 10-15% longer than the time before, which means that if you used just a simple doubling of the clip-test time, you have underfixed.

BTW, I fix for three times the clearing time with TMax films, as per Anchell and Troop's recommendation, since there is evidence to suggest that the silver iodide in the emulsion of these "high-tech" films takes longer to fix.

Plus, since film is coated on an impermeable base, a little extra fixing time will not hurt. And, it often helps get rid of the pink cast on Kodak films to fix it a bit longer.

Best,

Doremus

www.DoremusScudder.com

Leigh B said:

Why do you care?

Follow the manufacturer's instructions. I guarantee they've done more extensive testing than you have.

- Leigh

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Because I mix my fixer from scratch using the Kodak F24 recipe from The Darkroom Cookbook. There isn't any published data on clearing time or shelf life (that I know of), and the clearing time lengthens as the fixer ages and becomes exhausted. Over fixing is bad for film and paper. So testing and knowing the clearing time is important.


Edit: I just read Doremus' reply and he covered the reasons why one should test his fixer more thoroughly than I did. Plus I learned something. I have never accounted for the 10% to 15% degradation before. Thank you Doremus.

SkipA said:

Over fixing is bad for film and paper.

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If you leave it in there for hours instead of minutes perhaps, but doubling or tripling the time will show no noticeable effect.


Steve.

Thanks Steve. It has been my understanding for years that 2 to 3 times the clearing time is the recommended amount, so that is why I've routinely tested my fixer for clearing time before processing a batch of film, then just doubled the time to avoid overfixing. From what Doremus said, tripling the time from clearing may be better, especially for certain films.

Does anyone know just how much overfixing a film can take before the damage is noticeable? What is the "fixing lattitude", so to speak?

SkipA said:

Thanks Steve. It has been my understanding for years that 2 to 3 times the clearing time is the recommended amount, so that is why I've routinely tested my fixer for clearing time before processing a batch of film, then just doubled the time to avoid overfixing. From what Doremus said, tripling the time from clearing may be better, especially for certain films.

Does anyone know just how much overfixing a film can take before the damage is noticeable? What is the "fixing lattitude", so to speak?

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I have always thought that the correct fixining time is twice the clearing time. But unlike development this time is not critical.

That was an interesting thread, MIchael. The fact that many BTZS tube users report never having any problems with fogged film when turning lights on at the end of developing and before stopping suggests that ill effects are not especially noticeable. I can see that the BTZS tubes could be more difficult to manage in total darkness. I've never tried them, and leaving the lights off throughout sheet film processing in trays isn't a problem for me. It seemed like you came to the same conclusion.

I've used nothing but the F24 fixer recipe from Anchell's book for many years. It's an acid non-hardening formula, super easy to mix up, as it only contains three ingredients plus water.

Ralph Lambrecht has some interesting thoughts on fixing paper for more than two minutes (fiber paper), causing a scenario of making it impossible to actually wash it out of the paper.

Just an aside, but possibly important.

Film loses some, but not all, of its sensitivity during development. If you expose it to light while any residual developer remains, it will fog - maybe not a lot, but some. Even if development is well stopped and the film is rinsed, exposure to light will darken the remaining silver, which is similar to fogging. That darkening is silver metal, and it will not be removed by the fixer. If the negative is on a reel or in some sort of holder that cast shadows, the fogging will form a pattern on the film. While turning on the lights after a stop bath may sort of work, it is much better to keep the film in the dark until it is fully fixed.

Thomas Bertilsson said:

Ralph Lambrecht has some interesting thoughts on fixing paper for more than two minutes (fiber paper), causing a scenario of making it impossible to actually wash it out of the paper.

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Good argument for using a clearing agent to change the chemical to one more soluble, rather than relying on a simple wash.

- Leigh

Early panchromatic films did not have full red sensitivity. They would best be described as ortho chromatic with some red sensitivity. It all depends on which sensitizing dyes are used.

Our species evolved under a leafy forest canopy where green light predominated. So our eyes are more sensitive to the green portion of the spectrum. This also accounts for why we see more shades of green than any other color.