A challenge to Farmer's Reducer?

Discussion in 'B&W: Film, Paper, Chemistry' started by David Lyga, Jul 29, 2013.

  1. David Lyga

    David Lyga Subscriber

    Messages:
    1,872
    Joined:
    Nov 25, 2007
    Location:
    Philadelphia
    Shooter:
    35mm
    In my Kodak formula book they state that a reducer can be made from Ammonium Thiuosulfite and Citric Acid. Has anyone tried this and how does it compare with Farmer's Reducer?

    I love Farmer's Reducer for prints: it gives that slight amount of needed contrast with age-fogged papers in that it reduces the lightest parts and leaves the heaviest densities largely untouched (thus, preserving that rich black tone). But, with negatives, I cannot get that same minor contrast increase because ALL densities are removed. I have tried both single and combined solutions (I usually use combined). Can anyone shed some light on this problem and talk about the 'other' reducer using citric acid. (By the way, where can one buy citric acid conveniently?) - David Lyga
     
  2. michael_r

    michael_r Subscriber

    Messages:
    6,542
    Joined:
    Feb 2, 2010
    Location:
    Montreal, Canada
    Shooter:
    Multi Format
    I'd first take a step backward and ask what you are trying to accomplish because I'm a little unclear. It seems like you're saying you want an increase in negative contrast. In order to do this by reduction, you need a sub-proportional reducer (ie one that will act more on the low densities than the high densities). This can be done, but the problem there, of course, is you're basically bleaching away shadow detail in order to increase contrast. I'd then have to ask if intensification might be a preferable way to increase negative contrast.
     
  3. johnielvis

    johnielvis Member

    Messages:
    940
    Joined:
    May 21, 2010
    Shooter:
    Medium Format
    what you're seeing is the result of prints being developed to their maximum silver "to completion". your negatives are not developed to completion, so the reducer eats it like the lighter portions of the print--there are no very very heavy silver portions on regular negatives.

    If you develop reversal film, then you will be able to use farmers to get the contrast bang because reversal second development, like with paper, is done "to completion".

    so yes, you do need a special formularion of bleach that will not attack the "mid" tones but only the light tones (the max density of a standard negative is like a mid tone for a reversal processed transparancy)--a sub proportional as stated above.
     
  4. michael_r

    michael_r Subscriber

    Messages:
    6,542
    Joined:
    Feb 2, 2010
    Location:
    Montreal, Canada
    Shooter:
    Multi Format
    I also should have stated in my first response my understanding is even in the case of so called sub-proportional reducers, most if not all of them are essentially cutting (subtractive) reducers - ie they remove equal amounts of silver from all densities. The degree to which a direct reducer is cutting or proportional also seems to depend to some extent on the film. So, on balance my guess is it would be pretty difficult to increase negative contrast with a direct reducing formula.

    A cutting reducer, when applied to an entire print, probably "appears" to increase contrast simply because the human eye is more sensitive to small differences in low reflection densities (highlights) than in high reflection densities (blacks). In other words the blacks lighten along with the highlights, but we don't notice the effect in the blacks.
     
  5. David Lyga

    David Lyga Subscriber

    Messages:
    1,872
    Joined:
    Nov 25, 2007
    Location:
    Philadelphia
    Shooter:
    35mm
    Kodak says that Farmer's can be used either as a 'cutting' reducer or as a 'proportional' reducer, depending upon whether it is mixed or not. Used mixed, it should be 'cutting', as it is for prints that need to have a slight fog removed. They attain a nice contrast as if the reducer worked only upon the lower densities.

    But...I cannot get it to act in this way (ie, removing EQUAL amounts of silver) when I use it for negatives. It acts proportional, thus removing too much highlight (dense parts of the negative) density as opposed to removing only a bit of shadow density. Because of this, the negatives look underdeveloped and lacking contrast. johnielvis touched upon this with his 'development to completion' information.

    Is there a way to achieve an enhanced contrast with age-fogged negative material? That is why I mentioned the citric acid reducer. I wonder if that would allow negatives to achieve this better contrast. Even when I overdevelop the negatives (talking about bad stuff here: 2484 or Kodak 4x or old Kodak Recording Film), due to the greatly increased age-fog the achievement of contrast is elusive. I have had papers that were just as fogged but was able to get remarkable quality using the mixed Farmer's. - David Lyga
     
  6. David Allen

    David Allen Member

    Messages:
    760
    Joined:
    Nov 6, 2008
    Location:
    Berlin
    Shooter:
    Med. Format RF
    Tackling age-fogged film is something I recently had to deal with when presented with a couple of old Tri-X films by a friend that had been exposed by his father. I did a couple of clip tests before processing the whole film and found that HC-110 Dilution B worked well. This is probably because HC110 has a bromide level and can quickly build up contrast. The final working solution that I used for the films included the addition of some benzotriazole. Development time used was 20% more than recommended and the films came out with acceptably low base fog and good contrast that gave good prints on Grade 3. After fully washing the films and doing a couple of test prints I then toned the films in selenium for 5 minutes and that provided me with negatives that printed on Grade 2.5 with good mid-tone 'punch' and required only minimal burning-in of the highlights.

    Best,

    David
    www.dsallen.de
     
  7. Rudeofus

    Rudeofus Subscriber

    Messages:
    2,566
    Joined:
    Aug 13, 2009
    Shooter:
    Medium Format
    How about not developing those foggy parts to begin with? Add more restrainer to your developer, overexpose the film and develop for as long as you need to get the contrast you like. Or start with one of these "super duper ultra fine grain developer that loses 2-3 stops" recipes like D-23, Microdol or whatever. If you already developed your negs and they have too much base fog and to little contrast, you could also try toning them in selenium toner before bleaching them. Also take a look in Haist's books, they contain a good chapter on reducers.

    Besides that, I have some strong doubts that Citric Acid and Ammonium Thiosulfate do much good together. Citric Acid is quite strong and will quickly push pH low enough for sulfuring out the Thiosulfate. Either the recipe you referred to contains some additional caustic ingredients and the Citric Acid is only in there to get pH back to neutral, or I seriously doubt that it works all that well. Yes, you can bleach and fix emulsions with acidic fixers, but pH should stay well above 4, which means you should either use Metabisulfite or Acetic Acid instead of Citric Acid.
     
  8. michael_r

    michael_r Subscriber

    Messages:
    6,542
    Joined:
    Feb 2, 2010
    Location:
    Montreal, Canada
    Shooter:
    Multi Format
    The simple answer is the Fix+Citric route (ie Ammonium Thiosulfate + citric) won't help because this type of reduction is proportional. The citric acid is added to reduce the pH since bleaching of silver by thiosulfate is directly related to acidity. A potential problem is sulfurization as the pH is reduced.

    I went through Haist again yesterday and single solution Farmer's/Kodak R4a is probably the best bet for a cutting reducer. Why isn't it working? Two variables according to Haist: 1) The wider the size distribution of silver particles, the more the reducer will tend towards proportional rather than cutting reduction. Perhaps that is the case with your films. 2) The concentrations and also the proportions of Ferricyanide to Thiosulfate in the solution have an influence on whether the solution acts subtractively (cutting) or proportionately. Depending on the film, tweaking the concentrations and proportions may or may not help.
     
  9. Rudeofus

    Rudeofus Subscriber

    Messages:
    2,566
    Joined:
    Aug 13, 2009
    Shooter:
    Medium Format
    Citric Acid is a terrible buffer, so it will be difficult to dial in a proper pH without a pH meter. I have no idea why that recipe wouldn't use Acetic Acid or Bisulfite instead.
     
  10. michael_r

    michael_r Subscriber

    Messages:
    6,542
    Joined:
    Feb 2, 2010
    Location:
    Montreal, Canada
    Shooter:
    Multi Format
    The studies cited in Haist mention particularly high thiosulfate bleaching activity below pH 4 so presumably that is a/the reason for using citric acid. I'm assuming buffering is not much of a consideration in this case.
     
  11. nworth

    nworth Subscriber

    Messages:
    2,191
    Joined:
    Aug 27, 2005
    Location:
    Los Alamos,
    Shooter:
    Multi Format
    The original post sounds like you want to apply the reducer to prints, as is frequently done for local control. The version of Farmer's reducer usually used for prints is a cutting formula, rather than proportional. As to whether the ammonium thiosulfate - citric acid brew would work, try it and find out. Both ingredients are cheap, and an experiment is a good way to find out if it works for your situation. If it doesn't, you haven't lost much. Fog reduction, with some contrast increase, in prints (usually due to aging paper) is usually best handled by adding benzotriazole or a similar anti-foggant to the developer.
     
  12. David Lyga

    David Lyga Subscriber

    Messages:
    1,872
    Joined:
    Nov 25, 2007
    Location:
    Philadelphia
    Shooter:
    35mm
    Ok thank you all: I wondered if anyone had had direct experience. I have lots of experience with Farmer's and I do expose adequately and overdevelop but it is always a race between the fog increasing and the highlights increasing. The fog often wins the race. - David Lyga
     
  13. Rudeofus

    Rudeofus Subscriber

    Messages:
    2,566
    Joined:
    Aug 13, 2009
    Shooter:
    Medium Format
    With a bigger than normal amount of restrainer you should be able to reduce fog much more than highlights. This way you lose speed but gain contrast.
     
  14. David Lyga

    David Lyga Subscriber

    Messages:
    1,872
    Joined:
    Nov 25, 2007
    Location:
    Philadelphia
    Shooter:
    35mm
    Rudeofus, I woke up at 4 AM this morning and, without having read what you just wrote, did what you just said. I have a stock of one percent benzotriazole and added about 35 ml of the stock to a liter of diluted (D-76 type: 1 + 3) working solution developer. I processed the Eastman 4x (ancient with fog) for 15 minutes at 100 F (!) at EI of 2 (!) and I could not believe how beautiful my negatives were! Almost fog free and the only 'bad' part was a bit of blocked up highlights due to the gross overexposure. Shadow detail and contrast were just about perfect.

    This was a LOT of restrainer to use and it worked as I had hoped. Thank you and I hope others try this because the film was just about hopeless. It requires an amazing amount of exposure but, if used on a tripod, my 100 foot roll is fine. Best of all: given that this is a very high speed-designated film, I can say to all that there most likely will NEVER be a B&W film in your possession that you will ever have to throw away. I also tried the Kodak 2484 and got the same spectacular results. - David Lyga
     
  15. Truzi

    Truzi Subscriber

    Messages:
    1,770
    Joined:
    Mar 18, 2012
    Shooter:
    Multi Format
    Just out of curiosity, what (if anything) would happen if you added the restrainer but your film was not fogged (in other words, fresh-dated film)?
     
  16. michael_r

    michael_r Subscriber

    Messages:
    6,542
    Joined:
    Feb 2, 2010
    Location:
    Montreal, Canada
    Shooter:
    Multi Format
    Generally speaking, from a sensitometric perspective (image structure characteristics are another story) adding a restrainer, or more restrainer to a developer that had already been balanced, will tend to reduce film speed.
     
  17. David Lyga

    David Lyga Subscriber

    Messages:
    1,872
    Joined:
    Nov 25, 2007
    Location:
    Philadelphia
    Shooter:
    35mm
    Truzi, nothing bad would happen to restrainer used when film was not fogged other than development would take longer. Restrainer slows down development, especially the lowest densities, but since the lowest densities (fog) would not be there, the negative would develop normally or maybe a tiny bit more contrast than usual. As Michael says: It 'tends' to reduce film speed but, Truzi, only because development takes longer and (only a tiny bit) because the shadow densities are now very slightly suppressed with the restrainer. -David Lyga
     
  18. Rudeofus

    Rudeofus Subscriber

    Messages:
    2,566
    Joined:
    Aug 13, 2009
    Shooter:
    Medium Format
    David, what is overshadowed by fog in your film could hold image detail in new film. In other words, fog did on the whole surface what proper exposure would do selectively, and by eliminating fog you also eliminate details in low exposure areas that could be there if you used less restrainer and new film stock.

    Restrainers do reduce film speed but sometimes that's what it takes.
     
  19. Gerald C Koch

    Gerald C Koch Member

    Messages:
    6,242
    Joined:
    Jul 12, 2010
    Location:
    Southern USA
    Shooter:
    Multi Format
    While an acidified ammonium thiosulfate solution will act as a bleach the action is fairly slow. Thus Haist recommends a pH of 4. The only problem is that acidified thiosulfate solutions are unstable and the lower the pH the faster they sulfurize. So the pH of 4 is probably a compromise between bleaching rate and stability. Still I don't see such a bleach as competing with Farmer's. Ilford in their book on photochemistry gives a large number of bleach formulas for the three difference bleach types, sub-proportional, proportional, and super-proportional.
     
  20. David Lyga

    David Lyga Subscriber

    Messages:
    1,872
    Joined:
    Nov 25, 2007
    Location:
    Philadelphia
    Shooter:
    35mm
    Rudeofus:This is why one must expose for shadow detail well into the middle of the characteristic curve, because the fog occupies the first half of that curve! With heavily age-fogged film the threshold is in the middle of that curve.

    This is why some fast, but age-fogged, films like Kodak 2484 and Easman 4x, will then have highlight detail that is rather contracted and not nicely separated. The highlights have to be 'forced and compacted' in order to allow shadow detail to be registered. That is one of the trade-offs to getting such films to 'perform'.

    Gerald: Thank you: so the enigma is really not so arcane: it's only acid that is needed to cause the fixer to become a reducer. (Apparently, there is nothing so special about the 'citric' type?) I will never forget an incident that happened back in the 60s when I was a teen-ager, about 15. I used #2 Kodabromide for paper and was very naive about darkroom matters. I processed the print but it was a tiny bit too dark. My mother called me for lunch and I simply left that print in the full strength fixer (Kodak Fixer powder did not differentiate between film and paper fixer: they were the same strength). After lunch I went down to the basement to my darkroom and was flabbergasted to find a print in the fixer that had the most beautiful tones that I had ever seen. The acid fixer had 'reduced' the density and did so in a 'cutting' fashion that yielded such beautiful tonality and rich contrast. I will never forget that print. - David Lyga
     
  21. michael_r

    michael_r Subscriber

    Messages:
    6,542
    Joined:
    Feb 2, 2010
    Location:
    Montreal, Canada
    Shooter:
    Multi Format
    Thiosulfate bleaching action is proportional to acidity, and gives proportional bleaching, not cutting.