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Thread: Film emulsions

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    Film emulsions

    I have now repeated the film emulsion on paper and film support at 3 workshops and about 6 times alone. All the results indicate that the film speed is about 25 to 50 and the paper speed is about 100 - 200 with significantly higher fog.

    The higher speed and fog on paper is normal due to back reflection and the relative coated silver levels.

    Now, here are the problems as I see them:

    1. Contrast and Dmax vary and are much too low. There is too much unused silver and I have to fix that.

    2. There is too much variation in contrast, dmax and fog from coating to coating and batch to batch.

    3. Under magnification there is a slight appearance of specks. These are not pepper grain, as they are colorless and are not present in fixed out stock. I believe it is just darkroom grunge and I need to use a finer filter for the emulsion before coating and just patiently wait for the thick emulsion to run through the filter.

    4. This is an SRAD (Single Run Ammonia Digest) emulsion and the smell of ammonia during digestion is so strong even in a large darkroom that it is hard to make large batches. The small batch size may be contributing to the overall variability.

    5. The chemical sensitization and the digestion take too long to get the speed I want.

    6. I am starting to run out of transparent subbed support, and may have to find another source for continuing these experiments. My thanks to Jim Browning for the supply that I do have.

    Therefore, I am going to revisit this emulsion and try for a better design that uses another solvent than ammonia for digestion and a better workup method than the one presently used. My speed aim will remain in the ISO 50 speed range and the sensitivity aim will remain orthochromatic. The results to date do not seem to suffer from a lack of sharpness or any problems associated with having no AH layer, but I do have the dye for addressing this problem.

    I may have to continue this work making paper negatives for a while to conserve film support and only make film coatings when I know things have been 'fixed'.

    PE

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    For those interested, here is the latest ISO 40 effort. It is ortho sensitive.

    This is a scan of a portion of a 4x5 negative that is about 2x3 in size. The scanning process improved image quality, but there were no intentional changes made to the image.

    It is grainy, but surprisingly sharp. There are a number of defects due to scratching of the soft emulsion, and some signs of what might be a bit of reticulation. It was processed as soon as it was dry after being coated, so it was pretty 'fresh'. The ISO 20 test negative was considerably lighter and lower in contrast by virtue of being on the real toe, so this is an affirmation of the speed of the emulsion being close to 40.

    I hope this looks ok after uploading. BTW, there was no residual color from the erythrosine sensitizing dye which was used to get ortho sensitivity.

    PE
    Attached Thumbnails Attached Thumbnails VHS ortho 2 for posting.jpg  

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    For those interested, here is the wedge spectrogram of the ortho film. The sensitizing dye was erythrosine.

    It was an example on paper from a different run of the emulsion.

    I'm sorry to say, the only film sample from this run with a wedge spectrogram was from a defective piece of film, and the only paper sample from this run was ruined because the shutter on the spectrosensitometer hung up.

    The image was done with no UV absorber, so you see the full UV sensitivty on the left of the image out beyond 400 nm and on the right, you see some indication of red sensitivity, but this is actually an artifact of having no UV absorber. It is a harmonic of the UV.

    Ah well, nothing is perfect.

    PE
    Attached Thumbnails Attached Thumbnails Wedge spectrogram - ISO 100 paper.jpg  

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    r-s
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    Very impressive image. Good "evenness" of the image compared to some other efforts I've seen.

    I have not tried making any emulsion (yet), but I've had some ideas bouncing around in my head, that I thought I'd bounce off you to see what you thought of them.

    Two main themes at the moment. First is a (maybe) novel method for forming emulsion, which would allow daylight coating (if it works). Basically, I would mix colloidal silver into gelatine, and then coat the support (glass or flexible) with the gelatine/colloidal silver emulsion. (At this point, the emulsion would be black, entirely DMax across the surface.)

    Then, I'd go "lights out" (or, put it in a tank), and soak it in a halogenating bleach (i.e., potassium bromide and potassium ferricyanide, to make a silver bromide emulsion), and then, rinse, and dry.

    In theory (my theory, at least), I'd then have a silver bromide emulsion (non-color sensitized).

    You think this'd work?

    Next theme is coating methods. From what I've read, the "blade" technique causes people a lot of grief, trying to get a nice, even coating. It seems to me that this technique will work nicely if everything is done just right, but, it is inherently lacking in any "self-regulating" characteristics,

    So, what I am thinking is that two "possibles" would be to either spray the emulsion onto the support, or, use some type of laminar flow system to "run" it over the support.

    A third possibility, which I think I recall having read that G. Eastman patented as his first "simple" method for coating plates, would be to use what I'd call a sort of "offset" system: A roller (rather large) sitting in a tray of liquid emulsion, which rotates, picking up a coating of emulsion, which is then transferred to a sheet of glass that passes horizontally along the top of the roller. (The roller would be "wet" with emulsion just prior to contacting the plate, and then "dry" (emulsion layer completely transferred) on the side that had passed the plate.)

    I think this system would have a good measure of "self-regulation" of the coating process, but, be more trouble than it's worth for a very small hobby enterprise.

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    Two main themes at the moment. First is a (maybe) novel method for forming emulsion, which would allow daylight coating (if it works). Basically, I would mix colloidal silver into gelatine, and then coat the support (glass or flexible) with the gelatine/colloidal silver emulsion. (At this point, the emulsion would be black, entirely DMax across the surface.)

    Then, I'd go "lights out" (or, put it in a tank), and soak it in a halogenating bleach (i.e., potassium bromide and potassium ferricyanide, to make a silver bromide emulsion), and then, rinse, and dry.

    In theory (my theory, at least), I'd then have a silver bromide emulsion (non-color sensitized).

    You think this'd work?


    Actually, it has been done to make Lippmann emulsions. There's a 1929 French paper (http://www.holographyforum.org/lippm...es_a_grain.pdf) describing such a method (by the way, there are a great many papers dealing with the making of Lippmann emulsions available at:
    http://www.holographyforum.org/HoloW...ppmann_Papers).
    Ferricyanide doesn't seem to be a good solution for the bleach though. Leroy used a diluted copper sulfate bleach. Ultimately, the emulsion was spectrally sensitized.


    A third possibility, which I think I recall having read that G. Eastman patented as his first "simple" method for coating plates, would be to use what I'd call a sort of "offset" system: A roller (rather large) sitting in a tray of liquid emulsion, which rotates, picking up a coating of emulsion, which is then transferred to a sheet of glass that passes horizontally along the top of the roller. (The roller would be "wet" with emulsion just prior to contacting the plate, and then "dry" (emulsion layer completely transferred) on the side that had passed the plate.)

    Mayer bars might be another option...

    H

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    Quote Originally Posted by Photo Engineer View Post

    6. I am starting to run out of transparent subbed support, and may have to find another source for continuing these experiments. My thanks to Jim Browning for the supply that I do have.

    PE
    I have been making emulsions for a short time and I have found that "Grafix Dura-lar Wet Media Film" coats very well.

    It is available in the US in Hobby Lobby Stores or online at Dick Blick http://www.dickblick.com/zz555/07/


    Ron

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    Ronqui;

    Thanks. I'll have to look it up.

    PE

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    r-s;

    Yes, as stated above, your method will work but the emulsion will be very slow as no method is provided to control grain size or apply chemical (sulfur) sensitization. Spectral sensitization could work, but would require massive amounts of dye due to the grain size, as this is a surface effect. See the other thread on this regarding dying coatings by imbibition.

    Spray coating is covered in the book "Silver Gelatin" and is a way to achieve film and paper coatings. Using a paintbrush works. The offset roller method works and was used in production. The blade works also and was once used in production as well as being the method used for hand coating. One thing common to all of these is what you point out, in an indirect manner. It is an art and takes a lot of practice. The fortunate thing is that you can do it with dyed gelatin which is a lot less expensive than silver.

    Denise Ross has been able to achieve exellent coating quality within just a few weeks effort, as you can see from her posts.

    Hope that helps.

    PE

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    r-s
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    I wonder if melted emulsion would have viscosity conducive to a laminar flow setup? It wouldn't take much by way of equipment -- wouldn't even need a recirculating pump for a minimal system, i.e., place paper in angled holder, fill upper trough with melted emulsion, open the floodgate, and then collect the excess at a "catch-trough" at the bottom (and then remove the coated sheet).

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    r-s
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    With respect to dyes, couldn't they be coated on the metallic (colloidal) silver prior to embedding it in the emulsion?

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