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Home processing of b/w reversal film...


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#1 Marc Roessler

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Posted 21 August 2007 - 04:06 PM

Hi Guys,

some questions...

1. what's the shelf life of the developing solutions (developer, bleach, fix etc)?
The problem is that there are developer kits available that will (chemically) suffice for two 30
meter rolls of 16mm film, but the tank needs that amount to develop just one 30m roll of film.
So obviously it is desirable to develop two films right after each other, reusing the chemicals.
The problem is that the developing process takes roughly 60 minutes, which means that the
solutions will have to wait for that long until they are going to be reused. How critical is this?
I read it especially critical with the bleach bath, but this can be done by preparing an additional
bleach bath (for which the chemicals are obtained quite easily, as long as no chromate is used).

2. The processing times usually are given for full immersion of the film material...
What if I built a processing tank myself that does not use total immersion, but used
intermittent immersion (e.g. rolling the film through the developer solution on a large spool)..?
What factor do i need to prolong the development times? Are there any drawbacks
of intermittent immersion vs. full time immersion?

3. Some sources suggest the use of potassium permanganate and sulphuric acid as bleach
bath, others suggest potassium permanganate and sodium bisulfate... while the "original"
thing seems to the the potassium chromate based bleach bath. What's the real deal, what bath
is best?

4. Sodium bisulfate is available through pool stores as "ph-minus" for lowering the pH level
of the pool water. Has anyone checked with the manufacturers of this stuff whether this is
pure enough, or has anyone even tried this for processing?

5. What's the minimum suggested speed of a continuous processing machine that uses several tanks?
My idea was to build such a processing machine with minimal tank size so 800 ml or maybe
1600 ml of processing solution will suffice for each bath... Is this possible? I have some bad
feeling especially about the transitions from bath to bath, as the film might start to dry there
already...?

Greetings,
Marc

Edited by Marc R., 21 August 2007 - 04:08 PM.

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#2 Marc Roessler

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Posted 21 August 2007 - 04:39 PM

Oh and by the way...

Many bleach mixtures call for "concentrated sulfuric acid".. which is quite precise... :rolleyes:
What concentration is actually referred to here? I suppose this is 95% to 98% concentration,
is this correct? This seems to be quite high... ?
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#3 Nick Mulder

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Posted 22 August 2007 - 03:20 AM

1. what's the shelf life of the developing solutions (developer, bleach, fix etc)?


I use a Lomo 100' tank (the biggy) - I re-use all my soups (dev, bleach, clearing bath and 2nd dev then drying agent/hardener) up to about 10 times before they become contaminated with crud - they still work fine chemically but may leave blotches here and there, I could filter them I suppose, but hey why not just mix up some fresh mix ...

Longer usage is also better for the environment ... Try to dump your chems responsibly, I personally am allowed to drop them off at the local lab for whatever recycling they do with it when I drop off color film

I dont know what you've been reading but it really isn't super-duper critical - I get excellent results consistently now (I didn't to start with, but that was because I had drying problems)

One thing that I never understood was the requirement of fixer in reversal, you shouldn't need it huh - couldn't get much info on why it was always listed as needed so went ahead and stopped using it as a test - results are indistinguishable from similar footage that used it ... Also, dont stress about the re-exposure times - i left film outside in the sun for days before 2nd dev (also out in the sun) and it came out fine

2. The processing times usually are given for full immersion of the film material...
What if I built a processing tank myself that does not use total immersion, but used
intermittent immersion (e.g. rolling the film through the developer solution on a large spool)..?
What factor do i need to prolong the development times? Are there any drawbacks
of intermittent immersion vs. full time immersion?

Good question... not sure - full immersion is better as the chemicals are kept relatively 'together' and dont slop about oxidizing themselves - keep them in plastic bottles you can squeeze the excess air out of when in storage -

3. Some sources suggest the use of potassium permanganate and sulphuric acid as bleach
bath, others suggest potassium permanganate and sodium bisulfate... while the "original"
thing seems to the the potassium chromate based bleach bath. What's the real deal, what bath is best

I've only ever used sulphuric acid and potassium di/bi-chromate - works nice, smells(a little) and looks like orange juice - I got some %98 acid from a local chem supply outfit (they supply the local universities) - its like an oil, add it to water, not the other way around - its an exothermic reaction and if there isn't sufficient water too keep it cool it will instantly boil and splash you in the eyes :blink:


5. What's the minimum suggested speed of a continuous processing machine that uses several tanks?
My idea was to build such a processing machine with minimal tank size so 800 ml or maybe
1600 ml of processing solution will suffice for each bath... Is this possible? I have some bad
feeling especially about the transitions from bath to bath, as the film might start to dry there already...?

Yikes, no idea - sounds tricky, remember you should really do a wash of water between soups so there is minimal contamination - my Lomo tank is sweet, honestly - small, way cheaper than setting up a continuous system and it uses around the ~1600ml that you spec
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#4 Brian Pritchard

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Posted 22 August 2007 - 04:31 PM

Most of the silver halide that was originally in the film is either developed by the first developer and bleached or re-developed by the second developer, however a small quantity is left in the film which if it is not fixed out can leave a haziness in the film. Heavily re-exposing can also reduce the maximum density. These things only matter if you are trying to achieve the best possible results. Please take great care when using Concentrated Sulphuric Acid it is a very dangerous material NEVER add water to the acid and ALWAYS use gloves and goggles when pouring.

Brian
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Media Blackout - Custom Cables and AKS

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