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  1. #1
    David Lyga's Avatar
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    A challenge to Farmer's Reducer?

    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

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    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.

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    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.

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    David Lyga's Avatar
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    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

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    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.

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  6. #6
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    Quote Originally Posted by David Lyga View Post
    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.
    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.
    Trying to be the best of whatever I am, even if what I am is no good.

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    Quote Originally Posted by David Lyga View Post
    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
    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.

  8. #8
    Rudeofus's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    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.
    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.
    Trying to be the best of whatever I am, even if what I am is no good.

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    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.

  10. #10

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    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.

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