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Re: [PPLetterpress] Re:resolution for negatives to make polymerplates

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  • Gerald Lange
    Bev I m not sure why the double washout should work, though I ve heard it mentioned here before. I don t see how the drying out process (theoretically, or
    Message 1 of 20 , Mar 25, 2007
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      I'm not sure why the double washout should work, though I've heard it
      mentioned here before. I don't see how the drying out process
      (theoretically, or technically) would contribute (since it has no effect
      on the solubility of the photopolymer). But if it works. . .

      Traditionally, and this is not just limited to processing photopolymer
      plates, the exposure is staged for the various elements by masking them
      off. For instance, when a solid has reached its maximum exposure, the
      exposure is halted, the solid masked off, and exposure continued for the
      remaining elements; fine dots and lines getting the maximum exposure.

      Bit more tricky though to achieve the gradation you have mentioned.
      Before photomechanical engraving lost the personal touch of the
      craftsman there were all kinds of tricks and techniques employed to
      achieve certain effects, but most of that information is now only
      available in long out of print manuals.

      I did a series of plates for a printmaker a while back where dampened
      Japanese silk tissue was used as intermediate masking between elements
      of the imaging and that served for a very interesting effect.


      Bev Dittberner wrote:
      > Hello, this is my first post- I run the prepress dept at
      > Full Circle Press, One thing I haven't seen mentioned in this thread
      > is that you need to think about what you want your final outcome
      > to be- If you require pixalation for a "screened" look, or area that
      > would otherwise be a second color in a lighter PMS, but need to cut
      > corners
      > leaving a line drawing or area in grayscale will achieve this.
      > 100% black is required for a plate without pixalation.
      > Making a plate that has an image that has solid areas that blend out
      > to tiny dots can be tricky. It's a dance between exposure and
      > washout.
      > I've done pencil drawings and scanned them into Photoshop as full
      > color scans, then changed the mode to grayscale, then adjusted the
      > contrast until the black was as dense as I could get it and still
      > keep the "scetched" look of the drawing. As long as my file can
      > convert to an ESP in CS2 my file will make it to the RIPP and be
      > re-written to 2400 dpi.
      > The trick is to do a double wash out when making the plate.
      > When you expose the plate,the rule of thumb is the smaller the window
      > to the light, the longer the exposure- however when you
      > have a drawing where you have a solid area that blends out to an area
      > that is basically a lot of tiny dots, you don't want to lose the dots
      > in your wash out- SO you expose for the solid and save the dots in
      > the wash out process. You wash the plate for 1 and half to 2 minutes,
      > then put the plate in the oven and baked it for 5 - 7 minutes, then
      > wash it again , checking every30 - seconds until you get a clean
      > plate that still has the tiny dots.,
      > Bev
      > hope this helps
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