Color Screen Plate - Moderate Success

Discussion in 'Alternative Processes' started by htmlguru4242, Jan 21, 2006.

  1. htmlguru4242

    htmlguru4242 Member

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    My Autochrome project has temporarily turned to the creation of a color scree-plate process with a prescisely ruled screen. I have made a screen digitally consisting of vertical Red Green and Blue lines. When printed in my photo printer ( on an unexposed, fixed peice of sheet film ), the screen is clear and the lines are sharp. When held up to the light, it has an overall grey shade, though it is ever so slightly green.

    I have not yet tried this photographically, but I did print an image consiting of blocks of color (made with photoshop as if it was taken "through the screen"). It is therefore what a reversal-processed sheet would look like after it has been exposed. When it is held up behind the screen - plate and registered properly (which is quite a trick, even though the screen is regular), the original colors appear; they are dark, but DEFINETELY visible. When I have time to reversal process some sheets of film, I'll try it with this mask.

    Placing the screen mask over my meter (both handheld and TTL in my SLR), says that the screen cuts the light down by about two stops, maybe a little more. This is not as bad as I thought it would be, especially considering that hte Fortepan 200 sheet film that i have has at least a stop of exposure latitude before processing needs any adjustment.

    I'll report back when I get this working even better, and I'll TRY to post some examples. I'll probably have to photograph them on a lightbox or projected with a (gasp) digit@l camera, as I really can't scan them, and it takes too long to have color film processed.
     
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  2. Photo Engineer

    Photo Engineer Subscriber

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    Sounds like progress. I look forward to seeing some of the results.

    PE
     
  3. htmlguru4242

    htmlguru4242 Member

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    Ok, I registered it perfectly, FINALLY. The original image used consisted of horizontal blocks or Red, Green, Blue, purple and yellow, with black lines in between.

    The well-reproduced image shows very good red, excellent blue and good yellow and purple. The green, however, is a bit light. In order to keep the screen neutral grey, I had to reduce the saturation of the green slightly. This results in a sligtly light green on the viewed image.

    Also, the film's emulsion side and the mask's printed side must face each other; if they don't the space in between causes the colors to vary according to viewing angle.

    I was able to nab a shot with a digit@l camera, and I'll upload it here later on today; the computer with the camera drivers is out of commission, and the drivers CD has gone to places unknown ...
     
  4. Donald Qualls

    Donald Qualls Member

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    And there's a problem you'll never have with film... :wink:

    Looking forward to seeing what you get for actual pictorial results. Your ruled screen is going to be equivalent to the Polaroid 35 mm slide film (for the desktop processor), but if you can come up with a way to do pin registration of the mask with unexposed film in the holder, you might get away with printing a randomized stochastic pattern to avoid moire effects...
     
  5. glbeas

    glbeas Member

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    Seeing the results tells you the screen itself doesn't have to be perfectly neutral, try changing the green ratio a bit and see if you can get the color saturation of the positive to come up. You might try a foursquare pattern of red, blue and two greens and see what results.
     
  6. htmlguru4242

    htmlguru4242 Member

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    More good news; I discovered today that the anti-halation layer on my Fortepan 200 film is VERY easily removeable. I wiped the back of the film with a paper towel soaked in developer, and it came off quite easily. This leaves a film with an almost crystal clear backing and a grey emulsion.

    Now, I can just wipe of the AH layer, let the film dry and glue the screen onto the back of the film: registration problems, be gone!
     
  7. Andre R. de Avillez

    Andre R. de Avillez Member

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    I remember reading that a sodium sulfite solution removes the AH layers quite easily. Might be a better option then developer (definately cheaper, anyway).

    just a thought
     
  8. htmlguru4242

    htmlguru4242 Member

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    Thanks, Andre, that's a good idea. If I'm not mistaken, the Sodium Sulfite is for the Rem-Jet back on Kodachrome, but with this film, it seems that any alkaline solution will remove the AH backing.

    And, now that I have a way to coat onto the BACK of the film, I can go back to the random Autochrome screen idea.
     
  9. Donald Qualls

    Donald Qualls Member

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    Actually, sodium carbonate will probably work for both. I *know* it will work for remjet; I've used it to take the remjet off a roll of Kodachrome I was trying to process as B&W (it was so fogged there was nothing visible on it, but the remjet came off nicely).

    Just remember -- if you get any liquid on the emulsion side of the film, it'll show in the final image as a dark (after reversal) spot, because the water will wash out sensitizing dyes. I've seen this effect on film even from just a few drops of condensation.

    To glue the two together -- could you print your screen on the gelatin side of fixed-out film, then dampen the gelatin and apply it to the back of your Fortepan? Gelatin is terrific glue. However -- you're back to having the film base thickness between the emulsion and the screen, which I recall you already verified to cause color shifts with veiwing angle...
     
  10. htmlguru4242

    htmlguru4242 Member

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    Good point about the film base, Donald. Do keep in mind, however, that in my previous tests, I had film base + the thickness of the transparency film involved. The coor shifts, I also think, were partially a result of inproper alignment of the color screen mask. I'll try this & see how it goes.

    Also, when you say sticking them together with the gelatine is a good idea, will this be permanent, even through processing? It needs to be completely watertight; water causes the dyes in the screen to bleed, developer does even more so, and dichromate + acid, I don't even want to think about ...
     
  11. Donald Qualls

    Donald Qualls Member

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    Ack -- water soluble dyes, right. Never mind...

    I'd expect the gelatin to stay stuck through processing if you once get it stuck, certainly; it takes *days* of soaking to free two negatives that get stuck together by drying in contact, if you ever manage it at all. But you would certainly get some bleeding around the edges, and the dampening to get the gelatin to stick would likely cause some pain with the dyes too. Dichromate bleach will decolor a lot of dyes, too.

    I suspect the only way to tell if it'll work is to try it.

    Otherwise, I don't know what glue you could use that will leave the film flexible, not add too much thickness, and dries waterproof. Silicone caulk comes to mind, but it's almost impossible to spread thinly enough, not to mention its transparency is only so-so...

    Might actually be simplest to use a pin registration system. They're accurate enough, if the pins aren't worn smaller than the punches...