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  1. #21
    Ian Grant's Avatar
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    Quote Originally Posted by Rudeofus View Post

    @Ian: Note that the difference between 6B-3 and the other two bleaches is not only the nitric acid but also the halide used for rehal.
    Yes. I had realised that. I did try the bleaches in this toner in the late 1970's when I was working on Toners commercially. I particularly liked the chloride based bleaches for their more yellowy/orange tones.

    It's often not realised that the developer used initially can also affect the final image colour after toning.

    Ian

  2. #22
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    Quote Originally Posted by Ian Grant View Post
    Yes. I had realised that. I did try the bleaches in this toner in the late 1970's when I was working on Toners commercially. I particularly liked the chloride based bleaches for their more yellowy/orange tones.
    There was a thread here some time ago about chloride rehal bleach and the consensus was that chloride bleach killed the highlights in a print. Is this problem still there or was there some solution to this? Or maybe the nitric acid is the solution?
    Trying to be the best of whatever I am, even if what I am is no good.

  3. #23
    Ian Grant's Avatar
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    Quote Originally Posted by Rudeofus View Post
    There was a thread here some time ago about chloride rehal bleach and the consensus was that chloride bleach killed the highlights in a print. Is this problem still there or was there some solution to this? Or maybe the nitric acid is the solution?
    It's not so much that any bleach / toner kills the highlights rather that the overall Dmax of a very warm toned yellow/brown print has a very significant drop in density across all the tones.

    If you redevelop a print bleached in a simple rerricyanide/chloride or ferricyanide/bromide based bleach it should return to the same density, hover add something like Nitric acid, Ammomia maybe as you suggest Bisulphate then you interfer with the simple rehalogenation process adding the pprobability that some silver is dissolved may diffuse slightly in the print emulsion before being converted to halide again, this gives the finer grain whin in turn results in warmer tones.

    Remember that another variable in bleaches is the excess or lack of excess of the halide, so Agfa 500 uses a ratio of 15:1 Ferricyanide to Bromide while 501 uses a 5:1 ration (ratios by weight). If there's no excess of halide in the bleach then Silver Ferricyanide complexes are formed which are less stable and will reduce theeffects of the subsequent toner.

    In this case the ratio is closer to the 1:1 used in a typical Bleach such as used in Ilford IT-1or Kodak T-52 & T-56, so great excess of halide but with a silver solvent present.

    Because of the overall density loss many toners require over exposer at the printing stage to compensate.

    Ian

  4. #24
    Photo Engineer's Avatar
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    Quote Originally Posted by Rudeofus View Post
    There was a thread here some time ago about chloride rehal bleach and the consensus was that chloride bleach killed the highlights in a print. Is this problem still there or was there some solution to this? Or maybe the nitric acid is the solution?
    I am afraid that the use of a Chloride rehal bleach can lead to loss of highlight detail due to dissolution of the resulting AgCl. Some AgNO3 will also form in this particular bleach thus increasing loss of Ag. This should be noticeable in the final prints, but the toning may obscure it.

    PE

  5. #25

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    Nitric acid reacts with certain proteins to form yellow nitrated products. This reaction is known as the xanthoproteic reaction. This test is carried out by adding concentrated nitric acid to the substance being tested. If proteins that contain amino acids with aromatic rings are present, the mixture turns yellow. Upon adding a strong base such as liquid ammonia, the color turns orange. These color changes are caused by nitrated aromatic rings in the protein. This is a common chemical test that is often used in biology classes, ie to show that cooked egg white contains protein.

    Of the three concentrated acids found in chem labs hydrochloric acid produces an immediate stinging or burning sensation. With nitric acid one often does not even know that there was skin contact until the next day when the yellow color appears. The oil in the skin provides some protection against sulfuric acid. After contact one can walk slowly to the sink to wash it off and never be burned, A woman student in a lab I was in fumbled a bottle of conc sulfuric acid all over herself. She was immediately put under the safety shower. Her clothes were destroyed but she suffered no burns.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  6. #26

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    While neutral and basic solutions of potassium ferricyanide are relatively safe, the addition of acid can release hydrogen cyanide. Even relatively weak acids can do this. There is a case where a man committed suicide by adding a teaspoon of potassium ferricyanide to a glass of lemonade. Another point to remember is that cyanide ions pass readily through the skin. So avoid skin contact with acidified solutions such as the bleach mentioned in the post.

    Since modern papers are quite different from the old Defender papers the toners mentioned may no longer be very useful. This is a common problem when trying to use old formulas with modern emulsions.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  7. #27
    Photo Engineer's Avatar
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    Jerry;

    I'm afraid that all of those stories about release of HCN from Potassium Ferricyanide are apocryphal. See here:

    http://en.wikipedia.org/wiki/Potassium_ferricyanide

    This argument has been carried out here and on Photo Net several times. You have to really beat on the Ferricyanide ion to release HCN. That is why it was considered so safe in color processes up until the 70s when it was found that due to Biological degradation or UV degradation in the effluent slowly released HCN.

    You need acid and heat to really release HCN fast enough to harm yourself. So, some acidified Ferricyanide dropped on a hot hotplate will do the job.

    Nevertheless, I still recommend extreme caution to avoid this problem from arising.

    PE

  8. #28

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    I would just like to thank all that contributed to this thread for their frankly amazing level of knowledge. APUG can be an amazing resource.

    I've noticed a slight amount of highlight bleaching with the B3 bleach. This is tested on Ilford Multigrade IV FB. By slight, I mean much less than a third of a stop on my Stouffer step wedge. I'm not doing any densitometry; just judging visually. And I agree with Ian Grant's statement that there will be an overall loss of density. The blacks are slightly but noticeably weaker as well. I guess that can be said for most sepia toners, I suspect. I'm not chasing absolute dmax, so it's not a massive concern.

    I wouldn't use this bleach all the time, but it does produce a brilliant 'sunlit' tone in the highlights with the right toner combination, and I can see the potential for use in some images.

  9. #29
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    Quote Originally Posted by Photo Engineer View Post
    Jerry;

    I'm afraid that all of those stories about release of HCN from Potassium Ferricyanide are apocryphal. See here:

    ....You have to really beat on the Ferricyanide ion to release HCN...

    PE
    The Autotype formula for Carbro processing mixes ferricyanide and chromic acid - sounds like a fairly ferocious mixture to me, but I've not heard tales of HCN poisonings. Nontheless, exercising caution and never taking a cavalier attitude toward chems is always a good policy.
    - Ian

  10. #30

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    Usually, when an odd acid is called for in a formula, there is a reason. Here it is probably, as suggested, to control grain. The additional loss of silver by production of AgNO3 may have been intentional with the old style emulsions.

    As for the more general question, sulfamic acid is often used as a solid alternative to sulfuric acid. It is fairly expensive, however. I have used it in a couple of situations where hauling around a bottle of concentrated acid was ill advised, and it is a good substitue. Ilfochrome uses sulfamic acid in its bleach to avoid liquid packaging problems. Sodium bisulfate can be used in many formulas, but it takes quite a lot of it to generate enough sulfuric acid. A mixture of sodium bisulfate and sodium chloride has been suggested (Anschell and Troop) as a substitute for small quantities of hydrochloric acid as well.
    Last edited by nworth; 02-22-2012 at 04:27 PM. Click to view previous post history. Reason: Error

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