Dyes, hardners, freezing... many questions

Discussion in 'Silver Gelatin Based Emulsion Making & Coating' started by narigas2006, Feb 5, 2007.

  1. narigas2006

    narigas2006 Member

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    Hi all,

    As the photo-engineer has said, freezing destroys the emulsion. However, as I was (nearly) sure that my frozen gelatin would be ruined, I tried a few things...

    I mix to the gelatin (previously frozen) another solution that contained:

    as a surfactant (the gelatine had previously photo-flo):
    Ethanol;

    as a hardner:
    chromic K sulphate (chrom allum);

    as a sensitiser:
    Sodium tiocyanate (i did not have on hands tiosulphate);

    as a dye:
    Methilene Blue;

    I have immersed another film I made on this solution and I liked very much how it sticked to the acetate. But at this time, the gelatin was unflexible and friable. The question is, why do you think the gelatin was not sticking to the acetate this time? Was it because of the freezing process? The ethanol? the chrom allum?

    Also, for my next batch, can I immerse the film in chrom allum after it has dried on the acetate (previously to expose it). The reason why I want the film hard enough is because I want to make an emulsion for motion picture, hence, it needs to survive the motion... Many many thanks.

    richard
     
  2. Hologram

    Hologram Member

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    You have to treat your acetate film with a strong alkali (5% potassium hydroxide for example). Otherwise the gelatin won't stick to the substrate.

    By the way, methylene blue is not a spectral sensitizer for silver halide emulsions.
     
  3. Photo Engineer

    Photo Engineer Subscriber

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    Hmm, well, I never heard of potassium hydroxide making the acetate capable of allowing gelatin to stick to the acetate. Usually we used a mix of gelatin or something similar in an organic solvent.

    None of this works on estar. There you need electron bombardment followed by a gelatin and solvent wash and then you can coat.

    Chrome alum cannot be used after coating. If you do, it hardens too slowly for the soft gelatin and the gelatin silides off the film support. It may work with paper support. I think formalin would be faster and better in this case if you want to harden after coating.

    Ethanol is not a surfactant. It is more of an antifoamant in this case.

    Methylene blue is not a sensitizer.

    Adding thiocyanate or thiosulfate and coating will not add sensitivity. You need a specific amount of heating to achieve any effect whatsoever. Otherwise nothing happens at all except perhaps for some fog.

    Frozen gelatin in water can denature the gelatin and render it less capable of sustaining a good coating. It can also reduce its ability to protect silver halide. Therefore you can get clumps of silver and specks of fog.

    PE
     
  4. richard ide

    richard ide Member

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    Hello Ron
    I have not done any coating for a long time (previously limited to liquid light), but have all the chemistry at hand so will start to experiment in the near future.
    I have some polyester film with a cellulose nitrate lacquer coating to make it receptive to aqueous media. I assume it would be suitable for coating?
    Is the electron bombardment the same as the corona treatment given polyethylene to make it printing ink receptive?
    I have found that a dilute solution of ethanol with various trace contaminants is a good idea to have on hand at the experimenters bench.
    Many thanks for sharing your knowledge.
     
  5. Photo Engineer

    Photo Engineer Subscriber

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    Richard;

    Corona discharge and electron bombardment are identical. The treatment lasts for about 24 hours before the effect is lost, so you must coat something aqueous before the charge dissipates. This method is used on both Estar and RC support.

    Ethanol (sold in the US as Everclear) is useful, but hard to get in the US. It is illegal in most states. It is an excellent antifoamant, but I prefere iso-propyl alcohol or t-butyl alcohol. They don't evaporate as fast.

    As for a cellulose nitrate lacquer, I have no idea. Cellulose nitrate (guncotton) is quite explosive and also subject to decomposition. I have never experimented with it or read up on the subject due to the danger.

    For example, sodium azide is suggested for use as a preservative in emulsions, but I avoid use of it due to its being quite explosive as a solid and subject to decomposition in solutions. So, I know little about it.

    There are many things in that category that I know about, but in a very very limited sense. Sorry I can't help you more on that one.

    I have some formulas hereabouts somewhere for subbing layers, but it is so difficult to do, that I prefer buying pre-subbed estar or acetate.

    PE
     
  6. richard ide

    richard ide Member

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    Ron
    If you ever are in Quebec, the liquor stores sell a 94% concentration. A little strong for drinking but perfect for other uses. On second thought; wouldn't vodka be pure enough to use as a source for ethanol? I only had one accident cooking explosives and gave that up long ago. That sort of hobby does not go over too well these days.
    Many thanks
     
    Last edited by a moderator: Feb 5, 2007
  7. Photo Engineer

    Photo Engineer Subscriber

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    Richard;

    My trips that way have been to Toronto and Montreal, but I usually drank the alcohol containing products that I came in contact with rather than use them photographically.

    Vodka should not be used due to the other ingredients in it. No denatured alcohol should be used, especially if it produces a cloudy mixture when added to water. This cloudy ingredient can be detrimental to photo materials.

    PE
     
  8. PHOTOTONE

    PHOTOTONE Member

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    Fortunately, here in Arkansas, we can legally purchase "Everclear" although the brand carried at my favorite liquor store is "Gem Clear", same stuff, though 94% PGA. I have been told that the tiny, small quantity of water doesn't matter. (6%). This was in relation to using it in the "wet collodion" process.
     
  9. Photo Engineer

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    Alcohol at that concentration is made by distillation, and to get to that degree of purity what is called an "azeotrope" is formed with water and sometimes another facilitating ingredient. This other ingredient in some cases is benzene.

    It is not present in versions that are consumbable, but in other versions (still with tax stamps mind you) it is present, and one should be careful not to drink any without proper insurance that there is no benzene present. Benzene is quite bad for your liver (as if alcohol isn't), but benzene should be avoided like poison. Well, it is.

    In coating, the benzene acts as an oil and can increase repellancies with the coating surface so that more or better surfactants have to be used.

    PE
     
  10. Hologram

    Hologram Member

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    If you want to coat on “polyester” (PET), you might have a look into coating on transparency films used for overhead projection. Some of those films are made of very clear polyester (not the ones for inkjet prints!). For example, here in Europe FOLEX sells a product that seems to have been surface treated (”Write On film”). It does accept certain kinds of gelatin.


    That's interesting. Maybe it's a question of grain size. There are methods to produce enhanced silver concentrations that actually involve several freezing/thawing cycles. Incidentally, that's the way Slavich is said to manufacture their holographic emulsions.