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  1. #11
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    Georges, Keith;

    B&W films have always been hard enough for their intended use, but compared to color films, the way silver developed or its form in the coating is more important in B&W than color. In color, the dye image is more important.

    So, if you harden too much, the silver that forms will not 'explode' from the grain in just the same way as it will in a less hardened film and will give a different density per unit mass. This is termed 'covering power'. The idea is that you want to get the most image out of the silver.

    So, overhardening can lower apparent contrast and speed as well as increase development times. Color runs at 100 F to speed up the processing, but even that might not be enough to allow very hard B&W to form good dense silver images. Also, color is more diffusion limited due to the thickness, but B&W is not.

    So, a compromise had to be reached. A lower level of hardener is used in B&W films to allow a good silver image to form and to allow fixation to take place at a reasonable rate without giving a lot of coating defects. And yet the process temperature should not be too high which might give rise to uneven development and other problems.

    This is one of the problems with formaldehyde hardening which continues to go on for years and causes soft coatings early in their life, good coatings in the middle ages, and hard brittle coatings late in life with slower speed and higher fog. And, this may be the original source of the myth. The early formalin hardened coatings had a specific optimum life time.

    Interestingly enough, I find that my own coatings using gloxal hardening are usable in about 4 hours on paper, but require up to a week on film support to be as hard. I find little change in my paper coatings over a year at room temperature. I have no extensive experience with formalin beyond my first year at Kodak, but I seem to remember pretty much the same thing with the formaldehyd hardened coatings there.

    PE

  2. #12

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    PE,

    The only time I have heard "aging" in the past decade is with Michael A. Smith and his Lodima paper. He stated the emulsion had to "age" in order to reduce the contrast a bit.

    Any thoughts?

    Thanks for sharing all of your knowledge and insights with this forum!

  3. #13

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    Quote Originally Posted by pentaxuser View Post
    Pat I can only speak from one incident but while on a B&W introductory course, I had to use the taps in the print processing room under safelights rather than the film processing room under normal light. I failed to notice the hot and cold taps were the other way around and processed to wash the film( Ilford HP5+ or Delta 400) under the hot tap for probably a couple of minutes before checking water temp. It was just about bearable on the back of my hand!

    Result: no damage to the emulsion. So it seems that modern films or at least the above two are remarkably tough.

    pentaxuser

    Pentaxuser:

    Wow! I'm familiar with the phrase "hot negs" but until now thought it only referred to blown highlights!

    Pat

  4. #14

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    Quote Originally Posted by pentaxuser View Post
    Pat I can only speak from one incident but while on a B&W introductory course, I had to use the taps in the print processing room under safelights rather than the film processing room under normal light. I failed to notice the hot and cold taps were the other way around and processed to wash the film( Ilford HP5+ or Delta 400) under the hot tap for probably a couple of minutes before checking water temp. It was just about bearable on the back of my hand!

    Result: no damage to the emulsion. So it seems that modern films or at least the above two are remarkably tough.

    pentaxuser
    I did the same last week whilst processing FP4 Plus. I mistakenly ran the hot tap for a couple of minutes at least - just about bearable to wash hands with - into the dev tank through a hose. No damage whatsoever.
    testing...

  5. #15
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    Quote Originally Posted by jgjbowen View Post
    PE,

    The only time I have heard "aging" in the past decade is with Michael A. Smith and his Lodima paper. He stated the emulsion had to "age" in order to reduce the contrast a bit.

    Any thoughts?

    Thanks for sharing all of your knowledge and insights with this forum!
    Ummm, well about all I can say is that from the posts Michael has made since, it didn't work.

    Now, I can add from personal experience that if you design a good emulsion it will stay good and have the same result over and over and over every time you coat it, but it will eventually go bad with time over a long period. That is inevitable. An emulsion does not normally start bad and become good.

    OTOH, if you design a bad emulsion, and here is the key, it starts out looking bad, aging to a point where it may appear good, but then it keeps on going rapidly into emulsion oblivion. Therefore, in a normal situation, an emulsion that started bad and became good in 6 months would eventually become bad in another 6 months or so. (this is a generalization)

    As it seems from Michael's posts elsewhere, the emulsion started bad and just stayed there and for all I know is still where it started. It is stable and not right for matching azo, but it is a 'good' emulsion. It is just not doing what was desired and probably never will. From his description it is too fast in speed and too high in contrast IIRC.

    PE

  6. #16
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    I have seen from experience that it is much more difficult to get modern films to do things like reticulate, or have partial reversal (the "black sun" effect), and now I know why. Thank you so much for sharing your knowledge, PE. I find all of your posts very interesting!

  7. #17

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    PE, any idea what sort of hardener was used in the old ortho Verichrome film, back in the 1940's? Unlike the Verichrome Pan that followed it, it seems to be really unstable, just fogs up completely with age. Or is that a consequence of the bright magenta colored sensitizing dye it used?

    (Nothing matches the shelf life of Verichrome Pan!)

  8. #18
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    It was either chrome alum or formaldehyde. IDK if they used formaldehyde and mucochloric acid at that time. They were transitioning from chrome alum over to formaldehyde.

    All emulsions tend to go bad with time due to ambient radiation and heat. I cannot say why the original verichrome went bad, but if it was due to fog, then likely it used a high level of formaldehyde which eventually fogged the emulsion.

    PE

  9. #19
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    PE, curious about the keeping properties of azo paper in general. There have been stories on the web about old boxes from the 30's being good for printing, after storage in less than ideal conditions (heat, humidity, cold cycles, etc.). What was it about azo that made it a unique paper in this respect? Aside from the keeping properties, it was a very good paper with respect to contrast, keeping and image quality in general. It seems that the search for a "new" azo may be tilting at windmills (only due to the constraints of time left for film and paper in the market place).

    As an aside, my wife just asked me about any statistics which may exist from cancer in the worker population at Kodak, due to this older chemistry. She had mentioned that she knows Kodak had very strict policies with respect to clothing and protective gear in the 70's. She is a nurse who grew up in Buffalo and was very aware of problems in the Love Canal area (close to home, so to speak). Thanks, tim

    P.S. If liability issues exist with respect to internal information, I can certainly understand.

  10. #20

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    I may have a faulty memory, but when Kodak replaced Kodachrome II and Kodachrome X with Kodachrome 25 and Kodachrome 64 back in the 70's there were some stories about the first batches of the film being released before it had properly aged. I do remember having shot some of the new stuff back then and not being particularly happy with the change in the film. Film bought later on was fine and I happily used it for many years. Please correct if I'm mistaken about this.

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