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  1. #101
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    And, I am working on a preservative to replace Thymol that is 40x more effective. If I can get the chemicals, I have one that is 40x more effective than that as well.

    PE

  2. #102

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    PE, did you consider the use of sodium benzoate? It should not interfere chemically (redox-wise), it is nicely soluble in water etc.

    I have another question, a bit off-topic, but anyway-if I understand well, the incorporation of dichromate directly in the glop before coating (instead of putting the tissue to "swim" in it, thus handling loads of dichromate) is undesirable because there is the "dark" reaction (reduction) occurring in the coated tissue. BUT, there is sucrose as a plasticizer and thymol, both having some "nice" reducing properties, giving us the reduced Cr(III). IF we replace sucrose with sorbitol, thymol with, say benzoate (or something similar), the tissue with dichromate should be stable for a long time, provided it is kept away from UV light. Correct?
    Is there anybody who tried this before (I am not into carbon, although intend to, someday...)?

  3. #103
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    Well, there are several answers here. Benzoate is too weak to stabilize gelatin against bug attacks except at high concentrations so I don't use it. It was used in the old color stabilizers but it made the film or paper tacky to the touch at the concentrations needed. Sorbitol does the same thing, rendering things tacky. Thymol is not a notable oxidant or reductant AFAIK.

    You need a stabilizer (Bacteriostat) that works against gram negative and gram positive bacteria and also against molds and fungi. This can take 3 chemicals to do the job properly. And, the bacteriostat must not hurt the photographic process.

    PE

  4. #104

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    sodium azide (a bit poisonous, yes) ?

    so there isn't a good replacement for sucrose? maybe inulin (polyfructane)? it doesn't have any reducing sugar unit.....

  5. #105
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    Sodium Azide is quite toxic. I will not use it. Phenol is very good, but now on a restricted list.

    PE

  6. #106

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    Quote Originally Posted by CMB View Post
    The "recipe" for the UltraStable pigment films is based on (except for the sensitizer) the formulation published in "The Home Manufacture of Materials for Carbon Printing" ( Wm. D. Fleming, American Photography, Vol 32, 1938, August, No. 8)
    Thanks Charles!

  7. #107

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    Quote Originally Posted by Photo Engineer View Post
    Sodium Azide is quite toxic. I will not use it. Phenol is very good, but now on a restricted list.

    PE
    but also phenol is not really benign.....
    anyway, what do you think about those substances?
    Benzalkonium_chloride
    Polyaminopropyl_biguanide
    Polyhexanide


    what are the bactericides-fungicides in contemporary commercial (film/paper) emulsions?

  8. #108
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    T-grain;

    Many companies today use Phenol in their emulsions. When you open a fresh bag of Ilford paper, the odor hits you right off. It is also used in the subbing on Baryta and RC papers IIRC. Kodak used several natural products in theirs, but now uses a complex mix of heterocyclic compounds that cannot be easily obtained without a special license.

    The ones listed in your post 107 are not in common use. The last chemical on that list appears to be misspelled. Is that correct?

    No bacteriostat is benign.

    I am considering Chloramphenicol as a possible bacteriostat. It is cheap and can be made available. I have to test its photographic effects.

    PE

  9. #109

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    PE
    I wasn't aware of the fact Ilford uses phenol-actually I haven't been using Ilford paper for over a decade......thanks for the info

    polyhexanide is just an abbreviation for polyhexamethylene biguanide

  10. #110
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    Ahhh, PHMB. That may affect the emulsion. IDK, I have never tested it. Many guanadine derivatives are used as mordants in emulsions requiring polymeric quaternary salts, but some do fog emulsions.

    PE



 

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