sodium thiosulfate and b/w resersal question
I was reading the ilford reversal process and it said to add sodium thiosulfate (8-12g/L) to the first developer. I was wondering if this step was necessary, and why (i thought sodiu thiosulfate was also used as a fixer?), and if this step isnt used what is the consequence.
pentax 6x7,canon eos 300, crown graphic 4x5
Originally Posted by NDP_2010
i am not sure what the reversal process is ..
but sometimes the first developer is converted to a monobath
by adding fixer ( hypo - sodium thio ) to it. this can weaken
and slow down the development process ...
i am in the middle of learning the quirks of a tintype process
where it is similar, there is a fixer in the developer, AND some sort of bleaching agent ...
lots of fun
good luck !
It will work w/o the thiosulfate - it's only really needed if you are making slides for projection. I use reversal processing for enlarged negatives for new cyanotype with lith film and don't bother with it.
The addition of thiosulfate gives clearer highlights(slide)/shadows(enlarged negatives). It removes undeveloped silver. The greatest relative reduction is where there is the most development [the parts that go black in the first development] and the least undeveloped silver. This undeveloped silver then gets developed in the second developer.
John, the B&W reversal process creates B&W slides from clear based B&W film just like E6 process creates color slides from E6 film stock.
About the fixer component in B&W reversal: This appears to be a common pattern in reversal processes, E6 uses thiocyanate, Ilfochrome uses thiosulfate, B&W uses either thiosulfate or thiocyanate.
This page attempts an explanation why the extra silver solvent must be in the first dev.
In case you try this with a permanganate based bleach: By all means make sure the permanganate is completely dissolved before use, however long it takes. I was careless once and got nasty uncorrectable spots on my B&W slides!
Trying to be the best of whatever I am, even if what I am is no good.
hi rudeofus -
thanks for the explanation and links
the more i think i know about photography,
the more i realize i have less than a clue about photography !
... and even after doing it for another 38 years, i will be just as clueless
the tintype process i mentioned is the rockland's silver gelatin tintypes .. and it uses both thiosulfate AND thiocyanate in the developer
and then a regular fix bath afterwards ...
chemical photography certainly is a form of alchemy ... base materials ( clear plastic base, tin/aluminum, paper ) and magic potions
(looking for my conical hot with stars and moons)
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I found out that the amount Ilford suggested was WAY too much for some films; at least Agfa APX100 I tested. 8-12 g/l is probably tested for some Ilford films. Better to have too little than too much. I would start at 1 g/l and go up if unsatisfied with hilights in real-world photography.
The idea is, as said, to clear the highlight fog by dissolving (just like fixer does) halides - it takes smallest grains first; those small grains that probably didn't get enough exposure to render them developable.
So as you can see, it really works like fixer, competing with developer. At the suitable level, it fixes the image away "just a bit" to lighten it up. So, the level is critical and depends heavily on film. If you have too much, it works too quickly and fixes most of the image away during the development. You can leave it out but then you will have somewhat muddy, foggy highlights no matter what.
I could not have said it better.
Originally Posted by hrst
From my own work, I started with the Ilford recommendations and progressively reduced the amount of hypo. For the most part I don't use any hypo at all now. I process predominately 16mm cine (Fomapan R100 and ORWO UN54) and to a lesser extent all the other formats 35mm 120 and sheet. I have processed Foma, Ilford, Kodak, Efke, Shanghai and ORWO. Each having their own peculiar behaviour to the reversal process and the results have been excellent for projection.
What I have found is when using permanganate bleach the emulsion is REALLY softened and easily damaged. I switched to dichromate bleaching and have yet to damage a film.
Cheers - Andy C
16mm Cine, 35mm, 120, 5x4 & 7x5.
very good info here thanks everyone.
Originally Posted by Oxleyroad
oxley, where do you obtain the hypo in australia? Also can you give more details on the dichromate bleach, is it still used with sulfuric acid? what concentrations (and also where do you purchase it?)
pentax 6x7,canon eos 300, crown graphic 4x5
The devloper (what ever chosen) devlops enough silver to give the required contrast. The hypo is *required* to remove the excess silver to allow the highlights to be highlights. Like everything in life, it's a balence.
Think of it like this..... You are hollowing out a 2x4 with a 3d shape of a human. It does not go all the way through the wood. The hypo is the equivelent of plaining off the excess wood until the bottom of your carving is on the other side. So now the depth of you carving is the depth of the wood. If you have a high depth of a carving, not much plaining is required.
You use a strong enough developer to get as much contrast as required. You then use enough hypo to brighten the immage to look correct. To say you never need hypo is as just as incorrect as saying you always need it. It will always depend on the film you are using.
What I do is desolve 16g of hypo in 250 ml of distilled water. I then add amounts to the developer I put in the can. This makes work with any film I want to use and not to have a "special developer" version for each one.
I keep my most recient notes over here... http://myfilmstuff.blogspot.ca/2011/...l-process.html
Yes I agree, it's about balancing. But even without any hypo, you will always get an image!
When I started with the Ilford recommendation, I got completely blank film with nothing in it! The high amount of hypo fixed the image completely away, which I found a little bit surprising. Maybe APX100 was so different from Ilford films. Anyway, it took a few attempts to understand what was going on as it was my first attempt on reversal processing and when I got nothing, I was first suspicious about bleach, clearing bath and 2nd developer.
Of course, I could have noticed that the film looked too clear after 1st dev, while it should look like unprocessed ("milky") film with black negative image superimposed, like a paper.
So practically, the 1st developer was working like a negative developing monobath.