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  1. #11

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    I can see that I confused the issue myself by mentioning hypo eliminator prior to mentioning selenium toner in the list of what I do. I have always used the hypo eliminator at the end of the process just prior to print washing.
    Claire (Ms Anne Thrope is in the darkroom)

  2. #12

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    The mechanism of image protection by impregnation of the gelatin layer with thiocyanate is completely different from the mechanism of image protection by residual thiosulfate. The image protection by thiocyanate can be removed by water rinse after Sistan treatment. However, image protection by thiosulfate persists even after brief water rinse. I'm not going to get into details but the chemistry of these image protection mechanisms is discussed in a few papers written by Fuji people in 1980s. Unfortunately, all in-depth discussions (including one review paper) are written in Japanese language.

    I STRONGLY recommend anyone who is serious about image permanence to stick with one of the well tested treatments and refrain from jumping on untested homebrews.


    Quote Originally Posted by Photo Engineer
    If you allow a small amount of hypo to remain in a print, it decomposes slowly releasing sulfur compounds which coat the silver and protect it from oxidation much like sulfide toning.

    Sistan, and other stabilizers like it contain similar sulfur releasing compounds in low concentration which work to stabilize the silver in a siimilar manner and prevent image degradation.

    All of them are pretty much the same. And, you can use Sodium Thiocyanate instead of Potassium Thiocyanate by adjusting the quantity for the change in molecular weight of Sodium vs Potassium.

    There is an article publised by Ctein on this subject. I recommend it to you all.

    PE

  3. #13

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    Sistan is cheap, especially if you consider how much time, work and other archival storage/mounting/framing supplies cost. Stick with Sistan. However, a better option is Fuji Ag Guard, which uses an organic thiol compound that is even more effective than thiocyanate. The Fuji product is great because some image protection power remains even if the treated print is rinsed in plain water. The Sistan treatment is unreliable if there is humidity cycle in the paper storage. Also, Sistan treatment is even harmful if the amount of thiocyanate in the emulsion/paper is too high.

    A better approach is to use paper-developer combination that would give you cold black tone when toned in polysulfide toner. I've posted here and also on photo.net about how to think about developer's influence on the hue of polysulfide-toned prints. I've made quite a few samples of neutral black print (after polysulfide toning) which showed excellent resistance to oxidative attacks in peroxide fuming testing.

    Quote Originally Posted by Claire Senft
    I, cheap guy that I be, am looking for a formula and other information regarding home preparation of a Sistan equivalent. I already realize that the principal ingredient is potassium thiocyanate. Here are my questions.

    Formula for mixing.
    concentrate usage.
    amount of time in the bath
    the amount of coverage for a given amount of bath will process.

    It should be easy to discern what I know about this chemistry...virtually nothing.

    All I am trying to do is to produce prints with an enhanced LE. The prints will be subjected to a 2 baths of hardening fixer, hypo eliminator..not hypo clearing agent, 1:40 selenium toning. I realize that there is a school of thought that says that some residual hypo is good for the print in terms of resistance to air pollution. What is not stated is what amount of hypo should be left in the print and a technique to measure it that one may apply with confidence at home. I am neither taking issue with the accuracy of these statements nor am I trying to pick a quarrel who process in a different manner..different strokes for different folks. I believe a hardened print may have some benefits in terms of abrasion resistence or the application of pressure to the face of the print. I realize that hardening will reduce washing efficiency..hence the use of hypo eliminator and make spotting more difficult...nothing is quite as satisfactory as a print that does not require spotting. I also realize that I could enhance print LE though the use of heavy sulphide toning whose print colors I ordinarily dislike for my own work...I like slightly cool to neutral print colors. So, it seems to me that a Sistan like solution may be helpful.

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